The Effect Of Environmental Fators On The Growth And Competition Of Toxic And Non-toxic Microcystis Strains

It has been observed that toxic and non-toxic Microcystis often coexist innatural water body, the proprotion of toxic cells to total Microcystis population has asignificant effect on the safety of water environment under the global warming andeutrophication. In order to reveal the dynamics of toxic and non-toxic Microcystis, weinvestigated the effects of temperature, light intensity, nitrogen and phophrousconcentrations on the dynamic of MC-producing and non-MC-producing strains inmonoculture and competition experiments. More, SongZikeng Reservoir andDaShenghe Reservoir which both existed Microcystis were observed on the spot,respectively. The proportion of toxic Microcystis genotypes was quantified using areal-time PCR with2primer sets for the mcyB and pc operon genes to determine thetotal Microcystis population cells and potentially toxic Microcystis cells, respectively.The microcystins were detected by ELISA kit and the growth rate of toxic andnon-toxic Microcystis were also compared in monocultrue experiments. The resultsshowed that:（1） The nitrogen was the fundamental regulating factor for cyanobacterialproliferation. A positive correlation between the ratio of toxic strains and nitrogenconcentrations were observed, also a positive correlation between totalmicrocystin concentrations and nitrogen concentrations. In monocultrueexperiments, except the highest phosphorus concentrations treatment (1450mmol·L^-1), the growth rate of non-toxic Microcysits were larger than that of toxicMicrocystis in other treatments. Under the nitrogen-limited (2.8993mmol·L^-1and28.993mmol·L^-1) conditions, the ratio of the toxic cells to total cells fluctuated inthe vicinity of50%. While in other treatments, toxic Microcystis were dominantin the end.（2） In competition experiments, non-toxic Microcystis were only dominant at thelowest phosphorus concentrations (2.258mmol·L^-1), and as the phosphorusconcentrations were higher, the toxic Microcystis was more easlily dominant over non-toxic Microcystis, while total microcystin concentrations wasn’t related withthe phosphorus concentrations.（3） As the temperature arised, it would be more towards the potentially toxicgenotypes and the total microcystin concentrations would be more high.Furthermore, concurrent hight temperature and high light intensity would jieldedthe higher proportion of toxic genetypes and more microcystin concentrations.The celluar MC quotas decreased as the temperature or light intensity increased.（4） In the sampling period, toxic Microcystis cells comprised between0.08%and79.9%of total Microcystis population in Songzikeng Reservoir, and between0.08%and15.01%in Dashanghe Reservoir. The microcystins concentrationsvaried from0.53μgL^-1to24.7μg·L^-1in Songzikeng Reservoir, and varied from0.37μg·L^-1to2.63μg·L^-1in Dashanghe Reservoir, showing that the ratio of toxicstrains and total microcystin concentrations in Songzikeng Reservoir were higherthan that in Dashanghe Reservoir and the variations of the proportion of thenon-toxic and toxic strains would depend on physical and chemical characteristicof the system and a variety of environmental fators.