Occurrence of ferredoxin:NAD+oxidoreductase activity and its ion specificity in several Gram-positive and Gram-negative bacteria

A ferredoxin:NAD + oxidoreductase was recently discovered as a redox-driven ion pump in the anaerobic, acetogenic bacterium Acetobacterium woodii . The enzyme is assumed to be encoded by the rnf genes. Since these genes are present in the genomes of many bacteria, we tested for ferredoxin:NAD + oxidoreductase activity in cytoplasmic membranes from several different Gram-positive and Gram-negative bacteria that have annotated rnf genes. We found this activity in Clostridium tetanomorphum , Clostridium ljungdahlii , Bacteroides fragilis, and Vibrio cholerae but not in Escherichia coli and Rhodobacter capsulatus . As in A. woodii , the activity was Na + -dependent in C. tetanomorphum and B. fragilis but Na + -independent in C. ljungdahlii and V. cholerae . We deleted the rnf genes from B. fragilis and demonstrated that the mutant has greatly reduced ferredoxin:NAD + oxidoreductase activity. This is the first genetic proof that the rnf genes indeed encode the reduced ferredoxin:NAD + oxidoreductase activity.