Effects of light, salinity and nutrient limitation on the production of β-1,3- d-glucan and exo- d-glucanase activity in Skeletonema costatum (Grev.) Cleve

Abstract

Dilution cultures of the marine diatom Skeletonema costatum (Grev.) Cleve were used to study the effect of photon flux density (PFD), salinity and nutrient limitation on the accumulation of the reserve polysaccharide β-1,3- d-glucan and β-1,3- d-glucanase activity. Generally, both the glucan content and the glucanase activity increased markedly with decreasing growth rates (increasing nutrient deficiency). The lowest PFD in this work (20 μE·m −2·s −1) was below saturation for growth while the highest (800 μE·m −2·s −1) was slightly inhibitory. The glucan accounted for between 7 and 80% of the total carbon content of the cells. The highest percentage was found in cells grown under strong nutrient limitation and subsaturating light conditions. The highest PFD led to a marked decrease in both glucan content and glucanase activity, while the lowest PFD had the opposite effect. At the lowest salinity tested (9%.), Skeletonema showed a marked decrease in growth rate while a salinity of 15%. gave no significant effect on growth rate. The glucanase activity as a main feature increased with decreasing salinity. Nutrient- limited cells containing large amounts of reserve material (β-1,3- d-glucan) assimilated nitrate when incubated in the dark. This assimilation led to a pronounced reduction in the glucan content of the cells.