The effects of different nitrogen compounds on the growth and microcystin production of Microcystis aeruginosa

The effects of different nitrogen compounds, which include bicine, sodium nitrate, ammonium chloride, glutamic acid and urea, on growth and microcystin (MC) production were studied in batch cultures. The results showed that growth and microcystin production were promoted by bicine, sodium nitrate and ammonium chloride and could not be supported by urea and glutamic acid. It is likely that the cells of Microcystis aeruginosa have no urease which can be utilized to decompose urea. Glutamic acid enters the cell and may interrupt the normal metabolic processes. This would inhibit growth and microcystin production, resulting in the death of the organism. Bicine kept the pH of the medium at about 8.5 and offered a preferential environment for growth and microcystin production. Ammonium chloride could be utilized by Microcystis aeruginosa indirectly. During the process of assimilation, hydroxy ions were continuously consumed, which would lead to a reduction in pH to less than 7 and retard growth and microcystin production. In the presence of sodium nitrate, the metabolic and biochemical mechanisms, which use sodium nitrate as a source of nutrition during the process of expanding vaccination, were impossible to change in a short time. Thus, sodium nitrate promoted growth and microcystin production.