LIGHT DARK CYCLES IN THE GROWTH OF THE RED MICROALGA PORPHYRIDIUM SP/

The effect of light/dark cycles on the growth of the red microalga Por phyridium so. was studied in a tubular loop bioreactor with light/dark cycles of different frequencies and in two 35-L reactors: a bubble co lumn reactor and an air-lift reactor. Photon flux densities were in th e range of 50 to 300 mu E m(-2) s(-1), and flow rates were 1 to 10 L m in(-1). Under conditions of low illumination and high flow rates, simi lar results were obtained for the bubble column and air-lift reactors. However, higher productivities-in terms of biomass and polysaccharide -were recorded in the air-lift reactor under high light intensity and low gas flow rates. The interactions of both photosynthesis and photoi nhibition with the fluid dynamics in the bioreactors was taken as the main element that allowed us to interpret the differences in performan ce of the bubble column and the air-lift reactor. It is suggested that the cyclic distribution of dark periods in the air-lift reactor facil itates better recovery from the photoinhibition damage suffered by the cells. (C) 1998 John Wiley & Sons, Inc.