Fig. 3: D. alkaliphilus is capable of reducing ferrihydrite and oxidizing sulfide or FeS.
From: Microbial iron oxide respiration coupled to sulfide oxidation
a, D. alkaliphilus oxidizes formate (triangles) while reducing ferrihydrite (Fh) to Fe(ii) (circles). No Fe(ii) or formate consumption occurred in the absence of Fh or formate. b, Left and middle, D. alkaliphilus couples oxidation of poorly crystalline FeS to sulfate with reduction of Fh. Sulfate and Fe(ii) formation were not detected in abiotic controls or in cultures with FeS or Fh alone. Right, the ratio of sulfate to Fe(ii) formation (solid line) is close to predicted 1:8 stoichiometry (dashed line). c, Sulfate, HCl-extractable Fe(ii), elemental sulfur and Cline-extractable sulfide during the incubation of D. alkaliphilus cultures with Fh and daily spike of sulfide (1 mM). Parallel incubations with killed cells, or living cells without Fh or sulfide served as controls. Arrows indicate sulfide spike. d, Kinetics of dissolved sulfide and first-order rate constant in the incubations described in c. e, The canonical biogeochemical scenario of sulfate formation considering chemical sulfide oxidation to elemental sulfur (S(0)), followed by bacterial disproportionation. f, Updated scenario considering the contribution of sulfate formation from microbial oxidation of sulfide or FeS with iron oxides. g, Biphasic sulfate formation by D. alkaliphilus during 24 h incubation with ferrihydrite and sulfide. Phases I and II differ by sulfide availability. Phase I is shown with a larger scale on the x axis for visualization. A control for phase II was conducted by inoculating cells after the chemical reaction between sulfide and ferrihydrite (cells + Fh + S(0)/FeS). h, Faster consumption of a low concentration (approximately 50 µM) of sulfide by D. alkaliphilus compared with chemical controls lacking cells. Three spikes of sulfide were supplied at 1.5 h intervals. Results with different cell density are shown in Extended Data Fig. 1. In a–d,g,h, triplicate cultures (n = 3) were used for each incubation condition.
