Ferric reductase is associated with the membranes of anaerobically grown Shewanella putrefaciens MR-1

Abstract

The expression and distribution of ferric reductase activity was examined in Shewanella putrefaciens MR-1. Formate-dependent ferric reductase was not detected in aerobically grown cells but was readily detectable in anaerobically grown cells. Ferric reductase activity was found exclusively in the membrane fractions, with 54–56% in the outer membrane. In contrast, the majority of formate dehydrogenase was in the soluble fraction with lesser amounts associated with the various membrane fractions. Outer membrane ferric reductase activity was markedly inhibited by p-chloromercuriphenylsulfonate, 2-heptyl-4-hydroxyquinolone-N-oxide, and antimycin A, but was unaffected by the presence of alternate electron acceptors (nitrate, nitrite, fumarate, and trimethylamine N-oxide). Both formate and NADH served as electron donors for ferric reductase; activity with l-lactate or NADPH was poor. The addition of FMN markedly stimulated formate- and NADH-dependent ferric reductase.