Bacterial community composition at anodes of microbial fuel cells for paddy soils: the effects of soil properties

Anode electrogenic bacteria (AEB) widely exist in paddy soils and play an important role in element biogeochemical cycling. However, little information is available on the role of soil characteristics in shaping AEB community. Therefore, the objective of this study was to evaluate the role of soil properties in driving the evolution of anode bacterial communities. Microbial fuel cells (MFCs) were constructed for five paddy soils with different chemical properties. The bacterial communities at anodes of closed (MFC running) and open (control) circuit MFCs were characterized using 16S rRNA gene-based Illumina sequencing. Paddy soils with higher dissolved organic carbon (DOC) and ammonium (NH4 (+)) concentrations in porewater showed higher MFC performance. Without MFC running, the dominant bacterial community composition was similar among the used five soils with Clostridia as the dominant bacteria at class level. Compared to control treatments, MFC running significantly decreased bacterial diversity and altered the bacterial community composition at anodes. However, the shift of bacterial communities varied with different types of soils. Betaproteobacteria was enriched by 4-30 times after MFC running for low MFC performance soils, while Deltaproteobacteria enriched (4-20 times) for high MFC performance soils. Redundancy analysis (RDA) indicated that DOC, NH4 (+), and dissolved ferrous (Fe2+) significantly shift anode bacterial communities for the five soils with MFC running. We found that high-performing MFCs constructed from paddy soils with high DOC and NH4 (+) concentrations in porewater selected for an active, highly electrogenic bacterial community (dominated by Deltaproteobacteria) at anodes, while the dominant bacterial community for the low-performing MFCs from soils with low DOC and NH4 (+) was Betaproteobacteria. These findings imply that soil properties shape the AEB composition, therefore influencing MFC performance. This study provides new insights into the microbial-mediated carbon and nitrogen cycling in paddy soils.