Co-existence of Methanogenesis and Sulfate Reduction with Common Substrates in Sulfate-Rich Estuarine Sediments

Abstract

The competition between sulfate reducing bacteria and methanogens over common substrates has been proposed as a critical control for methane production. In this study, we examined the co-existence of methanogenesis and sulfate reduction with shared substrates over a large range of sulfate concentrations and rates of sulfate reduction in estuarine systems, where these processes are the key terminal sink for organic carbon. Incubation experiments were carried out with sediment samples from the sulfate-methane transition zone of the Yarqon (Israel) estuary with different substrates and inhibitors along a sulfate concentrations gradient from 1 to 10 mM. The results show that methanogenesis and sulfate reduction can co-exist while the microbes share substrates over the tested range of sulfate concentrations and at sulfate reduction rates up to 680 μmol L-1 day-1. Rates of methanogenesis were two orders of magnitude lower than rates of sulfate reduction in incubations with acetate and lactate, suggesting a higher affinity of sulfate reducing bacteria for the available substrates. The co-existence of both processes was also confirmed by the isotopic signatures of δ34S in the residual sulfate and that of δ13C of methane and dissolved inorganic carbon. Copy numbers of dsrA and mcrA genes supported the dominance of sulfate reduction over methanogenesis, while showing also the ability of methanogens to grow under high sulfate concentration and in the presence of active sulfate reduction.

Biogeochemistry, microbial activity, and diversity in surface and subsurface deep‐sea sediments of South China Sea

“…Although the concave‐up shape of methane profile was often interpreted as the diffusion of methane from SMTZ, increasing evidence suggested endogenous methane production could occur in the sulfate‐rich sediments (Maltby et al ; Sela‐Adler et al ; Xiao et al ; Zhuang et al ), as observed in this study. Therefore, the low but detectable concentrations of methane could be a collective result of production, consumption, and diffusion from underlying sediment below SMTZ.…”

Widespread microbial mercury methylation genes in the global ocean

“…Among the 10 HgcA sequences found in the gene ocean catalogue, none was affiliated to methanogenic Archaea . Even if the co-existence of methanogens and sulfate-reducers has been evidenced in marine sediments 24 , sulfate reduction usually outcompetes methanogenesis in seawater under non-limiting sulfate concentrations 25 . Our results thus show that Hg-methylators in the ocean span a large taxonomic diversity, not limited to sulfate-reducing bacteria.…”

Methylotrophic methanogenesis fuels cryptic methane cycling in marine surface sediment

“…This supports the dominance of methylotrophic methanogenesis, which is over 90% of total CH 4 production rates at 0–2 cm and over 60% at other depths except for 2–4 cm. As the anoxic incubation condition excluded the possibility of aerobic CH 4 production from methylphosphonate (Karl et al ; Repeta et al ), the methylotrophic methanogenesis from methylated compounds appears to be the only possible explanation for such a difference (Sela‐Adler et al ). A large potential of this methanogenic pathway in the sediment was shown by slurry incubation experiments (Fig.…”

“…Methane was measured by gas chromatography via a flame ionization detector (SRI 310C, SRI Instruments, U.S.A.). The isotope ratio of 13 C-CH 4 was determined by coupling a pre-concentration gas chromatograph (GC) with an isotope ratio mass spectrometer system (IRMS) (Thermo Fisher Scientific, Germany) (Rice et al 2001), and the same GC/IRMS without pre-concentration system was used for DIC measurement (Torres et al 2005). The Vienna Pee Dee Belemnite (VPDB) standard was used for the d 13 C values reference.…”