Effect of mixed carbon substrate on exopolysaccharide production of cyanobacterium Nostoc flagelliforme in mixotrophic cultures

Abstract

The effects of organic carbon sources on cell growth and exopolysaccharide (EPS) production of dissociated Nostoc flagelliforme cells under mixotrophic batch culture were investigated. After 7 days of cultivation, glycerol, acetate, sucrose, and glucose increased the final cell density and final EPS concentrations, and mixotrophic growth achieved higher biomass concentrations. The increase in cell growth was particularly high when glucose was added as the sole carbon source. On the other hand, EPS production per dry cell weight was significantly enhanced by adding acetate. For more effective EPS production, the effects of the mixture of glucose and acetate were investigated. Increasing the ratio of glucose to acetate resulted in higher growth rate with BG-11 medium and higher EPS productivity with BG-11₀ medium (without NaNO₃). When the medium was supplemented with a mixture of glucose (4.0 g L⁻¹) and acetate (2.0 g L⁻¹), 1.79 g L⁻¹ biomass with BG-11 medium and 879.6 mg L⁻¹ of EPS production with BG-11₀ medium were achieved. Adopting this optimal ratio of glucose to acetate established in flask culture, the culture was also conducted in a 20-L photobioreactor with BG-11 medium for 7 days. A maximum biomass of 2.32 g L⁻¹ was achieved, and the EPS production was 634.6 mg L⁻¹.