Production characterization and biotechnological potential of extracellular bacterial biopolymer

Abstract

Cyanobacteria can grow in diverse inhospitable environments, like arid environments, hypersaline ponds, marine waters, brackish waters, soda lakes, rocks, hot springs and polar regions resisting temperature, desiccation and osmotic stress. To survive and grow under such extremes they have evolved various mechanisms to protect themselves. Elaboration of extracellular polysaccharides is one of the contrivance mechanisms to stress. These exopolymers modify the rheology of aqueous systems, produce gels, act as glass to help cyanobacteria survive stress. This property of exopolysaccharides can prove useful in a number of applications. In near future they could possibly replace the plant and macroalgal polysaccharides traditionally used in food, pharmaceutical, textile and oil industries. This study attempted to unravel such a potential in some cyanobacterial isolates of the arid regions of the Thar Desert. newlineStudies on forty three cyanobacteria showed presence of anionic polymer as sheath or slime in thirteen forms. Of these, five cyanobacteria viz . Anabaena oryzae (2221), Aulosira prolifica (2300), Anabaena sp. (2224), and two strains of Nostoc calcicola (1205), Nostoc commune (1203) showed altered rheology of the culture medium increasing its viscosity. These organisms were optimised for pH and culture conditions at which a high medium viscosity was achieved along with good growth and polymer yield. All the organisms showed increase in polymer production under phosphorous limitation. newlineBiopolymer was extracted from select forms by precipitation after steam treatment using chilled isopropanol. Aulosira prolifica (2300) showed the best polymer yield of 12.17mg (w/w) when grown at pH 10 and phosphorous limitation with 0.2M salt, followed by Anabaena oryzae (2221) that produced 11.8 mg biopolymer under the same set of conditions but without salt.