不同时期条纹环沟藻可培养藻际细菌研究

通过梯度稀释法分离出条纹环沟藻5个生长时期的可培养藻际细菌,利用基于单菌落16S rDNA V3区序列测定对细菌进行了分子分类鉴定,与GenBank上的相似菌株序列构建了邻接系统发育树并计算遗传距离,同时对不同时期的细菌进行了定量分析.结果表明,在分离培养出的32株细菌中,有12株不同种属细菌.12株细菌分属于a-变形菌纲(Alphaproteobacteria)、g-变形菌纲(Gammaproteobacteria)、拟杆菌门(Bacteroidetes)和放线菌门(Actinobacteria)4大细菌类群,在种类和数量上均以α-变形菌纲为主,其次为g-变形菌纲和拟杆菌门.每个生长时期可培养藻际细菌的种类数为5~8种,其中稳定生长期细菌种类数较为丰富,而在迟滞期和衰亡后期细菌种类较少.从各时期的细菌总数来看,对数生长期细菌数量最低,仅为2.83×106CFU/mL;在衰亡前期细菌数量最高,达到1.72×109CFU/mL;衰亡后期虽然细菌数量有所降低,但仍达到1.37×108CFU/mL.聚类分析和多维尺度分析结果显示,衰亡前期细菌群落结构与其它时期差异较大,而藻细胞快速生长阶段的对数生长期和稳定生长期菌落结构相近.衰亡前期特异性菌株鲍氏不动杆菌(Acinetobacter baumannii)的大量出现,可能与藻类迅速进入衰亡阶段有关;而各个时期均出现的一株麦氏交替单胞菌(Alteromonas macleodii)可能对条纹环沟藻的种群竞争起作用.在条纹环沟藻不同生长时期藻际细菌的种类与数量有所差异,藻际细菌的群落结构可能对条纹环沟藻的生长、种群竞争以及赤潮的生消具有重要作用.

Culturable phycosphere bacteria from different growth stages of Gyrodinium instriatum

Culturable bacteria were isolated from the five different growth stages of Gyrodinium instriatum by gradient dilution method and identified based on sequence of 16S rDNA V3region. A phylogenetic tree was constructed using the twelve sequences in this study and fourteen closest related sequences from GenBank, and the genetic distances were calculated. Meanwhile, bacteria in different growth stages of G. instriatum were analyzed quantitatively. Among the thirty two strains of bacteria isolated, twelve different strains were identified which belonged to Alphaproteobacteria, Gammaproteobacteria, Bacteroidetes, and Actinobacteria. Alphaproteobacteria was the most diversified and abundant group, followed by Bacteroidetes and Actinobacteria. The species number of culturable bacteria ranged from 5to 8in each growth stage, and was highest in the stationary stage but lower in the lag stage and late decline stage. The abundance was lowest in the exponential stage (2.83×106CFU/mL), reached the maxmium in early decline stage (1.72×109CFU/mL), and then slightly decreased in late decline stage (1.37×108CFU/mL). Cluster analysis and multidimensional scaling analysis showed that the bacteria community in early decline stage was quite different from those of the other growth stages, whereas the community stuctures were comparable in the exponential stage and stationary stage when bacteria experienced fast growth. The massive occurrence of a particular bacterium in early decline stage, Acinetobacter baumannii, might be related to the rapid decline of algal cells. Moreover, the ubiqutous Alteromonas macleodii might be play a role in the population competition for G. instriatum. These results suggested that the abundance and community composition in phycosphere bacteria differed in various growth stages of G. instriatum, and bacterial community might play important roles in the growth, population competition, and bloom dynamics of G. instriatum.