Nitric Oxide Reductase Gene Expression and Nitrous Oxide Production in Nitrate-Grown Pseudomonas mandelii

Abstract

Pure cultures of Pseudomonas mandelii were incubated with or without nitrate, which acts as a substrate and an electron acceptor for denitrification. Nitric oxide reductase ( cnorB ) gene expression was measured using a quantitative reverse transcription-PCR, and nitrous oxide emissions were measured by gas chromatography. P. mandelii cells in either the presence or absence of nitrate demonstrated an increase in cnorB gene expression during the first 3 h of growth. The level of expression of cnorB in nitrate-amended cells remained high (average, 2.06 × 10 ⁸ transcripts/μg of RNA), while in untreated cells it decreased to an average of 3.63 × 10 ⁶ transcripts/μg of RNA from 4 to 6 h. Nitrous oxide accumulation in the headspace was detected at 2 h, and cumulative emissions continued to increase over a 24-h period to 101 μmol in nitrate-amended cells. P. mandelii cnorB gene expression was not detected under aerobic conditions. These results demonstrate that P. mandelii cnorB gene expression was induced 203-fold at 4 h when nitrate was present in the medium. Accumulations of N ₂ O indicated that the cNorB enzyme was synthesized and active.