Nitrogen and oxygen isotope fractionation during dissimilatory nitrate reduction by denitrifying bacteria

Granger, J. and Sigman, D. M. and Lehmann, M. F. and Tortell, P. D.. (2008) Nitrogen and oxygen isotope fractionation during dissimilatory nitrate reduction by denitrifying bacteria. Limnology and Oceanography, 53, 6. pp. 2533-2545.

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Official URL: http://edoc.unibas.ch/dok/A5249288

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We report the first measurements of coupled nitrogen (N) and oxygen (O) isotope fractionation of nitrate by laboratory cultures of denitrifying bacteria. Two seawater strains (Pseudomonas stutzeri, Ochrobactrum sp.) and three freshwater strains (Paracoccus denitrificans, Pseudomonas chlororaphis, Rhodobacter sphaeroides) were examined. Among four strains of facultative anaerobic denitrifiers, N and O isotope effects were variable, ranging from 5 parts per thousand to 25 parts per thousand, with evidence for a drop in the isotope effects as nitrate concentrations approached the half-saturation constant for nitrate transport. O isotope effects were similar to their corresponding N isotope effect, such that the progressive increase in nitrate delta O-18, when plotted against that in delta N-15 (where delta O-18(sample) = [(O-18 : O-16) sample/(O-18 : O-16)(reference) - 1] x 1000, and delta N-15(sample) = [(N-15 : N-14)(sample)/(N-15 : N-14)(reference) - 1] x 1000), yielded slopes of 0.86 to 1.02, with a mean value of 0.96. R. sphaeroides, a photo-heterotroph that possesses only a periplasmic (nonrespiring) dissimilatory nitrate reductase, showed less variability in nitrate N isotope effects, between 13 parts per thousand and 20 parts per thousand, with a modal value of similar to 15 parts per thousand. In contrast to the respiratory denitrifiers, R. sphaeroides consistently showed a distinct ratio of delta O-18 to delta N-15 change of similar to 0.62. We hypothesize that heavy N and O isotope discrimination during respiratory denitrification occurs during the intracellular reduction of nitrate by the respiratory nitrate reductase, and the observed magnitude of fractionation is likely regulated by the ratio of cellular nitrate efflux relative to uptake. The data for R. sphaeroides are consistent with isotope discrimination directly reflecting the N and O isotope effects of the periplasmic nitrate reductase NAP, without modification by nitrate uptake and efflux.
Faculties and Departments:05 Faculty of Science > Departement Umweltwissenschaften > Geowissenschaften > Aquatic and Isotope Biogeochemistry (Lehmann)
UniBasel Contributors:Lehmann, Moritz F
Item Type:Article, refereed
Article Subtype:Research Article
Publisher:American Society of Limnology and Oceanography
Note:Publication type according to Uni Basel Research Database: Journal article
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Last Modified:22 Mar 2012 14:28
Deposited On:22 Mar 2012 14:05

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