Mcr-dependent methanogenesis in Archaeoglobaceae enriched from a terrestrial hot spring

Abstract

The preeminent source of biological methane on Earth is methyl coenzyme M reductase (Mcr)-dependent archaeal methanogenesis. A growing body of evidence suggests a diversity of archaea possess Mcr, although experimental validation of hypothesized methane metabolisms has been missing. Here, we provide evidence of a functional Mcr-based methanogenesis pathway in a novel member of the family Archaeoglobaceae, designated Methanoglobus nevadensis, which we enriched from a terrestrial hot spring on the polysaccharide xyloglucan. Our incubation assays demonstrate methane production that is highly sensitive to the Mcr inhibitor bromoethanesulfonate, stimulated by xyloglucan and xyloglucan-derived sugars, concomitant with the consumption of molecular hydrogen, and causing a deuterium fractionation in methane characteristic of hydrogenotrophic and methylotrophic methanogens. Combined with the recovery and analysis of a high-quality M. nevadensis metagenome-assembled genome encoding a divergent Mcr and diverse potential electron and carbon transfer pathways, our observations suggest methanogenesis in M. nevadensis occurs via Mcr and is fueled by the consumption of cross-fed byproducts of xyloglucan fermentation mediated by other community members. Phylogenetic analysis shows close affiliation of the M. nevadensis Mcr with those from Korarchaeota, Nezhaarchaeota, Verstraetearchaeota, and other Archaeoglobales that are divergent from well-characterized Mcr. We propose these archaea likely also use functional Mcr complexes to generate methane on the basis of our experimental validation in M. nevadensis. Thus, divergent Mcr-encoding archaea may be underestimated sources of biological methane in terrestrial and marine hydrothermal environments.

Methylotrophic methanogenesis in the Archaeoglobi revealed by cultivation ofCa.Methanoglobus hypatiae from a Yellowstone hot spring

“…M. hypatiae. We hypothesize these subunits are associating together in vivo to bifurcate electrons from hydrogen (H2) to reduce both menaquinone (MQ) and ferredoxin (Fdox), as proposed recently (35,49). Lastly, Ca.…”

“…Collectively, our results and the studies by Wang et al . and Buessecker et al ., who reported that Mcr-encoding Archaeoglobi are present (35) and transcriptionally active in hot spring mesocosms (34), demonstrate the previously overlooked role Archaeoglobi might play in the anaerobic carbon cycle of geothermal environments.…”

“…M. hypatiae expressed the methyl-branch of the Wood-Ljungdahl pathway (WLP) and the acetyl-CoA decarbonylase/synthase complex (Cdh, cdhABCDE ), which is consistent with genes observed and shown to be expressed in sulfate-reducing Archaeoglobi genomes (55). This includes two paralogous copies of 5,10-methylenetetrahydromethanopterin reductase ( mer ) which might function as a traditional Mer, considering that these genes are also members of the large luciferase-like monooxygenase family (pfam00296)(35). The expression of genes in the WLP varied.…”

“…n. Methanoglobus , methane producing organism spherical in shape. This genus was named by Buessecker et al (1). Hy.pa.ti.ae.…”

“…Last, Buessecker et al reported the establishment of a methanogenic enrichment culture of Ca. Methanoglobus nevadensis from Great Boiling Spring (NV, USA) (35). The culture yields up to 158 µmol of methane per liter after two weeks of incubation at its optimal growth temperature of 75 °C.…”