Metabolic Difference Analysis of Clostridium cellulovorans Grown on Glucose and Cellulose

Abstract

As an anaerobic butyrate-producing bacterium, Clostridium cellulovorans can secrete a variety of extracellular enzymes to degrade plant-based cellulose. However, with glucose as the carbon source, it still secretes a large amount of protein in the broth. The metabolism and regulation are obscure and need to be further studied. Hence, in this study, C. cellulovorans was used to conduct fed-batch fermentation of glucose and microcrystalline at pH 7.0 to produce a higher level of butyrate in the bioreactor. It produced 16.8 mM lactate, 22.3 mM acetate, and 132.7 mM butyrate in 72 h during glucose fermentation. In contrast, it produced only 11.5 mM acetate and 93.9 mM butyrate and took 192 h to complete the fermentation with cellulose as the carbon source. Furthermore, there was no lactate detected in the broth. The analysis of carbon source balance and redox balance showed that 57% of the glucose was consumed to form acids in glucose fermentation, while only 47% of the cellulose was used for acid generation in the cellulose fermentation. Meanwhile, a large amount of protein was detected in the fermentation broth in both glucose (0.9 ± 0.1 g/L) and cellulose (1.1 ± 0.2 g/L) fermentation. These results showed that protein was also a main product. C. cellulovorans metabolized glucose to generate intermediate metabolites and reducing powers (NADH and Fdred), then protein and acid synthesis consumed this reducing power to maintain the carbon source balance and redox balance in the cell metabolism. The results of comparative transcriptomics and comparative proteomics also supported the above conclusion. The method of studying the protein during Clostridium species fermentation provides a new perspective for further study on metabolic regulation.