Azotobacter species didn't make HD unless ATP and electrons were present. They actually made less hydrogen and HD with nitrogen than with argon, contradicting earlier findings. 10% CO did inhibit HD formation but not hydrogen formation. Acetylene and methyl isocyanide inhibited HD completely. Cyanide partially or fully inhibited.
There was more exchange with D2O than with D2 for some reason, but this was inhibited more by nitrogen or cyanide.
This seems to have implications for nitrogenase's functions relating to hydrogen.