Department of Biological Sciences, University of Southern California, Los Angeles, CA, 90089, USA.
Department of Earth Sciences, University of Southern California, Los Angeles, CA, 90089, USA.
Environ Microbiol. 2020 Jun;22(6):1971-1976. doi: 10.1111/1462-2920.14982. Epub 2020 Mar 18.
Chemotrophic microorganisms gain energy for cellular functions by catalyzing oxidation-reduction (redox) reactions that are out of equilibrium. Calculations of the Gibbs energy ( ΔG ) 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 , we predict a novel microbial metabolism - sulfur comproportionation (3H S + + 2H ⇌ 4S + 4H 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 <0), yielding ~30-50 kJ mol . 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 (H S + ⇌ + H O) and to sulfite (H S + 3 ⇌ 4 + 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.
化能微生物通过催化非平衡氧化还原（redox）反应来获取细胞功能所需的能量。吉布斯自由能（ΔG）的计算可以确定反应是否在热力学上有利，并量化在感兴趣的系统中的温度、压力和化学成分下伴随的能量产量。基于精心计算的 ΔG 值，我们预测了一种新的微生物代谢途径——硫歧化作用（3H2S + 2H ⇌ 4S + 4H2O）。我们表明，在酸性环境中，当硫化物和硫酸盐浓度升高且温度范围广泛时，这种假定的代谢途径可以是放能的（ΔG <0），产生约 30-50 kJ/mol。我们认为，这可能足以支持目前文献中缺失的化学生物代谢。这种代谢的其他版本，即歧化作用到硫代硫酸盐（H2S + ⇌ S2O32- + H2O）和亚硫酸盐（H2S + 3 ⇌ 4SO42- + 2H），即使在理想的地球化学条件下，也只是中度放能或吸能。自然和受影响的环境，包括硫化岩溶系统、浅海热液喷口、酸性矿山排水和酸性硫酸盐火山口湖，可能是寻找微生物硫歧化剂的理想场所。
