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Biotechnological applications of algal polysaccharide as emulsifiers, thickeners and laxatives have led to the screening and selection of certain diazotrophic filamentous cyanobacteria from saline/alkaline soil of Madhya Pradesh, India. Strain specific variation in cell bound, extracellular and total polysaccharide content was quantified under laboratory conditions. Among the cyanobacterial isolates examined Nostoc calcicola RDU-3 was found to produce highest amount (105 mg l) of extracellular polysaccharide on 44th day of growth under diazotrophic growth conditions. Extracellular polysaccharide production of cyanobacterium Nostoc calcicola RDU-3 was optimal at pH-10, temperature 35°C, photoperiod of 24 h and in white light. The Gas Chromatographic analysis of polysaccharide from Nostoc calcicola RDU-3 revealed the presence of ribose (36.03%), xylose (34.13%), rhamnose (29.67%) and glucose (4.0%). The polysaccharide is novel in that it possesses ribose as the predominant monosaccharide with very low levels of glucose. Predominance of ribose monosaccharide is the unique feature which is reported to be used as metabolic supplement to the heart. IR spectrum of extracellular polysaccharide revealed the presence of sulphate group. Such sulphated polysaccharide is reported to have antiviral properties. [ABSTRACT FROM AUTHOR]