Cyanobacterial Exopolysaccharides: Their Nature and Potential Biotechnological Applications

Cyanobacteria (blue-green algae) are photosynthetic prokaryotic organisms which are unicells or filaments. Of great significance biologically is the fact that certain cyanobacteria can fix elemental nitrogen (Carr and Whitton, 1982). Some cyanobacteri a are capable of movement by gliding when in contact with the substrate (Bold and Wynne, 1985). Some cyanobacteria have the ability to survive desiccation and extremes of temperature, and can grow at high pH and salinity (Flaibani et al., 1989). Cyanobacteria occur in most environments on earth. Their distribution in freshwater and marine environment is cosmopolitan. Cyanobacteria are also commonly found in the soil and in rocks from the tropics to polar regions, and from temperate climates to extreme arid deserts, where they sometimes participate in the formation of microbial crusts or mats (Bold and Wynne, 1985; Mazor et al., 1996). A number of diazotrophic cyanobacteria grow easily in association or symbiosis with certain green algae, liverworts, water ferns, and angiosperms (Bold and Wynne, 1985). Cyanobacteria have been known, for a long time, to produce large amounts of exopolysaccharide (Drews and Weckesser, 1982). Recently, this massive production has received increasing attention due to the potential applications of these substances as industrial gums, bioflocculants, soil conditioners and biosorbants, and to their participation in symbiotic processes in plants, in the gliding movement, and in the general interactions between microorganisms and their habitats (Bertocchi et al., 1990; Painter. 1993; Morvan et al, 1997; De Philippis and Vincenzini, 1998).