Growth and extracellular polysaccharides production of nostoc flagelliforme cells in mixotrophic culture

Nostoc flagelliforme cells were studied with regard to the growth and extracellular polysaccharides (EPS) formation in a mixotrophic culture. Organic carbon sources increased cell growth and EPS production of N. flagelliforme cells. The highest specific growth rate, cell concentration and EPS production were respectively 0.539 d^-1, 1.77 g·L^-1 and 595.98 mg·L^-1 on 3.98 g·L^-1of glucose concentration. Which were 4.34, 4.72 and 14.28 folds of those obtained under phototrophic culture. The specific growth rate of cells on 3.98 g·L^-1of glucose concentration was markedly increased with increasing light intensity from 10 to 40 μmolphoton·m^-2·s^-1. Further increase of the light intensity did not have evident effects on the specific growth rate. Light favored EPS formation. The effects of light intensity and glucose concentration on the growth were depended on each other. At the light intensity of 60μmol photon m^-2 s^-1, the optimal glucose concentration for cell growth was 3.98 g·L^-1. When the light intensity decreased to 10μmol photon m^-2 s^-1, the optimal initial glucose concentration for cell biomass production changed to 5.95 g·L^-1.