Oxidative Stress and Antioxidant Cell Protection Systems in the Microaerophilic Bacterium Spirillum winogradskii

Abstract

The influence of oxygen availability during cultivation on the biosynthetic processes and enzymatic activities in the microaerophilic bacterium Spirillum winogradskii D-427 was studied, and the roles played by different systems of the defense against oxidation stress were determined. The metabolic adjustments caused by transition from microaerobic (2% O₂) aerobic conditions (21% O₂ of the gas phase) were found to slow down constructive metabolism and increase synthesis of exopolysaccharides as a means of external protection of cells from excess oxygen. This resulted in a twofold decline of the growth yield coefficient. Even though the low activity of catalase is compensated for by a multifold increase in the activities of other cytoplasmic enzymes that defend against toxic forms of O₂—peroxidase and enzymes of the redox system of glutathione (glutathione peroxidase and glutathione reductase)—massive lysis of cells starts in the midexponential phase and leads to culture death in the stationary phase because of H₂O₂ accumulation in the periplasm (up to 10 μg/mg protein). The absence in cells of cytochrome-c-peroxidase, a periplasmic enzyme eliminating H₂O₂, was shown. It follows that the major cause of oxidative stress in cells is that active antioxidant defenses are located in the cytoplasm, whereas H₂O₂ accumulates in the periplasm due to the lack of cytochrome-c-peroxidase. The addition to the medium of thiosulfate promotes elimination of H₂O₂, stops cell lysis under aerobic conditions, lends stability to cultures, and results in a threefold increase in the growth yield.