Introduction
Cyanobacteria are prokaryotic oxygenic phototrophs found in almost every conceivable habitat on earth (Ferris et al. 1996; Ward et al. 1997; Nübel et al. 1999, 2000; Abed and Garcia-Pichel 2001; Garcia-Pichel and Pringault 2001). They exist in different morphologies including unicellular and filamentous forms (Castenholz 2001). While unicellular types exist as single cells, suspended or benthic, or aggregates, filamentous types may be thin or thick, single trichome or bundles either with or without a sheath. Cyanobacteria are able to perform different modes of metabolism with the capacity to switch from one mode to another (Stal 1995). All cyanobacteria carry out oxygenic photosynthesis but some cyanobacterial species can switch to the typical bacterial anoxygenic photosynthesis using sulfide as electron donor (Cohen et al. 1986). Under anoxic conditions and during the dark, cyanobacteria carry out fermentation (Stal 1997). Some cyanobacteria form heterocysts and have the ability to fix atmospheric nitrogen (Capone et al. 2005). Phylogenetic analysis of cyanobacteria based on 16S rRNA genes showed that they are a diverse, monophyletic phylum of organisms within the bacterial radiation. Research on cyanobacteria in the last decades focused largely on their ecology, morphology, physiology and 16S rRNA-based phylogeny but relatively little has been done on their potential uses in biotechnology.