title: Nitrite Control over Dissimilatory Nitrate/Nitrite Reduction Pathways in Shewanella loihica Strain PV-4.
abstract: Shewanella loihica strain PV-4 harbors both a functional denitrification (NO3 (-)→N2) and a respiratory ammonification (NO3 (-)→NH4 (+)) pathway. Batch and chemostat experiments revealed that NO2 (-) affects pathway selection and the formation of reduced products. Strain PV-4 cells grown with NO2 (-) as the sole electron acceptor produced exclusively NH4 (+). With NO3 (-) as the electron acceptor, denitrification predominated and N2O accounted for ∼90% of reduced products in the presence of acetylene. Chemostat experiments demonstrated that the NO2 (-):NO3 (-) ratio affected the distribution of reduced products, and respiratory ammonification dominated at high NO2 (-):NO3 (-) ratios, whereas low NO2 (-):NO3 (-) ratios favored denitrification. The NO2 (-):NO3 (-) ratios affected nirK transcript abundance, a measure of denitrification activity, in the chemostat experiments, and cells grown at a NO2 (-):NO3 (-) ratio of 3 had ∼37-fold fewer nirK transcripts per cell than cells grown with NO3 (-) as the sole electron acceptor. In contrast, the transcription of nrfA, implicated in NO2 (-)-to-NH4 (+) reduction, remained statistically unchanged under continuous cultivation conditions at NO2 (-):NO3 (-) ratios below 3. At NO2 (-):NO3 (-) ratios above 3, both nirK and nrfA transcript numbers decreased and the chemostat culture washed out, presumably due to NO2 (-) toxicity. These findings implicate NO2 (-) as a relevant modulator of NO3 (-) fate in S. loihica strain PV-4, and, by extension, suggest that NO2 (-) is a relevant determinant for N retention (i.e., ammonification) versus N loss and greenhouse gas emission (i.e., denitrification).
authors.affiliation: Center for Environmental Biotechnology, University of Tennessee, Knoxville, Tennessee, USA Department of Microbiology, University of Tennessee, Knoxville, Tennessee, USA Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Daejeon, South Korea syoon80@kaist.ac.kr frank.loeffler@utk.edu.
authors.forename: Sukhwan
authors.initials: S
authors.lastname: Yoon
authors.affiliation: Department of Geology, University of Illinois, Urbana, Illinois, USA.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Sanford
authors.affiliation: Center for Environmental Biotechnology, University of Tennessee, Knoxville, Tennessee, USA Department of Microbiology, University of Tennessee, Knoxville, Tennessee, USA Department of Civil and Environmental Engineering, University of Tennessee, Knoxville, Tennessee, USA University of Tennessee and Oak Ridge National Laboratory (UT-ORNL) Joint Institute for Biological Sciences (JIBS) and Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA syoon80@kaist.ac.kr frank.loeffler@utk.edu.
authors.forename: Frank E
authors.initials: FE
authors.lastname: Löffler
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D058440:Denitrification; D009566:Nitrates / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism*; D010084:Oxidation-Reduction; D020592:Shewanella / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D009566:Nitrates; D009573:Nitrites