| Hydrogen Limitation and Syntrophic Growth among Natural Assemblages of Thermophilic Methanogens at Deep-sea Hydrothermal Vents - :16508 | Office of Oceanic and Atmospheric Research (OAR)
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Hydrogen Limitation and Syntrophic Growth among Natural Assemblages of Thermophilic Methanogens at Deep-sea Hydrothermal Vents
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Hydrogen Limitation and Syntrophic Growth among Natural Assemblages of Thermophilic Methanogens at Deep-sea Hydrothermal Vents
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    Thermophilic methanogens are common autotrophs at hydrothermal vents, but their growth constraints and dependence on H-2 syntrophy in situ are poorly understood. Between 2012 and 2015, methanogens and H2-producing heterotrophs were detected by growth at 80 degrees C and 55 degrees C at most diffuse (740 degrees C) hydrothermal vent sites at Axial Seamount. Microcosm incubations of diffuse hydrothermal fluids at 80 degrees C and 55 degrees C demonstrated that growth of thermophilic and hyperthermophilic methanogens is primarily limited by H-2 availability. Amendment of microcosms with NH4+ generally had no effect on CH4 production. However, annual variations in abundance and CH4 production were observed in relation to the eruption cycle of the seamount. Microcosm incubations of hydrothermal fluids at 80 degrees C and 55 degrees C supplemented with tryptone and no added H-2 showed CH4 production indicating the capacity in situ for methanogenic H-2 syntrophy. 16S rRNA genes were found in 80 degrees C microcosms from H-2-producing archaea and H-2-consuming methanogens, but not for any bacteria. In 55 degrees C microcosms, sequences were found from H-2-producing bacteria and H-2-consuming methanogens and sulfate-reducing bacteria. A co-culture of representative organisms showed that Thermococcus paralvinellae supported the syntrophic growth of Methanocaldococcus bathoardescens at 82 degrees C and Methanothermococcus sp. strain BW11 at 60 degrees C. The results demonstrate that modeling of subseafloor methanogenesis should focus primarily on H-2 availability and temperature, and that thermophilic H-2 syntrophy can support methanogenesis within natural microbial assemblages and may be an important energy source for thermophilic autotrophs in marine geothermal environments.

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