Structure and functions of hydrocarbon-degrading microbial communities in bioelectrochemical systems

Bioelectrochemical systems (BES) exploit the interaction between microbes andelectrodes. A field of application thereof, is bioelectrochemical remediation, an effective strategy inenvironments where the absence of suitable electron acceptors limits classic bioremediationapproaches. Understanding the microbial community structure and genetic potential of anodebiofilms is of great interest to interpret the mechanisms occurring in BES. In this study, by using awhole metagenome sequencing approach, taxonomic and functional diversity patterns in theinoculum and on the anodes of three continuous-flow BES for the removal of phenol, toluene andBTEX were obtained. The genus Geobacter was highly enriched on the anodes and tworeconstructed genomes were taxonomically related to the Geobacteraceae family. To functionallycharacterize the microbial community, the genes coding for the anaerobic degradation of toluene,ethylbenzene and phenol were selected as genetic markers for the anaerobic degradation of thepollutants. The genes related with direct extracellular electron transfer (EET) were also analyzed.The inoculum carried the genetic baggage for the degradation of aromatics but lacked the capacityof EET, while anodic bacterial communities were able to pursuit both processes. Themetagenomic approach provided useful insights into the ecology and complex functions withinhydrocarbon degrading electrogenic biofilms.