Metabolic analyses of the improved ε-poly-l-lysine productivity using a glucose–glycerol mixed carbon source in chemostat cultures
The glucose–glycerol mixed carbon source remarkably reduced the batch fermentation time of ε-poly-l-lysine (ε-PL) production, leading to higher productivity of both biomass and ε-PL, which was of great significance in industrial microbial fermentation. Our previous study confirmed the positive influence of fast cell growth on the ε-PL biosynthesis, while the direct influence of mixed carbon source on ε-PL production was still unknown. In this work, chemostat culture was employed to study the capacity of ε-PL biosynthesis in different carbon sources at a same dilution rate of 0.05 h−1. The results indicated that the mixed carbon source could enhance the ε-PL productivity besides the rapid cell growth. Analysis of key enzymes demonstrated that the activities of phosphoenolpyruvate carboxylase, citrate synthase, aspartokinase and ε-PL synthetase were all increased in chemostat culture with the mixed carbon source. In addition, the carbon fluxes were also improved in the mixed carbon source in terms of tricarboxylic acid cycle, anaplerotic and diaminopimelate pathway. Moreover, the mixed carbon source also accelerated the energy metabolism, leading to higher levels of energy charge and NADH/NAD+ ratio. The overall improvements of primary metabolism in chemostat culture with glucose–glycerol combination provided sufficient carbon skeletons and ATP for ε-PL biosynthesis. Therefore, the significantly higher ε-PL productivity in the mixed carbon source was a combined effect of both superior substrate group and rapid cell growth.
Keywordsε-Poly-l-lysine Mixed carbon source Chemostat culture Metabolic analyses
This work was financially supported by the National Natural Science Foundation of China (31671846, 31301556), the Science and Technology Department of Jiangsu Province (BY2016022-25), the Fundamental Research Funds for the Central Universities (JUSRP51504), the Open Project Program of the Key Laboratory of Industrial Biotechnology, Ministry of Education, China (KLIBKF201302), and the Jiangsu Province Collaborative Innovation Center for Advanced Industrial Fermentation Industry Development Program.
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Conflict of interest
The authors declare that they have no conflict of interest.
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