Occurrence of pyruvate:ferredoxin oxidoreductase in Campylobacter, Wolinella, Helicobacter and Arcobacter species
Pyruvate:ferredoxin oxidoreductase activity was demonstrated in microaerophilic members of Campylobacter, Wolinella, and Helicobacter. Arcobacter cryaerophila (sic) and Arcobacter nitrofigilis, two aerobic species, lacked any detectable activity. Under anaerobic conditions crude extracts of Campylobacter, Helicobacter and Wolinella were capable of reducing the electron carriers benzyl viologen and metronidazole in the presence of pyruvate. Addition of Clostridium pasteurianum ferredoxin to the metronidazole-linked reaction enhanced metronidazole-reducing activity, suggesting that electron transport to artificial electron carriers is facilitated by ferredoxin. All species exhibited varying degrees of sensitivity to metronidazole (MIC = <0.8 to 25 µg/ml) except Arcobacter cryaerophila, which was resistant to > 100 µg/ml. This further supports the theory that these organisms possess ferredoxin-linked reactions. The presence of the oxygen-labile enzyme pyruvate:ferredoxin oxidoreductase may be related to the inability of these microaerophilic bacteria to grow in normal atmospheric levels of oxygen.
Under aerobic conditions crude extracts of the organisms were also capable of reducing NAD in the presence of pyruvate. This might be accounted for by an NAD-linked pyruvate dehydrogenase; alternatively, it might be due to an enzymatic reduction of NAD by electrons from the reduced ferredoxin generated during the ferredoxin-linked pyruvate oxidoreductase reaction.