Effect of urea on growth and microcystins production of Microcystis aeruginosa

The effects of urea on the growth and toxin content of Microcystis aeruginosa isolated from Dianchi Lake in China were investigated. Experiments were carried out in lab using (15)N isotopic technique to characterize urea-N biosynthesis to microcystins. High urea concentration (3.6 mmol-N L(-1)) would restrict the growth of M.aeruginosa and the production of microcystin-LR, while low urea concentration (0.4-1.4 mmol-N L(-1)) would promote the growth of M.aeruginosa and the production of microcystin-LR. The (15)N labeling experiment further demonstrated that there existed selectivity when M.aeruginosa assimilated urea to form its structure. The majority of M.aeruginosa assimilated 1 urea molecule at first which was biosynthesized into the Ala or Leu residue. On day 18, The m/z=1004 parent ion assimilated 9 (15)N except that the Mdha residue did not assimilate any urea-(15)N. The results give deeper insight to the biosynthesis of urea into microcystins.