Department of Microbiology, University of Helsinki, Viikinkaari 9, FI-00014 Helsinki, Finland.
Genetics & Experimental Bioinformatics, Institute of Biology III, University Freiburg, Schänzlestraße 1, D-79104, Freiburg, Germany.
Sci Rep. 2019 Mar 20;9(1):4888. doi: 10.1038/s41598-019-40883-1.
The Baltic Sea is a shallow basin of brackish water in which the spatial salinity gradient is one of the most important factors contributing to species distribution. The Baltic Sea is infamous for its annual cyanobacterial blooms comprised of Nodularia spumigena, Aphanizomenon spp., and Dolichospermum spp. that cause harm, especially for recreational users. To broaden our knowledge of the cyanobacterial adaptation strategies for brackish water environments, we sequenced the entire genome of Dolichospermum sp. UHCC 0315, a species occurring not only in freshwater environments but also in brackish water. Comparative genomics analyses revealed a close association with Dolichospermum sp. UHCC 0090 isolated from a lake in Finland. The genome closure of Dolichospermum sp. UHCC 0315 unraveled a mixture of two subtypes in the original culture, and subtypes exhibited distinct buoyancy phenotypes. Salinity less than 3 g L NaCl enabled proper growth of Dolichospermum sp. UHCC 0315, whereas growth was arrested at moderate salinity (6 g L NaCl). The concentrations of toxins, microcystins, increased at moderate salinity, whereas RNA sequencing data implied that Dolichospermum remodeled its primary metabolism in unfavorable high salinity. Based on our results, the predicted salinity decrease in the Baltic Sea may favor toxic blooms of Dolichospermum spp.
波罗的海是一个浅的咸水盆地，其中空间盐度梯度是导致物种分布的最重要因素之一。波罗的海以其一年一度的由节旋藻、鱼腥藻和束丝藻组成的蓝藻水华而臭名昭著，这些水华对娱乐性用水者尤其有害。为了扩大我们对蓝藻适应咸水环境的策略的了解，我们对不仅存在于淡水环境中，而且存在于咸水环境中的束丝藻 UHCC 0315 进行了全基因组测序。比较基因组学分析显示，它与从芬兰一个湖泊中分离出的鱼腥藻 UHCC 0090 密切相关。束丝藻 UHCC 0315 的基因组闭合揭示了原始培养物中存在两种亚型的混合物，并且亚型表现出明显的浮力表型。盐度低于 3 g/L 的氯化钠可以使束丝藻 UHCC 0315 正常生长，而在中等盐度（6 g/L 氯化钠）下生长则被抑制。在中等盐度下，毒素微囊藻毒素的浓度增加，而 RNA 测序数据表明，束丝藻在不利的高盐度下重塑了其初级代谢。根据我们的结果，波罗的海预计的盐度下降可能有利于束丝藻属的有毒水华。
