DataSheet1_Natural products, including a new caboxamycin, from Streptomyces and other Actinobacteria isolated in Spain from storm clouds transported by Northern winds of Arctic origin.DOCX

Actinobacteria, mostly Streptomyces species, are the main source of natural products essential in medicine. While the majority of producer microorganisms of secondary metabolite are reported from terrestrial or marine environments, there are limited reports of their isolation from atmospheric precipitations. Clouds are considered as atmospheric oases for microorganisms and there is a recent paradigm shift whereby atmospheric-derived Actinobacteria emerge as an alternative source for drug discovery. In this context, we studied a total of 18 bioactive Actinobacteria strains, isolated by sampling nine precipitation events with prevailing Northern winds in the Cantabrian Sea coast, Northern Spain. Backward trajectories meteorological analyses indicate that air masses were originated mostly in the Arctic Ocean, and their trajectory to downwind areas involved the Atlantic Ocean and also terrestrial sources from continental Europe, and in some events from Canada, Greenland, Mauritania and Canary Islands. Taxonomic identification of the isolates, by 16S rRNA gene sequencing and phylogenetic analyses, revealed that they are members of three Actinobacteria genera. Fifteen of the isolates are Streptomyces species, thus increasing the number of bioactive species of this genus in the atmosphere to a 6.8% of the total currently validated species. In addition, two of the strains belong to the genus Micromonospora and one to genus Nocardiopsis. These findings reinforce a previous atmospheric dispersal model, extended herein to the genus Micromonospora. Production of bioactive secondary metabolites was screened in ethyl acetate extracts of the strains by LC-UV-MS and a total of 94 secondary metabolites were detected after LC/MS dereplication. Comparative analyses with natural products databases allowed the identification of 69 structurally diverse natural products with contrasted biological activities, mostly as antibiotics and antitumor agents, but also anti-inflammatory, antiviral, antiparasitic, immunosuppressant and neuroprotective among others. The molecular formulae of the 25 remaining compounds were determined by HRMS. None of these molecules had been previously reported in natural product databases indicating potentially novel metabolites. As a proof of concept, a new metabolite caboxamycin B (1) was isolated from the culture broth of Streptomyces sp. A-177 and its structure was determined by various spectrometric methods. To the best of our knowledge, this is the first novel natural product obtained from an atmospheric Streptomyces, thus pointing out precipitations as an innovative source for discovering new pharmaceutical natural products.

放线菌门（Actinobacteria，尤以链霉菌属（Streptomyces）物种为代表）是医药领域必需天然产物的核心来源。尽管绝大多数次生代谢产物的生产微生物已被报道分离自陆地或海洋环境，但从大气降水中分离得到此类微生物的报道却十分有限。云被视作微生物栖息的大气绿洲，而近期研究范式正发生转变：源自大气的放线菌正成为药物发现的新兴替代来源。
在此研究背景下，本研究对西班牙北部坎塔布连海沿岸、受北风主导的9次降水事件采集样本中分离得到的18株具有生物活性的放线菌展开了研究。气象后向轨迹分析显示，这些气团主要源自北冰洋，其向顺风区域的运移路径途经大西洋，以及欧洲大陆的陆地源地，部分事件中还涉及加拿大、格陵兰、毛里塔尼亚与加那利群岛。
通过16S rRNA基因测序与系统发育分析对分离株进行分类鉴定，结果显示它们隶属于3个放线菌属。其中15株为链霉菌属物种，这使得大气中该属具有生物活性的物种数量增加至当前已验证物种总数的6.8%。此外，2株隶属于小单孢菌属（Micromonospora），1株隶属于诺卡氏菌属（Nocardiopsis）。上述发现进一步验证了此前提出的大气扩散模型，本研究还将该模型的适用范围拓展至小单孢菌属。
通过液相色谱-紫外-质谱联用技术（LC-UV-MS）对各菌株的乙酸乙酯提取物进行生物活性次生代谢产物筛选，经LC/MS数据库去重复分析后，共检测到94种次生代谢产物。与天然产物数据库的比对分析共鉴定出69种结构多样、生物活性各异的天然产物，其中以抗生素与抗肿瘤剂为主，同时还涵盖抗炎、抗病毒、抗寄生虫、免疫抑制剂以及神经保护类化合物等类别。剩余25种化合物的分子式通过高分辨质谱（HRMS）得以确定。上述分子均未在现有天然产物数据库中被报道过，提示其为潜在的新型代谢产物。
作为概念验证，研究人员从链霉菌属菌株Streptomyces sp. A-177的发酵液中分离得到一种新型代谢产物卡博霉素B（caboxamycin B，1），并通过多种光谱学方法确定了其化学结构。据我们所知，这是首个从大气来源链霉菌中获得的新型天然产物，由此证明大气降水是发现新型药用天然产物的创新来源。