Metatranscriptomic insights into the microbial electrosynthesis of acetate by Fe2+/Ni2+ addition

As important components of enzymes and coenzymes involved in energy transfer and Wood-Ljungdahl (WL) pathways, Fe2+ and Ni2+ supplementation may promote the acetate synthesis through CO2 reduction by the microbial electrosynthesis (MES). However, the effect of Fe2+ and Ni2+ addition on acetate production in MES and corresponding microbial mechanisms have not been fully studied. Therefore, this study investigated the effect of Fe2+ and Ni2+ addition on acetate production in MES, and explored the underlying microbial mechanism from the metatranscriptomic perspective. Both Fe2+ and Ni2+ 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 Fe2+ and Ni2+ addition. Gene expression of ‘Energy metabolism’, especially in ‘Carbon fixation pathways in prokaryotes’ was up-regulated by Fe2+ and Ni2+ addition. Hydrogenase was found as an important energy transfer mediator for CO2 reduction and acetate synthesis. Fe2+ addition and Ni2+ 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 Fe2+ and Ni2+ on acetate production by CO2 reduction in MES. λ Acetate microbial electrosynthesis was enhanced by Fe2+ and Ni2+ addition. λ Fe2+ and Ni2+ addition caused small changes in genus-level microbial composition. λ Genes expression of hydrogenase was increased with Fe2+ and Ni2+ addition. λ Fe2+ improved methyl and Ni2+ improved carboxyl branch expression of WL pathway.