DOI: https://doi.org/10.56669/YJZG5650
ABSTRACT
The genus Streptomyces comprising of filamentous actinobacteria (belonging to the phylum Actinomycota), are renowned for their remarkable metabolic capacity and production of copious bioactive metabolites, including more than two-thirds of all clinically used antibiotics. Due to the environmental degradation caused by traditional agriculture’s heavy reliance on chemical fertilizers and pesticides, there is an urgent global need for sustainable agricultural practices. As plant growth-promoting rhizobacteria, the genus Streptomyces has emerged as a potential option for reducing chemical inputs, enhancing crop yield and providing resilience against stress. Streptomyces facilitates plant growth through multifaceted mechanisms. Direct mechanisms include the synthesis of phytohormones to stimulate growth and the production of ACC deaminase to modulate stress. Furthermore, they aid in nutrient solubilization and acquisition by releasing organic acids to dissolve inorganic phosphate. Certain strains can also weather potassium-bearing rock or secrete siderophores to acquire iron. Indirect mechanisms are mainly represented by their biocontrol potential against pathogens. Streptomyces achieves this through antibiosis by generating broad-spectrum antifungal, bactericidal, and nematicidal compounds. They also facilitate enzymatic lysis by secreting hydrolytic enzymes that break down pathogen cell walls. Additionally, they can induce systemic resistance in plants, offering broad-spectrum protection against subsequent infections. Streptomyces has demonstrated potential applications in various crops, including rice, wheat, potato, and tomato, often serving dual roles as biofertilizers and biocontrol agents. While commercial products like Mycostop (S. griseoviridis K61) and Actinovate (S. lydicus WYEC 108) are commercialized, large-scale adoption faces significant challenges. Primary hurdles include the instability of formulations during storage and the uncertainty of efficacy under diverse field conditions. Future research should prioritize developing advanced formulations, using synthetic biology tools to unlock the vast, untapped metabolic potential within the Streptomyces genome, and focusing on the utilization of more stable metabolites or microbial consortia to improve the predictability and longevity of commercial products.
Keywords: Streptomyces, plant growth-promoting rhizobacteria, biocontrol, bioactive metabolites, sustainable agriculture
INTRODUCTION
The growing world population and escalating food demand pose a serious challenge to global agriculture (Godfray et al., 2010; Sugumar et al., 2024). Traditional Green Revolution strategies that rely heavily on chemical fertilizers and pesticides have indeed boosted crop yields, but often at the cost of environmental degradation (Foley et al., 2011; Ni et al., 2025). Overuse of synthetic agrochemicals has led to soil acidification, biodiversity loss, water pollution, and even been linked to human health risks in the long term. There is an urgent need for sustainable agricultural practices that can ensure high yields with minimal environmental impact. In this context, plant growth-promoting rhizobacteria have emerged as a promising component of sustainable crop management (Bhattacharyya and Jha, 2012; Wahab et al., 2025). These beneficial microorganisms can enhance plant nutrition and health, thereby reducing reliance on chemical inputs.
Among plant-beneficial microbes, the genus Streptomyces has attracted growing attention for its multifaceted roles in promoting plant growth and offering protection against biotic and abiotic stresses (Vurukonda et al., 2018; Olanrewaju and Babalola, 2019). Streptomyces are filamentous actinobacteria renowned in medicine as prolific producers of antibiotics – indeed, actinomycetes (especially Streptomyces) produce the majority of known antimicrobial compounds (Bérdy, 2005). In agriculture, those same metabolic capabilities endow Streptomyces with biocontrol potential against plant pathogens, as well as the ability to synthesize phytohormones and other metabolites that directly stimulate plant growth (Palaniyandi et al., 2013; Sousa and Olivares, 2016). This review elucidates the principal mechanisms by which Streptomyces facilitate plant growth and provides representative examples of their applications across various crops. Also discussed are the challenges of harnessing Streptomyces in the field and prospects for their use in sustainable agriculture. The aim is to provide a comprehensive overview of Streptomyces–plant interactions and their potential in improving crop productivity and resilience.
STREPTOMYCES BIOLOGICAL CHARACTERISTICS
Taxonomy and morphology
Streptomyces is a genus of filamentous bacteria in the phylum Actinomycetota (family Streptomycetaceae). They grow as branching mycelia, forming a network of hyphae analogous to fungal mycelium. A distinctive feature is their sporulation; Streptomyces develop chains of conidiospores on specialized aerial hyphae, giving colonies a powdery appearance (Barka et al., 2016). These spores allow Streptomyces to disperse and survive harsh conditions, contributing to their ecological success. The genus is taxonomically rich and currently has 810 species with validly published and correct names (https://lpsn.dsmz.de/genus/streptomyces; accessed on 8 March 2026). The high genomic GC content and large genome size correlate with a capacity to produce diverse secondary metabolites and enzymes (Liu et al., 2013).
Ecological distribution
Most of the Streptomyces are soil-dwelling bacteria with a free-living life cycle in the soil. They can efficiently colonize the rhizosphere - the soil area surrounding plant roots, rhizoplane and endosphere - internal part of plants (Sousa and Olivares, 2016; Vurukonda et al., 2018). Metagenomic analyses of plant microbiota have recently strengthened the view that Streptomyces spp. are natural major endophytes of plants, capable of colonizing roots or living in the rhizosphere (Rey and Dumas, 2017).
Metabolic diversity
A hallmark of Streptomyces is their prolific secondary metabolism. They produce a wide variety of bioactive metabolites, including more than two-thirds of the clinically used antibiotics (Bérdy, 2005). Classic examples are streptomycin, chloramphenicol, tetracyclines, and macrolides. Many Streptomyces also secrete extracellular enzymes-including amylase, chitinase, cellulase, invertase, lipase, keratinase, peroxidase, pectinase, proteases, phytase, and xylanase-which make the complex nutrients into simple mineral forms (Vurukonda et al., 2018). This not only helps in nutrient cycling but also contributes to biocontrol by degrading pathogen cell walls. Uniquely, certain Streptomyces produce phytohormones and other metabolites that can directly influence plant physiology (Tokala et al., 2002; Palaniyandi et al., 2013; Ly et al., 2026). The metabolic versatility of Streptomyces is reflected in their genomes, which harbor an exceptional number of biosynthetic gene clusters (Barka et al., 2016). This rich chemistry is one reason Streptomyces are invaluable in biotechnology and plant health applications.
Interactions with plants
Streptomyces interact with plants in multiple modes, ranging from free-living, associative relationships in the rhizosphere to intimate endophytic symbioses (Sousa and Olivares, 2016). Some strains exhibit chemotaxis toward root exudates, allowing targeted colonization of the root vicinity. Endophytic Streptomyces have been isolated from crops like wheat and rice, often conferring growth or health benefits to their hosts (Worsley et al., 2020). The relationships can be mutualistic: the plants provide habitat and nutrients, while the bacteria produce growth-promoting substances or guard the plants against pathogens. Notably, while most Streptomyces are beneficial or neutral to plants, a few species are plant pathogens (for example, S. scabies, the causal agent of potato scab, produces thaxtomin phytotoxin (Loria et al., 2008)). This dual nature underscores the importance of understanding Streptomyces-plant interactions. In beneficial interactions, Streptomyces can simultaneously act as biofertilizers (enhancing nutrient availability), as phytostimulators (releasing hormones that stimulate plant growth), and as biocontrol agents (producing antibiotics or eliciting plant immunity) (Viaene et al., 2016; Vurukonda et al., 2018). These multiple roles often overlap in a single strain. Overall, the adaptive biology of Streptomyces– including their resilience, metabolic wealth, and ability to associate with plants, forms the foundation for their plant growth-promoting activities discussed in the following sections.
DIRECT MECHANISMS OF PLANT GROWTH PROMOTION BY STREPTOMYCES
Certain Streptomyces promote plant growth through direct interactions that improve plant physiology and nutrition. These mechanisms include phytohormone production, nutrient solubilization, and acquisition.
Phytohormone production
Perhaps the most documented direct mechanism is the synthesis of plant hormones (phytohormones) by plant growth-promoting bacteria. Indole-3-acetic acid (IAA), a principal auxin, is commonly produced by many rhizosphere and endophytic Streptomyces (Sousa and Olivares, 2016; Olanrewaju and Babalola, 2019). For example, S. fradiae NKZ-259 was found to produce substantial IAA in culture, and application of this strain and its IAA-rich metabolites significantly increased root length, shoot length, and biomass in tomato seedlings (Myo et al., 2019). Besides, some species have been reported to produce gibberellins and cytokinin-like substances to enhance growth vigor and crop yield of wheat plants (Aldesuquy et al., 1998). Another hormone-related activity responsible for stress modulation is the production of the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase found in beneficial bacteria. The ACC deaminase-overexpressing mutant of S. venezuelae was found to enhance rice growth and salt tolerance more than the original strain (Yoolong et al., 2019).
Nutrient solubilization and acquisition
Streptomyces also promotes plant growth by improving nutrient availability in soil (Sousa and Olivares, 2016). Jog et al. (2014) reported that acidification resulting from the release of malic acid and gluconic acid by Streptomyces sp. mhcr0816 and mhce0811, respectively, facilitated the solubilization of inorganic phosphate. Wheat plants inoculated with these strains exhibited enhanced branching and lateral root formation, increased shoot length, and elevated concentrations of Fe, Mn, and P. Moreover, a Streptomyces strain designated EGT was found to weather potassium-bearing rock and has potential use as an inoculant for potassium biofertilizer production (Liu et al., 2016). Some Streptomyces strains also exhibit free-living nitrogen fixation potential, as demonstrated by the acetylene reduction assay (Sarwar et al., 2019). Although Streptomyces cannot fix nitrogen symbiotically, studies indicate that they can enhance the efficiency of symbiotic nitrogen fixation through their interactions with rhizobia. For example, the root-colonizing strain S. lydicus WYEC108 has been shown to influence pea root nodulation by increasing nodulation frequency, possibly by facilitating Rhizobium infection (Tokala et al., 2002). Colonization of strain WYEC108 within the surface cell layers of nodules also increases nodule size and improves bacteroid vigor. Iron is another critical nutrient, and Streptomyces help plants acquire iron by secreting siderophores, high-affinity iron-chelating compounds to scavenge ferric iron and make it more bioavailable (Rungin et al., 2012). The inoculation of Streptomyces sp. GMKU 3100 significantly increased root and shoot biomass in both rice and mung bean plants compared with siderophore-deficient mutant treatments.
INDIRECT MECHANISMS OF PLANT GROWTH PROMOTION BY STREPTOMYCES
Apart from directly aiding growth, Streptomyces promote plant health and growth indirectly by protecting plants against diseases and stresses. They do so by antagonizing plant pathogens and triggering plant immune responses. Streptomyces are renowned in agricultural microbiology for their robust capacity to act as an antagonist against a wide array of plant pathogenic microorganisms, offering a sustainable alternative to synthetic chemical pesticides (Sousa and Olivares, 2016; Vurukonda et al., 2018; Pacios-Michelena et al., 2021). These filamentous, Gram-positive bacteria are widespread in soils and are highly efficient colonizers of the rhizosphere and endosphere, positioning them as key players in plant protection (Vurukonda et al., 2018; Worsley et al., 2020). Streptomyces deploy diverse strategies, categorized broadly into direct and indirect mechanisms, to suppress plant diseases:
Antibiosis through secondary metabolites
This is the most famous trait of Streptomyces, involving the production of numerous bioactive compounds, including antibiotics, which act as a core competitive strategy in the root zone (Pacios-Michelena et al., 2021).
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Antifungal compounds: many strains produce metabolites effective against fungal pathogens. For instance, three antimicrobial compounds with antifungal activity were discovered in S. violaceusniger YCED-9 (Trejo-Estrada et al., 1998). The Azalomycin F complex is an antifungal substance produced by S. malaysiensis MJM1968 (Cheng et al., 2010). S. libani produces the macrolide antibiotic oligomycin A, which exhibits potent antifungal activity (Kim et al., 1999). Furthermore, metabolites produced by the antagonistic strain N2, identified as filipin-like polyenes including 14-hydroxyisochainin, have been shown to inhibit the crucial cereal pathogen, the take-all fungus (Gaeumannomyces graminis var. tritici) (Worsley et al., 2020). Certain antibiotics, such as Prodiginines from S. lividans, are known to suppress pathogens like Verticillium dahliae (Meschke et al., 2012).
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Bactericidal and nematicidal activity: Streptomyces produce compounds with broad-spectrum activity against bacterial pathogens and nematodes (Suárez-Moreno et al., 2019). S. diastatochromogenes sk-6 shows a highly antagonistic effect on soft rot bacteria (Erwinia carotovora ssp. carotovora) and successfully reduced disease of potatoes in storage (Doolotkeldieva et al., 2016). Compounds isolated from S. hydrogenans DH-16 exhibit nematicidal activity against the destructive root-knot nematode, Meloidogyne incognita (Sharma et al., 2020).
Enzymatic lysis
Streptomyces strains attack pathogen cell walls directly by secreting hydrolytic enzymes (Palaniyandi et al., 2013). The antifungal biocontrol activity of S. lydicus WYEC108, for example, is characterized by its chitinase activity (Mahadevan and Crawford, 1997). The chitinase produced by S. griseus MG3 exhibited antifungal activity against five phytopathogenic fungi (Hoster et al., 2005). Glucanase-producing S. spiralis was demonstrated to suppress pathogenic activities of Pythium aphanidermatum on seedling and mature cucumber plants (El-Tarabily et al., 2009). Both chitinase and beta-1,3-glucanase are produced by S. violaceusniger YCED-9 under induction by fungal cell walls (Trejo-Estrada et al., 1998). Besides, cellulases also contribute to the antagonism, aiding in the control of pathogens such as Phytophthora drechsleri (Sadeghi et al., 2017).
Induced systemic resistance (ISR)
Indirectly, Streptomyces triggers the plant’s defense system, resulting in ISR, which provides broad-spectrum resistance against subsequent infections (Viaene et al., 2016). Analysis using Streptomyces sp. strain EN27 and defense-compromised mutants of Arabidopsis thaliana indicated that resistance to Erwinia carotovora subsp. carotovora occurred via an NPR1-independent pathway and required salicylic acid whereas the jasmonate/ethylene (JA/ET) signaling molecules were not essential (Conn et al., 2008). In contrast, resistance to Fusarium oxysporum mediated by Streptomyces sp. EN27 occurred via an NPR1-dependent pathway but also required salicylic acid and was JA/ET independent. A study shows that Streptomyces sp. AcH 505 suppresses oak powdery mildew by inducing a systemic defense response that intensifies upon pathogen challenge, activating JA/ET and likely salicylic acid-dependent pathways (Kurth et al., 2014). In tomato, a strain of Streptomyces was reported to induce systemic resistance against the root-knot nematode (Meloidogyne incognita), by boosting the plant’s production of defense-related compounds such as phenolics and antioxidant enzymes, thereby reducing nematode infestation and improving plant vigor (Sharma et al., 2020).
APPLICATIONS OF STREPTOMYCES IN DIFFERENT CROPS
Due to the extensive metabolic capabilities and high colonization potential of Streptomyces in the rhizosphere and the endosphere, they are prime candidates for use in agriculture as plant growth-promoting streptomycetes (PGPS), serving dual roles as biofertilizers and biocontrol agents (Sousa and Olivares, 2016; Vurukonda et al., 2018). These applications provide a sustainable, environmentally friendly alternative to traditional chemical pesticides and synthetic fertilizers, thereby helping address global food security challenges (Rey and Dumas, 2017; Pacios-Michelena et al., 2021). The versatile benefits of Streptomyces have been demonstrated in a wide range of plant species, including cereal and vegetable crops. Here, we highlight some representative cases and the development of Streptomyces-based bioinoculants.
Rice (Oryza sativa)
The genus has been extensively studied for the management of rice blast disease caused by the fungus Magnaporthe oryzae (anamorph Pyricularia oryzae) (Law et al., 2017). S. globisporus JK-1 inhibited Magnaporthe oryzae in laboratory assays, and its culture filtrate reduced rice blast by 88.3% in greenhouse tests (Li et al., 2011). The Streptomyces sp. UPMRS4 treatment reduced disease severity by 67.9% and significantly improved plant growth, including shoot and root development, leaf area, tiller number, yield, panicle length, and spikelet production after three months (Awla et al., 2017). An antifungal aliphatic compound SPM5C-1 obtained from Streptomyces sp. PM5 completely inhibited the growth of Pyricularia oryzae and Rhizoctonia solani (Prabavathy et al., 2006). Greenhouse experiments revealed that spraying of SPM5C-1 at 500 μg ml-1 on rice significantly decreased blast and sheath blight development by 76.1% and 82.3%, respectively, as compared to the control, with a corresponding increase in rice grain yield.
S. aurantiogriseus VSMGT1014, an indigenous strain that exhibits antagonistic potential against sheath blight (Rhizoctonia solani) (Harikrishnan et al., 2014). Streptomyces spp. A20, 5.1, and 7.1, which possess biocontrol properties against the bacterial rice pathogen Burkholderia glumae, the cause of Bacterial Panicle Blight (Suárez-Moreno et al., 2019). Strain A20, originally isolated from rice sown soil, showed potential for both growth promotion and biocontrol in rice. In terms of growth promotion, S. palmae PC 12 was found to increase rice plant height, root length, root dry weight, and tiller number in greenhouse conditions (Chaiharn et al., 2020). Additionally, S. venezuelae ATCC 10712 has been shown to modulate salt tolerance in Thai jasmine rice by expressing ACC deaminase (Yoolong et al., 2019).
Wheat (Triticum aestivum)
Streptomyces plays a critical role in managing fungal pathogens in wheat, notably, take-all disease caused by Gaeumannomyces graminis var. tritici. Streptomyces sp. N2, isolated from Arabidopsis thaliana roots, produced potent filipin-like antifungals and was successfully used to protect germinating wheat seeds against the take-all fungus when applied as a spore coating (Worsley et al., 2020). S. fulvissimus Uts22 has also demonstrated biocontrol efficiency against Gaeumannomyces graminis (Saberi-Riseh and Moradi-Pour, 2021). S. mutabilis IA1 isolated from Saharan soil, exhibited biocontrol properties against Fusarium culmorum on wheat seedlings (Toumatia et al., 2016). In biofertilization experiments, Streptomyces isolates from the rhizosphere and roots of wheat enhanced growth parameters and significantly increased plant mineral content, particularly iron, manganese, and phosphorus (Jog et al., 2014). Culture filtrates derived from species like S. olivaceoviridis, S. rimosus, and S. rochei have also been evaluated for their positive effects on wheat growth and productivity (Aldesuquy et al., 1998).
Potato (Solanum tuberosum)
One of the most notable applications involves managing Potato Common Scab (PCS), an economically devastating disease caused by pathogenic Streptomyces species (e.g., S. scabies) (Loria et al., 2008; Viaene et al., 2016). A specific strain, S. violaceusniger AC12AB, has been identified as a potent dual-purpose agent for potatoes (Sarwar et al., 2019). This strain demonstrated significant antagonistic activity against S. scabies. Greenhouse and field trials showed that when potato tubers were inoculated with S. violaceusniger AC12AB, PCS disease severity was reduced by up to 90% and 80%, respectively. This antagonistic effect is attributed mainly to the production of the bioactive compound azalomycin RS-22A. Furthermore, S. violaceusniger AC12AB acts as a plant growth promoter. Its attributes include production of IAA (up to 17 µg mL−1 titers), siderophore synthesis, nitrogen fixation, and phosphates solubilization. These plant growth-promoting traits provided a significant secondary benefit. The field trial reported a substantial increase in potato crop yield, up to 26.8%. Other Streptomyces species, such as Streptomyces sp. TP199, have been tested against potato soft rot caused by Pectobacterium carotovorum subsp. carotovorum and Pectobacterium atrosepticum (Padilla-Gálvez et al., 2021).
Tomato (Solanum lycopersicum)
In a study of the biological control of tomato diseases using antagonistic Streptomyces spp., El-Abyad et al. (1993) demonstrated that S. canescens effectively reduced infections of Fusarium wilt (Fusarium oxysporum f. sp. lycopersici), Verticillium wilt (Verticillium albo-atrum), and early blight (Alternaria solani). They also reported that S. pulcher showed strong potential in suppressing bacterial wilt (Pseudomonas solanacearum) and bacterial canker (Clavibacter michiganensis subsp. michiganensis). S. griseus was successfully used to control the Fusarium oxysporum f. sp. lycopersici induced fusarium wilt disease in tomato (Anitha and Rabeeth, 2009).
A talcum powder formulation of Streptomyces sp. Di-944, delivered as a seed coating, effectively suppressed Rhizoctonia damping-off in tomato transplants (Sabaratnam and Traquair, 2002). Coating tomato seeds with S. mutabilis CA-2 or S. cyaneofuscatus AA-2 significantly reduced the severity of seedling damping-off and led to notable increases in seedling fresh weight, seedling length and root length compared with the untreated control (Goudjal et al., 2014). S. filipinensis no. 15 produced both ACC deaminase and IAA, and its application lowered endogenous ACC, the direct ethylene precursor, in roots and shoots, leading to enhanced tomato plant growth (El-Tarabily, 2008). Besides, S. lydicus A01 was found to enhance the utilization of nitrogen, phosphorus, and potassium in tomato seedlings (Wu et al., 2019).
Bioformulations and commercial products
Despite the vast potential discovered through research, only a few Streptomyces-based products are currently commercialized globally (Vurukonda et al., 2018). The most prominent commercial microbial products include Mycostop and Actinovate. Mycostop derived from S. griseoviridis K61 is used to control damping-off and wilt diseases caused by soilborne fungal pathogens such as Alternaria, Rhizoctonia solani, Fusarium, Phytophthora, and Pythium. Actinovate derived from S. lydicus WYEC 108 is used against soilborne pathogens (Pythium, Fusarium, Phytophthora, Rhizoctonia, Verticillium) and foliar diseases like powdery and downy mildew (Botrytis and Alternaria, Postia, Geotrichum, and Sclerotinia).
In addition to living microbial preparations, metabolites derived from Streptomyces species are widely commercialized as active ingredients for crop protection against fungi, bacteria, and insects (Vurukonda et al., 2018). For example, Validamycin, derived from S. hygroscopicus, is used globally to control Rhizoctonia solani in rice, potatoes, vegetables, strawberries, tobacco, ginger, cotton, and sugar beets. Streptomycin derived from S. griseus is registered as a bactericide against bacterial rots and canker, targeting pathogens like Xanthomonas oryzae, Xanthomonas citri, and Pseudomonas tabaci in various crops, including pome fruit, stone fruit, citrus, olives, vegetables, potatoes, tobacco, cotton, and ornamentals. Avermectin derived from S. avermitilis is used as an insecticide/nematicide to control mites, leaf miners, suckers, beetles, fire ants, and other insects in ornamentals, cotton, citrus, pome and nut fruit, vegetables.
CHALLENGES IN THE APPLICATION OF STREPTOMYCES
The genus Streptomyces has immense potential as a component of modern agriculture, serving as both biofertilizers and biocontrol agents, with the capacity to dominate agricultural markets in the coming decades (Pacios-Michelena et al., 2021). However, translating this biotechnological promise from the lab to large-scale commercialization faces several significant scientific, technical, regulatory, and economic hurdles.
Knowledge gaps on mechanisms and ecology
There is an urgent need for fundamental insights into the mechanisms of action of Streptomyces (Viaene et al., 2016). The complex environment of the Streptomyces-rhizosphere and the mechanisms of plant growth-promoting action require extensive future studies (Vurukonda et al., 2018). Key areas where knowledge is insufficient include:
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Ecological interactions: the interactions between rhizosphere Streptomyces and native microbiota, as well as the infection processes employed by endophytic Streptomyces, are still not sufficiently explained.
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Biosynthetic gene clusters: genome sequencing suggests that as much as 90% of the chemical potential of these organisms remains undiscovered and that the biosynthetic machinery encoded by many of these genetic loci may be activated under laboratory conditions (Wu et al., 2012). How and why these pathways are activated in nature, and their ecological functions, remain unclear (Rey and Dumas, 2017).
Formulation, viability, and shelf life
In the agro-pharmaceutical industry, the major obstacle to commercial success is product formulation (Vurukonda et al., 2018; Pacios-Michelena et al., 2021). Microbial inoculants, including Streptomyces, face the specific problem of loss of viability during storage, which complicates the requirement for a long shelf life and stability under typical grower storage conditions, often ranging from -5℃ to 30℃ (Pacios-Michelena et al., 2021). Improving the shelf life while maintaining biological activity is an essential aspect of formulation technology (Saberi-Riseh and Moradi-Pour, 2021). Studies focusing on vegetative propagules of strains like Streptomyces sp. Di-944 found that formulations stored at 4℃ had a longer shelf life and better efficacy than those stored at 24℃, indicating temperature dependence (Sabaratnam and Traquair, 2002). The decline in the efficacy of surviving viable propagules over time is also a serious concern.
Field efficacy and environmental variability
A crucial challenge in the industrial development of bio-inoculants is that biological control agents frequently do not show the same results in vitro and in vivo (Vurukonda et al., 2018; Pacios-Michelena et al., 2021). An experimentally excellent biocontrol agent may fail in greenhouse or field experiments. The effectiveness of Streptomyces strains is significantly affected by a multitude of factors in the field:
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Abiotic factors: soil type and characteristics (e.g., nutrient levels, water content, pH, and trace metals), climate, and agricultural practices affect treatment effectiveness. For instance, the production of antimicrobial molecules by actinobacteria, especially Streptomyces, is strictly dependent on the substrate where they grow.
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Biotic factors: crop species, plant genetics, root exudation profiles, plant age, and competing microorganisms from the native soil microbiome also influence efficiency.
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Lack of field data: most published studies demonstrate excellent activity under strictly standardized conditions, often lacking field research results to support the applicability of experimental data in commercial settings.
Biosafety and regulatory hurdles
Deploying Streptomyces at an industrial scale necessitates a thorough risk assessment (Barka et al., 2016). Potential risks include the release of microorganisms, particularly the horizontal transfer of entire or partial gene clusters conferring antibiotic resistance to unselected bacterial species (Pacios-Michelena et al., 2021). While this risk might be minimized by accurately characterizing prospective strains for the lack of known antibiotic-resistant genes before registration (Egan et al., 2001), regulatory standards currently are often inspired by synthetic chemicals, which is not adaptable to living microbial organisms and their derived preparations (Rey and Dumas, 2017). Furthermore, potential plant growth-promoting rhizobacteria must be confirmed to be non-pathogenic to both plants and animals (including humans) before being introduced into agriculture (Glick, 2015).
Adopting cost-effective strategies
Drawing on multiple case studies across diverse agroecological zones, the analysis reveals that cost-effective biopesticides are critical for advancing integrated pest management in traditional and smallholder farming systems. At the same time, branded formulations predominantly benefit large-scale farms with greater economic capacity (Fenibo and Matambo, 2025).
PROSPECTS AND OPPORTUNITIES
The increasing global demand for food, combined with the need for sustainable and environmentally friendly agricultural practices, positions Streptomyces as a vital resource for future development (Vurukonda et al., 2018).
Advanced formulation and delivery technologies
Future research needs to focus heavily on developing novel formulations that ensure the long-term viability and efficacy of Streptomyces (Pacios-Michelena et al., 2021).
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Encapsulation and nanotechnology: encapsulation offers an advantageous and environmentally friendly option for new biological control products. Interest in nanoencapsulation has increased, as it uses nanosized carriers to protect organisms or their compounds, offering benefits such as increased solubility, high adsorption, controlled release, and improved stability against environmental stresses. Encapsulation systems are an attractive alternative for the release of biological control products.
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Optimized delivery: research is needed to develop industrial processes for effective formulations using different additives and carriers, tailored for various methods of field inoculation (Vurukonda et al., 2018). Dry formulations (powders, granules) are generally preferred due to their extended shelf life, ease of transport, and storage (Sabaratnam and Traquair, 2002).
Molecular and ‘omics’ driven research
To fully exploit the potential of Streptomyces, advanced research tools must be employed:
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Mechanism elucidation: extensive studies utilizing metagenomics and molecular biology tools (such as green fluorescent protein tagging) are necessary to track the fate of microbial populations, their endophytic distribution, and colonization patterns in host plants (Vurukonda et al., 2018).
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Synthetic biology and metabolic engineering: the advent of synthetic biology tools, including CRISPR/Cas9 technology, provides innovative approaches for multiplex genetic modification to enhance or suppress secondary metabolites (Viaene et al., 2016; Rey and Dumas, 2017). This capability is critical for unlocking the vast number of biosynthetic gene clusters residing in the Streptomyces genome, potentially leading to a new generation of antimicrobials and specialized plant health compounds (Barka et al., 2016).
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Ecological insight: understanding the regulation and production of secondary metabolites and gene clusters using ‘omics’ approaches will contribute knowledge about rhizosphere colonization and crosstalk between Streptomyces and other organisms (Olanrewaju and Babalola, 2019).
Diversified product development strategy
Future strategies should prioritize product types that offer greater stability and predictability:
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Metabolite focus: using Streptomyces metabolites instead of living strains is expected to accelerate the replacement of chemically synthesized pesticides (Rey and Dumas, 2017; Pacios-Michelena et al., 2021). Metabolite formulations are much less challenging to stabilize than living organisms. Purified metabolites (such as polyoxin D, streptomycin, and kasugamycin) are already commercially available as foliar sprays.
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Consortia development: research into the symbiotic potential of Streptomyces in conjunction with other plant growth-promoting rhizobacteria may lead to highly effective and efficient bioinoculants suitable for diverse soil types and environmental conditions (Vurukonda et al., 2018). Designing tailored biofertilization programs using different consortia for specific crop phenological phases is a promising approach (Malusá and Vassilev, 2014; Gopalakrishnan et al., 2022).
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New applications: the great potential of Streptomyces to control post-harvest bacterial and fungal diseases of fruits and vegetables remains unexplored mainly (Vurukonda et al., 2018).
Ultimately, for Streptomyces to fulfill its potential, the scientific community must overcome the challenges of achieving predictable efficacy in variable field conditions and developing stable, regulatory-compliant commercial formulations. Harnessing the organism’s vast, largely silent metabolic potential with advanced molecular tools represents the next critical frontier in agricultural microbiology.
CONCLUSION
The genus Streptomyces can be addressed both as a biofertilizer and an effective biocontrol agent. The adoption of Streptomyces-based bioinoculants offers a desirable and environmentally friendly alternative to synthetic chemicals. The beneficial roles of Streptomyces are multifaceted, achieved through various mechanisms, including phytohormone production, nutrient solubilization, and acquisition. Furthermore, they protect plants against diseases and stresses through antibiosis, enzymatic lysis, and induced systemic resistance. Despite this confirmed biotechnological promise, the large-scale commercialization of Streptomyces strains remains limited. The critical challenge is translating results from controlled environments to field conditions. Crucially, greater attention is needed to develop novel formulations that can significantly extend the shelf life and long-term viability of these microbial-based agrochemicals. Ultimately, combining biocontrol and biofertilizer activities is necessary to ensure effective commercial products that promote plant growth even in the absence of pathogen pressure.
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Role of the Members of Streptomyces Genus in Promoting Plant Growth
DOI: https://doi.org/10.56669/YJZG5650
ABSTRACT
The genus Streptomyces comprising of filamentous actinobacteria (belonging to the phylum Actinomycota), are renowned for their remarkable metabolic capacity and production of copious bioactive metabolites, including more than two-thirds of all clinically used antibiotics. Due to the environmental degradation caused by traditional agriculture’s heavy reliance on chemical fertilizers and pesticides, there is an urgent global need for sustainable agricultural practices. As plant growth-promoting rhizobacteria, the genus Streptomyces has emerged as a potential option for reducing chemical inputs, enhancing crop yield and providing resilience against stress. Streptomyces facilitates plant growth through multifaceted mechanisms. Direct mechanisms include the synthesis of phytohormones to stimulate growth and the production of ACC deaminase to modulate stress. Furthermore, they aid in nutrient solubilization and acquisition by releasing organic acids to dissolve inorganic phosphate. Certain strains can also weather potassium-bearing rock or secrete siderophores to acquire iron. Indirect mechanisms are mainly represented by their biocontrol potential against pathogens. Streptomyces achieves this through antibiosis by generating broad-spectrum antifungal, bactericidal, and nematicidal compounds. They also facilitate enzymatic lysis by secreting hydrolytic enzymes that break down pathogen cell walls. Additionally, they can induce systemic resistance in plants, offering broad-spectrum protection against subsequent infections. Streptomyces has demonstrated potential applications in various crops, including rice, wheat, potato, and tomato, often serving dual roles as biofertilizers and biocontrol agents. While commercial products like Mycostop (S. griseoviridis K61) and Actinovate (S. lydicus WYEC 108) are commercialized, large-scale adoption faces significant challenges. Primary hurdles include the instability of formulations during storage and the uncertainty of efficacy under diverse field conditions. Future research should prioritize developing advanced formulations, using synthetic biology tools to unlock the vast, untapped metabolic potential within the Streptomyces genome, and focusing on the utilization of more stable metabolites or microbial consortia to improve the predictability and longevity of commercial products.
Keywords: Streptomyces, plant growth-promoting rhizobacteria, biocontrol, bioactive metabolites, sustainable agriculture
INTRODUCTION
The growing world population and escalating food demand pose a serious challenge to global agriculture (Godfray et al., 2010; Sugumar et al., 2024). Traditional Green Revolution strategies that rely heavily on chemical fertilizers and pesticides have indeed boosted crop yields, but often at the cost of environmental degradation (Foley et al., 2011; Ni et al., 2025). Overuse of synthetic agrochemicals has led to soil acidification, biodiversity loss, water pollution, and even been linked to human health risks in the long term. There is an urgent need for sustainable agricultural practices that can ensure high yields with minimal environmental impact. In this context, plant growth-promoting rhizobacteria have emerged as a promising component of sustainable crop management (Bhattacharyya and Jha, 2012; Wahab et al., 2025). These beneficial microorganisms can enhance plant nutrition and health, thereby reducing reliance on chemical inputs.
Among plant-beneficial microbes, the genus Streptomyces has attracted growing attention for its multifaceted roles in promoting plant growth and offering protection against biotic and abiotic stresses (Vurukonda et al., 2018; Olanrewaju and Babalola, 2019). Streptomyces are filamentous actinobacteria renowned in medicine as prolific producers of antibiotics – indeed, actinomycetes (especially Streptomyces) produce the majority of known antimicrobial compounds (Bérdy, 2005). In agriculture, those same metabolic capabilities endow Streptomyces with biocontrol potential against plant pathogens, as well as the ability to synthesize phytohormones and other metabolites that directly stimulate plant growth (Palaniyandi et al., 2013; Sousa and Olivares, 2016). This review elucidates the principal mechanisms by which Streptomyces facilitate plant growth and provides representative examples of their applications across various crops. Also discussed are the challenges of harnessing Streptomyces in the field and prospects for their use in sustainable agriculture. The aim is to provide a comprehensive overview of Streptomyces–plant interactions and their potential in improving crop productivity and resilience.
STREPTOMYCES BIOLOGICAL CHARACTERISTICS
Taxonomy and morphology
Streptomyces is a genus of filamentous bacteria in the phylum Actinomycetota (family Streptomycetaceae). They grow as branching mycelia, forming a network of hyphae analogous to fungal mycelium. A distinctive feature is their sporulation; Streptomyces develop chains of conidiospores on specialized aerial hyphae, giving colonies a powdery appearance (Barka et al., 2016). These spores allow Streptomyces to disperse and survive harsh conditions, contributing to their ecological success. The genus is taxonomically rich and currently has 810 species with validly published and correct names (https://lpsn.dsmz.de/genus/streptomyces; accessed on 8 March 2026). The high genomic GC content and large genome size correlate with a capacity to produce diverse secondary metabolites and enzymes (Liu et al., 2013).
Ecological distribution
Most of the Streptomyces are soil-dwelling bacteria with a free-living life cycle in the soil. They can efficiently colonize the rhizosphere - the soil area surrounding plant roots, rhizoplane and endosphere - internal part of plants (Sousa and Olivares, 2016; Vurukonda et al., 2018). Metagenomic analyses of plant microbiota have recently strengthened the view that Streptomyces spp. are natural major endophytes of plants, capable of colonizing roots or living in the rhizosphere (Rey and Dumas, 2017).
Metabolic diversity
A hallmark of Streptomyces is their prolific secondary metabolism. They produce a wide variety of bioactive metabolites, including more than two-thirds of the clinically used antibiotics (Bérdy, 2005). Classic examples are streptomycin, chloramphenicol, tetracyclines, and macrolides. Many Streptomyces also secrete extracellular enzymes-including amylase, chitinase, cellulase, invertase, lipase, keratinase, peroxidase, pectinase, proteases, phytase, and xylanase-which make the complex nutrients into simple mineral forms (Vurukonda et al., 2018). This not only helps in nutrient cycling but also contributes to biocontrol by degrading pathogen cell walls. Uniquely, certain Streptomyces produce phytohormones and other metabolites that can directly influence plant physiology (Tokala et al., 2002; Palaniyandi et al., 2013; Ly et al., 2026). The metabolic versatility of Streptomyces is reflected in their genomes, which harbor an exceptional number of biosynthetic gene clusters (Barka et al., 2016). This rich chemistry is one reason Streptomyces are invaluable in biotechnology and plant health applications.
Interactions with plants
Streptomyces interact with plants in multiple modes, ranging from free-living, associative relationships in the rhizosphere to intimate endophytic symbioses (Sousa and Olivares, 2016). Some strains exhibit chemotaxis toward root exudates, allowing targeted colonization of the root vicinity. Endophytic Streptomyces have been isolated from crops like wheat and rice, often conferring growth or health benefits to their hosts (Worsley et al., 2020). The relationships can be mutualistic: the plants provide habitat and nutrients, while the bacteria produce growth-promoting substances or guard the plants against pathogens. Notably, while most Streptomyces are beneficial or neutral to plants, a few species are plant pathogens (for example, S. scabies, the causal agent of potato scab, produces thaxtomin phytotoxin (Loria et al., 2008)). This dual nature underscores the importance of understanding Streptomyces-plant interactions. In beneficial interactions, Streptomyces can simultaneously act as biofertilizers (enhancing nutrient availability), as phytostimulators (releasing hormones that stimulate plant growth), and as biocontrol agents (producing antibiotics or eliciting plant immunity) (Viaene et al., 2016; Vurukonda et al., 2018). These multiple roles often overlap in a single strain. Overall, the adaptive biology of Streptomyces– including their resilience, metabolic wealth, and ability to associate with plants, forms the foundation for their plant growth-promoting activities discussed in the following sections.
DIRECT MECHANISMS OF PLANT GROWTH PROMOTION BY STREPTOMYCES
Certain Streptomyces promote plant growth through direct interactions that improve plant physiology and nutrition. These mechanisms include phytohormone production, nutrient solubilization, and acquisition.
Phytohormone production
Perhaps the most documented direct mechanism is the synthesis of plant hormones (phytohormones) by plant growth-promoting bacteria. Indole-3-acetic acid (IAA), a principal auxin, is commonly produced by many rhizosphere and endophytic Streptomyces (Sousa and Olivares, 2016; Olanrewaju and Babalola, 2019). For example, S. fradiae NKZ-259 was found to produce substantial IAA in culture, and application of this strain and its IAA-rich metabolites significantly increased root length, shoot length, and biomass in tomato seedlings (Myo et al., 2019). Besides, some species have been reported to produce gibberellins and cytokinin-like substances to enhance growth vigor and crop yield of wheat plants (Aldesuquy et al., 1998). Another hormone-related activity responsible for stress modulation is the production of the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase found in beneficial bacteria. The ACC deaminase-overexpressing mutant of S. venezuelae was found to enhance rice growth and salt tolerance more than the original strain (Yoolong et al., 2019).
Nutrient solubilization and acquisition
Streptomyces also promotes plant growth by improving nutrient availability in soil (Sousa and Olivares, 2016). Jog et al. (2014) reported that acidification resulting from the release of malic acid and gluconic acid by Streptomyces sp. mhcr0816 and mhce0811, respectively, facilitated the solubilization of inorganic phosphate. Wheat plants inoculated with these strains exhibited enhanced branching and lateral root formation, increased shoot length, and elevated concentrations of Fe, Mn, and P. Moreover, a Streptomyces strain designated EGT was found to weather potassium-bearing rock and has potential use as an inoculant for potassium biofertilizer production (Liu et al., 2016). Some Streptomyces strains also exhibit free-living nitrogen fixation potential, as demonstrated by the acetylene reduction assay (Sarwar et al., 2019). Although Streptomyces cannot fix nitrogen symbiotically, studies indicate that they can enhance the efficiency of symbiotic nitrogen fixation through their interactions with rhizobia. For example, the root-colonizing strain S. lydicus WYEC108 has been shown to influence pea root nodulation by increasing nodulation frequency, possibly by facilitating Rhizobium infection (Tokala et al., 2002). Colonization of strain WYEC108 within the surface cell layers of nodules also increases nodule size and improves bacteroid vigor. Iron is another critical nutrient, and Streptomyces help plants acquire iron by secreting siderophores, high-affinity iron-chelating compounds to scavenge ferric iron and make it more bioavailable (Rungin et al., 2012). The inoculation of Streptomyces sp. GMKU 3100 significantly increased root and shoot biomass in both rice and mung bean plants compared with siderophore-deficient mutant treatments.
INDIRECT MECHANISMS OF PLANT GROWTH PROMOTION BY STREPTOMYCES
Apart from directly aiding growth, Streptomyces promote plant health and growth indirectly by protecting plants against diseases and stresses. They do so by antagonizing plant pathogens and triggering plant immune responses. Streptomyces are renowned in agricultural microbiology for their robust capacity to act as an antagonist against a wide array of plant pathogenic microorganisms, offering a sustainable alternative to synthetic chemical pesticides (Sousa and Olivares, 2016; Vurukonda et al., 2018; Pacios-Michelena et al., 2021). These filamentous, Gram-positive bacteria are widespread in soils and are highly efficient colonizers of the rhizosphere and endosphere, positioning them as key players in plant protection (Vurukonda et al., 2018; Worsley et al., 2020). Streptomyces deploy diverse strategies, categorized broadly into direct and indirect mechanisms, to suppress plant diseases:
Antibiosis through secondary metabolites
This is the most famous trait of Streptomyces, involving the production of numerous bioactive compounds, including antibiotics, which act as a core competitive strategy in the root zone (Pacios-Michelena et al., 2021).
Antifungal compounds: many strains produce metabolites effective against fungal pathogens. For instance, three antimicrobial compounds with antifungal activity were discovered in S. violaceusniger YCED-9 (Trejo-Estrada et al., 1998). The Azalomycin F complex is an antifungal substance produced by S. malaysiensis MJM1968 (Cheng et al., 2010). S. libani produces the macrolide antibiotic oligomycin A, which exhibits potent antifungal activity (Kim et al., 1999). Furthermore, metabolites produced by the antagonistic strain N2, identified as filipin-like polyenes including 14-hydroxyisochainin, have been shown to inhibit the crucial cereal pathogen, the take-all fungus (Gaeumannomyces graminis var. tritici) (Worsley et al., 2020). Certain antibiotics, such as Prodiginines from S. lividans, are known to suppress pathogens like Verticillium dahliae (Meschke et al., 2012).
Bactericidal and nematicidal activity: Streptomyces produce compounds with broad-spectrum activity against bacterial pathogens and nematodes (Suárez-Moreno et al., 2019). S. diastatochromogenes sk-6 shows a highly antagonistic effect on soft rot bacteria (Erwinia carotovora ssp. carotovora) and successfully reduced disease of potatoes in storage (Doolotkeldieva et al., 2016). Compounds isolated from S. hydrogenans DH-16 exhibit nematicidal activity against the destructive root-knot nematode, Meloidogyne incognita (Sharma et al., 2020).
Enzymatic lysis
Streptomyces strains attack pathogen cell walls directly by secreting hydrolytic enzymes (Palaniyandi et al., 2013). The antifungal biocontrol activity of S. lydicus WYEC108, for example, is characterized by its chitinase activity (Mahadevan and Crawford, 1997). The chitinase produced by S. griseus MG3 exhibited antifungal activity against five phytopathogenic fungi (Hoster et al., 2005). Glucanase-producing S. spiralis was demonstrated to suppress pathogenic activities of Pythium aphanidermatum on seedling and mature cucumber plants (El-Tarabily et al., 2009). Both chitinase and beta-1,3-glucanase are produced by S. violaceusniger YCED-9 under induction by fungal cell walls (Trejo-Estrada et al., 1998). Besides, cellulases also contribute to the antagonism, aiding in the control of pathogens such as Phytophthora drechsleri (Sadeghi et al., 2017).
Induced systemic resistance (ISR)
Indirectly, Streptomyces triggers the plant’s defense system, resulting in ISR, which provides broad-spectrum resistance against subsequent infections (Viaene et al., 2016). Analysis using Streptomyces sp. strain EN27 and defense-compromised mutants of Arabidopsis thaliana indicated that resistance to Erwinia carotovora subsp. carotovora occurred via an NPR1-independent pathway and required salicylic acid whereas the jasmonate/ethylene (JA/ET) signaling molecules were not essential (Conn et al., 2008). In contrast, resistance to Fusarium oxysporum mediated by Streptomyces sp. EN27 occurred via an NPR1-dependent pathway but also required salicylic acid and was JA/ET independent. A study shows that Streptomyces sp. AcH 505 suppresses oak powdery mildew by inducing a systemic defense response that intensifies upon pathogen challenge, activating JA/ET and likely salicylic acid-dependent pathways (Kurth et al., 2014). In tomato, a strain of Streptomyces was reported to induce systemic resistance against the root-knot nematode (Meloidogyne incognita), by boosting the plant’s production of defense-related compounds such as phenolics and antioxidant enzymes, thereby reducing nematode infestation and improving plant vigor (Sharma et al., 2020).
APPLICATIONS OF STREPTOMYCES IN DIFFERENT CROPS
Due to the extensive metabolic capabilities and high colonization potential of Streptomyces in the rhizosphere and the endosphere, they are prime candidates for use in agriculture as plant growth-promoting streptomycetes (PGPS), serving dual roles as biofertilizers and biocontrol agents (Sousa and Olivares, 2016; Vurukonda et al., 2018). These applications provide a sustainable, environmentally friendly alternative to traditional chemical pesticides and synthetic fertilizers, thereby helping address global food security challenges (Rey and Dumas, 2017; Pacios-Michelena et al., 2021). The versatile benefits of Streptomyces have been demonstrated in a wide range of plant species, including cereal and vegetable crops. Here, we highlight some representative cases and the development of Streptomyces-based bioinoculants.
Rice (Oryza sativa)
The genus has been extensively studied for the management of rice blast disease caused by the fungus Magnaporthe oryzae (anamorph Pyricularia oryzae) (Law et al., 2017). S. globisporus JK-1 inhibited Magnaporthe oryzae in laboratory assays, and its culture filtrate reduced rice blast by 88.3% in greenhouse tests (Li et al., 2011). The Streptomyces sp. UPMRS4 treatment reduced disease severity by 67.9% and significantly improved plant growth, including shoot and root development, leaf area, tiller number, yield, panicle length, and spikelet production after three months (Awla et al., 2017). An antifungal aliphatic compound SPM5C-1 obtained from Streptomyces sp. PM5 completely inhibited the growth of Pyricularia oryzae and Rhizoctonia solani (Prabavathy et al., 2006). Greenhouse experiments revealed that spraying of SPM5C-1 at 500 μg ml-1 on rice significantly decreased blast and sheath blight development by 76.1% and 82.3%, respectively, as compared to the control, with a corresponding increase in rice grain yield.
S. aurantiogriseus VSMGT1014, an indigenous strain that exhibits antagonistic potential against sheath blight (Rhizoctonia solani) (Harikrishnan et al., 2014). Streptomyces spp. A20, 5.1, and 7.1, which possess biocontrol properties against the bacterial rice pathogen Burkholderia glumae, the cause of Bacterial Panicle Blight (Suárez-Moreno et al., 2019). Strain A20, originally isolated from rice sown soil, showed potential for both growth promotion and biocontrol in rice. In terms of growth promotion, S. palmae PC 12 was found to increase rice plant height, root length, root dry weight, and tiller number in greenhouse conditions (Chaiharn et al., 2020). Additionally, S. venezuelae ATCC 10712 has been shown to modulate salt tolerance in Thai jasmine rice by expressing ACC deaminase (Yoolong et al., 2019).
Wheat (Triticum aestivum)
Streptomyces plays a critical role in managing fungal pathogens in wheat, notably, take-all disease caused by Gaeumannomyces graminis var. tritici. Streptomyces sp. N2, isolated from Arabidopsis thaliana roots, produced potent filipin-like antifungals and was successfully used to protect germinating wheat seeds against the take-all fungus when applied as a spore coating (Worsley et al., 2020). S. fulvissimus Uts22 has also demonstrated biocontrol efficiency against Gaeumannomyces graminis (Saberi-Riseh and Moradi-Pour, 2021). S. mutabilis IA1 isolated from Saharan soil, exhibited biocontrol properties against Fusarium culmorum on wheat seedlings (Toumatia et al., 2016). In biofertilization experiments, Streptomyces isolates from the rhizosphere and roots of wheat enhanced growth parameters and significantly increased plant mineral content, particularly iron, manganese, and phosphorus (Jog et al., 2014). Culture filtrates derived from species like S. olivaceoviridis, S. rimosus, and S. rochei have also been evaluated for their positive effects on wheat growth and productivity (Aldesuquy et al., 1998).
Potato (Solanum tuberosum)
One of the most notable applications involves managing Potato Common Scab (PCS), an economically devastating disease caused by pathogenic Streptomyces species (e.g., S. scabies) (Loria et al., 2008; Viaene et al., 2016). A specific strain, S. violaceusniger AC12AB, has been identified as a potent dual-purpose agent for potatoes (Sarwar et al., 2019). This strain demonstrated significant antagonistic activity against S. scabies. Greenhouse and field trials showed that when potato tubers were inoculated with S. violaceusniger AC12AB, PCS disease severity was reduced by up to 90% and 80%, respectively. This antagonistic effect is attributed mainly to the production of the bioactive compound azalomycin RS-22A. Furthermore, S. violaceusniger AC12AB acts as a plant growth promoter. Its attributes include production of IAA (up to 17 µg mL−1 titers), siderophore synthesis, nitrogen fixation, and phosphates solubilization. These plant growth-promoting traits provided a significant secondary benefit. The field trial reported a substantial increase in potato crop yield, up to 26.8%. Other Streptomyces species, such as Streptomyces sp. TP199, have been tested against potato soft rot caused by Pectobacterium carotovorum subsp. carotovorum and Pectobacterium atrosepticum (Padilla-Gálvez et al., 2021).
Tomato (Solanum lycopersicum)
In a study of the biological control of tomato diseases using antagonistic Streptomyces spp., El-Abyad et al. (1993) demonstrated that S. canescens effectively reduced infections of Fusarium wilt (Fusarium oxysporum f. sp. lycopersici), Verticillium wilt (Verticillium albo-atrum), and early blight (Alternaria solani). They also reported that S. pulcher showed strong potential in suppressing bacterial wilt (Pseudomonas solanacearum) and bacterial canker (Clavibacter michiganensis subsp. michiganensis). S. griseus was successfully used to control the Fusarium oxysporum f. sp. lycopersici induced fusarium wilt disease in tomato (Anitha and Rabeeth, 2009).
A talcum powder formulation of Streptomyces sp. Di-944, delivered as a seed coating, effectively suppressed Rhizoctonia damping-off in tomato transplants (Sabaratnam and Traquair, 2002). Coating tomato seeds with S. mutabilis CA-2 or S. cyaneofuscatus AA-2 significantly reduced the severity of seedling damping-off and led to notable increases in seedling fresh weight, seedling length and root length compared with the untreated control (Goudjal et al., 2014). S. filipinensis no. 15 produced both ACC deaminase and IAA, and its application lowered endogenous ACC, the direct ethylene precursor, in roots and shoots, leading to enhanced tomato plant growth (El-Tarabily, 2008). Besides, S. lydicus A01 was found to enhance the utilization of nitrogen, phosphorus, and potassium in tomato seedlings (Wu et al., 2019).
Bioformulations and commercial products
Despite the vast potential discovered through research, only a few Streptomyces-based products are currently commercialized globally (Vurukonda et al., 2018). The most prominent commercial microbial products include Mycostop and Actinovate. Mycostop derived from S. griseoviridis K61 is used to control damping-off and wilt diseases caused by soilborne fungal pathogens such as Alternaria, Rhizoctonia solani, Fusarium, Phytophthora, and Pythium. Actinovate derived from S. lydicus WYEC 108 is used against soilborne pathogens (Pythium, Fusarium, Phytophthora, Rhizoctonia, Verticillium) and foliar diseases like powdery and downy mildew (Botrytis and Alternaria, Postia, Geotrichum, and Sclerotinia).
In addition to living microbial preparations, metabolites derived from Streptomyces species are widely commercialized as active ingredients for crop protection against fungi, bacteria, and insects (Vurukonda et al., 2018). For example, Validamycin, derived from S. hygroscopicus, is used globally to control Rhizoctonia solani in rice, potatoes, vegetables, strawberries, tobacco, ginger, cotton, and sugar beets. Streptomycin derived from S. griseus is registered as a bactericide against bacterial rots and canker, targeting pathogens like Xanthomonas oryzae, Xanthomonas citri, and Pseudomonas tabaci in various crops, including pome fruit, stone fruit, citrus, olives, vegetables, potatoes, tobacco, cotton, and ornamentals. Avermectin derived from S. avermitilis is used as an insecticide/nematicide to control mites, leaf miners, suckers, beetles, fire ants, and other insects in ornamentals, cotton, citrus, pome and nut fruit, vegetables.
CHALLENGES IN THE APPLICATION OF STREPTOMYCES
The genus Streptomyces has immense potential as a component of modern agriculture, serving as both biofertilizers and biocontrol agents, with the capacity to dominate agricultural markets in the coming decades (Pacios-Michelena et al., 2021). However, translating this biotechnological promise from the lab to large-scale commercialization faces several significant scientific, technical, regulatory, and economic hurdles.
Knowledge gaps on mechanisms and ecology
There is an urgent need for fundamental insights into the mechanisms of action of Streptomyces (Viaene et al., 2016). The complex environment of the Streptomyces-rhizosphere and the mechanisms of plant growth-promoting action require extensive future studies (Vurukonda et al., 2018). Key areas where knowledge is insufficient include:
Ecological interactions: the interactions between rhizosphere Streptomyces and native microbiota, as well as the infection processes employed by endophytic Streptomyces, are still not sufficiently explained.
Biosynthetic gene clusters: genome sequencing suggests that as much as 90% of the chemical potential of these organisms remains undiscovered and that the biosynthetic machinery encoded by many of these genetic loci may be activated under laboratory conditions (Wu et al., 2012). How and why these pathways are activated in nature, and their ecological functions, remain unclear (Rey and Dumas, 2017).
Formulation, viability, and shelf life
In the agro-pharmaceutical industry, the major obstacle to commercial success is product formulation (Vurukonda et al., 2018; Pacios-Michelena et al., 2021). Microbial inoculants, including Streptomyces, face the specific problem of loss of viability during storage, which complicates the requirement for a long shelf life and stability under typical grower storage conditions, often ranging from -5℃ to 30℃ (Pacios-Michelena et al., 2021). Improving the shelf life while maintaining biological activity is an essential aspect of formulation technology (Saberi-Riseh and Moradi-Pour, 2021). Studies focusing on vegetative propagules of strains like Streptomyces sp. Di-944 found that formulations stored at 4℃ had a longer shelf life and better efficacy than those stored at 24℃, indicating temperature dependence (Sabaratnam and Traquair, 2002). The decline in the efficacy of surviving viable propagules over time is also a serious concern.
Field efficacy and environmental variability
A crucial challenge in the industrial development of bio-inoculants is that biological control agents frequently do not show the same results in vitro and in vivo (Vurukonda et al., 2018; Pacios-Michelena et al., 2021). An experimentally excellent biocontrol agent may fail in greenhouse or field experiments. The effectiveness of Streptomyces strains is significantly affected by a multitude of factors in the field:
Abiotic factors: soil type and characteristics (e.g., nutrient levels, water content, pH, and trace metals), climate, and agricultural practices affect treatment effectiveness. For instance, the production of antimicrobial molecules by actinobacteria, especially Streptomyces, is strictly dependent on the substrate where they grow.
Biotic factors: crop species, plant genetics, root exudation profiles, plant age, and competing microorganisms from the native soil microbiome also influence efficiency.
Lack of field data: most published studies demonstrate excellent activity under strictly standardized conditions, often lacking field research results to support the applicability of experimental data in commercial settings.
Biosafety and regulatory hurdles
Deploying Streptomyces at an industrial scale necessitates a thorough risk assessment (Barka et al., 2016). Potential risks include the release of microorganisms, particularly the horizontal transfer of entire or partial gene clusters conferring antibiotic resistance to unselected bacterial species (Pacios-Michelena et al., 2021). While this risk might be minimized by accurately characterizing prospective strains for the lack of known antibiotic-resistant genes before registration (Egan et al., 2001), regulatory standards currently are often inspired by synthetic chemicals, which is not adaptable to living microbial organisms and their derived preparations (Rey and Dumas, 2017). Furthermore, potential plant growth-promoting rhizobacteria must be confirmed to be non-pathogenic to both plants and animals (including humans) before being introduced into agriculture (Glick, 2015).
Adopting cost-effective strategies
Drawing on multiple case studies across diverse agroecological zones, the analysis reveals that cost-effective biopesticides are critical for advancing integrated pest management in traditional and smallholder farming systems. At the same time, branded formulations predominantly benefit large-scale farms with greater economic capacity (Fenibo and Matambo, 2025).
PROSPECTS AND OPPORTUNITIES
The increasing global demand for food, combined with the need for sustainable and environmentally friendly agricultural practices, positions Streptomyces as a vital resource for future development (Vurukonda et al., 2018).
Advanced formulation and delivery technologies
Future research needs to focus heavily on developing novel formulations that ensure the long-term viability and efficacy of Streptomyces (Pacios-Michelena et al., 2021).
Encapsulation and nanotechnology: encapsulation offers an advantageous and environmentally friendly option for new biological control products. Interest in nanoencapsulation has increased, as it uses nanosized carriers to protect organisms or their compounds, offering benefits such as increased solubility, high adsorption, controlled release, and improved stability against environmental stresses. Encapsulation systems are an attractive alternative for the release of biological control products.
Optimized delivery: research is needed to develop industrial processes for effective formulations using different additives and carriers, tailored for various methods of field inoculation (Vurukonda et al., 2018). Dry formulations (powders, granules) are generally preferred due to their extended shelf life, ease of transport, and storage (Sabaratnam and Traquair, 2002).
Molecular and ‘omics’ driven research
To fully exploit the potential of Streptomyces, advanced research tools must be employed:
Mechanism elucidation: extensive studies utilizing metagenomics and molecular biology tools (such as green fluorescent protein tagging) are necessary to track the fate of microbial populations, their endophytic distribution, and colonization patterns in host plants (Vurukonda et al., 2018).
Synthetic biology and metabolic engineering: the advent of synthetic biology tools, including CRISPR/Cas9 technology, provides innovative approaches for multiplex genetic modification to enhance or suppress secondary metabolites (Viaene et al., 2016; Rey and Dumas, 2017). This capability is critical for unlocking the vast number of biosynthetic gene clusters residing in the Streptomyces genome, potentially leading to a new generation of antimicrobials and specialized plant health compounds (Barka et al., 2016).
Ecological insight: understanding the regulation and production of secondary metabolites and gene clusters using ‘omics’ approaches will contribute knowledge about rhizosphere colonization and crosstalk between Streptomyces and other organisms (Olanrewaju and Babalola, 2019).
Diversified product development strategy
Future strategies should prioritize product types that offer greater stability and predictability:
Metabolite focus: using Streptomyces metabolites instead of living strains is expected to accelerate the replacement of chemically synthesized pesticides (Rey and Dumas, 2017; Pacios-Michelena et al., 2021). Metabolite formulations are much less challenging to stabilize than living organisms. Purified metabolites (such as polyoxin D, streptomycin, and kasugamycin) are already commercially available as foliar sprays.
Consortia development: research into the symbiotic potential of Streptomyces in conjunction with other plant growth-promoting rhizobacteria may lead to highly effective and efficient bioinoculants suitable for diverse soil types and environmental conditions (Vurukonda et al., 2018). Designing tailored biofertilization programs using different consortia for specific crop phenological phases is a promising approach (Malusá and Vassilev, 2014; Gopalakrishnan et al., 2022).
New applications: the great potential of Streptomyces to control post-harvest bacterial and fungal diseases of fruits and vegetables remains unexplored mainly (Vurukonda et al., 2018).
Ultimately, for Streptomyces to fulfill its potential, the scientific community must overcome the challenges of achieving predictable efficacy in variable field conditions and developing stable, regulatory-compliant commercial formulations. Harnessing the organism’s vast, largely silent metabolic potential with advanced molecular tools represents the next critical frontier in agricultural microbiology.
CONCLUSION
The genus Streptomyces can be addressed both as a biofertilizer and an effective biocontrol agent. The adoption of Streptomyces-based bioinoculants offers a desirable and environmentally friendly alternative to synthetic chemicals. The beneficial roles of Streptomyces are multifaceted, achieved through various mechanisms, including phytohormone production, nutrient solubilization, and acquisition. Furthermore, they protect plants against diseases and stresses through antibiosis, enzymatic lysis, and induced systemic resistance. Despite this confirmed biotechnological promise, the large-scale commercialization of Streptomyces strains remains limited. The critical challenge is translating results from controlled environments to field conditions. Crucially, greater attention is needed to develop novel formulations that can significantly extend the shelf life and long-term viability of these microbial-based agrochemicals. Ultimately, combining biocontrol and biofertilizer activities is necessary to ensure effective commercial products that promote plant growth even in the absence of pathogen pressure.
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