South Tai Lake Phytoplankton Seasonal Changes And The Preliminary Studies Of Cyanophage

Recently,it has attracted great attention that cyanophage plays a potential role in controlling the algal blooms for high host-specificity.This paper aimed to investigate the annual changes of phytoplankton population,then extract cyanophage that could specifically infect the dominant species and identify it.In the present study,nearshore water samples of Southern Taihu Lake were collected continuously for 12 months.Then,the composition,annual changes of phytoplankton population and abundance of dominant species were analyzed.Furthermore,cyanobacteria was infected by cyanophage extracted from water samples and algae.Viral infection was confirmed through color changes and cyanophage infection of microcystis aeruginosa 912 was detected quantitatively through growth inhibition of cyanobacteria.Meanwhile,the purpose gene of cyanophage was estimated by PCR and morphological changes and ultrastructural changes were detected by optical microscopes and TEM.Main results:1.From November 2008 to October 2009,phytoplankon species,belonging to 11 genera of 5 phyla including Cyanophyta,Bacillariophyta,Chlorophyta,Pyrrophyta,Chrysophyta, were collected.Microcystis was the first dominant species and Anabaena was the second dominant species.2.The July's water sample and the August's water sample were successively filtered through 0.45-μm and 0.22-μm membranes and then inoculated into exponentially growing cultures of Microcystis aeruginosa 912,Microcystis ichthyoblabe 1005 and Microcystis-flos-aquae 1028.The cultures were incubated for two weeks.Compared to the control group,no significant color changes were observed in test groups.However,varying degrees of infection could be observed when the June's water sample,the July's water sample and the August's water sample were concentrated.3.The June's water sample,the July's water sample,the August's water sample and the September's water sample were successively filtered through 0.45-μm and 0.22-μm membranes.Then these water samples by gradient dilution were inoculated into exponentially growing cultures of Microcystis aeruginosa 912.Six days later,the growth of cyanobacteria was significantly inhibited by the water sample without dilution.4.Varying degrees of infection were observed when the cyanophage extracted from the June's algae and the July's algae was separately incubated into the exponentially growing cutures of Microcystis aeruginosa 912 and Microcystis ichthyoblabe 1005,but the infection was not observed for Microcystis-flos-aquae 1028.5.The PCR results of the cyanophage showed that purpose gene band of 400bp was only observed in the concentrated June's water sample,but was not observed in others.6.The cells of Microcystis aeruginosa 912 infected by the cyanophage became roundish in shape and dispersed,not in colony.Meanwhile cell membranes and organelles began to separate,cell membranes were dissolved gradually,organelles were damaged severely and cells were finally lysed.Main conclusion:1.The phytoplankton population in the Southern Taihu Lake from November 2008 to October 2009 belonged to 11 genera of 5 phyla.In the whole year,Microcystis was the first dominant species and Anabaena was the second dominant species.2.It was confirmed that cyanophage that could specifically infect Microcystis aeruginosa 912 existed in the Southern Taihu Lake through morphological changes,ultrastructural changes of cyanobacteria before and after infection and qualitative analysis for purpose gene by PCR.