Is required to sustain N(2)-dependent growth in the presence of low levels of carbon monoxide (CO). Probably acts by protecting the N(2) fixation ability of the nitrogenase complex, which is inactivated in the presence of CO. Is not required for CO-dependent growth. Up-regulated by RcoM in the presence of CO. Its expression is enhanced in the presence of a poor nitrogen source, like glutamate, that allows nif derepression. Strains lacking this gene are not able to grow with N(2) as a nitrogen source in the presence of CO. Belongs to the CowN family.