Nutrient Physiology Of Toxin-production And Physiological Functions Of Toxins In Alexandrium Tamarense Polar

Alexandrium tamarense Polar is a paralytic shellfish toxins (PSTs)-producing dinoflagellate which ever formed large scale toxic blooms in the Sourth Polar region, and caused adverse impacts on marine ecosystem and marine organisms. This study investigated nutrient physiology of toxin production and physiological functions of toxin in A. tamarense Polar using a combination approach of algal physiology, analytical chemistry and proteomics, including comparative studies on nutrient utilization characteristics between toxic and none-toxic A. tamarense strains, toxin production physiology of A. tamarense Polar under various nutrients and culture conditions, and proteomics of A. tamarense Polar under high ammonium concentration. The main results were as follows:1. Compared nutrient-utilization characteristics between toxic (A. tamarense Polar) and none-toxic (A. tamarense CCMP2023) Alexandrium strains with emphasis on two nitrogen assimilation enzyme, nitrate reductase (NR) and glutamine synthestase (GS) activities. The results showed that the toxic strains, A. tamarense Polar exhibited both higher NR and GS activities which made it more efficiently in utilizing different nitrogen sources, which might also lead to the accumulation of ammonium in cells of A. tamarense Polar. The biosynthesis of PSP toxins may be a celluar detoxification pathway to alleviate the ammonium toxicity to cells and a nitrogen storage ;2. Investigated the toxin production of A. tamarense Polar under various concentrations of nitrate and ammonium, the results showed that within a certain concentration range of nitrate enhanced cell growth and toxin production of A. tamarense Polar. However, the effects of ammonium on A. tamarense Polar were much more complex: low concentrations (under 100μmol/L) of ammonium had positive effects while high concentrations (above 150μmol/L) of ammonium exhibited an inhibitory effect on the growth of A. tamarense Polar and the inhibiting effect was increased with the concentrations of ammonium within a certain range. High concentrations of ammonium induced more PSP toxin productivity, indicating biosynthesis of PSP toxins might be a detoxification pathway of ammonium to cells and is an important physiological function of A. tamarense Polar;3. Variations of toxin content and composition of A. tamarense Polar under different nitrogen sources and various growh conditions, such as phosphate-limitation, low temperature (13℃) and GS-inhibitor (MSX) indicated that Cl/2 might be the first synthesized PSP toxin in cells of A. tamarense Polar, which was converted into other PSP derivatives, such as GTXs with the action of N- sulphatase. This biosynthesis pathway of PSP toxins was affected by nutrients, temperatre and other environmental factors. Low temperature might inhibite the biosynthesis of N-sulphortase or activity of N-sulphortase which resulted in undectation of GTXs;4. Compared differential expressions of proteomes of A. tamarense Polar under low (50μmol/L) and high (150μmol/L) concentrations of ammonium, and identified and characterized a group importanr proteins related to metabolism, cell division and cell motivation which were not observed in the later growth phase of A. tamarense Polar under high ammonium concentration while two proteins related taurine metabolism were found.. These proteins reflected the physiological reponse of A. tamarense Polar cells to the toxicity of ammomum and could be used as potential biomarkers as cells response to ammonium toxicity.