Study On The The Seasonal Change Of Thraustochytrids Diversity And Fatty Acid Composition In Coastal Waters Near Qingdao

The coastal area,the boundary between ocean and land,is seriously influenced by human activities.It receives rich nutrients from land and has high primary productivity,so its ecosystem differs from other marine environments.In recent years,as the study on marine environment becomes deeper,more and more studies have been made on heterotrophic protozoa such as thraustochytrium.The role of thraustochytrids in coastal marine ecosystem has been gradually recognized.In order to fully understand the seasonal variation of the diversity of culturable thraustochytrids in different ecologies near the coast of Qingdao,this study collected seawater samples from different sampling points and determined the physical and chemical factors of seawater.More than 420 isolates were obtained from seawater samples by pine pollen induction and direct coating,and 58 representative strains of chytrium were identified,including Thraustochytrium,Schizochytrium,Botryochytrium,Ulkenia,Sicyoidochytrium,Oblongichytrium and Aplanochytrium,among which the dominant genus is Thraustochytrium.According to the analysis,the abundance of culturable thraustochytrids was seriously affected by seasonal changes,and less influenced by ecologies.In addition,after analyzing relationships of thraustochytrids diversity,community composition and environmental factors,it was found that a direct relationship exits between the diversity of thraustochytrids and nitrogen salt and phosphate.Nitrate,salinity and total phosphorus are the important factors affecting the species composition of the community.It shows that thraustochytrids has rich diversity and huge biomass in the coastal waters of Qingdao.After the determination and analysis of fatty acid components of different genera in different seasons by gas chromatography,it was found that compared with other seasons,the content of fatty acid in the cells of thraustochytrids is the richest in autumn,which was more suitable for the isolation and culture of thraustochytrids.There are also other differences between different genera.In general,the optimal genus is Oblongichytrium.Then 15 strains with higher production of fatty acids were found from all strains,among which 3 strains were the most suitable for fermentation and culture.The most advantageous strain producing palmitic acid was Oblongichytrium sp.HK-920 and the dominant strains producing DHA were Thraustochytriidae sp.YZQ-931 and Thraustochytrium sp.YZQ-910.Therefore,thraustochytrids not only has a unique position in the marine ecosystem,but also has a strong biotechnology application potential.