Decreased lincomycin B content by regulating osmotic pressure in fermentation of Streptomyces lincolnensis

Abstract

Abstract Lincomycin, a clinically important antibiotic against gram-positive bacteria, is a sulfur-containing metabolite produced by Streptomyces lincolnensis. The content of lincomycin B is an important evaluation index of fermentation quality. In this study, we investigated the effects of NaCl as an osmotic regulator on lincomycin production. Based on the flask experiment, the optimal initial osmotic pressure for lincomycin fermentation was in the range between 0.860–1.355 Osmol/kg. The effect of osmotic pressure on the fermentation of lincomycin in 15 L bioreactor showed that the content of lincomycin B in the broth was decreased to 5.78% when adding 10 g/L NaCl while the content of lincomycin B was 8.20% in the control. During the fermentation process, the intracellular homocysteine and S-adenosylmethionine was higher when adding 10 g/L NaCl, which could provide more methyl donor for lincomycin production, causing the reduction of lincomycin B. Besides, high-throughput RNA sequencing was applied to study the mechanism of osmotic regulation on lincomycin fermentation. Under osmotic stimulation, the transcription of 23 genes in lincomycin biosynthesis cluster were significantly up-regulated at 41 h and the transcription of genes in HMP and EMP was up-regulated while the transcription of genes in TCA cycle were decreased. Notably, the genes involved in sulfur assimilation, mycothiol, ergothioneine and S-adenosylmethionine biosynthesis were up-regulated, which can provide more methyl donor (S-adenosylmethionine) and sulfur donor (mycothiol and ergothioneine) during lincomycin fermentation. This might be the reason of increased lincomycin A production and decreased lincomycin B content. Our study provides new insight into the mechanisms underlying osmotic pressure regulation on lincomycin fermentation and may be applied to improve secondary metabolite production.