Exopolysaccharide-producing cyanobacteria and their possible exploitation: A review

Since the early 1950s, more than one hundred cyanobacterial strains, belonging to twenty different genera, have been investigated with regard to the production and the released exocellular polysaccharides (RPS) into the culture medium. The chemical and rheological properties show that such polysaccharides are complex anionic heteropolymers, in about 80% cases containing six to ten different monosaccharides and in about 90% cases containing one or more uronic acids; almost all have non-saccharidic components, such as peptidic moieties, acetyl, pyruvyl and/or sulphate groups. Based on such ingredients, cyanobacterial RPSs show promise as thickening or suspending agents, emulsifying or cation-chelating compounds and the residual capsulated cyanobacterial biomass, following R-PS extraction, could be an effective cation-chelating material. Indeed, when eleven unicellular and filamentous RPS-producing cyanobacteria, selected on the basis of the anion density of their RPSs and on the abundance of their outermost investments, were screened for their ability to remove Cu2+ from aqueous solutions, a quick and most effective heavy metal adsorption was observed for the unicellular Cyanothece CE 4 and the filamentous Cyanospira capsulata. These results suggest the possibility to accomplish, through the exploitation of RPS-producing cyanobacteria, a multiproduct strategy to procure a wide range of biopolymers suited to various industrial applications, in addition to the residual biomass effective in the recovery of heavy metals from polluted waters.