混合营养型马勒姆杯棕鞭藻的重描述及其系统发育分析

REDESCRIPTION OF MIXOTROPHIC POTERIOOCHROMONAS MALHAMENSIS AND ITS PHYLOGENETIC ANALYSIS

马勒姆杯棕鞭藻(Poterioochromonas malhamensis)是典型的混合营养型单细胞鞭毛藻,因个体微小且形态多变,该鞭毛藻的正确鉴定十分困难,且至今针对该物种一直没有详细全面的形态描述。从小球藻的大规模培养中分离出一株捕食性鞭毛藻P. malhamensis CMBB008,利用荧光染色、扫描和透射电镜等方法,对其形态学特征进行了详尽的描述,并获取该物种的SSU rDNA和rbc L基因序列用于探讨该物种的系统发育地位。文章在前人形态描述的基础上,详细记录了囊壳和叶绿体的形态:囊壳柄长18.3—47.5μm,杯体宽8.5—11.3μm,深6.3—10.7μm;叶绿体1—2个,为中间桥接的二裂片状。文章还结合光镜和电镜观察首次报道了该物种的硅质胞囊,发现其具有独特的三层领状结构和顶端孔塞结构,并揭示了其主要细胞器的超微结构及重要代谢产物,如油滴和金藻昆布多糖液泡等。通过不同种株间的比较研究发现,作为Poterioochromonas属重要形态特征的囊壳和叶绿体,由于形态变异性高,不适合用于P. malhamensis的鉴定,而胞囊形态很可能作为Poterioochromonas种间区分的重要形态特征。分子系统发育分析显示Poterioochromonas所有株系聚为一大支,表明该属是单系类群。P. malhamensis CMBB008位于模式株P. malhamensis SAG933-1a所在的大分支内。Poterioochromonas支系可分为P. malhamensis和P. stipitata两个姊妹群, P. malhamensis支系可进一步分为两个姊妹支,其中CCMP3181可能并不是P. malhamensis。研究补充和完善了P. malhamensis的形态和分子数据,并从形态学和分子系统发育学角度为Poterioochromonas属的分类研究提供重要的参考信息。

Poterioochromonas malhamensis is a typical mixotrophic single-celled flagellate.Due to its small size and variable morphology,the correct identification of this flagellate is still challenging.So far,there is no detailed morphological description for the species.In this study,one algae-grazing flagellate from Chlorella mass culture was isolated,which was identified as P.malhamensis CMBB008.Through fluorescence dying,scanning and transmission electronic microscopy,the morphological features were described in detail.In addition,SSU rDNA and rbcL gene sequences were also obtained to investigate phylogenetic position of this species.Based on previous morphological description,the morphology of lorica and chloroplast was documented:lorica length varied between 18.3—47.5μm,the cup width was 8.5—11.3μm,the cup depth was 6.3—10.7μm,and the strain has one or two connected bilobed chloroplast.Using light and scanning electronic microscopy,siliceous cyst was firstly reported:a unique trilaminar collar and plug on the top.In addition,some primary organelles and metabolite such as oil droplets and chrysolaminarin vacuole were observed.Comparing different species and strains,the results revealed that lorica and chloroplast,which were regarded as important features of Poterioochromonas,were not suitable for identification of P.malhamensis because of high variable morphology.However,the cyst morphology was a candidate feature for species differentiation in Poterioochromonas.Molecular phylogenetic analysis showed that all strains of Poterioochromonas clustered in a clade supporting the genus was monophyly.P.malhamensis and P.stipitata formed sister clades in big clade of Poterioochromonas,and clade Poterioochromonas also divided in two sister clades,in which CCMP3181 probably be a species different from P.malhamensis.The study provides complete morphological and molecular data for P.malhamensis and valuable reference for the genus of Poterioochromonas in morphology and phylogeny.