A Mechanism for Complementation of the sodA sodBDefect in Escherichia coli by Overproduction of the rbo Gene Product (Desulfoferrodoxin) from Desulfoarculus baarsii

Overexpression of rbo in Escherichia coli prevents the inactivation of the [4Fe-4S]-containing fumarases that otherwise occurs in the sodA sodB strain. It similarly protects against the increased sensitivity toward H2O2, which is imposed by the lack of SOD A and SOD B. These results would be explained on the basis of scavenging of O-2 within the cells by RBO. This interpretation was supported by measurements of intracellular scavenging of O-2 by the lucigenin luminescence method. Since SOD activity could not be detected in dilute extracts, of the RBO-overexpressing sodA sodB strain, we propose that RBO catalyzes the reduction of O-2 at the expense of cellular reductants such as NAD(P)H. A similar mechanism may apply to other instances of complementation of SOD defects by non-SOD genes.