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Applied and Environmental Microbiology, June 2009, p. 3903-3911, Vol. 75, No. 12
0099-2240/09/$08.00+0     doi:10.1128/AEM.00080-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Effect of pH and Temperature on Denitrification Gene Expression and Activity in Pseudomonas mandelii{triangledown}

Saleema Saleh-Lakha,1,2 Kelly E. Shannon,1,2 Sherri L. Henderson,1 Claudia Goyer,1* Jack T. Trevors,2* Bernie J. Zebarth,1 and David L. Burton3

Potato Research Centre, Agriculture and Agri-Food Canada, Fredericton, New Brunswick E3B 4Z7, Canada,1 Department of Environmental Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada,2 Nova Scotia Agricultural College, Department of Environmental Sciences, Truro, Nova Scotia B2N 5E3, Canada3

Received 13 January 2009/ Accepted 6 April 2009

Pseudomonas mandelii liquid cultures were studied to determine the effect of pH and temperature on denitrification gene expression, which was quantified by quantitative reverse transcription-PCR. Denitrification was measured by the accumulation of nitrous oxide (N2O) in the headspace in the presence of acetylene. Levels of gene expression of nirS and cnorB at pH 5 were 539-fold and 6,190-fold lower, respectively, than the levels of gene expression for cells grown at pH 6, 7, and 8 between 4 h and 8 h. Cumulative denitrification levels were 28 µmol, 63 µmol, and 22 µmol at pH 6, 7, and 8, respectively, at 8 h, whereas negligible denitrification was measured at pH 5. P. mandelii cells grown at 20°C and 30°C exhibited 9-fold and 94-fold increases in levels of cnorB expression between 0 h and 2 h, respectively, and an average 17-fold increase in levels of nirS gene expression. In contrast, induction of cnorB and nirS gene expression for P. mandelii cells grown at 10°C did not occur in the first 4 h. Levels of cumulative denitrification at 10 h were 6.6 µmol for P. mandelii cells grown at 10°C and 20°C and 30 µmol for cells grown at 30°C. Overall, levels of cnorB and nirS expression were relatively insensitive to pH values over the range of pH 6 to 8 but were substantially reduced at pH 5, whereas gene expression was sensitive to temperature, with induction and time to achieve maximum gene expression delayed as the temperature decreased from 30°C. Low pH and temperature negatively affected denitrification activity.

* Corresponding author. Mailing address for Claudia Goyer: Potato Research Centre, Agriculture and Agri-Food Canada, Fredericton, New Brunswick E3B 4Z7, Canada. Phone: (506) 452-4851. Fax: (506) 452-3316. E-mail: claudia.goyer{at}agr.gc.ca. Mailing address for Jack T. Trevors: Department of Environmental Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada. Phone: (519) 824-4120, ext. 53367. Fax: (519) 837-0442. E-mail: jtrevors{at}uoguelph.ca

{triangledown} Published ahead of print on 17 April 2009.

Applied and Environmental Microbiology, June 2009, p. 3903-3911, Vol. 75, No. 12
0099-2240/09/$08.00+0     doi:10.1128/AEM.00080-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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