[Oxygen regulation of nitrogen metabolism in microorganisms]

Oxygen is one of the most important environmental factors for microorganisms. Many metabolic reactions of aerobic or facultative anaerobic bacteria are influenced by varying oxygen concentrations. A lot of enzyme reactions in respiration processes, catabolism, anabolism and gene expression depend upon oxygen. Other enzymes such as nitrogenase or hydrogenases can be inhibited by increasing oxygen levels. Also complex metabolic processes including anaerobic respiration and fermentations are regulated by oxygen. Finally toxic oxygen derivatives have to be eliminated by living cells to overcome damage of cell constituents. In this way also bacteria which are included into the nitrogen cycle in the nature are influenced by oxygen. The different strategies of microorganisms to protect their nitrogenases for oxygen inactivation and the regulation of dissimilative nitrate reduction by oxygen are demonstrated in detail.