Changes of microbial community structure in earthworm-microbial fuel cells

High-throughput sequencing technology was used to analyze the microbial community structure in four treatment groups (EMFC, MFC, ESoil, and Soil) .The microbial Chao1, Simpson and Shannon indices of the EMFC treatment group were higher than those of the other three treatment groups (MFC, Soil and E-Soil), indicating that the microbial diversity and richness of the EMFC coupling system after the addition of earthworms were higher. Based on the taxonomic classification of microorganisms at the phylum level, the predominant phyla identified in the soil samples from EMFC and MFC systems were Proteobacteria, Bacteroidetes, Chloroflexi, and Planctomycetes. These phyla accounted for 35.82-64.68%, 6.37%-14.26%, 4.27%-10.92%, and 4.14%-17.80% respectively . The top 15 genera with the highest abundance in each treatment were analyzed. Significant differences were observed in the bacterial communities at the genus level among soil samples from different treatment groups. For instance, Roseimaritima, Hydrogenophaga, and Luteimonas exhibited relatively high abundances in the anode layer of MFC. In contrast, Methanobacterium and Methanosaeta showed relatively high abundances in the EMFC anode layer with earthworms present. Furthermore, Azoarcus displayed a relative abundance 4.8 times higher in the EMFC cathode layer compared to that in MFC cathode layer. Additionally, Rhodobacter and Paracoccus exhibited significantly increased relative abundances when earthworms were added compared to soil samples from the middle layer of MFC alone. These results indicate that earthworm addition can induce significant changes to microbial community structure.