Identification Of 8 Water Bloom Diatoms And The Effect Of Temperature On The Physiological Activity Of Fragilaria Mesolepta

In May 2021,a water bloom broke out in a pond in Jiajiazhuang,Fenyang City,Shanxi Province.After microscopic examination in the laboratory,it was consideredto be a relatively rare Fragilaria water bloom,which attracted our attention.Since then,in the water samples collected from several regions,we have carried out monoclonal culture for the dominant species of diatoms,and conducted a series of observations and studies.First,we isolated and purified the dominant diatoms in the water sample to obtain eight pure cultured diatoms.The taxonomic and phylogenetic status of the eight diatoms was determined by morphological observation and molecular biological study.Subsequently,the effect of temperature on its growth ability and photosynthetic activity and the transcriptome analysis under low-temperature adaptation was explored around the water bloom diatom Fragilaria mesolepta in Jiajiazhuang.The results are as follows:1.By using Light microscope and Scanning electron microscope to observe the characteristics of diatom shell morphology and ornamentation,the eight diatoms were finally identified as Fragilaria mesolepta,Ulnaria ulna,Asterinella formosa,Cylotella menechiniana,Stephanidis hantzschii,Stephanidis hantzschii f.tenuis,Melosira varians,Aulacoseira ambigua.2.The rbc L and SSU r DNA genes of the above eight diatoms were amplified by PCR,and the phylogenetic tree was constructed based on the combined sequence.The results showed that the Coscinodiscophyceae is a syntaxa group,located at the base of the tree,followed by Bacillariophyceae and Mediophyceae,both of which are monotaxa.Stephanodiscus,Cyclostephanos and Discotella converge into one branch,while Cyclotella and Thalassiosira converge into one branch.Fragilaria and Ulnaria form sister groups,while Asterionella and Diatoma are closer in kinship.Aulacoseira and Melosira form sister groups.3.After sequencing,splicing,assembly and annotation,the chloroplast genomes of eight diatoms were obtained.Ranging from 116,024 bp to 129,563 bp in size.The nucleotide composition of the genome is highly conservative,with GC content ranging from 29.33% to 31.78%.The phylogenetic tree constructed using 92 diatom chloroplast genomes showed that Coscinodiscophycaee was a syntaxy,and Bacillariophycaee and Mediophycaee were monophyletic groups.The estimation results of divergence time show that the original time of Coscinodiscophycaee is the earliest,about 107.32 million years ago,followed by Mediophecaee and Bacillariophycaee.A total of 86 shared genes were obtained.Through Ka/Ks calculation,the Ka/Ks ratio of 86 genes was less than 0.5,and the genes were purified and selected,with strong conservation.The existence of 29 genes in 92 diatoms was summarized,and it was found that some genes were repeatedly lost during the evolution of diatoms.4.The temperature gradient experiment of F.mesolepta showed that the temperature of 23-28℃ was the most suitable temperature range for the growth and photosynthetic activity of the algae.In this temperature range,the enzyme activity in the cells was strong,the growth rate of the algae cells was fast,and the dominant diatoms were easy to form.The enzyme activity decreased and increased slowly in the low-temperature environment of 10-15℃.This temperature range is appropriate for species preservation.Under the high temperature of 35℃,the chloroplast structure of algae cells was destroyed and the algae cells died.Analysis of FM10 and FM28 transcriptional levels showed that 2,524 genes were up-regulated and 2,931 genes were down-regulated under 10℃ low temperature conditions,among which the transcriptional expression of genes related to photosynthetic activities(Photosynthesis-antenna protein,Photosynthesis,Porphyrin and chlorophyll metabolism,Carbon fixation related genes in photosynthetic organisms)was downregulated,indicating that low temperature inhibited the photosynthetic capacity of the algae.