Diversity of Polysaccharides in Cyanobacteria

Abstract

Polysaccharides show immense structural variability by virtue of their monomer composition, linkages, oligomer units, branching, size, and interactions with non-saccharide components. In cyanobacteria, polysaccharides are found as storage molecules, in cell envelopes, and as extracellular polysaccharides (EPS). Storage molecules exist as glycogen and cyanobacterial starch and exhibit lowest diversity. As part of the cell envelope, lipopolysaccharides (LPS) in the outer membrane contribute 70–75% to the cyanobacterial cell surface. O-antigen polysaccharide imparts structural heterogeneity and thus strains specificity even in the cyanobacterial species sharing the same habitat. LPS is responsible for a diverse range of health effects in man. EPS that interfaces with the surrounding environment shows maximal structural diversity and functional versatility. Functions of the EPS vary with the species and provide as the primary mechanism for survival in extremes, defence against toxins, heavy metals, predators, and other antagonists. They modify fluidity of the external milieu and are involved in cellular communication important in structuring the biofilm community. In fact, both survival and growth of the organism are dependent on the organisms’ EPS arsenal. Thus, the cyanobacteria spend up to 70% of the total energy reserve in the production of EPS. Such diversity of polysaccharides is not easy to be replicated through synthetic processes. This chapter provides glimpses of the diversity of polysaccharides found in cyanobacteria and their industrial potential to encourage prospective work in this area.