RT Journal Article
SR Electronic
T1 Lifeless <em>Clostridia</em> stimulate methanogenesis on Fe<sup>0</sup> in an urban lake corrosive community
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 556704
DO 10.1101/556704
A1 Paola Andrea Palacios
A1 Amelia-Elena Rotaru
YR 2019
UL http://biorxiv.org/content/early/2019/02/21/556704.abstract
AB Urban environments are webbed with iron-steel structures above and belowground. Underground, in non-sulfidic environments, it has been suggested that interspecies interactions cause Fe0 corrosion. Particularly, Methanosarcinales were assumed to interact syntrophically with acetogenic bacteria during Fe0 corrosion. Here we challenge this assumption and show that a community of methanogens (38% Methanosarcinales) prospers on Fe0 especially after the demise of the acetogens. Acetogens were mainly represented by Clostridium (81% of Bacteria). Methanogens were however more diverse including Methanosarcina (22% of Archaea), Methanosaeta (17% of Archaea) and Methanothermobacter (22% of Archaea) as key groups. Surprisingly, acetogens started using electrons from Fe0 immediately, unchallenged by competing methanogens. Acetogens were expected to be outcompeted by energy efficient methanogens with comparatively lower H2-uptake thresholds. However, acetogens prevailed, perhaps because in contrast to methanogens they contain [FeFe]-hydrogenases (encoded in the lake-Clostridia metagenome). [FeFe]-hydrogenases from Clostridium were previously shown effective at retrieving electrons from Fe0 for proton reduction. When acetogens thrived, methanogenic rates were low (25.2±8 µM/day) but increased appreciably (62.5±5 µM/day) when acetogens collapsed. Acetate could not explain more than a third of the observed methanogenic rates. The remaining methane could be explained by methanogens reducing their energy expenses while exploiting Clostridium remains such as readily fixed nitrogen and/or exuded [FeFe]-hydrogenases producing H2 on Fe0. This has implications on our understanding of viable interactions between autotrophic species retrieving electrons from Fe0 or other insoluble electron donors.Implications Corrosion damages to underground iron-structures distress both the local environment and the economy. Here we studied an urban lake community corroding Fe0. The corrosive community was dominated by Clostridium and Methanosarcinales, which sequentially produced first more acetate and later methane. Here we bring evidence for an unusual interaction mechanism on Fe0, showing that methanogenesis is enhanced by inactive acetogens. Alone, the Clostridium-acetogens discovered in this study, could retrieve electrons from Fe0 effectively, which makes them a good candidate for electrosynthesis of fossil-fuels’ alternatives -a future biotechnological application.