AUTHOR=Zhu Hai-Feng , Liu Zi-Yong , Zhou Xia , Yi Ji-Hong , Lun Zeng-Min , Wang Shu-Ning , Tang Wen-Zhu , Li Fu-Li 

TITLE=Energy Conservation and Carbon Flux Distribution During Fermentation of CO or H2/CO2 by Clostridium ljungdahlii

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.00416

DOI=10.3389/fmicb.2020.00416

ISSN=1664-302X

ABSTRACT=<p>Both CO and H<sub>2</sub> can be utilized as energy sources during the autotrophic growth of <italic>Clostridium ljungdahlii</italic>. In principle, CO is a more energetically and thermodynamically favorable energy source for gas fermentation in comparison to H<sub>2</sub>. Therefore, metabolism may vary during growth under different energy sources. In this study, <italic>C. ljungdahlii</italic> was fed with CO and/or CO<sub>2</sub>/H<sub>2</sub> at pH 6.0 with a gas pressure of 0.1 MPa. <italic>C. ljungdahlii</italic> primarily produced acetate in the presence of H<sub>2</sub> as an energy source, but produced alcohols with CO as an energy source under the same fermentation conditions. A key enzyme activity assay, metabolic flux analysis, and comparative transcriptomics were performed for investigating the response mechanism of <italic>C. ljungdahlii</italic> under different energy sources. A CO dehydrogenase and an aldehyde:ferredoxin oxidoreductase were found to play important roles in CO utilization and alcohol production. Based on these findings, novel metabolic schemes are proposed for <italic>C. ljungdahlii</italic> growing on CO and/or CO<sub>2</sub>/H<sub>2</sub>. These schemes indicate that more ATP is produced during CO-fermentation than during H<sub>2</sub>-fermentation, leading to increased alcohol production.</p>