Another chemolithotrophic metabolism missing in nature: sulfur comproportionation.
Environ Microbiol 2020;
22:1971-1976. [PMID:
32157786 PMCID:
PMC7384060 DOI:
10.1111/1462-2920.14982]
[Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Revised: 02/28/2020] [Accepted: 03/07/2020] [Indexed: 11/30/2022]
Abstract
Chemotrophic microorganisms gain energy for cellular functions by catalyzing oxidation-reduction (redox) reactions that are out of equilibrium. Calculations of the Gibbs energy ( ΔG r ) can identify whether a reaction is thermodynamically favourable and quantify the accompanying energy yield at the temperature, pressure and chemical composition in the system of interest. Based on carefully calculated values of ΔG r , we predict a novel microbial metabolism - sulfur comproportionation (3H2 S + SO 4 2 - + 2H+ ⇌ 4S0 + 4H2 O). We show that at elevated concentrations of sulfide and sulfate in acidic environments over a broad temperature range, this putative metabolism can be exergonic ( ΔG r <0), yielding ~30-50 kJ mol-1 . We suggest that this may be sufficient energy to support a chemolithotrophic metabolism currently missing from the literature. Other versions of this metabolism, comproportionation to thiosulfate (H2 S + SO 4 2 - ⇌S 2 O 3 2 - + H2 O) and to sulfite (H2 S + 3 SO 4 2 - ⇌ 4 SO 3 2 - + 2H+ ), are only moderately exergonic or endergonic even at ideal geochemical conditions. Natural and impacted environments, including sulfidic karst systems, shallow-sea hydrothermal vents, sites of acid mine drainage, and acid-sulfate crater lakes, may be ideal hunting grounds for finding microbial sulfur comproportionators.
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