The Study On Bloom Pattern And Genetic Diversity Of Cyanobacteria In Yuqiao Reservoir

Cyanobacteria is the main contributor to freshwater bloom,cyanobacteria often produce harmful odor,toxins and other secondary metabolites.In recent years,the increasing eutrophication of water and the change of temperature have caused great harm to the ecological safety and health of cyanobacteria.Cyanobacteria bloom represented by Microcystis in Yuqiao Reservoir became more and more serious.In this paper,the species,occurrence and harm of cyanobacteria bloom were summarized.At the same time,with the ecology of cyanobacteria bloom in Yuqiao Reservoir as the research focus,the relationship between cyanobacteria community structure and environmental factors and the genetic diversity of Microcystis in Yuqiao Reservoir were studied,which provided the theory and basis for the ecological protection of Yuqiao Reservoir and the genetic diversity of Microcystis:1.In 2017,40 samples were collected from Yuqiao Reservoir,and the 16 Sr RNA gene sequence was used to amplify the prokaryotic microorganisms in the water and to conduct highthroughput sequencing.By clustering 97% similarity sequences,a total of 4956 OTUs were obtained.Based on the diversity index of samples Chao1,ACE,Shannon,Simpson,etc.,higher microbial diversity was found on August 18,and the maximum abundance value of cyanobacteria was captured on August 18.In terms of the overall cyanobacteria community structure,although Microcystis had an absolute advantage in most samples,the cyanobacteria composition in Yuqiao Reservoir underwent several dominant species changes during the sampling period,and the dominant cyanobacteria in Yuqiao Reservoir were successively replaced by Microcystis,Planktothrix and Synechococcus.The highest proportion of actinomycetes was found in Yuqiao Reservoir,and when the abundance of actinomycetes was higher,the abundance of microcystis was lower,and there was a certain effect between Prochlorothrix and Microcystis.Prokaryotic microorganisms are significantly affected by environmental factors.Compared with the traditional counting method,the high-throughput sequencing method provides a higher resolution for the study of cyanobacteria community structure.2.In 2018,the raw water of Yuqiao Reservoir was sampled,and 176 algae strains were isolated from the water of Yuqiao Reservoir.The results of algae culture showed that the success rate of expansion was 60.23%,the pollution rate was 18.75%,and the mortality rate was 21.02%.At the same time,the spatiotemporal dynamic changes of the dominant genus cell density in Yuqiao Reservoir were studied.During the sampling period,the overall dominant genus cell density was August > June > July > September > October> November,and the dominant genera in June and July in Yuqiao Reservoir were Microcystis,Aphanizomenon in August,and Planktothrix in September.The study on the correlation between dominant cyanobacteria and environmental factors in Yuqiao Reservoir found that the microcystis in eutrophication water had a significant positive correlation with temperature.The influence of thermally dissolved oxygen on Pseudanabaena was obvious,and the negative correlation between Planktothrix and TN?TP was significant.3.Based on 7 housekeeping genes(fts Z,gln A,glt X,gyr B,pgi,rec A and tpi),MLST was applied to analyze the sequence types of 10 Microcystis isolated from the Yuqiao Reservoir.Comparing single gene analysis with MLST method,it can be found that the phylogenetic topology of single gene is incomplete,which indicates that MLST can provide more detailed information.The statistical results of Microcystis gene diversity showed that microcystis in Yuqiao Reservoir had a high genetic diversity,with an average genetic diversity H = 0.938.The MLST based evolutionary tree distinguished the sequences of the bridge region,indicating that some variations with the characteristics of small regions were generated in the small area.