Identification of potential electrotrophic microbial community in paddy soils by enrichment of microbial electrolysis cell biocathodes

Electrotrophs are microbes that can receive electrons directly from cathode in a microbial electrolysis cell(MEC).They not only participate in organic biosynthesis,but also be crucial in cathode-based bioremediation.However,little is known about the electrotrophic community in paddy soils.Here,the putative electrotrophs were enriched by cathodes of MECs constructed from five paddy soils with various properties using bicarbonate as an electron acceptor,and identified by 16 S rRNA-gene based Illumina sequencing.The electrons were gradually consumed on the cathodes,and 25%–45% of which were recovered to reduce bicarbonate to acetic acid during MEC operation.Firmicutes was the dominant bacterial phylum on the cathodes,and Bacillus genus within this phylum was greatly enriched and was the most abundant population among the detected putative electrotrophs for almost all soils.Furthermore,several other members of Firmicutes and Proteobacteria may also participate in electrotrophic process in different soils.Soil p H,amorphous iron and electrical conductivity significantly influenced the putative electrotrophic bacterial community,which explained about 33.5% of the community structural variation.This study provides a basis for understanding the microbial diversity of putative electrotrophs in paddy soils,and highlights the importance of soil properties in shaping the community of putative electrotrophs.