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Applied and Environmental Microbiology, June 1999, p. 2577-2584, Vol. 65, No. 6
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Temperature Dependence of Inorganic Nitrogen Uptake: Reduced Affinity for Nitrate at Suboptimal Temperatures in Both Algae and Bacteria

David S. Reay,1,* David B. Nedwell,1 Julian Priddle,2 and J. Cynan Ellis-Evans2

Department of Biological Sciences, University of Essex, Wivenhoe Park, Colchester CO4 3SQ,1 and British Antarctic Survey, Natural Environment Research Council, High Cross, Cambridge CB3 0ET,2 United Kingdom

Received 16 November 1998/Accepted 11 March 1999

Nitrate utilization and ammonium utilization were studied by using three algal isolates, six bacterial isolates, and a range of temperatures in chemostat and batch cultures. We quantified affinities for both substrates by determining specific affinities (specific affinity = maximum growth rate/half-saturation constant) based on estimates of kinetic parameters obtained from chemostat experiments. At suboptimal temperatures, the residual concentrations of nitrate in batch cultures and the steady-state concentrations of nitrate in chemostat cultures both increased. The specific affinity for nitrate was strongly dependent on temperature (Q10 approx  3, where Q10 is the proportional change with a 10°C temperature increase) and consistently decreased at temperatures below the optimum temperature. In contrast, the steady-state concentrations of ammonium remained relatively constant over the same temperature range, and the specific affinity for ammonium exhibited no clear temperature dependence. This is the first time that a consistent effect of low temperature on affinity for nitrate has been identified for psychrophilic, mesophilic, and thermophilic bacteria and algae. The different responses of nitrate uptake and ammonium uptake to temperature imply that there is increasing dependence on ammonium as an inorganic nitrogen source at low temperatures.

* Corresponding author. Mailing address: Department of Biological Sciences, University of Essex, Wivenhoe Park, Colchester CO4 35Q, United Kingdom. Phone: 01206 872818. Fax: 01206 873416. E-mail: dsreay{at}essex.ac.uk.

Applied and Environmental Microbiology, June 1999, p. 2577-2584, Vol. 65, No. 6
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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