Anaerobic oxidation of methane in hypersaline cold seep sediments

Abstract

Life in hypersaline environments is typically limited by bioenergetic constraints. Microbial activity at the thermodynamic edge, such as the anaerobic oxidation of methane (AOM) coupled to sulphate reduction (SR), is thus unlikely to thrive in these environments. In this study, carbon and sulphur cycling was investigated in the extremely hypersaline cold seep sediments of Mercator mud volcano. AOM activity was partially inhibited but still present at salinity levels of 292 g L(-1) (c. eightfold sea water concentration) with rates of 2.3 nmol cm(-3) day(-1) and was even detectable under saturated conditions. Methane and evaporite-derived sulphate comigrated in the ascending geofluids, which, in combination with a partial activity inhibition, resulted in AOM activity being spread over unusually wide depth intervals. Up to 79% of total cells in the AOM zone were identified by fluorescence in situ hybridization (FISH) as anaerobic methanotrophs of the ANME-1. Most ANME-1 cells formed monospecific chains without any attached partner. At all sites, AOM activity co-occurred with SR activity and sometimes significantly exceeded it. Possible causes of these unexpected results are discussed. This study demonstrates that in spite of a very low energy yield of AOM, microorganisms carrying this reaction can thrive in salinity up to halite saturation.

Archaeal and anaerobic methane oxidizer communities in the Sonora Margin cold seeps, Guaymas Basin (Gulf of California)

“…Combined with geochemical data, these results confirmed that ANME-1 preferred completely anoxic and highly sulfidic sediments and suggested that ANME-1 ecophysiology could depend on environmental conditions and more particularly on sulfate concentrations. In sulfate-poor and methanerich EWM14 sediments, ANME-1 could support a bacterial-independent AOM as suggested previously (Orphan et al, 2002;Maignien et al, 2012), using a different metabolic pathway providing terminal electron acceptors for AOM, such as the use of extracellular proteins, as mentioned by recent metaproteomic analyses (Stokke et al, 2012). Such metabolism, independent of bacterial association and then metabolic bacterial requirements, could occur and be more competitive than syntrophic AOM in EWM14 sediments.…”

Inter-comparison of the potentially active prokaryotic communities in the halocline sediments of Mediterranean deep-sea hypersaline basins

“…Although no sequences affiliating with the candidate division MSBL--1 (originally described from anoxic DHAB brines and thought to have a methanogenic metabolism; van der Wielen et al 2005) were detected, the archaeal OTUs we detected in our cDNA libraries are believed to have a putative methanogenic metabolism based on their phylogeny (van der Wielen et al 2005). Representatives of the archaeal ANME--1 group have also been suggested to be halotolerant as they have been found in high--salt concentration environments (Lloyd et al 2006;Maignien et al 2013;Pachiadaki et al 2014). Our results indicate that there may be additional important archaeal taxa involved in DHAB methane cycling aside from MBSL--1, and possibly ANME--1.…”

Unveiling microbial activities along the halocline of Thetis, a deep-sea hypersaline anoxic basin

“…Although ANME-1 archaea have been found most frequently in sulfate-depleted environments (Yanagawa et al, 2011), they are known to be adapted to hypersalinity (Lloyd et al, 2006;Maignien et al, 2013). This suggests salinity is a stronger selective force for this group than sulfate concentration.…”