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Appl. Environ. Microbiol., Nov 1997, 4588-4592, Vol 63, No. 11
Copyright © 1997, American Society for Microbiology

Regulation of the Synthesis and Activity of Ammonia Monooxygenase in Nitrosomonas europaea by Altering pH To Affect NH(inf3) Availability

LY Stein, DJ Arp and MR Hyman
Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331

The obligately ammonia-oxidizing bacterium Nitrosomonas europaea was incubated in medium containing 50 mM ammonium. Changes in the concentration of nitrite, the pH, and the NH(inf4)(sup+)- and NH(inf2)OH-dependent O(inf2) uptake activities of the cell suspension were monitored. The NH(inf4)(sup+)-dependent O(inf2) uptake activity doubled over the first 3 h of incubation and then slowly returned to its original level over the following 5 h. The extent of stimulation of NH(inf4)(sup+)-dependent O(inf2) uptake activity was decreased by lowering the initial pH of the medium. Radiolabeling studies demonstrated that the stimulation of NH(inf4)(sup+)-dependent O(inf2) uptake activity involved de novo synthesis of several polypeptides. Under O(inf2)-limited conditions, the stimulated NH(inf4)(sup+)-dependent O(inf2) uptake activity was stabilized. Rapid, controlled, and predictable changes in this activity could be caused by acidification of the medium in the absence of ammonia oxidation. These results indicate that the NH(inf4)(sup+)-dependent O(inf2) uptake activity in N. europaea is strongly regulated in response to NH(inf3) concentration.

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