Abstract
Unicellular diazotrophic cyanobacteria synthesize insoluble α-glucans, instead of glycogen. In one of these species, Cyanobacterium sp. NBRC 102756, the cellular content of polysaccharide was increased from 15% to 40% per dry weight, under Fe deficiency. Effect of Fe nutrition and illumination conditions on the polysaccharide production in this strain was investigated. Within 24 h after dilution, the rate of polysaccharide synthesis in Fe-replete (0.47 ppm) medium was much lower than the growth rate, resulting in the decrease in the polysaccharide per cell. Under Fe-deplete conditions, on the other hand, a dramatic increase of polysaccharide was observed within 24 h of growth. To minimize the energy requirement for biomass production, we examined polysaccharide accumulation in different light conditions. In Fe-sufficient medium, the amount of polysaccharide after 120 h of the culture was comparable whether the cells were grown in continuous light or in 18 h L / 6 h D conditions. In Fe-deficient conditions, in contrast, the amount of polysaccharide was progressively decreased with increasing dark period. No significant turnover of polysaccharide was observed in the dark.
