Phylogenetic Analysis Of Picoplanktonic Green Algae In Shanxi Province

Photosynthetic picoeukaryotes(0.2～3 μm)have small individuals,wide distribution and rich phylogenetic diversity,which make very important contributions to algal biomass,primary productivity of aquatic ecosystems,and production of clean energy.At present,there are few studies on the diversity of photosynthetic picoeukaryotes in freshwater in China,and the existing knowledge of people is poor.Some studies have shown that the diversity of picoplanktonic green algae in freshwater is very rich,but due to their tiny individuals and similar morphological characteristics,it is difficult to identify them accurately by traditional taxonomic methods.In this study,in order to explore the species diversity of picoplanktonic green algae in freshwater of Shanxi Province and to identify their phylogenetic position,we collected water samples from freshwater such as reservoirs,rivers and lakes in several places in Shanxi Province,and 37 strains were isolated,purified and cultured,by the observation of morphological characteristics under light microscope and phylogenetic analysis results of three gene sequences(18S r RNA,rbc L,tuf A),3 genera and 13 species are identified.Specific results are as follows:(1)The genus Mychonastes belongs to the order Sphaeropleales in Chlorophyceae,and the species of this genus are widely distributed.Based on morphological characteristics and phylogenetic analysis of three molecular markers(18S r RNA,rbc L,tuf A),18 strains are identified as 7 species,including 1 known species Mychonastes homophaera,and 1 newrecorded species in China,M.Jurisii.Due to the limited molecular data of known species in the database,such as rbc L and tuf A gene sequences,the remaining 5 species cannot be identified as known or new species.Therefore,they are identified as 5 undetermined species temporarily,and in the future,more molecular data are needed for further classifying and revising the species of the genus Mychonastes.(2)The genus Choricystis belongs to the class Trebouxiophyceae.There are different genetic structures in the genus Choricystis,mainly represented by two phylogenetic lineages,which are widely distributed in rivers,lakes,and reservoirs in Shanxi Province,China.Based on morphological observations,phylogenetic tree analysis of two chloroplast genes,rbc L and tuf A sequences,and the molecular data currently available for the genus Choricystis,11 strains were identified as at least 5 different species,including 1 known species,Choricystis parasitica,1 new-recorded species in China,C.Krienitzii,and 3undetermined species.(3)The genus Medakamo,a new-recorded genus in China,belongs to the class Trebouxiophyceae.The species of this genus have been discovered and studied in recent years.In this study,combines with the morphological characteristics and the phylogenetic results of 18 S r RNA,rbc L,and tuf A molecular markers,8 strains are identified as 1undetermined species of the genus Medakamo,a new-recorded genus in China.The combination of using different molecular markers with traditional taxonomic methods can make our results more accurate and reliable.The discovery and establishment of new-recorded genus,new-recorded species from China and new species will help us enrich the species diversity and geographical distribution of the genera Mychonastes,Choricystis and Medakamo,and provide us theoretical basis for the research on the diversity of picoplanktonic green algae and the development and utilization of their resources.