Ability of marine cyanobacterium Synechococcus sp. VDW to remove ammonium from brackish aquaculture wastewater

Nitrogen-rich wastewater is a major problem for the aquaculture industry. To investigate whether algae could be used to remove ammonium from brackish shrimp aquaculture wastewater, marine cyanobacterium Synechococcus sp. VDW was cultured in BG11 medium supplemented with Turks Island salt solution and different concentrations of NH4Cl (1.0–40.0 mg L−1) for 18 days. The cell density of the Synechococcus sp. VDW cultures increased in medium containing between 1 and 10 mg L−1 of NH4Cl, while ammonium concentrations greater than 20.0 mg L−1 had a negative effect on growth. Glutamine synthetase and glutamate synthase activities were also examined, and were found to increase with cell density. Meanwhile, glutamate dehydrogenase activity increased in response to high NH4Cl concentrations (20.0–40.0 mg L−1). The cellular response to ammonium excess was confirmed by measuring gene expression levels using quantitative PCR. Expression of both glnA and gltB was down-regulated compared with the control, while that of gdhA was up-regulated. At an initial concentration of 1–10 mg L−1, 98–100% of the ammonium was removed by day 6 of cultivation. Therefore, these findings suggest that Synechococcus sp. VDW can remove ammonium from contaminated brackish water, and may be helpful for improving the quality of aquaculture wastewater.