Metabolism, morphology and transcriptome analysis of oscillatory behavior of Clostridium butyricum during long-term cont
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Biotechnology for Biofuels Open Access
RESEARCH
Metabolism, morphology and transcriptome analysis of oscillatory behavior of Clostridium butyricum during long‑term continuous fermentation for 1,3‑propanediol production Jin‑Jie Zhou, Jun‑Tao Shen, Xiao‑Li Wang, Ya‑Qin Sun and Zhi‑Long Xiu*
Abstract Background: Oscillation is a special cell behavior in microorganisms during continuous fermentation, which poses threats to the output stability for industrial productions of biofuels and biochemicals. In previous study, a spontane‑ ous oscillatory behavior was observed in Clostridium butyricum-intensive microbial consortium in continuous fermen‑ tation for 1,3-propanediol (1,3-PDO) production from glycerol, which led to the discovery of oscillation in species C. butyricum. Results: Spontaneous oscillations by C. butyricum tended to occur under glycerol-limited conditions at low dilution rates. At a glycerol feed concentration of 88 g/L and a dilution rate of 0.048 h−1, the oscillatory behavior of C. butyricum was observed after continuous operation for 146 h and was sustained for over 450 h with an average oscillation period of 51 h. During oscillations, microbial glycerol metabolism exhibited dramatic periodic changes, in which productions of lactate, formate and hydrogen significantly lagged behind that of other products including biomass, 1,3-PDO and butyrate. Analysis of extracellular oxidation–reduction potential and intracellular ratio of N AD+/NADH indicated that microbial cells experienced distinct redox changes during oscillations, from oxidized to reduced state with decreasing of growth rate. Meanwhile, C. butyricum S3 exhibited periodic morphological changes during oscil‑ lations, with aggregates, elongated shape, spores or cell debris at the trough of biomass production. Transcriptome analysis indicated that expression levels of multiple genes were up-regulated when microbial cells were undergoing stress, including that for pyruvate metabolism, conversion of acetyl-CoA to acetaldehyde as well as stress response. Conclusion: This study for the first time systematically investigated the oscillatory behavior of C. butyricum in aspect of occurrence condition, metabolism, morphology and transcriptome. Based on the experimental results, two hypotheses were put forward to explain the oscillatory behavior: disorder of pyruvate metabolism, and excessive accumulation of acetaldehyde. Keywords: Clostridium butyricum, Oscillatory behavior, 1,3-Propanediol, Glycerol metabolism, Morphology, Transcriptome
*Correspondence: [email protected] School of Bioengineering, Dalian University of Technology, Dalian, Liaoning 116024, People’s Republic of China
Background Glycerol is the byproduct of biodiesel and oleochemical industries with worldwide oversupply and low price [1– 3]. Bioconversion of such a waste material to value-added chemicals is an attractive option in consideration of both economic and environmental benefits. Glycerol can be
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