Increased growth of the microalga Chlorella vulgaris when coimmobilized and cocultured in alginate beads with the plant-growth-promoting bacterium Azospirillum brasilense

Coimmobilization of the freshwater microalga Chlorella vulgaris and the pla nt-growth-promoting bacterium Azospirillum brasilense in small alginate bea ds resulted in a significantly increased growth of the microalga. Dry and f resh weight, total number of cells, size of the microalgal clusters (coloni es) within the bead, number of microalgal cells per cluster, and the levels of microalgal pigments significantly increased. Light microscopy revealed that both microorganisms colonized the same cavities inside the beads, thou gh the microalgae tended to concentrate in the more aerated periphery while the bacteria colonized the entire bead. The effect of indole-3-acetic acid addition to microalgal culture prior to immobilization of microorganisms i n alginate beads partially imitated the effect of A. brasilense. Ne propose that coimmobilization of microalgae and plant-growth-promoting bacteria is an effective means of increasing microalgal populations within confined en vironments.