Influence of Dissolved Oxygen Concentration on Intracellular pH and Consequently on Growth Rate of Aspergillus niger

Abstract

With the results presented we would like to emphasize the influence of dissolved oxygen concentration in a medium on intracellular pH values and consequently on overall metabolism of microorganisms. Intracellular pH of mycelium grown under different concentrations of dissolved oxygen in the medium was determined by recently developed cryo 31P-NMR method. Sensitivity of proteins toward proton concentration was well recognised, therefore pH influences on the activities of some key regulatory enzymes of Aspergillus niger were determined at pH values similar to those detected in the cells grown under lower dissolved oxygen concentrations. The results have shown significantly reduced specific activities of hexokinase, 6 phosphofructokinase and glucose-6-phosphate dehydrogenase in more acidic environment, while pyruvate kinase was found to be relatively insensitive toward higher proton concentration. As expected, due to reduced specific activities of some key regulatory enzymes under more acidic conditions, overall metabolism should be hindered in media with lower dissolved oxygen concentration, as confirmed by detecting reduced specific growth rates.

Keywords

• Aspergillus niger
• intracellular pH
• dissolved oxygen concentration
• specific growth rate
• metabolism