Analysis On The Community Structure And Eco-Physiological Functions Of Microbe In Pyropia Haitanensis

Pyropia haitanensis is a widely cultivated economic macrolagae in southern coast of China.Various problems exist in the nursery and cultivation of P.haitanensis,such as disease and rotten thallus caused by high temperature.Previous studies ignored the important role of the symbiotic microorganism.In this study,we investigated the microbial communities of seven periods(filamentous conchocelis,sporangial branchlets,conchospores,young thallus,adult thallus,mature thallus,and later mature)of P.haitanensis using 16S/18S rDNA sequencing.We also elucidated the microbial communities and physiological function of P.haitanensis thallus and conchocelis stages through metatranscriptomic sequencing and fluorescence in situ hybridization.In this study,the effects of P.haitanensis cultivation on marine microbial ecology were analyzed from the ecological perspective through the comparison of culture zone seawater and the outside culture zone seawater.The main results are follows:1.16S/18S rDNA sequencing was used to analyze the microbial community of seven periods of P.haitanensis.3,854,079 paired-end reds with an average length of 437 bp were generated in 16S libraries;3,850,766 paired-end reds with an average length of 398 bp were generated in 16S libraries.2.We found that the microbial community structures of P.haitanensis were varied between different development stages.There were representative microbial communities at all stages,indicate that microbial community structure may have an effect on the growth and development of P.haitanensis.3.The seawater from the culture zone and outside the culture zone seawater showed similar microbial communities structure,which indicates that the cultivation of P.haitanensis did not affect the structure of microbial community in the surrounding environment.4.We found a large number of bacteria attached on the cells of P.haitanensis through fluorescence in situ hybridization,even in young thallus with only 10 cells.Most bacteria adhered on the surface of cell wall,and a few bacteria distributed in the cell wall.5.The metatranscriptomic results indicate that heterotrophic bacteria can using the algal cell wall or organic carbon released by algae as a carbon source.Bacteria provide algae vitamins,nitrogen sources,and some microelements,such as iron,and regulate the growth and development of algae.On the other hand,bacteria adhere to the cell surface through a series of adhesion mechanisms and compete with other microorganisms;algal cells can produce reactive oxygen species or other antibacterial substances to prevent bacterial invasion,bacteria protect themselves from algal rejection by producing antioxidant enzymes and protective proteins.6.Addition of vitamin B12 significantly improve the heat tolerance of P.haitanensis and protected the photosynthetic system.Therefore,the high content of vitamin B12 in P.haitanensis can help to improve the tolerance to high temperature.