Anaerobic methane oxidation in sulfate depleted sediments: effects of sulfate and molybdate additions

Abstract

Anaeroblc methane oxldation and sulfate reduction were investigated in intact marine sedlment cores and in headspace-free, undiluted, homogenized, incubation bags In intact cores the typical upward concave methane concentration proflle indicated methane oxidation in the anoxic part of the sediment Generally, sulfate reduction rates exceeded methane oxidation rates many-fold, except in one case, where methane oxidation exceeded sulfate reduction 2 to 8 times In the sulfatemethane transition zone, sulfate reductlon was stimulated compared to rates measured above and below Methane ox~datlon rates determlned In incubation bags were equivalent to rates determlned in intact sedlment cores Methane oxidation rates were proportional to the concentrations of methane and also increased wlth Increasing methane concentrations in the absence of sulfate or the presence of molybdate When sulfate was added to sulfate-depleted incubation bags, methane oxidation rates decreased unmediately to less than half the rate measured pnor to the addition, while sulfate reduction was stmulated When molybdate ( a specific inhibitor of sulfate-reducing bactena) was added to a sulfate-free incubation bag, methane oxidahon responded after a lag penod of approximately 3 d , by uncoupling methane oxidation rates from methane concentrations Methane production was not affected From the outcome of our incubation bag expenments we conclude that methane is not, as previously proposed oxidized by sulfate reducers alone Our results support the hypothesis of Hoehler et a1 (1994, Global Biogeochem Cycles 8 451-463), who proposed that a consortium of methanogenlc bactena and sulfate reducers is responsible for net oxldat~on of methane under anoxlc conditions, a process called 'reverse methanogenesis'

Carbonate-hosted methanotrophy represents an unrecognized methane sink in the deep sea

“…Porous and massive carbonates from active seep sites performed AOM at rates commensurate with active seep sediment [42][43][44] , while sediment and carbonate rates from off-seep, low-activity areas were similar to those reported from continental shelves 10,45,46 . Within the comparative context of FISH-nanoSIMS analysis, active porous carbonate-hosted Archaea-DSS aggregates under anoxic conditions display substantial 15 N incorporation compared with aggregates from unlabelled incubations, confirming significant anabolic activity associated with cells residing in carbonate interiors.…”

“…4), exhibiting mixed or clustered species distributions. When modelling large aggregates (25 mm), Orcutt and Meile 39 found that consortia 43 Hydrate Ridge active seep sediment 32-2,358 Wegener et al 42 North Sea active seep sediment 25-450 Joye et al 70 Gulf of Mexico active seep sediment 121-501 Girguis et al 44 Monterey Bay active seep sediment 82.3 Hansen et al 45 Norsminde Fjord inner shelf sediment 14.3 Hoehler et al 10 Cape Lookout Bight inner shelf sediment 14-18 Reeburgh 46 Skan Bay outer shelf sediment 4.9-9.3 AOM, anaerobic oxidation of methane.…”

Diversity and Distribution of Methanotrophic Archaea at Cold Seeps

“…The AOM metabolic process is assumed to be a reversal of methanogenesis coupled to the reduction of sulfate to sulfide involving methanotrophic archaea (ANME) and sulfate-reducing bacteria (SRB) as syntrophic partners (7,20,21,23,69). Neither the ANME groups nor their sulfate-reducing partners have been isolated yet, and the enzymes and biochemical pathways involved in AOM remain unknown (18,19).…”

Growth and Population Dynamics of Anaerobic Methane-Oxidizing Archaea and Sulfate-Reducing Bacteria in a Continuous-Flow Bioreactor

“…Phylogenetic and isotopic analyses have shown that two groups of anaerobic methanotrophic archaea (ANME-1 and ANME-2) cooccur in sediments with sulfate-reducing bacteria and incorporate methane-derived carbon into cellular biomass (19, 30). Genomic and biochemical analyses suggest that microbial AOM may be achieved in part by reversal of the canonical methanogenic pathway (15, 23), and ongoing studies have shown that ANME-1 and ANME-2 methane-oxidizing archaea (or MOA) are distributed throughout the world in anoxic marine sediments where methane and sulfate are available (22,26,31,35,37,39,41).Our understanding of MOA physiology has been advanced by employing both in situ isotopic tracers and serum vial incubations to examine the relation between AOM and sulfate reduction and the effect of physical factors, such as pressure and temperature, on MOA methane oxidation rates (1,8,9,16,20,27,40). Whereas these studies have identified the primary metabolites used by the consortia and the influence of some environmental parameters on metabolite consumption, much remains to be learned about MOA, including some basic aspects of MOA ecology and physiology, such as population growth rates and modes of syntrophic metabolite exchange.…”