The effect of some important nutritional and growth conditions on the released polysaccharides (RPS) by Anabaena variabilis and Nostoc muscorum which were grown on the standard BG11 medium was studied. The decrease, and/or increase in the concentrations of nitrate and carbonate caused reduction in the RPS production as compared with the standard one. The RPS production was increased with increasing phosphate concentration and with decreasing the concentrations of magnesium and calcium. The RPS production exhibited a reduction at the lowest and the highest pH values. The modified nutrient medium did not cause any increase in the RPS production. The results demonstrated that the standard BG11 medium at 30oC with continuous aeration and illumination was the best for the maximum production of RPS in both organisms. The intrinsic viscosity of the RPS showed its maxima in 1% MgSO4 and 1% CaCl2 at the RPS viscosity concentration 1.4 g%. Also, marked parallel increment in the electrical conductivity, as well as a parallel pH decrements were detected as the concentrations of the RPS increased in these salts. The viscosity of the RPS also showed a considerable stability under elevated values of temperature, pH and ionic strength. The RPS of tested organisms can produce gelling properties with the solutions of FeCl3 or CaCl2 providing another proof for their anionic characters.
cyanobacteria, released polysaccharides, nutrients, temperature, pH, aeration, light, viscosity, gel formation