Effects Of Nutrients And Microorganisms On The Growth And Toxin Production Of Alexandrium Minutum

Studies on toxic algal blooms and their impacts, which related to both biomassand toxicity of toxic species, have been paid more and more attention recently. Formerstudies revealed that nutrients and microorganisms were two major factors affectingthe growth and toxin production of toxic dinoflagellate species. Therefore, this thesisis inclined to find out the effects of different types of nitrogen and phosphorusnutrients, as well as microorganisms, on the growth and toxin production ofdinoflalgellates, using Alexandrium minutum as a model organism. The results showed that addition of NH4Cl, yeast extract and NaNO3 after Ndepletion could promote the growth and toxin production of A. minutum. Highconcentration of NH4Cl at the time of nutrient addition showed temporal toxicity on A.minutum. The algae cultures showed similar growth and toxin production propertieswith the three nitrogen substrates. The specific growth rates were 0.21, 0.21 and 0.16and the highest toxin content per cell were11.85, 14.64 and 12.86fmol/ml, respectively.But the effects of urea on the growth and toxin production of A. minutum were muchweaker than the other three nutrients. During the experiment, the cell concentrationremained at about 10,000cells/ml and toxin content fluctuated between 6.00fmol/celland 8.00fmol/cell with urea as nitrogen substrate. All of the four nitrogen substrateshad little effects on toxin composition of A. minutum. Addition of KH2PO4, glycerophosphate, ATP three phosphorus substrates couldpromote the growth and toxin production of A. minutum under phosphorus depletecondition. The maximum cell concentration, growth rate and toxin contention instable phage were 22,700, 28,400,27,800cells/ml and 0.12, 0.14, 0.15 and 22.87,23.98, 21.80fmol/cell, respectively. Phosphorus limitation could make the toxincomposition and toxin content change dramatically. There were more GTX1/4 andless GTX2/3 compared with the algae cultured under normal condition. The analytical i张清春 氮,磷营养物质与微生物对微小亚历山大藻生长和毒素产生的影响 硕士学位论文results of alkaline phosphatase (AP) activity showed that the groups with DOP addedhad higher activity of AP than that with DIP added. But the group without phosphorusaddition had the highest AP activity. A method of antibiotic cocktails were developed in our experiment to eliminatethe bacteria in the culture medium of A. minutum. The results showed that antibioticcocktails containing either ciprofloxacin, gentamicin, streptomycin and penicillin G orciprofloxacin, gentamicin , streptomycin, penicillin G, kanamycin sulfate andneomycin could eliminate bacterium effectively in the culture medium of A. minutumexamined by 2216E plate inoculation and PCR amplification of bacterial DNA.However, after the elimination of bacterial, the fungi proliferated in the culturemedium. And the fungi couldn't be eliminated with fungicide like amphotericin B,since A. minutum very sensitive to the fungicide. The method of cyst induction with 5-methoxytryptamine was studied in theexperiment and the possibility of using this method for axenic culture preparation wasdiscussed. The results showed that most of the cyst appeared in 8 hours after treatmentwith 5-methoxytryptamine. The algae at stationary growth phase is more resistant tothe treatment of 5-methoxytryptamine than the algae at exponential growth phase.After 24 hours, the concentration group with highest cyst formation rate of the cells atstationary phase is 4.0×10-5 M. However, for the the cells at the exponential growthphase, the concentration group with highest cyst formation rate is 2.0×10-5 M. Thecysts formationrate decreased in groups with higher concentration of5-methoxytryptamine due to the broken cells. The resistance of induced cysts to thetreatment of antibiocs was studied. The cysts in all the treatments, except for thattr...