Answer:
Reduction of iron to prevent oxidation.
Step-by-step explanation:
Bacteria has several mechanisms to protect the enzyme nitrogenase, one of them involves the increase of their metabolism to reduce the oxygen availability.
Besides this mechanism, there is also a conformational protection. This involves an interaction with FeSII protein, a ferredoxin. This protein is found as a homodimer that contains a 2[Fe-S] cluster, so reduction of Fe is not one of the mechanisms.