|Wankel, SD, MA Adams, DT Johnston, CM Hansel, SB Joye, PR Girguis, Anaerobic methane oxidation in metalliferous hydrothermal vent sediments: Influence on carbon and decoupling from sulfate reduction, Environmental Microbiology, 2012|
The anaerobic oxidation of methane (AOM) is a globally significant sink that regulates methane flux from sediments into the oceans and atmosphere. Here we examine mesophilic to thermophilic AOM in hydrothermal sediments recovered from the Middle Valley vent field, on the Juan de Fuca Ridge. Using continuous-flow sediment bioreactors and batch incubations, we characterized 1) the degree to which AOM contributes to net dissolved inorganic carbon flux, 2) AOM and sulfate reduction (SR) rates as a function of temperature, and 3) the distribution and density of known anaerobic methanotrophs. In sediment bioreactors, inorganic carbon stable isotope mass balances results indicated that AOM accounted for between 16 to 86% of the inorganic carbon produced, underscoring the role of AOM in governing inorganic carbon flux from these sediments. At 90°C, AOM occurred in the absence of SR, demonstrating a striking decoupling of AOM and SR. An abundance of Fe(III)-bearing minerals resembling mixed valent Fe oxides, such as green rust, suggests the potential for an important coupling of AOM to Fe(III) reduction in these metalliferous sediments. While SR bacteria were only observed in cooler temperature sediments, anaerobic methanotrophs allied to ANME-1 ribotypes, including a putatively new ANME-1c group, were found across all temperature regimes and represented a substantial proportion of the archaeal community. In concert, these results extend and reshape our understanding of the nature of high temperature methane biogeochemistry, providing insight into the physiology and ecology of thermophilic anaerobic methanotrophy and suggesting that AOM may play a central role in regulating biological DIC fluxes to the deep ocean from the organic-poor, metalliferous sediments of the global mid-ocean ridge hydrothermal vent system.