Transcriptional study of the enhanced ε-poly-L-lysine productivity in culture using glucose and glycerol as a mixed carbon source.

A glucose-glycerol mixed carbon source (MCS) can substantially reduce batch fermentation time and improve ε-poly-L-lysine (ε-PL) productivity, which was of great significance in industrial microbial fermentation. This study aims to disclose the physiological mechanism by transcriptome analyses. In the MCS, the enhancements of gene transcription mainly emerged in central carbon metabolism, L-lysine synthesis as well as cell respiration, and these results were subsequently proved by quantitative real-time PCR assay. Intracellular L-lysine determination and exhaust gas analysis further confirmed the huge precursor L-lysine pool and active cell respiration in the MCS. Interestingly, in the MCS, pls was remarkably up-regulated than those in single carbon sources without transcriptional improvement of HrdD, which indicated that the improved ε-PL productivity was supported by other regulators rather than hrdD. This study exposed the physiological basis of the improved ε-PL productivity in the MCS, which provided references for studies on other biochemicals production using multiple substrates.

Production of natamycin by Streptomyces gilvosporeus Z28 through solid-state fermentation using agro-industrial residues.

At present, submerged fermentation (SmF) is the unique approach for natamycin production. This study aims to propose a strategy for natamycin production through solid-state fermentation (SSF). The maximum natamycin concentration (9.62 mg·gds-1) was obtained with a substrate mixture containing wheat bran, rapeseed cake, rice hull and crude glycerol in a 5 L flask at 28 °C, and the initial moisture content and inoculum size was set as 70% and 15%, individually. A 30 L scale-up fermentation showed similar parameters and produced 9.27 mg·gds-1 natamycin at the 8th day. Besides, natamycin could be continuously produced by repeated-batch fermentation for 5 cycles through SSF. Compared to SmF, SSF led to a 50.05% cost reduction of raw materials, less energy consumption and waste water discharge, which was of great significance in industrial fermentation. To our best knowledge, this is the first report on natamycin production through SSF process.

Insights into the simultaneous utilization of glucose and glycerol by Streptomyces albulus M-Z18 for high ε-poly-L-lysine productivity.

The simultaneous consumption of glucose and glycerol led to remarkably higher productivity of both biomass and ε-poly-L-lysine (ε-PL), which was of great significance in industrial microbial fermentation. To further understand the superior fermentation performances, transcriptional analysis and exogenous substrates addition were carried out to study the simultaneous utilization of glucose and glycerol by Streptomyces albulus M-Z18. Transcriptome analysis revealed that there was no mutual transcriptional suppression between the utilization of glucose and glycerol, which was quite different from typical "glucose effect". In addition, microorganisms cultivated with single glycerol showed significant demand for ribose-5-phosphate, which resulted in potential demand for glucose and xylitol. The above demand could be relieved by glucose (in the mixed carbon source) or xylitol addition, leading to improvement of biomass production. It indicated that glucose in the mixed carbon source was more important for biomass production. Besides, transcriptional analysis and exogenous citrate addition proved that single carbon sources could not afford enough carbon skeletons for Embden Meyerhof pathway (EMP) while a glucose-glycerol combination could provided sufficient carbon skeletons to saturate the metabolic capability of EMP, which contributed to the replenishment of precursors and energy consumed in ε-PL production. This study offered insight into the simultaneous consumption of glucose and glycerol in the ε-PL batch fermentation, which deepened our comprehension on the high ε-PL productivity in the mixed carbon source.