RESUMEN
Although toxic cyanobacterial blooms and their toxins threaten drinking water and ecology and are promoted by nutrient loading, the precise nutrient regime that increases cyanobacterial populations and toxin production is poorly understood. Here, the influences of arginine (Arg), as a common amino acid with high nitrogen content, on the growth and microcystins (MCs) production of Microcystis aeruginosa (M. aeruginosa) were investigated by an isotope method (15N). The results showed that the biomass and production of microcystin-LR (MC-LR) increased with an increase in initial Arg concentrations in the range of 0.3-1.4â¯mmol-Nâ¯L-1, whereas a higher Arg concentration (3.6â¯mmol-Nâ¯L-1) inhibited the growth. MC-LR on different days (days 0, 6, 12, and 18) was detected by liquid chromatography with tandem mass spectrometry (LC-MS/MS) after incubation with 15N-Arg. The MC-LR molecular weight increased from 995 to 1004 with 100% relative abundance with 10 15N atoms bound by the Adda, Arg (4 15N), Glu, Mdha, Ala, Leu, and MeAsp residues on day 18. It seems that there was a sequential order when M. aeruginosa assimilated Arg to synthesize MC-LR. The Arg residue in the molecule of MC-LR was the last one to be labeled by 15N from 15N-arginine. This study not only presents a deeper insight into the biosynthesis of free amino acids that are incorporated into MCs but also reminds us of the potential risk caused by Arg, which should arouse concerns.
Asunto(s)
Arginina/metabolismo , Microcistinas/metabolismo , Microcystis/crecimiento & desarrollo , Toxinas MarinasRESUMEN
The effects of synthetic wastewater that contained 20 mg/L Cu(II) on the removal of organic pollutants in a sequencing batch reactor were investigated. Results of continuous 20 mg/L Cu(II) exposure for 120 days demonstrated that the chemical oxygen demand (COD) removal efficiency decreased to 42% initially, followed by a subsequent gradual recovery, which peaked at 78% by day 97. Effluent volatile fatty acid (VFA) concentration contributed 67 to 89% of the influent COD in the experimental reactor, which indicated that the degradation of the organic substances ceased at the VFA production step. Meanwhile, the varieties of soluble microbial products (SMP) content and main components (protein, polysaccharide, and DNA) were discussed to reveal the response of activated sludge to the toxicity of 20 mg/L Cu(II). The determination of Cu(II) concentrations in extracellular polymeric substances (EPS) and SMP throughout the experiment indicated an inverse relationship between extracellular Cu(II) concentration and COD removal efficiency.
Asunto(s)
Reactores Biológicos , Sulfato de Cobre/toxicidad , Aguas Residuales/química , Contaminantes Químicos del Agua/química , Análisis de la Demanda Biológica de Oxígeno , Sulfato de Cobre/química , Ácidos Grasos Volátiles/análisis , Sustancias Peligrosas/análisis , Sustancias Peligrosas/química , Compuestos de Nitrógeno/análisis , Compuestos de Nitrógeno/química , Proteínas/análisis , Aguas Residuales/análisisRESUMEN
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.
Asunto(s)
Alanina/metabolismo , Amoníaco/metabolismo , Microcistinas/metabolismo , Microcystis/crecimiento & desarrollo , Microcystis/metabolismo , Biomasa , Marcaje Isotópico , Isótopos de Nitrógeno/metabolismoRESUMEN
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.
Asunto(s)
Microcistinas/biosíntesis , Microcystis/crecimiento & desarrollo , Microcystis/metabolismo , Urea/farmacología , Recuento de Células , Toxinas Marinas , Espectrometría de Masas , Microcystis/efectos de los fármacos , Peso Molecular , Isótopos de Nitrógeno , Factores de TiempoRESUMEN
This study describes the change of organic degradation capability and soluble microbial products (SMP) generated in activated sludge under continuous exposure to Zn (II) in a sequencing batch reactor (SBR). In 338 days of operation, the added Zn (II) concentrations were gradually increased from 50 to 100, 200, 400 to 600 and 800 mg/L. Results showed that after adaptation, the activated sludge could endure 400mg/L Zn (II) without showing evident reduction in organic degradation ability (92±1% of chemical oxygen demand (COD) removal in stable state). However, when 600 and 800 mg/L Zn (II) were applied, the effluent water quality significantly deteriorated. Meanwhile, under increasing Zn (II) concentrations, the SMP content in the activated sludge, together with its main biochemical constituents, first increased slightly below 400mg/L of Zn (II), then rose sharply under 600 and 800 mg/L Zn (II). Furthermore, a close correlation was found between SMP content and effluent soluble COD in both the Experimental Reactor and Control Reactor. In addition, the Zn (II) concentrations in the effluent and SMP extraction liquid were further analyzed and discussed to reveal the role that SMP constituents played in defense and resistance to the toxicity of Zn (II).