5株北极微藻藻际环境的细菌多样性

Analysis of bacterial diversity in the phycosphere of five Arctic microalgae

对5株北极微藻,如脆杆藻(Fragilariopsis sp.)、微单胞藻(Micromonas sp.)、四棘藻(Attheya septentrionalis)、海链藻(Thalassiosira sp.)和小球藻(Chlorella sp.)的不同生长时期的粘附细菌和游离细菌的16S rRNA基因进行PCR-DGGE分析,研究藻际环境的细菌多样性。结果表明,5株微藻具有不同的藻际微生物群落结构组成,其中微单胞藻、脆杆藻、四棘藻和海链藻的藻际细菌主要由Cyanobacteria(藻蓝细菌)、α-Proteobacteria(α-变形菌纲)和γ-Proteobacteria(γ-变形菌纲)组成,仅微单胞藻和脆杆藻检测出CFB(Cytophaga-Flexibacter-Bacteroides,噬纤维菌-屈挠杆菌-拟杆菌)。小球藻由Cyanobacteria、CFB、α-Proteobacteria和β-Proteobacteria(β-变形菌纲)组成。微单胞藻的藻际菌群结构稳定,不同生长时期的游离细菌和粘附细菌组成差异不明显。3株硅藻-脆杆藻、四棘藻和海链藻的游离细菌主要由γ-Proteobacteria组成,小球藻的游离细菌主要为β-Proteobacteria,而5株微藻的粘附细菌主要由Cyanobacteria组成。从DGGE图谱来看,在脆杆藻生长的延滞期、指数期和稳定期,其藻际游离细菌和粘附细菌的16S rRNA基因扩增条带数量和位置均有明显差异,但优势扩增条带较稳定;其他4株藻粘附细菌和游离细菌的扩增条带比较稳定,说明藻际关联菌群结构较稳定。藻菌种间特异性关系为不同微藻藻株提供了重要的线索,同时也带来更多的隐藏在藻际环境中的信息。

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.