Changes Of Phyloplankton Population Of Lake Dianchi,Isolation And Preliminary Study On Protozoan And Algicidal Bacteria

The scope of lake eutrophication is broad and harmful algae bloom happens regularly and frequently, which trend is probably to increase in the world-wide range. Cyanobacteria, mostly dominated by Microcystis, thrive in eutrophic waters producing blooms rich in toxins and metabolites that reduces water quality with adverse effects on lake ecology, livestock, human water supply and recreational amenities. In recent years, more and more researchers have realized the possibility that algicidal microorganism could be used as a potential useful tool for preventing harmful algal blooms.Firstly, in the present study, nearshore water samples of Lake Dianchi were collected continuously for9months. Then, the composition, annual changes of phytoplankton population and abundance of dominant species were analyzed. The experimental result indicated that:1.harmful algal blooms, mostly dominated by Microcystis, were occured in Lake Dianchi from May to October in2011;2. the content of chl.a was higher than8ug/ml from June to September;3. the cell number of Microcystis was the most and up to4.71×107cell/ml in the July of2011.Secondly, ten micro-algal were isolated from harmful algal blooms. Two micro-algal were identified as Scenedesmaceae and Closterium according to optical microscope morphological characters and taxonomy. The other two micro-algal were identified as Syenchocystis and Phormidium autumnale by phylogenetic construction based in DNA sequence of cyanobacteria16S-23S rDNA internal space (ITS). The strains of DC23and DC27were two new micro-algal.Thirdly, four protozoan were isolated from harmful algal blooms. Two effective strains of them (protozoan p1and h1) were identified as Ochromonas and Plearonema respectively by their morphological and molecular characters. The main influencing factors of the protozoan grazing properties including:algae species, protozoan density, culture temperature, time and pH etc. were investigated in batch experiments. The results showed that the protozoan p1had strong ability to graze the cells of Microcystis wesenbergii and the protozoan h1to graze the cell of Coelosphaerium respectively. The greater the initial protozoan density, the faster the degradation of chlorophyll-a. that:The optimum temperature of grazing was30℃, There was no obvious difference of the protozoan pl’s grazing ability between pH5to pH7. The grazing ability of protozoan p1would not impact by low concentration phenol, but was inhibited by high concentration phenol. The protozoan p1was easy to cultivate and reproduce rapidly. It could be applied in the ecological environment to control the Microcystis water bloom.Last, four algicidal bacteria were isolated from harmful algal blooms, according to the algicidal extent, effects and growth curve of bacteria, we could reach a conclusion that the strains DCJ-2has the best algae-lysing effect. The experimental result indicated that:the bacteria strains DCJ-2could effectively inhibit the growth of plectonema-boryanum and Aphanizomenonflos-aquae. The bacteria strain DCJ-2lyses the algae by the direct way. when the concentration of strain DCJ-2OD600-2.2, most of algae cells were dissolved after6days.