Metatranscriptomic insights into the microbial electrosynthesis of acetate by Fe/Ni addition.

As important components of enzymes and coenzymes involved in energy transfer and Wood-Ljungdahl (WL) pathways, Fe and Ni supplementation may promote the acetate synthesis through CO reduction by the microbial electrosynthesis (MES). However, the effect of Fe and Ni addition on acetate production in MES and corresponding microbial mechanisms have not been fully studied. Therefore, this study investigated the effect of Fe and Ni addition on acetate production in MES, and explored the underlying microbial mechanism from the metatranscriptomic perspective. Both Fe and Ni addition enhanced acetate production of the MES, which was 76.9% and 110.9% higher than that of control, respectively. Little effect on phylum level and small changes in genus-level microbial composition was caused by Fe and Ni addition. Gene expression of 'Energy metabolism', especially in 'Carbon fixation pathways in prokaryotes' was up-regulated by Fe and Ni addition. Hydrogenase was found as an important energy transfer mediator for CO reduction and acetate synthesis. Fe addition and Ni addition respectively enhanced the expression of methyl branch and carboxyl branch of the WL pathway, and thus promoted acetate production. The study provided a metatranscriptomic insight into the effect of Fe and Ni on acetate production by CO reduction in MES.