Periplasmic oxygen reduction by Desulfovibrio species

Abstract.

Washed cells of Desulfovibrio vulgaris strain Marburg (DSM 2119) reduced oxygen to water with H₂ as electron donor at a mean rate of 253 nmol O₂ 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 H₂ were inhibited by CuCl₂. After further separation of the periplasm by ultrafiltration (exclusion sizes 30, 50, and 100 kDa), oxygen reduction with H₂ occurred with the retentates only. Ascorbate plus tetramethyl-p-phenylenediamine (TMPD), however, were also oxidized by the filtrates. The stoichiometry of 1 mol O₂ 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.