Growth and phosphorus removal by Synechococcus elongatus co-immobilized in alginate beads with Azospirillum brasilense

This study examined the co-immobilization of the cyanobacterium Synechococcus elongatus with the plant growth-promoting bacterium Azospirillum brasilense in alginate beads and its potential application for the removal of phosphorus from aquaculture wastewater. Co-immobilization of both microorganisms significantly increased the cell density of S. elongatus (2852.5 x 10(4) cells mL(-1)) compared with that of immobilization of cyanobacteria alone (1325.2 x 10(4) cells mL(-1)). Chlorophyll a content was similar in co-immobilized (11.1 +/- 3.5 pg cell(-1)) and immobilized S. elongatus (14.5 +/- 4.9 pg cell(-1)). Azospirillum brasilense showed continuous growth until day 2, after which its cell concentration declined until the end of the assay. Co-immobilized S. elongatus removed more phosphorus (44.8 %) than immobilized cyanobacteria cells alone (32.0 %). In conclusion, phosphate removal was greater with free cells of S. elongatus but overlapped with the values that were obtained with the treatment of co-immobilization of cells. Our results demonstrate that A. brasilense enhances the growth of S. elongatus and improves its removal of phosphorus when they are co-immobilized in alginate beads compared with only immobilization of cyanobacteria cells alone.