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Nitrogen Fixation

Nitrogen Fixation. Kristen Sanchez Bot 437 – Phycology Spring 2009. Nitrogen Fixation:. Taken from www.nano-reef.com. Cyanobacterial heterocyte:. Specialized cells in cyanobacteria that function in nitrogen fixation

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Nitrogen Fixation

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  1. Nitrogen Fixation Kristen Sanchez Bot 437 – Phycology Spring 2009

  2. Nitrogen Fixation: • Taken from www.nano-reef.com

  3. Cyanobacterial heterocyte: • Specialized cells in cyanobacteria that function in nitrogen fixation • Regulated by environmental levels of ammonium (NH4+) or nitrate (NO3-) • Thickened cell walls of heterocytes reduce diffusion of O2 into the cell

  4. Cardona et al, 2009: • Study subject: heterocysts of Nostoc punctiformes • Goal of the study: analysis of heterocyst membranes and pigment absorption • Results: • Membrane proteome dominated by Photosystem I and ATP-synthase complexes • Monomeric Photosystem II complexes were found in the heterocyst thylakoid membranes! • Phycobilisomes are present in heterocysts, however, emission intensity is much lower than in vegetative cells

  5. Cardona et al, 2009: • Fluoresence emission spectra from vegetative cells/intact filaments (-) and heterocysts (- -) after excitation at 570 nm (A) and 427 nm (B) • Insert in B is a 5x enlargement, enhancing the peaks originating from PS II

  6. Cardona et al, 2009: • Conclusions: • PSII complexes are not degradation products • Phycobilisomes contribute in energy transfer to PS I, though to a lesser degree than in vegetative cells

  7. Carpenter and Price, 1976: • Study site: eastern Carribean • Goal of the study: to find an explanation for why Oscillatoria (Trichodesmium) spp. can fix nitrogen in an aerobic environment without heterocysts • Results: • Oscillatoria spp. form colonies • differentiated cells in the middle of the colony have reduced pigmentation, do not photosynthesize, do not incorporate CO2, do not produce O2 • Nitrogenase is deactivated in the presence of O2 • Conclusion: Nitrogen fixation by Oscillatoria spp. is most efficient in calm seas characterized by low wind speeds and light sky cover

  8. The Nitrogen Cycle: • Taken from www.nano-reef.com

  9. Fulweiler et al, 2007: • Study site: Narragansett Bay, USA; summer 2006 • Hypothesis: A decrease in organic matter deposition to the benthos, and an observed reversal of the net sediment N2 flux, was caused by a decrease in primary production • Results: Sediment core data show that the sediments have switched from being a nitrogen sink to a nitrogen source • Conclusion: Some estuaries are feeding nitrogen into the water column that can then be exported to the continental shelf and out to the open ocean

  10. References: • Cardona, T., N. Battchikova, P. Zhang, K. Stensjö, E.-M. Aro, P. Lindblad, and A. Magnuson. 2009. Electron transfer protein complexes in the thylakoid membranes of heterocysts from the cyanobacterium Nostoc punctiforme. Biochimica et Biophysica Acta. Vol 1787: 252-263. • Carpenter, E.J., and C.C. Price IV. 1976. Marine Oscillatoria (Trichodesmium): Explanation for Aerobic Nitrogen Fixation Without Heterocysts. Science. Vol 191: 1278-1280. • Fulweiler, R.W., S.W. Nixon, B.A. Buckley, and S.L. Granger. 2007. Reversal of the net dinitrogen gas flux in coastal marine sediments. Nature. Vol 448: 180-182. • Graham, L.E., J.M. Graham, and L.W. Wilcox. 2009. Algae, 2nd Edition. Pearson Benjamin Cummings. • Lalli, Carol M., and T.R. Parsons. 1997. Biological Oceanography an Introduction: 2nd Edition. Butterworth Heinemann.

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