Table_1_The Metabolome of a Cyanobacterial Bloom Visualized by MS/MS-Based Molecular Networking Reveals New Neurotoxic Smenamide Analogs (C, D, and E).DOCX

Members of the cyanobacterial genus Trichodesmium are well known for their substantial impact on nitrogen influx in ocean ecosystems and the enormous surface blooms they form in tropical and subtropical locations. However, the secondary metabolite composition of these complex environmental bloom events is not well known, nor the possibility of the production of potent toxins that have been observed in other bloom-forming marine and freshwater cyanobacteria species. In the present work, we aimed to characterize the metabolome of a Trichodesmium bloom utilizing MS/MS-based molecular networking. Furthermore, we integrated cytotoxicity assays in order to identify and ultimately isolate potential cyanotoxins from the bloom. These efforts led to the isolation and identification of several members of the smenamide family, including three new smenamide analogs (1–3) as well as the previously reported smenothiazole A-hybrid polyketide-peptide compounds. Two of these new smenamides possessed cytotoxicity to neuro-2A cells (1 and 3) and their presence elicits further questions as to their potential ecological roles. HPLC profiling and molecular networking of chromatography fractions from the bloom revealed an elaborate secondary metabolome, generating hypotheses with respect to the environmental role of these metabolites and the consistency of this chemical composition across genera, space and time.

蓝藻门类中Trichodesmium属成员因其对海洋生态系统氮输入的显著影响以及它们在热带和亚热带地区形成的巨大表面浮游生物群而广为人知。然而，这些复杂环境浮游生物事件中的次级代谢物组成并不为人所熟知，同样，其他浮游生物形成的海洋和淡水蓝藻物种中观察到的强效毒素产生的可能性也尚未明确。在本研究中，我们旨在利用基于MS/MS的分子网络分析技术来表征Trichodesmium浮游生物群的代谢组。此外，我们还结合了细胞毒性测试，以从浮游生物中识别并最终分离出潜在的蓝藻毒素。这些努力导致了smenamide家族中数个成员的分离与鉴定，包括三种新的smenamide类似物（1-3）以及先前报道的smenothiazole A杂合聚酮肽化合物。其中两种新的smenamides对神经-2A细胞具有细胞毒性（1和3），它们的存在引发了对其潜在生态角色的进一步质疑。对浮游生物的色谱馏分进行HPLC分析和分子网络分析，揭示了复杂的次级代谢物组成，从而提出了有关这些代谢物在环境中的作用以及这一化学组成在属、空间和时间上的一致性的假设。