The role of carbohydrate accumulation in the growth of planktonic Oscillatoria species

Abstract

Laboratory growth experiments with two blue-green algae, Oscillatoria redekei Van Goor and Oscillatoria agardhii Gomont showed improved growth efficiencies under light/dark cycles compared with continuous light. This was due to photosynthetic production in the light period in excess of the protein synthesis requirement being stored in the algae as carbohydrate which in turn was used to generate cell protein, DNA and chlorophyll a during the following dark period. The optimum light/dark cycles observed were when the algae were able to store all their surplus production as carbohydrate. Under longer light periods the cells had either insufficient storage capacity or insufficient dark time to use all their stored carbohydrate. The larger species, O. agardhii, had a low rate of protein synthesis in the light which led to a higher rate of carbohydrate accumulation compared to O. redekei. As a result O. agardhii showed maximum efficiency under short light/dark cycles (3:21 and 6:18 L:D) while O. redekei showed maximum growth efficiencies up to 12:12 L:D cycle. Dark nitrate uptake was the main source of nitrogen for dark protein synthesis and the maximum dark nitrate uptake rate observed was 29% of that in the light. Under L:D cycles of less than 9 h light protein synthesis and nitrate uptake in the light were depressed so that 39% of the total N uptake in an O. redekei culture took place in the dark under 6:18 L:D cycle. Both species showed evidence of metabolic control because carbohydrate synthesis was reduced on long light periods. No evidence was found for any extracellular production of nitrogenous compounds.