Abstract

The culture of microalgae and cyanobacteria in open systems has been improved through the novel approach of thin-layer raceway ponds. The importance of studying mass cultivation of the cyanobacterium Nostoc calcicola (further as Nostoc) lies in its biotechnological potential as a source of bioactive compounds for food and non-food applications. These compounds include polysaccharides, mycosporine-like amino acids and phycocyanin. Nostoc was cultured outdoors in a thin-layer raceway pond where the biomass production, physiological status, photosynthetic activity, and biochemical composition were monitored through the experimental period of 5 days. The biomass, as did the maximal quantum yield of PSII, maximal electron transport rate (ETRmax) and photosynthetic efficiency (alpha ETR) increased throughout the experimental period showing the optimal operation of the thin-layer raceway ponds, due to the light penetrates deeper into the thin culture layer and thus more light is available to the cells. Oxygen levels in the culture increased over time, but no photoinhibition was evident indicating optimal action of non-photochemical mechanisms. Nostoc increased the total internal carbon content over the experimental period. Chlorophyll increased, whereas the N compounds such as the biliprotein phycocyanin decreased. Among the UV-absorbing compounds, polyphenols, mycosporine-like amino acids, such as shinorine and other unknown UV-A absorbing compounds were detected. There components showed a positive correlation to antioxidant activity. Thus, the optimal accumulation of biomass and the accumulation of bio-active compounds having antioxidant capacity show the possible biotechnological applications of Nostoc.