Optimization of fermentation medium and conditions for enhancing valinomycin production by <i>Streptomyces</i> sp. ZJUT-IFE-354

Abstract

Valinomycin is a cyclodepsipeptide antibiotic with a broad spectrum of biological activities, such as antiviral, antitumor, and antifungal activities. However, the low yield of valinomycin often limits its applications in medicine, agriculture, and industry. In our previous report, Streptomyces sp. ZJUT-IFE-354 was identified as a high-yielding strain of valinomycin. In this study, Plackett–Burman design (PBD) and response surface methodology (RSM) were used to optimize components of medium. The optimal medium contained 31 g/L glucose, 22 g/L soybean meal, and 1.6 g/L K2HPO4·3H2O, which could generate 262.47 ± 4.28 mg/L of valinomycin. Then, the culture conditions were optimized by a one-factor-at-a-time (OFAT) approach. The optimal conditions for the strain included a seed age of 24 h, an inoculum size of 8% (v/v), an incubation temperature of 28 °C, an initial pH of 7.2, an elicitor of 0.1% Bacillus cereus feeding at 24 h cultivation, and the feeding of 0.6% L-valine at 36 h cultivation. The final valinomycin production increased to 457.23 ± 9.52 mg/L, which was the highest yield ever reported. It highlights that RSM and OFAT may be efficient methods to enhance valinomycin production by Streptomyces sp. ZJUT-IFE-354.