The role of cytochrome c in the chromate reduction by Rhodobacter sphaeroides

The photosynthetic purple non-sulphur bacterium Rhodobacter (R.) sphaeroides has been proposed as main actor in several bioremediation processes given its highly versatile metabolism. As previously showed, R. sphaeroides can grow photosynthetically in presence of chromate, a well know and dangerous water-soluble pollutant. The main strategy employed by the bacterium for chromate pollution abatement is its reduction to the less toxic Cr3+ form. Chromate reduction to trivalent chromium was investigated via X-ray Absorption Spectroscopy (XAS). To demonstrate the influence of the cytochrome protein (cyt c) on the reduction, we recovered Extended X-ray Absorption Fine Structure (EXAFS) spectra, varying the pH of the mixture containing the reduced cytochrome c (cyt c) protein and the chromate. We demonstrated that the effect of pH is relevant, specifically at pH 6 is evident the reaction between chromate and reduced cyt c, because are visible changes both in the intensity and features of the peaks in the EXAFS spectra.