Overview on cyanobacterial exopolysaccharides and biofilms: role in bioremediation

Ubiquitous presence of cyanobacteria even under extreme conditions since millions of years is due to their ease in adaptability to these environments through various cellular and molecular modifications. Formation of biofilms has been found to be one of the effective modes of survival under harsh environmental conditions, with exopolysaccharides (EPS) contributing to the formation of these biofilms. Cyanobacterial EPS are unique heteropolysaccharides and being anionic in nature, they have the capabilities for excellent heavy metal adsorption and thus, play a vital role in conferring tolerance against heavy metal toxicity. EPS biosynthesis occurs through multiple pathways involving a multitude of genes. A comprehensive overview on these genes in cyanobacteria using Nostoc sp. strain PCC7120 as the model organism has been discussed in this review. The review also emphasizes on the contribution of EPS to heavy metal remediation and biofilm formation. In the age of developing eco-friendly approaches for environmental clean-up, this information would help engineer cyanobacteria as a potential green technology tool for bioremediation and waste water management.