Partial characterization of extracellular polysaccharides from cyanobacteria

Four cyanobacterial strains, Cyanothece sp., Oscillatoria sp., Nostoc sp. and Nostoc carneum were studied for physico-chemical characterization of extracellular polysaccharide (EPS) secreted during the controlled growth condition. Hydrolyzed EPSs showed the compositional involvement of four sugar moieties viz. mannose, glucose, xylose and ribose in varying combinations. Infrared spectra of EPSs showed a specific absorbance of O–H stretching at 3448–3400 cm−1, asymmetrical–symmetrical C–H stretching at 2924 and 2854 cm−1 and a bending vibration of C–H at 1400–1380 cm−1. Absorbance at 1259 and 1140 cm−1 with Cyanothece sp. EPS, indicated the presence of sulfur containing functional group. Thermal gravimetric analysis and differential scanning calorimetric analysis confirmed the polysaccharides thermal stability as high as around 250 °C. In the presence of 0.1 M NaCl aqueous solution, the intrinsic viscosity of polysaccharides from Oscillatoria sp. and Nostoc sp. decreased 1.6 fold, whereas, 3–5 fold reduction in intrinsic viscosity was observed with commercially available guar and xanthan gum.