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

Abstract

A ferredoxin:NAD+oxidoreductase was recently discovered as a redox-driven ion pump in the anaerobic, acetogenic bacteriumAcetobacterium woodii. The enzyme is assumed to be encoded by thernfgenes. 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 annotatedrnfgenes. We found this activity inClostridium tetanomorphum,Clostridium ljungdahlii,Bacteroides fragilis, and Vibrio choleraebut not inEscherichia coliandRhodobacter capsulatus. As inA. woodii, the activity was Na+-dependent inC. tetanomorphumandB. fragilisbut Na+-independent inC. ljungdahliiandV. cholerae. We deleted thernfgenes fromB. fragilisand demonstrated that the mutant has greatly reduced ferredoxin:NAD+oxidoreductase activity. This is the first genetic proof that thernfgenes indeed encode the reduced ferredoxin:NAD+oxidoreductase activity.