Neisseria meningitidis is a facultative microaerophilic bacterium that can utilize oxygen, nitrite, and nitric oxide as terminal electron acceptors for its respiration. Oxygen can cause oxidation of both c-type and b-type cytochromes while nitrite or nitric oxide cause oxidation of b-type cytochrome predominantly. Nitrite as well as nitric oxide can directly inhibits oxidation of c-type cytochromes by oxygen. The meningococcus posseses many periplasmic electron transferring proteins. These proteins include cytochrome c2, cytochrome c4, cytochrome c5, and lipid-modified azurin. The cytochromes c2 and c4 are major electron donors to cytochrome cbb3 oxidase whereas the cytochrome c5 is a major electron donor to copper-containing nitrite reductase. The cytochrome c5 and lipid-modified azurin, to lesser extent, are also able to donate electrons to cytochrome cbb3 oxidase. Its respiratory flexibility may give the organism an advantage to adapt in environments where fluctuation of respiratory substrates occurs.