Description: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Frontiers in Microbiology 7 (2016): 1240, doi:10.3389/fmicb.2016.01240.

Description: Thermophilic methanogens are common autotrophs at hydrothermal vents, but their growth constraints and dependence on H2 syntrophy in situ are poorly understood. Between 2012 and 2015, methanogens and H2-producing heterotrophs were detected by growth at 80∘C and 55∘C at most diffuse (7–40∘C) hydrothermal vent sites at Axial Seamount. Microcosm incubations of diffuse hydrothermal fluids at 80∘C and 55∘C demonstrated that growth of thermophilic and hyperthermophilic methanogens is primarily limited by H2 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∘C and 55∘C supplemented with tryptone and no added H2 showed CH4 production indicating the capacity in situ for methanogenic H2 syntrophy. 16S rRNA genes were found in 80∘C microcosms from H2-producing archaea and H2-consuming methanogens, but not for any bacteria. In 55∘C microcosms, sequences were found from H2-producing bacteria and H2-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∘C and Methanothermococcus sp. strain BW11 at 60∘C. The results demonstrate that modeling of subseafloor methanogenesis should focus primarily on H2 availability and temperature, and that thermophilic H2 syntrophy can support methanogenesis within natural microbial assemblages and may be an important energy source for thermophilic autotrophs in marine geothermal environments.

Description: This work was funded by the Gordon and Betty Moore Foundation grant GBMF 3297, the NASA Earth and Space Science Fellowship Program grant NNX11AP78H, the National Science Foundation grant OCE-1547004, with funding from NOAA/PMEL, contribution #4493, and JISAO under NOAA Cooperative Agreement NA15OAR4320063, contribution #2706.

Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Trembath-Reichert, E., Butterfield, D. A., & Huber, J. A. Active subseafloor microbial communities from Mariana back-arc venting fluids share metabolic strategies across different thermal niches and taxa. Isme Journal, 13(9), (2019): 2264-2279, doi: 10.1038/s41396-019-0431-y.

Description: There are many unknowns regarding the distribution, activity, community composition, and metabolic repertoire of microbial communities in the subseafloor of deep-sea hydrothermal vents. Here we provide the first characterization of subseafloor microbial communities from venting fluids along the central Mariana back-arc basin (15.5–18°N), where the slow-spreading rate, depth, and variable geochemistry along the back-arc distinguish it from other spreading centers. Results indicated that diverse Epsilonbacteraeota were abundant across all sites, with a population of high temperature Aquificae restricted to the northern segment. This suggests that differences in subseafloor populations along the back-arc are associated with local geologic setting and resultant geochemistry. Metatranscriptomics coupled to stable isotope probing revealed bacterial carbon fixation linked to hydrogen oxidation, denitrification, and sulfide or thiosulfate oxidation at all sites, regardless of community composition. NanoSIMS (nanoscale secondary ion mass spectrometry) incubations at 80 °C show only a small portion of the microbial community took up bicarbonate, but those autotrophs had the highest overall rates of activity detected across all experiments. By comparison, acetate was more universally utilized to sustain growth, but within a smaller range of activity. Together, results indicate that microbial communities in venting fluids from the Mariana back-arc contain active subseafloor communities reflective of their local conditions with metabolisms commonly shared across geologically disparate spreading centers throughout the ocean.

Description: This work was funded by the NOAA Ocean Exploration and Research (OER) Program, the NSF Center for Dark Energy Biosphere Investigations (C-DEBI) (OCE-0939564), and NOAA/PMEL and JISAO under NOAA Cooperative Agreement NA15OAR4320063. ETR was supported by a NASA Postdoctoral Fellowship with the NASA Astrobiology Institute and a L’Oréal USA For Women in Science Fellowship. The data collected in this study includes work supported by the Schmidt Ocean Institute during cruise FK161129 aboard R/V Falkor. We thank the captains and crews of the R/V Falkor and ROV SuBastian. Critical support in cruise planning and sampling at sea was carried out by Andra Bobbitt, Bill Chadwick, Bob Embley, Ben Larson, and Kevin Roe. Caroline Fortunato, Connor Skennerton, Rika Anderson, Karthik Anantharaman, Jaclyn Saunders, Hank Yu, Lewis Ward, Elaina Graham, and Ben Tully aided bioinformatics pipeline development and Victoria Orphan and Yunbin Guan aided with NanoSIMS analysis. This is C-DEBI Contribution 470, JISAO Contribution 2018-0173, and PMEL Contribution 4867.