Daphnia magna Transcriptome to Decipher Microcystin Tolerance. Daphnia magna strain:Clone A

Cyanobacteria constitute a serious threat to freshwater ecosystems by producing toxic secondary metabolites, e.g. microcystins. These microcystins have been shown to harm livestock, pets and humans and to affect ecosystem service and functioning. Cyanobacterial blooms are increasing worldwide in intensity and frequency due to eutrophication and global warming. However, Daphnia, the main grazer of planktonic algae and cyanobacteria, has been shown to be able to suppress bloom-forming cyanobacteria and to adapt to cyanobacteria that produce microcystins. Since Daphnia’s genome was published only recently, it is now possible to elucidate the underlying molecular mechanisms of microcystin tolerance of Daphnia. Daphnia magna was fed with either a cyanobacterial strain that produces microcystins or its genetically engineered microcystin knock-out mutant. Thus, it was possible to distinguish between effects due to the ingestion of cyanobacteria and effects caused specifically by microcystins. By using RNAseq the differentially expressed genes between the different treatments were analyzed and affected KOG-categories were calculated. Our analysis of the data showed that the expression of transporter genes in Daphnia was regulated as a specific response to microcystins.蓝细菌（Cyanobacteria）通过产生有毒次生代谢产物（如微囊藻毒素（microcystins）），对淡水生态系统构成严重威胁。现已证实，这类微囊藻毒素会危害家畜、宠物及人类，并对生态系统服务与生态系统功能造成影响。受富营养化与全球变暖影响，全球范围内蓝藻水华的发生强度与频率均呈上升趋势。不过，作为浮游藻类与蓝细菌主要捕食者的水蚤（Daphnia），已被证实能够抑制形成水华的蓝藻，并可适应产微囊藻毒素的蓝藻菌株。鉴于水蚤的基因组直至近年才完成公布，如今我们得以阐明水蚤对微囊藻毒素耐受性的潜在分子机制。本研究将产微囊藻毒素的蓝藻菌株，与其经基因工程改造的微囊藻毒素敲除突变株分别喂食大型溞（Daphnia magna），由此得以区分蓝藻摄食本身引发的效应，以及微囊藻毒素特异性介导的效应。通过RNA测序（RNAseq）技术，本研究分析了不同处理组间的差异表达基因，并计算了受影响的KOG类别。数据分析结果显示，水蚤体内的转运蛋白基因表达受到调控，这是针对微囊藻毒素的特异性应答反应。