Biological methane cycling in serpentinization-impacted fluids of the Samail ophiolite of Oman
Abstract
Without sunlight for photosynthesis, microorganisms in subsurface environments are dependent on chemical energy to sustain metabolic activity. Yet little is known about the sources of chemical energy that support life in ophiolites. The Samail ophiolite of Oman, the largest and best exposed ophiolite in the world, is an ideal environment to study sources of chemical energy that support life activity. Serpentinization-impacted waters from 7 wells that intersect a range of gabbro and peridotite rocks were sampled in 2017 to recover genomic material from biomass. Sequencing of the V4/V5 hypervariable regions of small subunit ribosomal RNA (SSU rRNA) genes from recovered DNA revealed that water communities are unique between wells. Of the 10,761 genera identified in all waters, only 7 were shared across all wells including Meiothermus, unclassified Nitrospiraceae, Methanobacterium, and Methylococcus. When compared to previous years sampled (2014 - 2016), the community compositions appear similar, likely due to fluid geochemistry generated by water rock reactions. Corresponding cDNA (from RNA) indicates greater activity of several phylotypes in specific geochemical regimes. 16S rRNA gene transcripts affiliated with the methanogen Methanobacterium were abundant in H2-rich (164 μM), pH 11 waters sampled from the NSHQ14 well, whereas transcripts affiliated with the methanotroph Methylococcus were most abundant in CH4-rich (155 μM), pH 10 waters sampled from the NSHQ 04 well. Metagenomic sequencing of communities revealed that populations inhabiting waters with detectable H2 (NSHQ 14, WAB 71, WAB 188) encode mcr genes specific to methanogens but the substrates that support these populations may differ between wells. All genes for the hydrogenotrophic (H2/CO2) and acetoclastic (acetate disproportionation) pathways are present in metagenomes from NSHQ 14 and WAB 188. Populations inhabiting WAB 188 also encode the potential to use methanol and methylamines as methanogenic substrates while WAB 71 populations only encode for machinery to produce CH4 only from methanol. Additionally, the complete oxidation of methane is encoded in populations within most wells. Collectively, these data indicate that cycling of CH4 is an important process in sustaining the microbial community endemic to the Samail ophiolite.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.V13E0139K
- Keywords:
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- 0456 Life in extreme environments;
- BIOGEOSCIENCESDE: 8140 Ophiolites;
- TECTONOPHYSICSDE: 8416 Mid-oceanic ridge processes;
- VOLCANOLOGYDE: 8424 Hydrothermal systems;
- VOLCANOLOGY