Accumulated Acetate Serves as a Driving Force for the Succession of Heterotrophic Microbiome and Acetate Degradation in Microbial Electrosynthesis Systems

In microbial electrosynthesis (MES) systems, acetate is an important primary product generated through the reduction of oxidized CO2. However, microbes that negatively regulated acetate synthesis through acetate degradation in MES are still unclear. This study used DNA stable isotope probing (SIP) and sequencing techniques to explore the reason for acetate degradation and the taxa and succession patterns of the degrading microbiome. The results showed that with the transition from acetate synthesis to degradation, the relative abundance of unclassified_f_Rhodocyclaceae, which is identified as acetate-degrading bacteria, increased rapidly in suspensions and was significantly higher than its abundance in biofilms. Meanwhile, the quantity of DNA in suspensions is higher than that in biofilms, further demonstrating that the dominant unclassified_f_Rhodocyclaceae in the degrading microbiome were mainly present in suspensions. The results of DNA-SIP-coupled metagenomic sequencing revealed that the primary acetate-degrading species belonged to Rhodocyclaceae including Azonexus hydrophilus, Azonexus fungiphilus, etc. In addition, the potential syntrophic acetate-oxidizing bacteria Mesotoga infera could form a syntrophic relationship with Desulfolutivibrio sulfodismutans to participate in acetate degradation. In situ product removal experiments showed that acetate drove the degrading microbiome growth, and timely acetate removal could effectively inhibit the proliferation of degrading bacteria. This study fills the research gap of acetate degrading microbiome in MES systems.