In previous studies we have established that disruption of the fdxA gene that encodes A. vinelandii ferredoxin I (AvFdI) leads to overexpression of its redox partner, NADPH: ferredoxin reductase (FPR). Investigation of the mechanism of this regulatory system has shown that in response to FdI disruption, FPR levels are increased due to transcriptional activation at a specific palindromic sequence. That palindromic sequence is very similar to the defined SoxS binding site. To date that system has only been reported for E. coli.. Using A. vinelandii FPR-luciferase fusion reporter constructs we show that like E. coli SoxRS regulated genes, the A. vinelandii fpr gene is activated by the superoxide propagator paraquat and that the response occurs via the same palindrome that is responsive to FdI disruption. Using a ΔSoxR strain of E. coli and the same reporter constructs we show that when introduced into E. coli the A. vinelandii fpr promoter is controlled by SoxRS. Although the two systems are functionally similar and must have structural similarities at the level of DNA binding specificity for the SoxS-like component data are presented to show that they are likely to be significantly different at the protein/gene level. A model is presented that proposes that in A. vinelandii the specific function of FdI is to serve as the redox sensor that inactivates the SoxRS-like system and that other organisms (e.g. Pseudomonas, Caulobacter) that have homologous ferredoxins might have similar regulatory systems.