Peat: home to novel syntrophic species that feed acetate- and hydrogen-scavenging methanogens

Abstract

Syntrophic bacteria drive the anaerobic degradation of certain fermentation products (e.g., butyrate, ethanol, propionate) to intermediary substrates (e.g., H 2 , formate, acetate) that yield methane at the ecosystem level. However, little is known about the in situ activities and identities of these syntrophs in peatlands, ecosystems that produce significant quantities of methane. The consumption of butyrate, ethanol or propionate by anoxic peat slurries at 5 and 15°C yielded methane and CO 2 as the sole accumulating products, indicating that the intermediates H 2 , formate and acetate were scavenged effectively by syntrophic methanogenic consortia. 16S rRNA stable isotope probing identified novel species/strains of Pelobacter and Syntrophomonas that syntrophically oxidized ethanol and butyrate, respectively. Propionate was syntrophically oxidized by novel species of Syntrophobacter and Smithella, genera that use different propionate-oxidizing pathways. Taxa not known for a syntrophic metabolism may have been involved in the oxidation of butyrate (Telmatospirillum-related) and propionate (unclassified Bacteroidetes and unclassified Fibrobacteres). Gibbs free energies (ΔGs) for syntrophic oxidations of ethanol and butyrate were more favorable than ΔGs for syntrophic oxidation of propionate. As a result of the thermodynamic constraints, acetate transiently accumulated in ethanol and butyrate treatments but not in propionate treatments. Aceticlastic methanogens (Methanosarcina, Methanosaeta) appeared to outnumber hydrogenotrophic methanogens (Methanocella, Methanoregula), reinforcing the likely importance of aceticlastic methanogenesis to the overall production of methane. ΔGs for acetogenesis from H 2 to CO 2 approximated to − 20 kJ mol − 1 when acetate concentrations were low, indicating that acetogens may have contributed to the flow of carbon and reductant towards methane.

Hydrocarbon degraders establish at the costs of microbial richness, abundance and keystone taxa after crude oil contamination in permafrost environments

“…Other studies have described similar communities in analogous environments, i.e. the Arctic permafrost5354 and a methane-emitting wetland on Spruce Mountains55, which poses these bacterial OTUs as keystones within the carbon cycle network. Members of the family Syntrophaceae ( Synthrophus and Smithella ) have been additionally identified in hydrocarbon-impacted environments, implying that they may be players also in syntrophic hydrocarbon metabolism56.…”

Soil viruses are underexplored players in ecosystem carbon processing

“…Lastly, vOTU_28 was linked to the Deltaproteobacteria Smithella sp. SDB, another acidophilic chemoorganoheterotroph, but an obligate anaerobe, with a known syntrophic relationship with methanogens (94, 95). Collectively, these virus-host linkages provide evidence for the Mire’s viruses to be impacting the C cycle via population control of relevant C-cycling hosts, consistent with previous results in this system (46) and other wetlands (96).…”

Formate‐derived H2, a driver of hydrogenotrophic processes in the root‐zone of a methane‐emitting fen

“…S4). Methanoregula and Methanosarcina species can be abundant in mire soil cores that contain roots (Hunger et al, 2015;Schmidt et al, 2016) and were also detected from roots prior to incubation (Fig. 4, Supporting Information fig.…”

“…Although methanogenesis is facilitated by rootcontaining peat soils (Br€ auer et al, 2004;Hunger et al, 2011a;Hunger et al, 2015;Schmidt et al, 2016), functional links between methanogens and the root itself in peatlands are not well established. Formate is one of the most important organic acids that is released from the roots of wetland plants (Koelbener et al, 2010) and is a substrate that can be rapidly utilized by fen (a type of peatland) methanogens (Hunger et al, 2011a).…”