INFLUENCE OF NITROGEN-SOURCE AND PHOTOPERIOD ON EXOPOLYSACCHARIDE SYNTHESIS BY THE MICROALGA BOTRYOCOCCUS-BRAUNII-UC-58

The high exopolysaccharide (EPS) producing microalga Botryococcus brau nii UC 58 produced, under continuous illumination, highs concentration s of EPS (2.5 gl(-1) after 14 days of growth) when nitrate was used as the nitrogen source instead of urea or ammonium (2 mM of nitrogen). I n addition, broth viscosity decreased sharply with ammonium or urea wh en cultures entered the stationary phase, suggesting biopolymer hydrol ysis. In the range 0.5-8 mM NO3-, nitrogen appeared to be the growth-l imiting nutrient, as suggested by the onset of the stationary phase an d the final biomass concentration. Over 30 days of culture, the specif ic EPS production (EPS produced per unit of biomass) was minimal for 8 mM NO3- and similar for 0.5 and 2 mM, possibly related to the increas e in specific EPS synthesis along the exponential phase, reaching the highest levels after growth had stopped. Broth viscosity increased wit h growth accompanying EPS accumulation but sharply decreased a few day s after the cultures entered the stationary phase. This decrease was o bserved earlier for cultures with lower NO3- concentration. Considerin g a culture period above 10 days, the increase of NO3- concentration u p to 2 mM is recommended to reach higher EPS concentrations, but the u se of 8 mM NO3- is only of possible interest for extended growth perio ds (above 15 days). The introduction of a photoperiod fed to delayed g rowth and EPS production. However, the specific production is similar when the same phase of growth is considered.