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

Abstract 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.