五株北极微藻的藻际细菌多样性分析

Abstract

As an important primary producer in the marine ecosystem,phytoplankton cells excrete organic compounds.These include high proportions of carbohydrates,amino acids and organic acids,including glycolic acid which forms the base of the marine microbial food web,and affects bacterial growth. Bacteria can live free in the phycosphere and also attached to the surface of algal cells,consuming extracellular products and consequently participate in biogeochemical cycling. Phytoplankton-bacteria interactions range from symbiotic to parasitic interactions,which play an important part in the microbial loop. However,research into phytoplankton-bacterium interactions is limited and yet to be published. The object of this study was to determine the specific associations between dominant algae and associated bacteria in the North Polar Region. We analyzed bacterial diversity in the phycosphere of four Arctic marine microalgae isolates( Micromonas sp.,Fragilariopsis sp.,Attheya septentrionalis and Thalassiosira sp.) and one glacial isolate,Chlorella sp.. Fragilariopsis sp.,Attheya septentrionalis,and Thalassiosira sp. belong to Bacillariophyta,while Chlorella sp. and Micromonas sp. belong toChlorophyta. The 16 S rRNA gene of the attached and free bacteria related to these five microalgae during different growth phases was analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis. The associated bacterial diversity based on DGGE profiles was rich. These bacteria were clustered into Cyanobacteria, CFB, α-Proteobacteria, β-Proteobacteria,and γ-Proteobacteria. Bacteria in the phycosphere of marine isolates Micromonas sp.,Fragilariopsis sp.,Attheya septentrionalis and Thalassiosira sp. mainly belonged to cyanobacteria,α-Proteobacteria and γ-Proteobacteria. CFB was detected only in the phycosphere of Micromonas sp. and Fragilariopsis sp. With regard to the only glacial isolate Chlorella sp.,cyanobacteria,CFB,α-Proteobacteria,and β-Proteobacteria were detected in the majority. Differences in the dominant bacterial species of each microalgae,were distinguished. Cyanobacteria and α-Proteobacteria were detected in the phycosphere of these microalgae. Cyanobacteria bands from Fragilariopsis sp.,Attheya septentrionalis and Chlorella sp.differed from those of Micromonas sp. and Thalassiosira sp. Sulfitobacter of α-Proteobacteria coexisted with both Fragilariopsis sp. and Thalassiosira sp. β-Proteobacteria was traced only from the glacial isolate Cholrella sp. γ-Proteobacteria was commonly detected in the four marine microalgal cultures except the glacial isolate Chlorella sp..Shewanella was found closely associated with Micromonas sp., Attheya septentrionalis and Fragilariopsis sp., while Pseudoalteromonas was associated with Attheya septentrionalis and Fragilariopsis sp. and Thalassiosira sp. DGGE profiles and clustering analysis showed that the attached and free bacteria associated with Fragilariopsis sp. during the lag phase,exponential phase and stationary phase varied,except that the dominant bacteria was constant. Free bacteria in the phycosphere of the three diatom strains were claded into γ-Proteobacteria,while free bacteria associated with Chlorella sp.was clustered into β-Proteobacteria. Meanwhile,attached bacteria associated with these four microalgae were comprised mainly of cyanobacteria. However,the attached and free bacteria from the other four microalgae strains were invariable,indicating stability of the bacterial community structure in the phycosphere,except for a slight variation in the abundance of the dominant bacteria. The associated bacterial community related to the Arctic microalgae isolations was analyzed and it would help us recognize the mechanism of phytoplankton-bacteria interaction and their coexisting contribution in the Arctic ecosystem.