Comparative effects of inorganic and organic nitrogen on the growth and microcystin production of Microcystis aeruginosa

Abstract

Nitrogen causes the frequent occurrence of harmful algal blooms and possible microcystin production. The effects of ammonia and alanine (Ala) on the growth and microcystin production of Microcystis aeruginosa were investigated using an isotope tracer ((15)N). The results indicated that Ala was directly used by M. aeruginosa and contributed to biomass formation amounting to 2.1 × 10(7) cells mL(-1) on day 48, compared with only 6.2 × 10(6) cells mL(-1) from ammonia alone. Microcystin-LR production with Ala was less than that of ammonia, which peaked at 50.2 fg cell(-1) on day 6. Liquid chromatographic analysis with tandem mass spectrometry of (15)N-microcystin-LR suggested that (15)N from ammonia was probably synthesized into the arginine residue. By contrast, (15)N from Ala was assimilated into the Ala, leucine, the iso-linked (2R,3S)-3-methylaspartic acid, arginine, and certain unusual C20 amino acid residues. The results represent the forward steps in the determination of the nitrogen forms that fuel toxin production and blooms.

Spatiotemporal Dynamics of Microcystin Variants and Relationships with Environmental Parameters in Lake Taihu, China

“…Intracellular MC production is influenced directly by MC-containing cyanobacteria and indirectly by environmental factors [ 25 ]. Various studies [ 12 , 48 , 49 , 50 ] have investigated the role of environmental factors, including temperature, pH, light [ 51 ], nitrogen [ 24 ] and phosphorus [ 8 ] in the regulation of MC production. However, due to geographic distance, differing lake conditions and variation in analytical methods, no consistent conclusions have been reached.…”

“…Our results indicated that cyanobacteria biovolume, Chl-a and DOC had a positive effect, and nitrate, nitrite and DIC had a negative effect on MC-YR production. While some studies have focused on MC-LR and MC-RR [ 48 , 49 , 50 , 61 , 65 ], there has been much less focus on MC-YR. Given that MC-YR is almost as toxic as MC-LR according to toxicity equivalent factors (TEF) [ 66 , 67 ], more attention is warranted to better understand how environmental factors influence its production.…”

Stable isotope labeling to study the nitrogen metabolism in microcystin biosynthesis

“…And the biosynthesis of MC may be inuenced by the different forms of nitrogen. 22,23 In addition, previous results indicated positive relationships between nitrogen supply, MC production and MC content in M. aeruginosa. 33 And ammonia could facilitate the synthesis of MC in toxic strains of M. aeruginosa, which were more responsive to ammonia than non-toxic strains.…”

“…Through LC-MS-MS analysis, Yan et al 22 cultured a strain of M. aeruginosa and found that ammonia was incorporated into the Arg residue in MC-LR. However, the MC biosynthesis in M. aeruginosa PCC7806 analyzed by genetic tools indicated that Adda was the rst unit to be synthesized, followed by Glu, Mdha, Ala, Leu, MeAsp and Arg.…”

“…More recently, the effects of ammonia, alanine and urea on the cell growth and MC production of M. aeruginosa were investigated using 15 N-labeled ammonia, alanine and urea. 22,23 However, these results mainly focused on the inuence of labeled substrates on MC production and the biosynthesis of partial units consisting of MC. To our knowledge, the complete biosynthesis of MC in a specic strain of M. aeruginosa, and laboratory or commercial MC compounds with full isotopic labels are limited.…”