Cost‐effective natamycin production by Streptomyces lydicus JCK ‐6019 via solid‐state fermentation and development of a bioproduct with fungicidal and plant growth‐promoting activities

BACKGROUND: Natamycin is a polyene macrolide produced by Streptomyces spp. with broad-spectrum antifungal activity. Agro-industrial by-products are abundant and nutrient-rich resources that can be converted into sustainable bioproducts. This study aimed to investigate their application in natamycin production via solid-state fermentation (SSF) using Streptomyces lydicus JCK-6019, with the goal of developing a dual-function product with plant growth-promoting and biocontrol properties. RESULTS: Optimization results revealed that a substrate mixture of brown rice and sesame seed cake (2:1, w/w) supplemented with 3% (w/w) rice hull, 80% (v/w) initial moisture content, and 30% (v/w) inoculum size produced the highest natamycin yield (18.55 mg/gds) in 250 mL flasks at 28 °C on day 7. Scaling up to a 2.5 L system with 70% moisture and 15% inoculum size further increased the yield to 20.22 mg/gds on day 6. This SSF product significantly promoted cucumber seedling growth, increasing plant height, leaf width, and biomass. It also increased chlorophyll content by 147.40%, reduced malondialdehyde content by 36.72%, and enhanced antioxidant enzyme activities (polyphenol oxidase by 42.16% and peroxidase by 26.99%). The 300-fold diluted SSF product exhibited a control value of 90.91% against cucumber damping-off caused by Rhizoctonia solani, comparable to a commercial fungicide. Moreover, the SSF product exhibited high storage stability, retaining over 95% natamycin activity after 1 year of storage at 25 °C. CONCLUSION: This study showed a cost-effective and eco-friendly approach for natamycin production from agro-industrial by-products, highlighting its SSF product potential as a stable biofungicide and plant growth promoter in sustainable agriculture. © 2025 Society of Chemical Industry.