The changes of microbial abundance and functional genes in bioelectrochemistry at 15 ℃

Bioelectrochemistry system (BES) provides a new strategy for the improvement of low temperature anaerobic digestion (AD) for methane production. In this study, the BES with carbon brushes as electrodes was operated at 15 °C to analyze the changes of microbial abundance and functional genes. The microbial community structure showed that the application of voltage had no effect to type and relative abundance of bacteria based on 16S-rRNA sequencing. Metatranscriptomic analyses revealed that significantly enhanced the abundance of fermentation bacteria in the fluid activated sludge, and the relative abundance of biosynthesis of other secondary metabolites (61.56%) was also highly expressed. More than that, the abundance of electricigens (Pseudomonas, Syntrophomonas) was also enriched in the BES system. These electricigens could interact with methanogens to promote electron transfer by direct interspecies electron transfer (DIET). The expression level of functional enzyme related to electron transport was increased at the anode (30.60%), but decreased at the cathode (−33.84%). Analysis of methanogens found that the application of voltage decreased the relative abundance of Methanosarcinaand promoted the enrichment of Methanothrix. At 15 ℃, acetoclastic was the mainly methanogenic pathway. What’s more, the application of voltage could enhance the acetoclastic and inhibited the hydrogenotrophic and the methylotrophic pathway. Further, the acetoclastic pathway was changed from acetate kinase (EC: 2.7.2.1) and phosphate acetyltransferase (EC: 2.3.1.8) to acetate-CoA ligase (EC: 6.2.1.1) by applied voltage. These results are conducive to the further development of low-temperature AD treatment technology.