Effects of Acetate Supplementation on Autotrophic Growth of the Gas Fermenting Acetogen Clostridium sp. AWRP

Abstract

Clostridium sp. AWRP is an acetogen that grows autotrophically with either CO or CO2/H2 to form acetate and ethanol via the Wood-Ljungdahl pathway. In this study, the effect of acetate supplementation on the autotrophic growth of AWRP strain was investigated. In CO fermentation, the growth of AWRP was inhibited by high concentrations of CO, resulting in a long lag phase. Acetate supplementation mitigated CO inhibition: the lag period was shortened, and the maximum specific growth rate and maximum cell density were enhanced by 2.6- and 1.9-fold, respectively. In CO2/H2 fermentation, AWRP produced acetate as the main product, and its growth was inhibited by high concentrations of acetate. To investigate the cellular response to acetate stress, long-term serial transfers were performed in acetate-containing medium. Acetate-adapted strain showed increased cell density but reduced gas consumption. Transcriptome analysis revealed that the expression of most genes involved in the Wood-Ljungdahl pathway was down-regated, while genes involved in nucleoside and carbohydrate degradation were up-regulated. These results can provide practical guidance for the gas fermentation of acetogens.