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

Extracellular polysaccharides (EPSs) produced by microalgae and cyanobacteria are molecules with a great ecological significance for the producing organisms, serving in a wide array of biological processes and increasing the organism tolerance to environmental stresses. In addition, due to their distinctive chemical, rheological properties and the biological activity of some of them, these macromolecules could find application in industrial, pharmaceutical and medical fields. In this chapter, the current knowledge regarding the structure and composition of EPSs, the factors eliciting their synthesis, and the related codifying genes involved is reviewed. It is also underlined and discussed how, notwithstanding the huge number of studies available, different aspects still need to be clarified. For example, there are limited informations concerning EPS synthetic pathways, and how these processes are influenced by environmental factors. Expand the knowledge on these aspects could help elaborating biotechnological strategies to increase the yields and direct the synthesis to polymers with desired characteristics. Kywords: cyanobacteria, microalgae, extracellular polysaccharides (EPSs), EPS synthesis, EPS-encoding genes, sheath, capsular polysaccharides (CPSs), capsule, slime, EPS synthetic pathway.