Metal reduction by sulphate-reducing bacteria: physiological diversity and metal specificity

The reduction of Tc(VII), Cr(VI) Se(IV) and Te(IV) by representatives of three genera of sulphate-reducing bacteria was studied with respect to the specificity of electron donor and acceptor. Tc(VII) and Cr(VI) were reduced by different mechanisms involving a hydrogenase. Cr(VI) reduction was achieved using a new isolate with lactate as the electron donor or by using H2 in the presence of bicarbonate ion. Te(IV) and Se(IV) were reduced to base metals. The removal of Se(IV) was enhanced under sulphidogenic conditions, with metal sulphide identified by energy dispersive X-ray microanalysis. The order of preference of the electron acceptors was Te(IV)>S(VI)>Se(IV), which is in sharp contrast to that predicted by the redox potentials alone.