The influence of the oxidation-reduction potential of the medium upon the growth ofAzotobacter chroococcum

Abstract

1. Under aerobic conditions the development ofAzotobacter is suppressed by the presence of reducing substances in concentrations lowering the aerobic potential more than ±120 mV. 2. The development ofAzotobacter is not only retarded by the presence of these reducing substances, but the cells are killed. 3. Under anaerobic conditions no development ofAzotobacter could be observed even when the solution was poised at a high redox potential. The cells were not killed by the anaerobic conditions; as soon as aerobic conditions were restored, a rapid development ofAzotobacter was observed. 4. When the anaerobic conditions coincide with a low redox potentiale.g. in culture solutions containing glucose, the cells ofAzotobacter were killed. 5. The limits of potential endured byAzotobacter appeared to be dependent on the relations between the ions in the medium. 6. The cells ofAzotobacter secrete certain substances enabling them to develop at low potentials. 7. The conclusion is drawn that the development ofAzotobacter is in general influenced by the redox potential of the medium. However, this influence may be very complex, as the potential of the medium is only important in so far as the redox potential(s) in the cell are changed. The factors influencing the relation between the redox potential of the medium and the redox potentials of the cell are discussed. 8. ForAzotobacter, oxygen cannot be replaced by other redox systems with a suitable redox potential, most probably because these redox systems have to react with the respiratory enzymes of the cell.