Exopolysaccharide production by cyanobacteria grown in closed photobioreactors and immobilized using white cotton towelling

Two exopolysaccharide (EPS)-producing cyanobacteria, Chroococcus minutus and Nostoc insulare, were grown as batch cultures in closed cultivation systems (8-L flasks or 12-L and 250-L photobioreactors with internal illumination) at light intensities ranging between 25 and 150 mu mol photon m(-2) s(-1). Another batch of each organism was immobilized on white cotton towelling and grown in 470-ml and 17-L flat upright transparent chambers made of polycarbonate at light intensities of 0.5-1.5 mu mol photon m(-2) s(-1). Both cultivation systems were compared with regard to EPS productivity and technological feasibility. The EPS excreted by both cyanobacteria was separated into fractions which had different molecular weights (540-1600 kD) and analyzed for their sugar composition. Both organisms produced acidic EPS, which contained, respectively, 4.2 and 25.3% uronic acids.