Growth physiology of Spirulina platensis in tubular photobioreactor under natural light

An apparatus designed for investigating the growth of phototrophic microorganisms under natural light is briefly described. It is provided with eight tubular photobioreactors equipped with the instrumentation for monitoring and controlling the physicochemical parameters. The results of an investigation on Spirulina platensis grown under natural light having nitrate or ammonia as a nitrogen source showed that the daily course of the biosynthetic activities was affected by the light intensity to which culture was exposed, but also by the type of nitrogen sourcewich was used. In the culture grown on nitrate nitrogen the uptake of nitrate was completely suppressed when light intensity reached about 800 W/m2 and when the biomass concentration was lower than 1.5 g/l, while the cabon fixed was channelled into carbohydrate production. The carbohydrates synthesized during the day were almost completely used during the night for maintenance and biosynthesis of protein and othe cellular components. The ammonia uptake was less affected than nitrate uptake.