Morphology, cell growth, and polysaccharide production of Nostoc flagelliforme in liquid suspension culture at different agitation rates

Abstract

Noscoc flagelliforme is a terrestrial macroscopic cyanobacterium with high economic value. Free-living cells that were separated from a natural colony of N. flagelliforme were cultivated in a 20-L photobioreactor for 16 days at five agitation rates with impeller tip speeds at 0.3, 0., 0.8, 1.0, and 1.5 m·s⁻¹. With different impeller tip speeds there were significant differences in the cell growth and polysaccharide production, and different types of cell colonies appeared because of different shear forces caused by agitation. At harvest time, cell concentrations with tip speeds of 0.8 and 1.0 m·s⁻¹ were clearly higher than those with the other three tip speeds, but dry cell weights with the tip speeds of 0.3, 0.5, 0.8, and 1.0 m·s⁻¹ were almost the same. The highest RPS (polysaccharide that released into liquid medium) production was obtained with the tip speeds of 0.8 and 1.0 m·s⁻¹, while the highest EPS (polysaccharide that formed capsule or slime layer) production was obtained with the tip speed of 0.5 m·s⁻¹. The tip speed of 1.5 m·s⁻¹ was harmful for both cell growth and polysaccharide production, indicating that an appropriate shear force was needed in the liquid suspension culture of N. flagelliforme.