Periplasmic oxygen reduction by Desulfovibrio species

Washed cells of Desulfovibrio vulgaris strain Marburg (DSM 2119) reduced oxygen to water with H, as electron donor at a mean rate of 253 nmol O-2 min(-1) (mg protein)(-1). After separating the periplasm from the cells, more than 60% of the cytochrome c activity and 90% of the oxygen-reducing activity were found in the periplasmic fraction. Oxygen reduction and the reduction of cytochrome c with H, were inhibited by CuCl2. After further separation of the periplasm by ultrafiltration (exclusion sizes 30. 50, and 100 kDa), oxygen reduction with H-2 occurred with the retentates only. Ascorbate plus tetramethyl-p-phenylenediamine (TMPD), however, were also oxidized by the filtrates. The stoichiometry of 1 mol O-2 reduced per 2 mol ascorbate oxidized indicated the formation of water. Our experiments present evidence that in D. vulgaris periplasmic hydrogenase and cytochrome c play a major role in oxygen reduction. Preliminary studies with other Desulfovibrio species indicated a similar function of periplasmic c-type cytochromes in D. desulfuricans CSN and D. termitidis KH1.