The unicellular cyanobacteria

Synechococcus-like unicellular cyanobacteria are the second key component of the pelagic phytoplankton, found in practically all marine environments. Although bigger than the prochlorophytes, the unicellular cyanobacteria are also pico-planktonic measuring less than 2 pm in diameter. In the pelagic waters of the Levantine Basin, they are usually evenly distributed with depth between the surface and the DCM below which their concentrations decline with increasing depth (Li etal., 1993). 

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Antal, T.K., Lindblad, P. 2005. Production of Hj by sulphur-deprived cells of the unicellular cyanobacteria Gloeocapsa alpicola and Synechocystis sp. PCC 6803 during dark incubation with methane or at various extracellular pH. J Appl Microbiol 98 114-120. 

C.A. Ochs, L.P. Eddy (1998). Effects of UV-A (320-399 nanometers) on grazing pressure of a marine heterotrophic nanoflagellate on strains of the unicellular cyanobacteria Synechococcus spp. Appl. Environ. Microbiol, 64, 287-293. 

Howarth, D.C., Codd, G.A. 1985. The uptake and production of molecular hydrogen by unicellular cyanobacteria. J Gen Microbiol 131 1561-1569. 

In recent years, the unicellular nature of planktonic algae has been exploited for the construction of whole-cell based biosensors capable of real-time response on critical change of the aquatic ecosystems caused by pollutant emissions. Most of the proposed devices are based on the electrochemical detection of the inhibiting effect on the photosynthetic activity of algae and cyanobacteria exerted by some toxicants. 

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... 

Falcon, L. I., Cipriano, F., Christoserdov, A. Y., and Carpenter, E. J. (2002). Diversity of diazotrophic unicellular cyanobacteria in the tropical north Atlantic Ocean. Appl. Environ. Microbiol. 68,5760—5764. 

Zehr, J., et al. (2001). Unicellular cyanobacteria fix N2 in the subtropical North Pacific Ocean. Nature. 412, 635-638. 

We now recognize that NOs is not always the dominant source of new N in the open ocean (Table 7.1). N2 fixation is more widespread than previously thought. Filamentous diazotrophs (e.g., Trichodesmium sp. Capone et al., 1997), diazotrophic endosymbionts (Carpenter et al., 1999), and unicellular cyanobacteria aU fix N2 at high rates in nature (Carpenter and Capone, this volume Montoya et al., 2004 Zehr etai, 2001). In tropical and subtropical waters, it has been calculated that N2 fixation by Trichodesmium sp. alone fuels 50% of the new production (Capone et al., 2005 Karl et al., 1997). Montoya et al. (2004) estimated that diazotrophic uniceUs may contribute up to 10% of total oceanic new production globally. 

Zehr, J. P., Waterbury, J., Turner, P., Montoya, J., Omoregie, E., Steward, G., Hansen, A., and Karl, D. (2001). Unicellular cyanobacteria fix N2 in the subtropical North Pacific Ocean. Nature... 

Cyanophage of filamentous cyanobacteria (Flewson et al, 2001a, 2004 Ohki, 1999 Ohki and Fujita, 1996) and marine representatives of the unicellular... 

Unicellular cyanobacteria fix N2 in the subtropical North Pacific Ocean. Nature. 412, 635-638. Zehr, J. P., Jenkins, B. D., Short, S. M., and Steward, G. F. (2003). Nitrogenase gene diversity and microbial community structure a cross-system comparison. Environ. Microbiol. 5, 539—554. Zeidner, G., Preston, C. M., Delong, E. F., Massana, R., Post, A. F., Scanlan, D. J., and Beja, O. (2003). Molecular diversity among marine picophytoplankton as revealed by psM analyses. Environ. Microbiol. 5, 212—216. 

Florencio, F. J., Marques, S., and Candau, P. (1987). Identification and characterization of a glutamate dehydrogenase in the unicellular cyanobacterium Synechocystis PCC 6803. FEBS Lett. 223, 37-41. Flores, E., and Herrero, A. (1994). Assimmilatory nitrogen metabolism and its regulation. In The Molecular Biology of Cyanobacteria (Bryant, D. A., ed.). Kluwer Academic, Dordrect, The Netherlands, pp. 487-517. 

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