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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 (N 2 O) 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 mol, 63 mol, and 22 mol 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 mol for P. mandelii cells grown at 10°C and 20°C and 30 mol 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.Denitrification is a respiratory microbiological process in which nitrate (NO 3 Ϫ ) or nitrite (NO 2 Ϫ ) is reduced to gaseous nitric oxide (NO), nitrous oxide (N 2 O), or molecular nitrogen (N 2 ) under oxygen-limited conditions (33). Denitrification can result in substantial gaseous losses of N, an important plant nutrient, from agricultural fields (7,14). N 2 O depletes stratospheric ozone and contributes to global warming (28). An understanding of the environmental controls on denitrifier activity is essential for comprehending the spatial and temporal regulation of denitrification within agricultural production systems.Denitrification is carried out by various microorganisms belonging to several genera and species of bacteria (3,4,27,33). The strain of Pseudomonas mandelii used in this study was a dominant culturable denitrifier isolated from an agricultural field in a potato production system in New Brunswick, Canada (4).Several environmental factors control the process of denitrification. These include oxygen availability, substrate availability (i.e., NO 2 Ϫ and NO 3 Ϫ ), pH, temperature, and the abundance and species of denitrifiers. The availability of a substrate, the absence of oxygen, and the presence of active denitrifiers are the main controlling factors (24). However, pH and temperature also play a role in influencing denitrifier growth, metabolism, denitrification gene expression, and, subsequently, denitrification rate. A recent review of environmental controls on denitrifying communities and...

One hundred one strains of Listeria monocytogenes isolated from seafood and cheese industry samples and from patients with listeriosis were assessed using a microtiter plate method for adhesion to polystyrene and stainless steel surfaces. The adhesion rate for these strains ranged from 3.10 to 35.29% with an inoculum of 8 x 10(8) cells per well. A strong correlation was found between adhesion to polystyrene and stainless steel microtiter plates, indicating that the intrinsic ability of L. monocytogenes to adhere to inert surfaces is stronger than the influence of the surface's physicochemical properties. The clinical strains were less adherent to inert surfaces than were the industrial strains. By integrating other factors such as location of the industrial strains, contamination type of the clinical strains, serotype, and pulsotype into the analysis, some weak but significant differences were noted. For the industrial isolates, the number of cells attached to both surfaces differed significantly depending on whether they were isolated from food or food-processing environments in the seafood and cheese industry. For clinical isolates, sporadic strains exhibited greater adhesion to polystyrene than did epidemic strains. Strains belonging to the pulsed-field gel electrophoretype clusters A and M (lineages II and I, respectively) were less able to adhere to polystyrene and stainless steel than were strains in the more common clusters.