Previous Article | Next Article ![]()
Appl Environ Microbiol, April 1998, p. 1514-1521, Vol. 64, No. 4
Department of Botany and Plant Pathology,
Oregon State University, Corvallis, Oregon 97331
Received 30 October 1997/Accepted 22 January 1998
The effects of limiting concentrations of ammonium on the metabolic
activity of Nitrosomonas europaea, an obligate
ammonia-oxidizing soil bacterium, were investigated. Cells were
harvested during late logarithmic growth and were incubated for 24 h in growth medium containing 0, 15, or 50 mM ammonium. The changes in
nitrite production and the rates of ammonia- and
hydroxylamine-dependent oxygen consumption were monitored. In
incubations without ammonium, there was little change in the ammonia
oxidation activity after 24 h. With 15 mM ammonium, an amount that
was completely consumed, there was an 85% loss of the ammonia
oxidation activity after 24 h. In contrast, there was only a 35%
loss of the ammonia oxidation activity after 24 h in the presence
of 50 mM ammonium, an amount that was not consumed to completion. There
was little effect on the hydroxylamine oxidation activity in any of the
incubations. The loss of ammonia oxidation activity was not due to
differences in steady-state levels of ammonia monooxygenase (AMO) mRNA
(amoA) or to degradation of the active site-containing
subunit of AMO protein. The incubations were also conducted at a range
of pH values to determine whether the loss of ammonia oxidation
activity was correlated to the residual ammonium concentration. The
loss of ammonia oxidation activity after 24 h was less at lower pH values (where the unoxidized ammonium concentration was higher). When
added in conjunction with limiting ammonium, short-chain alkanes, which
are alternative substrates for AMO, prevented the loss of ammonia
oxidation activity at levels corresponding to their binding affinity
for AMO. These results suggest that substrates of AMO can preserve the
ammonia-oxidizing activity of N. europaea in batch
incubations by protecting either AMO itself or other molecules
associated with ammonia oxidation.
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Ammonium Limitation Results in the Loss of
Ammonia-Oxidizing Activity in Nitrosomonas europaea
*
Corresponding author. Mailing address: Department of
Botany and Plant Pathology, 2082 Cordley, Oregon State University,
Corvallis, OR 97331. Phone: (541) 737-1294. Fax: (541) 737-3573. E-mail: arpd{at}bcc.orst.edu.
This article has been cited by other articles:
Copyright © 2009 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»