Fig. 1.
Truncated denitrification pathway in M. catarrhalis. The truncated denitrification pathway in M. catarrhalis involves three enzymatic steps: reduction of nitrate (NO3−) to nitrite (NO2−) by the nitrate reductase complex NarGHJI, reduction of NO2− to nitric oxide (NO·) by the nitrite reductase AniA, and reduction of NO· to nitrous oxide (N2O) by the nitric oxide reductase NorB. M. catarrhalis apparently lacks the ability to reduce N2O to N2 (indicated by brackets). The M. catarrhalis transcriptional regulator NsrR represses the expression of both AniA and NorB under aerobic growth conditions.