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Applied and Environmental Microbiology, April 2008, p. 2447-2453, Vol. 74, No. 8
0099-2240/08/$08.00+0     doi:10.1128/AEM.01940-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Physiological State, Growth Mode, and Oxidative Stress Play a Role in Cd(II)-Mediated Inhibition of Nitrosomonas europaea 19718{triangledown}

Kartik Chandran{dagger} and Nancy G. Love*

Department of Civil and Environmental Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061

Received 23 August 2007/ Accepted 25 January 2008

The goal of this study was to determine the impact of physiological growth states (batch exponential and batch stationary growth) and growth modes (substrate-limited chemostat, substrate-sufficient exponential batch, and substrate-depleted stationary batch growth) on several measures of growth and responses to Cd(II)-mediated inhibition of Nitrosomonas europaea strain 19718. The specific oxygen uptake rate (sOUR) was the most sensitive indicator of inhibition among the different responses analyzed, including total cell abundance, membrane integrity, intracellular 16S rRNA/DNA ratio, and amoA expression. This observation remained true irrespective of the physiological state, the growth mode, or the mode of Cd(II) exposure. Based on the sOUR, a strong time-dependent exacerbation of inhibition (in terms of an inhibition coefficient [Ki]) in exponential batch cultures was observed. Long-term inhibition levels (based on Ki estimates) in metabolically active chemostat and exponential batch cultures were also especially severe and comparable. In contrast, the inhibition level in stationary-phase cultures was 10-fold lower and invariable with exposure time. Different strategies for surviving substrate limitation (a 10-fold increase in amoA expression) and starvation (the retention of 16S rRNA levels) in N. europaea cultures were observed. amoA expression was most negatively impacted by Cd(II) exposure in the chemostat cultures, was less impacted in exponential batch cultures, and was least impacted in stationary batch cultures. Although the amoA response was consistent with that of the sOUR, the amoA response was not as strong. The intracellular 16S rRNA/DNA ratio, as determined by fluorescence in situ hybridization, also did not uniformly correlate with the sOUR under conditions of inhibition or no inhibition. Finally, Cd(II)-mediated inhibition of N. europaea was attributed partially to oxidative stress.

* Corresponding author. Present address: Department of Civil and Environmental Engineering, University of Michigan, 2340 G. G. Brown Lab, 2350 Hayward St., Ann Arbor, MI 48109-2125. Phone: (734) 764-8495. Fax: (734) 764-4292. E-mail: nglove{at}umich.edu

{triangledown} Published ahead of print on 1 February 2008.

{dagger} Present address: Department of Earth and Environmental Engineering, Columbia University, New York, NY 10027.

Applied and Environmental Microbiology, April 2008, p. 2447-2453, Vol. 74, No. 8
0099-2240/08/$08.00+0     doi:10.1128/AEM.01940-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Park, S., Ely, R. L. (2008). Candidate Stress Genes of Nitrosomonas europaea for Monitoring Inhibition of Nitrification by Heavy Metals. Appl. Environ. Microbiol. 74: 5475-5482 [Abstract] [Full Text]  


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