Abstract

The effects of 2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol and 4-bromophenol on the acti-vities of periplasmic nitrate reductase and dehydrogenase enzymes  of Acinetobacter sp. iso-lated from a tropical soil were assessed via reduction of nitrate and 2,3,5-triphenyltetrazoluim chloride, respectively. There were significant differences in the response of dehydrogenase enz-yme but not periplasmic nitrate reductase to the various compounds. However, at different concentrations, the phenolic compounds had significant effects on periplasmic nitrate reductase but not dehydrogenase activity. Estimations of the degree of inhibition/stimulation of both enzyme activities showed a significant dose-dependent response. 2,4-Dinitrophenol showed decreasing progressive stimulation of dehydrogenase enzyme with increasing concentration (40 – 200 mg/l) while 2-nitrophenol, 4-nitrophenol and 4-bromophenol showed increasing progres-sive inhibition of both enzyme activities. The IC₅₀ of the phenolic compounds to the periplasmic nitrate reductase activity were comparable (33.46 – 44.75 mg/l) but lower than those for the dehydrogenase activity (>200 mg/l). This suggested greater sensitivity of periplasmic nitrate reductase than dehydrogenase enzyme to the phenolic compounds. This study suggested that the toxic effects of chemicals on specific microbiological activities are better studied using the appropriate enzymes involved rather than the dehydrogenase activity.

Key words: Acinetobacter sp., dehydrogenase, periplasmic nitrate reductase, phenolic compounds.