Preliminary Study On The Isolation And Identification Of Marine Microalgae

Marine microalgae are not only the main primary producers of marine ecosystem, but also the important component of marine biological resources. In the nature of various species, large quantities and fast reproduction, marine microalgae play an extremely important role in material circulation and energy flow of marine ecosystem. Meanwhile, microalgae are full of nutriments, such as necessary proteins, amino acids, unsaturated fatty acid, polysaccharide, carotenoids and other biological active substance. Marine microalgae present crucial developmental value in the fields of basic biology research, aquaculture, the exploitation of new energy and drugdevelopment. China has abundant marine microalgae with nearly 2000 kinds recorded. In recent years, marine microalgae have become the hot spot people concerned with the exhaustion of land resources. Getting more and more microalgae with high value from the ocean has become an important fundamental job.Researches in microalgae are based on identification and classification of them which has been one relatively difficult subject. Traditional identification methods mainly depend on the morphology observation with the microscope and some physiological and biochemical characteristics. However, it is difficult to determine the taxonomy position of picoplankton under ordinary light microscopy because there are few describable morphological features and the difference between related is very small. Molecular biological method is widely used in the taxonomic identification and phylogenetic evolution because of easy operation and reliable results. Selecting representative series clips as classification standard to distinguish different organisms and the genetic differences between different strains will become the main research direction.A strain of marine microalgae was separated from Qingdao offshore. The taxonomy position was determined by its 18S rRNA gene (rDNA) sequence and observation with normal optical microscope combined with scanning electron M,croscopy and transmission electron microscope. The blast result indicated that its 18S rDNA was coincident with that of Nannochloropsis gaditana. Evolutionary tree analysis showed that the algae strains gathered with all other strains of N. gaditana. Therefore, it is induced that the strain is N. gaditana.Genus Nannochloropsis has approximately 7 species whose taxonomic classification was first termed by Hibberd. The species mostly spread in the ocean, few in fresh and brackish water. All of the species are small, nonmotile spheres,having a diameter of about 2 micrometers,which do not exhibie any distinct morphological feature. They cannot be distinguished by either light or electron microscopy because of the very simple ultrastructure. It is considered a promising alga for industrial applications because of its ability to accumulate high levels of polyunsaturated fatty acids. At the same time, It is mainly used as an energy-rich food source for fish larvae and rotifers. The characterization is mostly done by 18S rRNA gene and ITS sequence analysis.This study analyzed 18S rDNA and ITS of 6 different nannochloropsis strains and the genetic relationship between them. The result of Blast showed that the sequenceses of the 6 strains is identical with the N.oceanica that is in NCBI, so we believed that they are different strains of N. oceanica. The result of ITS showed that C146 and Cdl were close. There is no difference in the sequenced 613bp. Another four strains are closer, with the same ten mutation site. Some strains have one or two different site confirming the richness of ITS variation sites. 5.8S fragment between the two ITS regions is 160bp, which is the same of the six strains, confirming the conservative property. The difference between the six strains is 0%~2.4%. According to the research results, it is deduced that the six strains all belong to one species of Nannochloropsis.Due to the resolution of magnification and restrictions, it is difficult to accurately identify Nannochloropsis which have no special surface structure with ordinary optical microscope. Because molecular biological classification is based on nucleic acid sequences which are not affected by environmental, it could guarantee the accuracy of the results. 18S rDNA and ITS analysis provide a molecular identification for those marine microalgae whose taxonomic position are difficult to determine only by morphological identification.