Nitrogen FixationNitrogen Fixation

Kristen SanchezKristen Sanchez

Bot 437 – PhycologyBot 437 – Phycology

Spring 2009Spring 2009

Nitrogen Fixation:Nitrogen Fixation:

• Taken from Taken from www.nano-reef.comwww.nano-reef.com

Cyanobacterial heterocyte:Cyanobacterial heterocyte:

• Specialized cells in cyanobacteria that function in nitrogen fixationSpecialized cells in cyanobacteria that function in nitrogen fixation• Regulated by environmental levels of ammonium (NHRegulated by environmental levels of ammonium (NH44

++) or nitrate ) or nitrate (NO(NO33

--))

• Thickened cell walls of heterocytes reduce diffusion of OThickened cell walls of heterocytes reduce diffusion of O22 into the into the cellcell

Cardona Cardona et alet al, 2009:, 2009:

• Study subject: heterocysts of Study subject: heterocysts of Nostoc Nostoc punctiformespunctiformes

• Goal of the study: analysis of heterocyst Goal of the study: analysis of heterocyst membranes and pigment absorptionmembranes and pigment absorption

• Results: Results: • Membrane proteome dominated by Membrane proteome dominated by

Photosystem I and ATP-synthase complexesPhotosystem I and ATP-synthase complexes• Monomeric Photosystem II complexes were Monomeric Photosystem II complexes were

found in the heterocyst thylakoid membranes! found in the heterocyst thylakoid membranes! • Phycobilisomes are present in heterocysts, Phycobilisomes are present in heterocysts,

however, emission intensity is much lower however, emission intensity is much lower than in vegetative cellsthan in vegetative cells

Cardona Cardona et alet al, 2009:, 2009:

• Fluoresence emission Fluoresence emission spectra from spectra from vegetative cells/intact vegetative cells/intact filaments (-) and filaments (-) and heterocysts (- -) after heterocysts (- -) after excitation at 570 nm excitation at 570 nm (A) and 427 nm (B)(A) and 427 nm (B)

• Insert in B is a 5x Insert in B is a 5x enlargement, enlargement, enhancing the peaks enhancing the peaks originating from PS IIoriginating from PS II

Cardona Cardona et alet al, 2009:, 2009:

• Conclusions: Conclusions: • PSII complexes are not degradation PSII complexes are not degradation

productsproducts• Phycobilisomes contribute in energy Phycobilisomes contribute in energy

transfer to PS I, though to a lesser transfer to PS I, though to a lesser degree than in vegetative cellsdegree than in vegetative cells

Carpenter and Price, Carpenter and Price, 1976:1976:• Study site: eastern CarribeanStudy site: eastern Carribean

• Goal of the study: to find an explanation for why Goal of the study: to find an explanation for why Oscillatoria (Trichodesmium)Oscillatoria (Trichodesmium) spp. can fix nitrogen spp. can fix nitrogen in an aerobic environment without heterocystsin an aerobic environment without heterocysts

• Results: Results: • OscillatoriaOscillatoria spp. form colonies spp. form colonies• differentiated cells in the middle of the colony have differentiated cells in the middle of the colony have

reduced pigmentation, do not photosynthesize, do not reduced pigmentation, do not photosynthesize, do not incorporate COincorporate CO22, do not produce O, do not produce O22

• Nitrogenase is deactivated in the presence of ONitrogenase is deactivated in the presence of O22

• Conclusion: Nitrogen fixation by Conclusion: Nitrogen fixation by OscillatoriaOscillatoria spp. spp. is most efficient in calm seas characterized by is most efficient in calm seas characterized by low wind speeds and light sky coverlow wind speeds and light sky cover

The Nitrogen Cycle:The Nitrogen Cycle:

• Taken from Taken from www.nano-reef.comwww.nano-reef.com

Fulweiler Fulweiler et alet al, 2007:, 2007:

• Study site: Narragansett Bay, USA; Study site: Narragansett Bay, USA; summer 2006summer 2006

• Hypothesis: A decrease in organic matter Hypothesis: A decrease in organic matter deposition to the benthos, and an deposition to the benthos, and an observed reversal of the net sediment Nobserved reversal of the net sediment N22 flux, was caused by a decrease in primary flux, was caused by a decrease in primary productionproduction

• Results: Sediment core data show that the Results: Sediment core data show that the sediments have switched from being a sediments have switched from being a nitrogen sink to a nitrogen sourcenitrogen sink to a nitrogen source

• Conclusion: Some estuaries are feeding Conclusion: Some estuaries are feeding nitrogen into the water column that can nitrogen into the water column that can then be exported to the continental shelf then be exported to the continental shelf and out to the open oceanand out to the open ocean

References:References:• Cardona, T., N. Battchikova, P. Zhang, K. StensjCardona, T., N. Battchikova, P. Zhang, K. Stensjöö, E.-M. Aro, P. , E.-M. Aro, P.

Lindblad, and A. Magnuson. 2009. Lindblad, and A. Magnuson. 2009. Electron transfer protein Electron transfer protein complexes in the thylakoid membranes of heterocysts complexes in the thylakoid membranes of heterocysts from the cyanobacterium from the cyanobacterium Nostoc punctiforme.Nostoc punctiforme. Biochimica et Biophysica Acta. Vol 1787: 252-263.Biochimica et Biophysica Acta. Vol 1787: 252-263.

• Carpenter, E.J., and C.C. Price IV. 1976. Carpenter, E.J., and C.C. Price IV. 1976. Marine Marine Oscillatoria Oscillatoria (Trichodesmium):(Trichodesmium): Explanation for Aerobic Nitrogen Explanation for Aerobic Nitrogen Fixation Without Heterocysts.Fixation Without Heterocysts. Science. Vol 191: 1278- Science. Vol 191: 1278-1280.1280.

• Fulweiler, R.W., S.W. Nixon, B.A. Buckley, and S.L. Granger. Fulweiler, R.W., S.W. Nixon, B.A. Buckley, and S.L. Granger. 2007. 2007. Reversal of the net dinitrogen gas flux in coastal Reversal of the net dinitrogen gas flux in coastal marine sediments.marine sediments. Nature. Vol 448: 180-182. Nature. Vol 448: 180-182.

• Graham, L.E., J.M. Graham, and L.W. Wilcox. 2009. Graham, L.E., J.M. Graham, and L.W. Wilcox. 2009. Algae, 2Algae, 2ndnd Edition.Edition. Pearson Benjamin Cummings. Pearson Benjamin Cummings.

• Lalli, Carol M., and T.R. Parsons. 1997. Lalli, Carol M., and T.R. Parsons. 1997. Biological Biological Oceanography an Introduction: 2Oceanography an Introduction: 2ndnd Edition. Edition. Butterworth Butterworth Heinemann. Heinemann.