东海赤潮异弯藻Heterosigma akashiwo的形态特征及其分子序列分析

摘要

Morphology and phylogenetics of an ECS strain (strain No. LAMB100718) were isolated from waters of Nanji Island, China is analyzed. The stepwise dilution method was employed for isolation of the single cell algae strain. The strain was cultured in f/2 medium with salinity of 28~31, temperature of 17~ 20 ℃ , light-dark cycle of 12 : 12 hours and photosynthetically active radiation (PAR)of 9. 6 ~10. 6 μmol/(m2 ? S). The morphological features were acquired with optical microscope and fluorescent microscope. And the molecular phylogenetic analysis was made according to phylogenetic tree and Jukes-Cantor distance matrix. The results show that the ECS strain (LAMB100718) is a single cell without cell wall but covered with a thin layer of colloid. The shape of the cell varies in ball, egg or long ellipse like "potato". The cellular dimension is similar to that of other Heterosigma akashiivo strains. Its mean cell length is (16. 0±1. 8)μm(range 12 ~ 20μm), and the mean cell width is (10.0±l. 4)μm (range 7~13μm). The thickness varies greatly. The front end of the cell is often rounded and back-end is relatively thin. There is an oblique furrow on the ventral part of the cell. At 1/2 (or 1/4~ 1/3) of the cell length subapically, there are two unequal flagella, which stretches out from the furrow, with the longer one swimming forward and the shorter one trailing behind. The cell nucleus is slightly rounded, located in the center of the cell. The chloroplasts are brown in color, discoid in shape, 9~22 in number, and distributed all over the periphery of the cell. The ITS rDNA sequence of the strain LAMB100718 is 557 base pair and the GC content is 52. 6%. Only one base pair is different from other four Heterosigma akashiivo strains (AB217657, AF134727, AF134728 and AY704164) in GeneBank. The phylogenetic tree shows that the Heterosigma akashiwo stain LAMB100718, AB217657, AF134727, AF134728 and AY704164 are clustered together, with a high bootstrap value (100%). The result from the Jukes-Cantor distance matrix suggests that the nucleotide divergence of the five strains is between 0. 000~ 0. 004, which belongs to intraspecific differences. According to the morphological and phylogenetic study, the ECS strain (LAMB100718) from waters of Nanji Islands, East China Sea can be confirmed as Heterosigma akashiwo. This strain was isolated for the first time from the East China Sea (ECS) and recorded for the first time in Zhejiang coastal waters.%将采集自东海南麂列岛海域水样进行分离、纯化,从中得到1株针胞藻,将其初步鉴定为赤潮异弯藻Heterosigma akashiwo(以下称东海藻株),并使用光学和荧光显微镜对其形态特征进行了详尽描述,及通过rDNA ITS序列测定、系统发育进化树构建和Jukes-Cantor距离矩阵分析,研究了其分子进化关系.结果表明:东海藻株(编号为LAMB100718)为单细胞,无细胞壁,背腹略扁,细胞厚度及形态变化较大,细胞核位于细胞中部,略呈圆形,叶绿体周生,呈黄褐色盘状.东海藻株与其它4株赤潮异弯藻rDNA ITS序列比对的结果显示仅有1个碱基位点存在差异.系统发育树显示东海藻株与其它4株赤潮异弯藻聚在一起,属同一物种,支持率为100％.Jukes-Cantor遗传距离矩阵则表明东海藻株与其它4株赤潮异弯藻的rDNA ITS核苷酸差异值范围为0.000～0.004,属于种内差异.综合细胞形态结构和分子序列的比较结果,分布于东海南麂列岛海域的东海藻株确为赤潮异弯藻,这是该种在浙江海域的首次记录.