Journal of Environmental Biology

Effect of nitrate, ammonium and phosphate on the growth and microcystin production of Korean Microcystis species

J.H. Lee1, K.L. Lee2, J.Y. Lee3 and? H.S. Kim1*

¹Department of Biology, Kyungpook National University, Daegu, 41566, Republic of Korea

²National Institute of Environmental Human Resources Development, Incheon,22689, Republic of Korea

³National Institute of Environmental Research, Incheon, 22689, Republic of Korea

*Corresponding Author Email : kimhsu@knu.ac.kr

Paper received: 04.10.2019 ?????? ???????????????????????????????????????Revised received: 03.02.2020 ???????????? ???????????????????????????????Accepted: 11.04.2020

Abstract

Aim: This study aimed to investigate the effects of nitrogen (NO₃-N, NH₃-N) and phosphorus (PO₄-P) on the growth and microcystin production of two bloom-forming Microcystis species (toxic M. aeruginosa MAHC160824 and non-toxic M. viridis MVHC160824).

Methodology: The two Microcystis species were isolated from the lower reaches of the Nakdong river, South Korea. In the culture experiments, the average nutrient concentrations (NH₃-N, NO₃-N and PO₄-P) at which Microcystis appeared (> 15?C) was used as control medium. Different concentrations of NH₃-N, NO₃-N and PO₄-P were then employed in nutrient testing (control, vs. 4 times and 16 times higher than the control). Microcystin levels were measured using a UPLC? (LC MS/MS) system.            

Results: Both toxic and non-toxic Microcystis strains exhibited a maximum cell density at 30?C and a maximum growth rate at 25-30?C. In the nutrient addition assays, the maximum growth of two Microcystis species were found at nutrient concentrations 4 to 16 times higher than the control (NH₃-N: 0.468 mg l^-1, PO₄-P: 0.100 mg l^-1, NO₃-N: 32.5 mg l^-1). The highest microcystin production levels were found under optimal growth conditions. The microcystin levels of toxic M. aeruginosa MAHC160824 were below the detection limit despite a higher number of cells (> 300,000 cells ml-1) at the same nutrients concentrations as those found in raw water from the Nakdong river.? ?????      

Interpretation: Higher production of microcystin occurs when there is an increase in NH₃-N and PO₄-P within a restricted range in toxic species M. aeruginosa MAHC160824, else the production is low.  

Key words: Microcystins, Microcystis species, Nakdong river, Nitrogen, Phosphorus

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