| dc.description.abstract | 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 mu mol, 63 mu mol, and 22 mu 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 degrees C and 30 degrees 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 degrees C did not occur
in the first 4 h. Levels of cumulative denitrification at 10 h were 6.6 mu mol for P.
mandelii cells grown at 10 degrees C and 20 degrees C and 30 mu mol for cells grown at
30 degrees 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 degrees C. Low pH and
temperature negatively affected denitrification activity. | en_US |
