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Postdoctoral Research Associate with Daniel Sigman. Sigman group

Princeton University, Department of Geosciences, Washington Road, Guyot Hall, 08544 N.J., U.S.A.

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I am interested in elucidating how physiological processes occurring on a microbial scale shape environmental processes on regional to global scales. I focus primarily on nitrogen cycling in marine systems, given the importance of N to ocean fertility, and also because N is the only plant nutrient whose biogeochemical cycling is effectuated entirely by biological processes. To evaluate N dynamics in the environment from the natural abundance ratios 15N/14N ratios of fixed N species. I measure the stable isotopic tracers of nitrate the water or sediment column using the denitrifier method (Sigman et al. 2001, Casciotti et al. 2002) which allows for precise quantification of the 15N/14N and 18O/16O ratios of nitrate at concentrations as low as 0.5 µM. Auxilliary methods also allow to measure the 15N/14N of more reduced fixed N species at equally low concentrations (nitrite, DON, and NH4: McIllvin and Altabet 2007, Knapp et al. 2005, Zhang et al. 2009), such that a comprehensive N isotope budget of a given system can be quantified.

Individual biological N transformations in the N cycle show characteristic patterns in fractionation of the N (and O) isotopes of N species, thus leaving an imprint on specific N pools. An important aspect of my work is to determine the imprints associated with biological N transformations, by growing mono-cultures of model micro-organisms to elucidate the physiological mechanisms underlying N and O isotope fractionation, and to determine the variability in the isotopic imprints and the sensitivity of the latter to various growth conditions. The patterns and pathways elucidated therein inform the interpretation of the distribution N and O isotope ratios in the environment, enabling to distinguish of the relative importance of particular N transformations. The distinct advantage of using N isotopic tracers to infer N cycling is that these integrate over spatial and temporal scales, and do not reflect bias otherwise introduced by bottle effects during on-deck incubations, and/or bias introduced by the inability to capture spatial and temporal variability from discrete on-deck rate measurements of biological N transformations.

Physio-ecology of marine plankton: nitrogen nutrition and iron nutrition: constraining biochemical pathways of nutrient utilization.

Bering Shelf Nutrient Cycling: the dual isotopes of nitrate reveal the importance of benthic processes.

Analytical Method Development: improving N-isotope measurements & N-pool specific analysis.

[…] Nitrate Reductase enzyme mechanism

Nitrate N and O isotope effects of a eukaryotic nitrate reductase in vitro (in collaboration with Kristen Karsh)

Investigating Nitrate Reductase enzyme mechanism(s) with ab initio quantum mechanical models (in collaboration with Weifu Guo)

Nitrate isotope dynamics in the Arctic Ocean

University of British Columbia, PhD, Oceanography, 2006

McGill University, MSc, Biology, 1998

McGill University, BSc, Biology, 1995

Granger, J., D. M. Sigman, M. M. Rohde, M. T. Maldonado, and P. D. Tortell (2010), N and O isotope effects during nitrate assimilation by unicellular prokaryotic and eukaryotic plankton cultures, Geochimica Et Cosmochimica Acta, 74(3), 1030-1040.

Granger, J., and D. M. Sigman (2009), Removal of nitrite with sulfamic acid for nitrate N and O isotope analysis with the denitrifier method, Rapid Communications in Mass Spectrometry, 23(23), 3753-3762.External Link

Granger, J., K. L. Karsh, W. Guo, D. M. Sigman, and K. Kritee (2009), The nitrogen and oxygen isotope composition of nitrate in the environment: The systematics of biological nitrate reduction, Geochimica Et Cosmochimica Acta, 73(13), A460-A460.

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

Lehmann, M. F., D. M. Sigman, D. C. McCorkle, J. Granger, S. Hoffmann, G. Cane, and B. G. Brunelle (2007), The distribution of nitrate N-15/N-14 in marine sediments and the impact of benthic nitrogen loss on the isotopic composition of oceanic nitrate, Geochimica Et Cosmochimica Acta, 71(22), 5384-5404.External Link

Granger, J., D. M. Sigman, M. G. Prokopenko, M. F. Lehmann, and P. D. Tortell (2006), A method for nitrite removal in nitrate N and O isotope analyses, Limnology and Oceanography-Methods, 4, 205-212.

Sigman, D. M., J. Granger, P. J. DiFiore, M. M. Lehmann, R. Ho, G. Cane, and A. van Geen (2005), Coupled nitrogen and oxygen isotope measurements of nitrate along the eastern North Pacific margin, Global Biogeochemical Cycles, 19(4).External Link

Ward, B. B., J. Granger, M. T. Maldonado, K. L. Casciotti, S. Harris, and M. L. Wells (2005), Denitrification in the hypolimnion of permanently ice-covered Lake Bonney, Antarctica, Aquatic Microbial Ecology, 38(3), 295-307.

Armstrong, E., J. Granger, E. L. Mann, and N. M. Price (2004), Outer-membrane siderophore receptors of heterotrophic oceanic bacteria, Limnology and Oceanography, 49(2), 579-587.External Link

Granger, J., D. M. Sigman, J. A. Needoba, and P. J. Harrison (2004), Coupled nitrogen and oxygen isotope fractionation of nitrate during assimilation by cultures of marine phytoplankton, Limnology and Oceanography, 49(5), 1763-1773.External Link

Granger, J., and B. B. Ward (2003), Accumulation of nitrogen oxides in copper-limited cultures of denitrifying bacteria, Limnology and Oceanography, 48(1), 313-318. External Link

Ward, B. B., J. Granger, M. T. Maldonado, and M. L. Wells (2003), What limits bacterial production in the suboxic region of permanently ice-covered Lake Bonney, Antarctica?, Aquatic Microbial Ecology, 31(1), 33-47.

Granger, J., and N. M. Price (1999), The importance of siderophores in iron nutrition of heterotrophic marine bacteria, Limnology and Oceanography, 44(3), 541-555.External Link

Tortell, P. D., M. T. Maldonado, J. Granger, and N. M. Price (1999), Marine bacteria and biogeochemical cycling of iron in the oceans, Fems Microbiology Ecology, 29(1), 1-11.External Link