Fig. 2: Three potential metabolic pathways for coupling sulfur oxidation with reduction of iron(iii) oxides in a single bacterium.
From: Microbial iron oxide respiration coupled to sulfide oxidation
Top, genomic reconstruction predicts that dissimilatory reduction of iron(iii) oxides is coupled with oxidation of sulfide to sulfate (reaction 1; a), oxidation of sulfide to elemental sulfur (reaction 2; b) and oxidation of thiosulfate to sulfate (reaction 3; c). Key enzymes from Desulfobacterota and Gammaproteobacteria taxa are indicated as examples. Bottom, Gibbs free energy (∆Gr) of the iron-dependent sulfur oxidation reactions across a range of pH was calculated, assuming two different environmental settings. Marine ecosystem conditions (red line): ionic strength (I) = 0.7 M, T = 25 °C, [total dissolved sulfide] = 100 μM, [SO42−] = 28 mM, [S2O32−] = 1 μM, [Fe2+] = 10 μM; freshwater ecosystem conditions (black line): I = 0.001 M, T = 25 °C, [total dissolved sulfide] = 100 μM, [SO42−] = 100 μM, [S2O32−] = 1 μM, [Fe2+] =10 μM. The red and black lines overlap in c. Sox, thiosulfate-oxidizing system; OmcS and OmcZ, outer membrane multi-haem c-type cytochromes; PCC, porin–cytochrome complex.
