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.
Key words: Aspergillus niger, intracellular pH, dissolved oxygen concentration, specific growth