Kinetics of nitrite oxidation by Nitrobacter winogradskyi.

Preliminary data on the kinetics of the oxidation of nitrite by Nitrobacter were presented by Laudelout & van Tichelen (1960). The present observations complete and extend the results concerning the effects of pH, concentrations of nitrite and of nitrate, temperature and oxygen partial pressure on the parameters of the rate equation for the oxidation of nitrite by intact cells and cell-free extracts. Results on some of these aspects of the physiology of Nitrobacter may be found in the literature; that they are not more abundant is largely due to problems connected with the growth of this organism in the Laboratory. Until recently (Goldberg & Gainey 1955) it was thought that suspended mineral matter was absolutely necessary for the normal growth of Nitrobacter. Harvesting of the cells from media containing calcium carbonate and phosphate gave mineral slurries in which, in view of the sorptive properties of the precipitates, uncertainties resulted during the study of the relationship between the rate of oxidation and the concentrations of ions. This is not, however, the main reason for ascertaining the kinetics of the oxidation rate of nitrite by Nitrobacter cells and cell-free extracts. The determination of the parameters of the rate equations should lead to a better understanding of the mechanism of the process. If the rate constants for intact cells and cell-free extracts are identical or nearly so, this would mean that the nitrite-oxidizing system may be localized at the cell surface or that permeability effects are entirely negligible, the latter being unlikely for a charged substrate and reaction product.