THE EXPRESSION OF REDOX PROTEINS OF DENITRIFICATION IN THIOSPHAERA-PANTOTROPHA GROWN WITH OXYGEN, NITRATE, AND NITROUS-OXIDE AS ELECTRON-ACCEPTORS

The redox proteins and enzymes involved in denitrification in Thiosphaera pantotropha exhibited a differential expression in response to oxygen. Pseudoazurin was completely repressed during batch or continuous culture under oxic conditions. Cytochrome ed, nitrite reductase was also heavily repressed after aerobic growth. Nitrite, nitric oxide, and nitrous oxide reductase activities were detected in intact cells under some conditions of aerobic growth, indicating that aerobic denitrification might occur in some circumstances. However, the rates of denitrification were much lower after aerobic growth than after anaerobic growth. Growth with nitrous oxide as sole electron acceptor mimicked aerobic growth in some respects, implying that expression of parts of the denitrification apparatus might be controlled by the redox state of a component of the electron transport chain rather than by oxygen itself. Nevertheless, the regulation of expression of nitrous oxide reductase was linked to the oxygen concentration.