Nitrogen fixation heterocysts

Anabaena cylindrica sp. PCC7I20 [NiFe] hydrogenase Putative membrane- bound cytochrome b reducing H2 recycling during N2 fixation O2, nitrogen limitation, heterocyst formation 2... 

Bohme, H. (1998) Regulation of nitrogen fixation in heterocyst forming bacteria. Trends Plant Sci., 3, 346-51. 

Golden, J. W., Robinson, S. J. and Haselkorn, R. (1985) Rearrangement of nitrogen fixation genes during heterocyst differentiation in the cyanobacterium Anabaena. Nature, 314, 419-23. 

In cyanobacteria nitrogen fixation occurs in the heterocysts, specialized cells with thickened cell envelopes. They supply NH4+ to other cells in the filament of which they are a part. 

Nitrogenases are also extremely labile in an O2 environment. Cyanobacteria have adopted two strategies to overcome the O2 sensitivity of the nitrogenase reaction, either temporal or spatial separation of O2 evolution and H2 production. Temporal separation has been achieved mainly in non-heterocystous unicellular cyanobacteria such as Gloeothece sp. strain ATCC 27152 and Plectonema boryanum. Nitrogen fixation occurs only in darkness, during which respiration of the carbohydrates, syn... 

Thiel, T., and Pratte, B. 2001. Effect of heterocyst differentiation of nitrogen fixation in vegetative cells of the cyanobacterium Anabaena variabilis ATCC 29413. J. Bacteriol. 183, 280-286. 

Carpenter, E. J., and Price, C. C. (1976). Marine Oscillatoria (Trichodesmium) explanation for aerobic nitrogen fixation without heterocysts. Science. 191, 1278—1280. 

Ohki, K., Zehr, J. P., Falkowski, P. G., and Fujita, Y. (1991). Regulation of nitrogen-fixation by different nitrogen sources in the marine non-heterocystous cyanobacterium Trichodesmium sp. NIBB 1067. Arch. Microbiol 156, 335-337. 

Paerl, H. W., Pinckney, J. L., and Kucera, S. A. (1995). Clarification of the strucmral and functional roles of heterocysts and anoxic microzones in the control of pelagic nitrogen-fixation. Limnol. Oceanogr. 40, 634—638. 

Fredriksson, C., and Bergman, B. (1997). Ultrastructural characterization of cells speciahzed for nitrogen fixation in a non-heterocystous cyanobacterium, Trichodesmium. Protoplasma 197, 76—85. 

Wasmimd, N., Voss, M., and Lochte, K. (2001). Evidence of nitrogen fixation by non-heterocystous cyanobacteria in the Baltic sea and re-calculation of a budget of nitrogen fixation. Mar. Ecol. Prog. Ser. 214, 1-14. 

Saino, T., and Hattori, A. (1982). Aerobic nitrogen fixation by the marine non-heterocystous cyanobacteria Trichodesmium Oscillatoria) spp. Its protective mechanism against oxygen. Mar. Biol. 70, 251-254. 

Masepohl, B., Schoelisch, K., Goerlitz, K., Kutzki, C. and B6hme, H. (1997). The heterocyst-specific fdxH gene product of the cyanobacterium Anabaena sp. PCC 7120 is important but not essential for nitrogen fixation. Mol. Gen. Genetics 253, 770-776. 

FIGURE 15.8 Annual course of concentrations of DIN, PO4, and biomass (wet weight) of heterocystous cyanobacteria in the upper mixed layer, as well as nitrogen fixation rates in the euphotic zone at station 271 in 2001, (after Wasmund et al., 2005b, coiTected). 

Nitrogen fixation has its peak in summer during the cyanobacteria bloom. Detailed analyses revealed that the most intensive nitrogen fixation occurred during the growth phase of the bloom, whereas the established bloom is less active (Fig. 15.8 cf. also Ohlendieck et al., 2000). Laamanen and Kuosa (2005) found the highest heterocyst frequency of Aphanizomenion flos-aquae before the annual biomass peak. 

Estuaries and eutrophic coastal waters provide a striking contrast with this behavior. With only a few exceptions anywhere in the world, nitrogen fixation by planktonic, heterocystic cyanobacteria is immeasurably low in mesotrophic and eutrophic coastal marine systems, even when they are quite nitrogen limited (Doremus, 1982 Fogg, 1987 Howarth et al, 1988b Paerl, 1990 Howarth and Marino, 1990, 1998). This major difference in the behavior between lakes and estuaries allows nitrogen limitation to continue in estuaries (Howarth, 1988 Vitousek and Howarth, 1991). 

Fay P, Stewart WDP, Walsby AE, Fogg GE (1968) Is the heterocyst the site of nitrogen fixation in blue-green algae Nature 220 810-812 Ferry JG (1992) Methane from acetate. J Bacteriol 174 5489-5495... 

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