CO2 conversion to methane and biomass in obligate methylotrophic methanogens in marine sediments

Abstract

Methyl substrates are important compounds for methanogenesis in marine sediments but diversity and carbon utilization by methylotrophic methanogenic archaea have not been clarified. Here, we demonstrate that RNA-stable isotope probing (SIP) requires 13 C-labeled bicarbonate as co-substrate for identification of methylotrophic methanogens in sediment samples of the Helgoland mud area, North Sea. Using lipid-SIP, we found that methylotrophic methanogens incorporate 60-86% of dissolved inorganic carbon (DIC) into lipids, and thus considerably more than what can be predicted from known metabolic pathways (~40% contribution). In slurry experiments amended with the marine methylotroph Methanococcoides methylutens, up to 12% of methane was produced from CO 2 , indicating that CO 2-dependent methanogenesis is an alternative methanogenic pathway and suggesting that obligate methylotrophic methanogens grow in fact mixotrophically on methyl compounds and DIC. Although methane formation from methanol is the primary pathway of methanogenesis, the observed high DIC incorporation into lipids is likely linked to CO 2-dependent methanogenesis, which was triggered when methane production rates were low. Since methylotrophic methanogenesis rates are much lower in marine sediments than under optimal conditions in pure culture, CO 2 conversion to methane is an important but previously overlooked methanogenic process in sediments for methylotrophic methanogens.

Subgroup level differences of physiological activities in marine Lokiarchaeota

“…δ 13 C-CO 2 in headspace of SIP incubations was monitored as previously published (Fig. S1 ) [ 16 ]. Incubations were stopped after up to 13 days according to the increase of δ 13 C-CO 2 in headspace (Fig.…”

“…Incubations amended with unlabelled protein and DIC were used as control. All incubations were stopped after 24 days based on the measurement of δ 13 C-CO 2 in the headspace [ 16 ].…”

Substrate‐dependent incorporation of carbon and hydrogen for lipid biosynthesis by Methanosarcina barkeri

“…Wegener et al, 2012), it is necessary to investigate the contribution of DIC for archaeal lipid biosynthesis during heterotrophic growth. For methanogenic archaea, lipid biosynthesis is associated with an IC demand not only for autotrophic but also for heterotrophic growth, i.e., IC is fixed into the intermediate acetyl-CoA catalysed by the carbon monoxide dehydrogenase (CODH) enzyme, and further utilized for lipid biosynthesis (Thauer, 1998;Yin et al, 2019). However, it is not clear how much IC is flowing into lipid biosynthesis of methanogenic archaea during heterotrophic growth (Londry et al, 2008), and it thus hinders the dual SIP application and the elucidation of the carbon metabolic routes of methanogenic and, more generally, archaeal lipid biosynthesis in environmental samples.…”

Biocatalytic C-C Bond Formation for One Carbon Resource Utilization

“…In methanotrophs, CH 4 can be continuously oxidized to CO 2 and then assimilated through the CBB cycle. In methanogens, CO 2 can be continuously reduced to CH 4 [ 97 ]. CO 2 also can be continuously reduced to CH 3 OH in vitro [ 98 ].…”