Changes in the metabolism of the microalga Chlorella vulgaris when coimmobilized in alginate with the nitrogen-fixing Phyllobacterium myrsinacearum

In an agroindustrial wastewater pond, a naturally occurring unicellular mic roalga, Chlorella vulgaris, was closely associated with the terrestrial pla nt-associative N-2-fixing bacterium Phyllobacterium myrsinacearum. When the two microorganisms were artificially coimmobilized in alginate beads, they shared the same internal bead cavities, and the production of five microal gal pigments increased, but there were no effects on the number of the cell s or the biomass of the microalga. The association, however, reduces the ab ility of C. vulgaris to remove ammonium ions and phosphorus from water. The bacterium produced nitrate from ammonium in synthetic wastewater with or w ithout the presence of the microalga, and fixed nitrogen in two culture med ia. Our results suggest that interactions between microalgae and associativ e bacteria should be considered when cultivating microalgae for wastewater treatment.