Phylogeny Of Oocystaceae And Screening Of Polysaccharide-rich Algae Strains

Oocystaceae is a very important type of small spherical green algae,most of which are planktonic species and common in freshwater bodies,such as small lakes and ponds.It has a variety of morphologies and a relatively rich colony formation mechanism.However,the degree of morphological variation of Oocystaceae is high,which makes it difficult to accurately identify.Nowadays,the progress of molecular phylogeny can help researchers to classify and identify Oocystaceae in combination with morphology.Oocystaceae is rich in polysaccharides,and the extracted algae polysaccharides have the functions of improving the body's immunity,anti-oxidation,anti-virus,anti-tumor and anti-radiation,which have a broad application prospect in the fields of medicine and food.In this article,morphological and molecular phylogenetic approaches were used to identify the 4 new strains of Oocystaceae in order to discover new species and deal with the original taxonomic problems.Subsequently,the physiological indexes of 40 Oocystaceae strains were determined and polysaccharides were extracted to screen out polysaccharide-rich Oocystaceae strains and explore the correlation between polysaccharides content and species and environment,which laid a foundation for further production and application.The experimental results were as follows:(1).The algae strains 12 and 191,collected from Tianjin and Yunnan Province respectively,and had very similar morphological characteristics with genus Oocystis and identical 18 S r DNA genes(including intron)and rbc L cp DNA genes,which both judged them as different strains of a same species.Morphological observations showed that this species has unique morphological characteristics within the genus Oocystis,that are more than one pyrenoids in one chloroplast and darker green chloroplasts.Molecular phylogeny analyses further positioned it in Oocystoideae and the closest relationship with Oocystis marssonii.Due to the taxonomic problem of genus Oocystis has not been resolved,we just identified the new strains as an undetermined species of Oocystis and recorded here as Oocystis sp.12 & 191.(2).The algae strain 14 was collected from freshwater habitat in Tianjin.Morphological observations indicated that this species was different from the typical Oocystis members in colony morphology.All three evolutionary trees showed that the algae strain 14 and another undetermined Oocystis-shaped species(Oocystis sp.CAUP H 1110,KY038331)formed a new clade located at the base of the main branch of Oocystoideae with the closest relationship with Granulocystis branch.Taking the unresolved taxonomic problem of genus Oocystis into account,we just identified the new strain as an undetermined genus in Oocystaceae and recorded here as Oocystaceae sp.14.(3).The algae strain 83 was collected from the fountain pool in Luoping County,Qujing City,Yunnan Province,and was a freshwater plankton group.Morphological observations showed that the strain had the typical characteristics of the genus Neglectella except the unique mucilage colony.Phylogenetic analyses showed that the members of the genus Neglectella were divided into two branches,namely,the Neglectella solitary branch and Neglectella peisonis branch.The algae strain 83 was located in the latter branch.Because of the lack of ultrastructure observation,we have not determined it a new species in Neglectella here but just recorded as Neglectella sp.83.(4).The algae strains of LXD-1,LXD-5,LXD-25,LXD-33,LXD-41,LXD-44,LXD-50,LXD-103 and LXD-128 were higher in chlorophyll a content.The chlorophyll b content of LXD-128 were higher.The carotenoid contend of LXD-2,LXD-24,LXD-43,LXD-54 and LXD-76 was higher.The algae strains of LXD-59,LXD-64,LXD-85,LXD-117,and 083 had higher extraction rates of polysaccharides.The pigment accumulation and polysaccharide content of the above mentioned Oocystaceae strains can be extracted and appied on a larger scale production.