Diversity and Ecological Relevance of Fumarate-Adding Enzymes in Oil Reservoir Microbial Communities

Oil reservoirs are important hydrocarbon-rich environments, where the addition of hydrocarbons to fumarate mediated by fumarate-adding enzymes (FAE) is one of the dominant mechanisms for anaerobic degradation of hydrocarbons. However, the currently available information about FaeA, the catalytic subunit of FAE, in in situ petroleum reservoirs is limited. Here, we investigated the diversity of FaeA and FaeA-harbouring microbes in oil reservoirs and compared them with marine sediments. We obtained 67 FaeA clusters and 46 FaeA-harbouring MAGs from oil reservoirs. Most FaeA sequences and all FaeA-containing microbes were endemic and unique. In oil reservoirs, FaeA sequences were affiliated with Archaeoglobus and 13 bacterial phyla. Fermentative metabolism was a common lifestyle amongst these organisms. Genomes assigned to Desulfobacterota, Caldatribacteriota and Firmicutes_B were the most diverse and prevalent, while Desulfobacterota and Chloroflexota were dominant in marine. Microbial community diversity at the phylum level was strongly related to FaeA in oil reservoirs but not in marine. This suggested that the ability of anaerobic hydrocarbon biodegradation may shape community structure in oil reservoirs. Together, this study provided systematic and comprehensive information regarding the high diversity of FaeA and FaeA-containing anaerobic hydrocarbon degraders in oil reservoirs and underlined the difference between hydrocarbon-rich environments of oil reservoirs and marine.