Among all the paralytic shellfish toxins (PSTs)-producing algae, Alexandrium tamarense is one of the most widespread harmful species posing a serious threat to marine resources and human health. Therefore, it is extremely important to establish a rapid and accurate monitoring method for A. tamarense that can provide early warnings of harmful algal blooms (HABs) caused by this alga and limit the contamination due to PSTs. In this study, an ssDNA library was first obtained by whole cell systematic evolution of ligands by exponential enrichment after 18 consecutive rounds of iterative screening. After sequencing in combination with subsequent multiple alignment of sequences and secondary structure simulation, the library could be classified into 2 families, namely, Family1 and Family2, according to sequence similarity. Flow cytometry was used to test the affinity and cross-reactivity of Ata19, Ata6, Ata25 and Ata29 belonging to Family2. Ata19 was selected to be modified by truncation, through which a new resultant aptamer named as Ata19-1-1 was obtained. Ata19-1-1 with a K_D of 75.16 ± 11.10 nM displayed a much higher affinity than Ata19. The specificity test showed that Ata19-1-1 has the same discrimination ability as Ata19 and can at least distinguish the target microalga from other microalgae. The observation under a fluorescence microscopy showed that the A. tamarense cells labeled with Ata19-1-1 are exhibiting bright green fluorescence and could be easily identified, factually confirming the binding of the aptamer with target cells. In summary, the aptamer Ata19-1-1 produced in this study may serve as an ideal molecular recognition element for A. tamarense, which has the potential to be developed into a novel detection method for this harmful alga in the future.

在所有产生麻痹性贝类毒素（PST）的藻类中，塔玛亚历山大藻是分布最广的有害物种之一，对海洋资源和人类健康构成严重威胁。因此，建立一种快速、准确的塔玛藻监测方法极其重要，该方法可以对该藻类引起的有害藻华（HAB）提供早期预警，并限制PSTs造成的污染。本研究通过连续18轮迭代筛选，通过指数富集的配体全细胞系统进化，首次获得了单链DNA文库。测序后结合后续序列多重比对和二级结构模拟，根据序列相似性将文库分为2个家族，即Family1和Family2。采用流式细胞术检测Family2的Ata19、Ata6、Ata25和Ata29的亲和力和交叉反应性。选择Ata19进行截短修饰，得到新的适配体，命名为Ata19-1-1。Ata19-1-1 的 KD_为75.16 ± 11.10 nM，显示出比 Ata19 高得多的亲和力。特异性测试表明，Ata19-1-1具有与Ata19相同的辨别能力，至少能够将目标微藻与其他微藻区分开来。荧光显微镜下观察， Ata19-1-1标记的A. tamarense细胞呈现亮绿色荧光，易于识别，证实了适配体与靶细胞的结合。综上所述，本研究产生的适体Ata19-1-1可能作为A. tamarense的理想分子识别元件，未来有潜力发展成为这种有害藻类的新型检测方法。