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

Abstract

10Urban environments are webbed with iron-steel structures above and belowground. Underground, in non-11 sulfidic environments, it has been suggested that interspecies interactions cause Fe 0 corrosion. Particularly, 12Methanosarcinales were assumed to interact syntrophically with acetogenic bacteria during Fe 0 corrosion. 13Here we challenge this assumption and show that a community of methanogens (38% Methanosarcinales) 14 prospers on Fe 0 especially after the demise of the acetogens. Acetogens were mainly represented by 15Clostridium (81% of Bacteria). Methanogens were however more diverse including Methanosarcina (22% of 16 Archaea), Methanosaeta (17% of Archaea) and Methanothermobacter (22% of Archaea) as key groups. 17 Surprisingly, acetogens started using electrons from Fe 0 immediately, unchallenged by competing 18 methanogens. Acetogens were expected to be outcompeted by energy efficient methanogens with 19 comparatively lower H2-uptake thresholds. However, acetogens prevailed, perhaps because in contrast to 20 methanogens they contain [FeFe]-hydrogenases (encoded in the lake-Clostridia metagenome).[FeFe]-21 hydrogenases from Clostridium were previously shown effective at retrieving electrons from Fe 0 for proton 22