Behavior of algae and bacteria co-immobilized in carrageenan, in a fluidized bed

Abstract Bacillus subtilis, immobilized in carrageenan, was used to synthesize alpha-amylase in two media. In complete medium with organic nitrogen growth was more rapid during the first hours than in minimal medium without organic nitrogen, but the maximum bacterial density was the same for both media. The alpha-amylase activity was always higher in the complete medium and the difference was 25% at the end of the fermentation. To overcome oxygen diffusion problems, bacteria were co-immobilized with the microalga Scenedesmus obliquus. This resulted in an increase of enzyme activity by 20% in the complete medium and 26% in the minimal one. Increasing the algal/bacterial ratio invariably led to a higher final bacterial density, but high algal concentrations were associated with repression of alpha-amylase activity. Axenic immobilized microalgae grew slowly, but when co-immobilized with bacteria, the generation time was significantly reduced .