Opportunistic interactions on Fe0 between methanogens and acetogens from a climate lake

Microbial-induced corrosion has been extensively studied in pure cultures. However, Fe0 corrosion by complex environmental communities, and especially the interplay between microbial physiological groups, is still poorly understood. In this study, we combined experimental physiology and metagenomics to explore Fe0-dependent microbial interactions between physiological groups enriched from anoxic climate lake sediments. Then, we investigated how each physiological group interacts with Fe0. We offer evidence for a new interspecies interaction during Fe0 corrosion. We showed that acetogens enhanced methanogenesis but were negatively impacted by methanogens (opportunistic microbial interaction). Methanogens were positively impacted by acetogens. In the metagenome of the corrosive community, the acetogens were mostly represented by Clostridium and Eubacterium, the methanogens by Methanosarcinales, Methanothermobacter and Methanobrevibacter. Within the corrosive community, acetogens and methanogens produced acetate and methane concurrently, however at rates that cannot be explained by abiotic H2-buildup at the Fe0 surface. Thus, microbial-induced corrosion might have occurred via a direct or enzymatically mediated electron uptake from Fe0. The shotgun metagenome of Clostridium within the corrosive community contained several H2-releasing enzymes including [FeFe]-hydrogenases, which could boost Fe0-dependent H2-formation as previously shown for pure culture acetogens. Outside the cell, acetogenic hydrogenases could become a common good for any H2/CO2-consuming member in the microbial community including methanogens that rely on Fe0 as a sole energy source. However, the exact electron uptake mechanism from Fe0 remains to be unraveled.