水华蓝藻——蒙氏浮丝藻的多相特征及分子系统研究

Polyphasic characterization and molecular systematic study on Planktothrix mougeotii (Microcoleaceae, Oscillatoriales), a bloom-forming cyanobacterium

关键词:  蓝藻, 浮丝藻属, 水华, 多相特征, 分子系统

Key words:  cyanobacteria, Planktothrix, water bloom, molecular systematics, molecular phylogeny

摘要:

水体的富营养化导致蓝藻水华频发,对生态系统构成严重威胁。明晰水华蓝藻的种类组成与分布是评估其生态风险的基础。浮丝藻属(Planktothrix)是重要的能形成水华的蓝藻之一,为探明其在亚热带地区,尤其是华南地区的物种多样性及分布规律,该研究以广西南宁一富营养化河流中发现的蒙氏浮丝藻(Planktothrix mougeotii)为研究对象,采用多相分类方法,结合形态学观察、16S rRNA基因序列分析及其转录间隔区(ITS)二级结构比较,系统鉴定了该藻株(WZU2314)的分类地位,并探讨其系统发育关系。结果表明:(1)藻株WZU2314藻丝宽5.78～7.48 μm,细胞长短于宽,气囊集中分布于细胞中部,形态特征与文献记录的蒙氏浮丝藻相符。(2)基于16S rRNA基因的系统发育分析表明,WZU2314与蒙氏浮丝藻参考藻株聚为一支(NJ和ML步展值分别为100%和94%; 贝斯后验概率为1),序列相似度高达99.91%。(3)ITS区域保守结构单元(D1-D1'、Box-B、V3螺旋)的二级结构在属内呈现保守性与特异性,进一步从分子构型上支持了其种级分类地位。该研究首次在广西确认了蒙氏浮丝藻的分布,该发现拓展了广西蓝藻多样性记录,为深入研究亚热带富营养化水体中的水华蓝藻分布现状提供了有力支撑。

Abstract:

The frequent occurrence of cyanobacterial blooms driven by water eutrophication poses a serious threat to aquatic ecosystems. Clarifying the species composition and distribution of bloom-forming cyanobacteria is fundamental for assessing their ecological risks. Planktothrix is one of the key genera responsible for cyanobacterial blooms. In order to explore its species diversity and distribution patterns in subtropical regions, particularly in South China, this study focused on a strain of Planktothrix mougeotii discovered in a eutrophic river in Nanning, Guangxi. A polyphasic approach was employed, integrating morphological examination, 16S rRNA gene sequencing, and comparative analysis of the secondary structure of the internal transcribed spacer(ITS)region, to systematically determined the taxonomic status of the strain(WZU2314), and discussed phylogenetic relationships. The results were as follows:(1)Strain WZU2314 exhibits filaments 5.78 - 7.48 μm wide, with cells shorter than wide and gas vesicles concentrated in the central part of the cells, matching the morphological descriptions of P. mougeotii.(2)Phylogenetic analysis based on the 16S rRNA gene revealed that WZU2314 clustered robustly within a clade containing reference strains of P. mougeotii (bootstrap values of NJ and ML were 100% and 94%, respectively; Bayesian posterior probability was 1), with a sequence similarity exceeding 99.91%.(3)The secondary structures of conserved ITS domains(D1-D1', Box-B, and V3 helices)showed both conserved features within the genus and species-specific characteristics, providing further corroboration at the molecular conformational level for its classification at the species level. This study confirms, for the first time, the presence of P. mougeotii in Guangxi. This finding extends the record of cyanobacterial diversity in Guangxi, and provides essential support for further research into the distribution status of cyanobacteria in subtropical eutrophic waters and their relationship with bloom formation.