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

Abstract

The atmospheric flux of methane from the oceans is largely mitigated through microbially mediated sulphate-coupled methane oxidation, resulting in the precipitation of authigenic carbonates. Deep-sea carbonates are common around active and palaeo-methane seepage, and have primarily been viewed as passive recorders of methane oxidation; their role as active and unique microbial habitats capable of continued methane consumption has not been examined. Here we show that seep-associated carbonates harbour active microbial communities, serving as dynamic methane sinks. Microbial aggregate abundance within the carbonate interior exceeds that of seep sediments, and molecular diversity surveys reveal methanotrophic communities within protolithic nodules and well-lithified carbonate pavements. Aggregations of microbial cells within the carbonate matrix actively oxidize methane as indicated by stable isotope FISH-nanoSIMS experiments and 14 CH 4 radiotracer rate measurements. Carbonate-hosted methanotrophy extends the known ecological niche of these important methane consumers and represents a previously unrecognized methane sink that warrants consideration in global methane budgets.

Microbial abundance and diversity patterns associated with sediments and carbonates from the methane seep environments of Hydrate Ridge, OR

“…The persistence of ANME Archaea and microbial aggregates typically associated with AOM in low-activity samples suggests that even at fluxes that do not support established sulfide-based chemosynthetic communities at the seabed (microbial mats or chemosynthetic clam beds), potential for anaerobic methanotrophy remains (Marlow et al, 2014). These findings imply that methanotrophic potential is pervasive on and below the seafloor across substrate types, and the degree to which ancient seep deposits preserve signals of microbial community succession is unknown.…”

“…Aerobic methanotrophic activity has been documented using radiotracer methods in sediments and carbonates from both actively seeping and low-activity locations at Hydrate Ridge (Marlow et al, 2014). Surprisingly, the majority of samples lacked 16S rRNA evidence of known aerobic methanotrophs with the exception of AC-5120, a dolomite sample collected from an active seep site, where sequences affiliated with gammaproteobacterial Methylococcales comprised 8% of recovered sequences (Supplementary Data file 2a).…”

“…Cell counts were performed on an epifluorescence microscope (Olympus BX51) under 60× magnification (Plan Apo N objective) using the general DNA stain DAPI (4 ,6-diamidino-2-phenylindole). 25 fields Values marked with * indicate data from Marlow et al (2014). SD = standard deviation.…”

“…The recent quantification of active metabolic rates of methanotrophic microbial biomass living within the pore spaces of authigenic carbonates in active and low-activity areas further motivates the study of endolithic microbial communities (Marlow et al, 2014). Previous literature has characterized the common taxa associated with carbonates in methane-rich regimes such as cold seeps and mud volcanoes by examining lipid biomarkers (Blumenberg et al, 2004;Stadnitskaia et al, 2005Stadnitskaia et al, , 2008Gontharet et al, 2009) and 16S rRNA gene signatures (Reitner et al, 2005;Stadnitskaia et al, 2005Stadnitskaia et al, , 2008Heijs et al, 2006).…”

From the Cell to the Ecosystem: The Physiological Evolution of Symbiosis

“…This led to the belief that ammonium and methane were inert under anoxic conditions. However, recent studies using molecular techniques have shown that anaerobic methane oxidation can be carried out by a syntrophic consortium made up of an archaeon and a sulfate-reducing bacterium, although it has been suggested that some archaea can oxidize CH 4 without the need for a syntrophic bacterial partner (Boetius et al 2000;Marlow et al 2014). …”