Abstract
High amounts of hydrogen are emitted in the serpentinite-hosted hydrothermal field of the Prony Bay (PHF, New Caledonia), where high-pH (~11), low-temperature (< 40°C), and low-salinity fluids are discharged in both intertidal and shallow submarine environments. In this study, we investigated the diversity and distribution of potentially hydrogen-producing bacteria in Prony hyperalkaline springs by using metagenomic analyses and different PCR-amplified DNA sequencing methods. The retrieved sequences of hydA genes, encoding the catalytic subunit of [FeFe]-hydrogenases and, used as a molecular marker of hydrogen-producing bacteria, were mainly related to those of Firmicutes and clustered into two distinct groups depending on sampling locations. Intertidal samples were dominated by new hydA sequences related to uncultured Firmicutes retrieved from paddy soils, while submarine samples were dominated by diverse hydA sequences affiliated with anaerobic and/or thermophilic submarine Firmicutes pertaining to the orders Thermoanaerobacterales or Clostridiales. The novelty and diversity of these [FeFe]-hydrogenases may reflect the unique environmental conditions prevailing in the PHF (i.e., high-pH, low-salt, mesothermic fluids). In addition, novel alkaliphilic hydrogen-producing Firmicutes (Clostridiales and Bacillales) were successfully isolated from both intertidal and submarine PHF chimney samples. Both molecular and cultivation-based data demonstrated the ability of Firmicutes originating from serpentinite-hosted environments to produce hydrogen by fermentation, potentially contributing to the molecular hydrogen balance in situ.
Highlights
Hydrogen (H2) can be naturally produced by both geochemical and biological processes in various environments
The distribution and role of these microorganisms in the H2 budget of serpentinization-related systems have been scarcely addressed; so far, only two studies have investigated the potential of anaerobic microorganisms to biologically produce H2 in these hyperalkaline environments (Brazelton et al, 2012; Mei et al, 2014)
This study revealed an unexpected high diversity of [FeFe]hydrogenase genes mostly related to Firmicutes in the hyperalkaline and serpentinite-hosted PHF
Summary
Hydrogen (H2) can be naturally produced by both geochemical and biological processes in various environments. H2 can be generated during the serpentinization of ultramafic rocks by the reduction of water coupled to the oxidation of ferrous Fe contained in olivines and pyroxenes (Schrenk et al, 2013). This reaction is accompanied by the production of exceedingly alkaline waters (pH up to 12). In addition to H2 production resulting from abiotic reactions, H2 could be produced biologically by various types of microorganisms in these anoxic serpentinite-hosted environments. The distribution and role of these microorganisms in the H2 budget of serpentinization-related systems have been scarcely addressed; so far, only two studies have investigated the potential of anaerobic microorganisms to biologically produce H2 in these hyperalkaline environments (Brazelton et al, 2012; Mei et al, 2014)
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