Integrated use of electrochemical anaerobic reactors and genomic based modeling for characterizing methanogenic activity in microbial communities exposed to BTEX contamination.

In soil polluted with benzene, toluene, ethylbenzene, and xylenes (BTEX), oxygen is rapidly depleted by aerobic respiration, creating a redox gradient across the plume. Under anaerobic conditions, BTEX biodegradation is then coupled with fermentation and methanogenesis. This study aimed to characterize this multi-step process, focusing on the interactions and functional roles of key microbial groups involved. A reactor system, comprising an Anaerobic Bioreactor (AB) and two Microbial Electrolysis Cell (MEC) chambers, designed to represent different spatial zones along the redox gradient, operated for 160 days with intermittent exposure to BTEX. The functional differentiation of each chamber was reflected by the gas emission profiles: 50%, 12% and 84% methane in the AB, anode and cathode chambers, respectively. The taxonomic profiling, assessed using 16S amplicon sequencing, led to the identification chamber-characteristic taxonomic groups. To translate the taxonomic shift into a functional shift, community dynamics was transformed into a simulative platform based on genome scale metabolic models constructed for 21 species that capture both key functionalities and taxonomies. Representatives include BTEX degraders, fermenters, iron reducers acetoclastic and hydrogenotrophic methanogens. Functionality was inferred according to the identification of the functional gene bamA as a biomarker for anaerobic BTEX degradation, taxonomy and literature support. Comparison of the predicted performances of the reactor-specific communities confirmed that the simulation successfully captured the experimentally recorded functional variation. Variations in the predicted exchange profiles between chambers capture reported and novel competitive and cooperative interactions between methanogens and non-methanogens. Examples include the exchange profiles of hypoxanthine (HYXN) and acetate between fermenters and methanogens, suggesting mechanisms underlying the supportive/repressive effect of taxonomic divergence on methanogenesis. Hence, the platform represents a pioneering attempt to capture the full spectrum of community activity in methanogenic hydrocarbon biodegradation while supporting the future design of optimization strategies.