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Applied and Environmental Microbiology, August 1999, p. 3487-3492, Vol. 65, No. 8
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Chloramphenicol Inhibition of Denitrifying Enzyme Activity in Two Agricultural Soils

Robert E. Murray1,* and Roger Knowles2

Department of Biology, Appalachian State University, Boone, North Carolina 28608,1 and Microbiology Unit, Department of Natural Resource Sciences, McGill University, Macdonald Campus, Ste.-Anne-de-Bellevue, Quebec H9X 3V9, Canada2

Received 19 January 1999/Accepted 18 May 1999

Chloramphenicol, at concentrations greater than 0.1 g/liter (0.3 mM), inhibited the denitrifying enzyme activity (DEA) of slurries of humisol and sandy loam soils by disrupting the activity of existing nitrate reductase enzymes. When the concentration of chloramphenicol was increased from 0.1 to 2.0 g/liter (6.0 mM), the rate of nitrite production from nitrate decreased by 25 to 46%. The rate of NO production from nitrate decreased by 20 to 39%, and the rate of N2O production from nitrate, in the presence of acetylene (DEA), decreased by 21 to 61%. The predicted values of DEA at 0 g of chloramphenicol/liter computed from linear regressions of DEA versus chloramphenicol concentration were 18 to 43% lower than DEA measurements made in the absence of chloramphenicol and within a few per cent of DEA rates measured in the presence of 0.1 g of chloramphenicol/liter. We conclude that DEA assays should be carried out with a single (0.1-g/liter) chloramphenicol concentration. Chloramphenicol at concentrations greater than 0.1 g/liter inhibits the activity of existing denitrifying enzymes and should not be used in DEA assays.


* Corresponding author. Mailing address: Department of Biology, Appalachian State University, Boone, NC 28608. Phone: (828) 262-6908. Fax: (828) 262-2127. E-mail: MurrayRE{at}appstate.edu.


Applied and Environmental Microbiology, August 1999, p. 3487-3492, Vol. 65, No. 8
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.