Exocellular Polysaccharides in Microalgae and Cyanobacteria: Chemical Features, Role and Enzymes and Genes Involved in Their Biosynthesis

Microalgae and cyanobacteria have complex carbohydrate metabolic pathways encompassing the ability to synthesize intracellular monosaccharides, polymeric reserve glucans and structurally complex extracellular polysaccharides (EPSs). The latter complex carbohydrates are synthesized following tightly regulated and energy-consuming processes (Coesel and Waardernar 1994) and can be incorporated in the cell-wall, excreted as definite structures (sheaths, capsules or stalks), or released as mucilage. In this chapter, the most important chemical features of the EPSs synthesized by microalgae and cyanobacteria will be reviewed along with the information available on the factors affecting their synthesis and on the metabolic pathways leading to the synthesis of these complex polymeric carbohydrates