铜绿微囊藻与藻际细菌Ma-B1菌株的相互作用

Interaction between Microcystis aeruginosa and Bacterium Ma-B1 Strain within Phycosphere

藻与细菌通常共生于淡水生境,形成藻-菌共生体系,藻际细菌是水体生态系统中的重要组成部分,对藻的消长起重要的调控作用,但有关藻际微环境中藻与细菌的互作机制还不清楚.采用传统的细菌平板培养方法,从太湖优势水华藻——铜绿微囊藻(Microcystis aeruginosa)细胞表面分离出一株藻际细菌Ma-B1,基于生理、生化试验和16S rRNA基因序列分析,初步鉴定为甲基营养芽孢杆菌(Bacillus methylotrophicus).通过测定细胞生长,分析藻-菌相互作用机理.结果表明:一定浓度(>60μg/mL)的Ma-B1的胞外代谢物可显著抑制铜绿微囊藻的生长(培养基为BG11,28℃/日,22℃/夜,3 000 lx,光暗比为14 h∶10 h);铜绿微囊藻的胞外滤液(500μL/mL)对Ma-B1的生长有一定的促进作用,但其总滤液(500μL/mL)显著促进Ma-B1的生长;MaB1细胞对铜绿微囊藻的生长没有显著影响,而高浓度(藻菌比10∶1)的铜绿微囊藻细胞则可显著抑制Ma-B1的生长.铜绿微囊藻与Ma-B1之间存在复杂的相互抑制或促进关系,共同影响着藻、菌在自然水体生态系统中的消长.

Algae and bacteria often live together in freshwater environments,resulting in the formation of alga-bacterial symbiotic systems.Algae,as a typical important primary producer,can secret extracellular substances to the surrounding environment during the growth process; this results in the formation of a special microenvironment-phycosphere to which bacteria are attracted. In return,bacteria within the phycosphere play important roles in the regulation of algal dynamics in the ecosystems. A series of bacteria species within the phycosphere have been reported in recent years,such as α-proteobacteria,γ-proteobacteria and bacteroidetes. Some of them promote for algal growth,while others exhibit growth inhibition or even kill algae. However,the interaction mechanisms between the algae and bacteria are still unclear. In this study,a bacterial strain Ma-B1 was isolated from the cell surfaces of Microcystis aeruginosa and identified to be Bacillus methylotrophicus based on physiological and biochemical assays and 16 S rRNA gene sequence analysis. According to a growth experiment,the metabolites（ 60 μg /mL） of strain Ma-B1 exhibited significant growth inhibition against the cyanobacteria M. aeruginosa,whose growth was cultured in BG11 medium at 28 ℃ /day and 22 ℃ /night with a 14 h light ∶ 10 h dark regime under an illumination of 3000 lx. However,the total-filtrates of M. aeruginosa showed significant growth promotion for the strain Ma-B1 at a concentration of 500 μL /mL. The extra-filtrates of M. aeruginosa also showed weak growth promotion for the strain at the same concentration of 500 μL /mL. The results indicated that the interaction between algae and bacteria within the phycosphere is quite complicated and requires for further study.