Metagenomes Of Cyanobacteria Aggregations And Microbiomes Funcion Of Formation In Lake Taihu

Lake Taihu,the third largest freshwater lake in China,located in the Yangtze River.In recent years,with the development of industrialization and change of climate,the Lake Taihu has been suffered from serious eutrophication,resulting in the accumulation of cyanobacteria assemblages and formation of water bloom.The cyanobacterial water bloom affected the water system regeneration and environmental ecology seriously.Therefore,in order to prevent and control the bloom effectively,it is urgent and important to study the cyanobacteria as well as the mechanism of cyanobacterial assemblage formation.In this study,the completed genomes of the main cyanobacterial species were interpreted with the help of high-throughput sequencing.In addition,the taxonomic and functional compositions of microbial community as well as the mechanism of assemblage formation was researched.The main results and conclusions in this study including:(1)Based on the third-generation sequencing technology,the completed genomes of Microcystis panniformis FACHB 1757(5.69Mb)and Dolichospermum flos-aquae CHAB1629(4.76Mb)were sequenced and assembled.By compared with Microcystis aeruginosa NIES 843,lots of genome structure variations were found in the genome of M.panniformis FACHB 1757,as well as a plasmid of 39 kb.According to the whole genome phylogenetic tree,it was found that the most closely related species of D.flos-aquae CHAB1629 were Dolichospermum circinale AWQC 131C.(2)Combining the 16S rRNA gene amplicon sequencing,the second generation high-throughput sequencing and the third-generation single-molecule sequencing,the taxonomic and functional compositions of assemblage samples collected from the field and cultured samples were studied.Besides,the nearly-completed genomes of four microbes in cultured assemblages were assembled,identified and annotated.In field samples,the richness of attached microbes is higher and the abundance is lower.A total of 23,944 single nucleotide polymorphisms(SNPs)were called in the field samples,whereas only 33 SNPs were called in the cultured ones,which indicates the genome is relatively stable under stable environment.(3)Observed the formation of cyanobacterial assemblages in Lake Taihu from March to September and collected samples in several different positions.By sequencing the 16S rRNA gene amplicon,the taxonomic compositions of microbial communities in Dolichospermum and Microcystis dominated assemblages were compared.In addition to Cyanobacteria,the main bacterial species in the assemblages were distributed in Proteobacteria and Bacteroidetes.In some samples,the proportions of Gemmatimonadetes and Verrucomicrobia are nearly 10%.The correlation between cyanobacteria and other bacteria was calculated based on the change of species abundance.Strong correlations between Proteobacteria,Chloroflexi and Cyanobateria were found.The alpha diversities of most samples are similar and samples which contained dead algae held the highest diversity.(4)By metagenomics sequencing,the reference metagenome and gene catalog of Lake Taihu cyanobacterial assemblages were constructed.According to the GC content and depth distribution,most of the sequences are around 20 X coverage.From March to September,there is a succession of the main species of assemblages,from Dolichospermum to Microcystis,and the average length of predicted protein sequences increased.Among the annotated functional genes,the percentage of known genes are around 60%.Considering the ammonia measured in Lake Taihu as well as the abundance of nitrogen metabolism genes,the ammonia nitrogen required for the generation of cyanobacteria was derived from the eutrophic lake water,the nitrogen fixation and the reduction of nitrate.