Departamento de Microbiología, Instituto de Investigaciones Biológicas Clemente Estable, Avenida Italia 3318, 11600 Montevideo, Uruguay; Laboratorio de Biología Computacional, Departamento de Desarrollo Biotecnológico, Instituto de Higiene, Facultad de Medicina, Avenida A. Navarro 3051, 11600 Montevideo, Uruguay.
Sección Limnología, Instituto de Ecología y Ciencias Ambientales. Facultad de Ciencias. Universidad de la República, Iguá 4225, 11400 Montevideo, Uruguay; Physiology and Ecology Phytoplankton Group, CSIC, Uruguay.
Mol Phylogenet Evol. 2020 Jul;148:106824. doi: 10.1016/j.ympev.2020.106824. Epub 2020 Apr 12.
Raphidiopsis (Cylindrospermopsis) raciborskii, a globally distributed bloom-forming cyanobacterium, produces either the cytotoxin cylindrospermopsin (CYL) in Oceania, Asia and Europe or the neurotoxin saxitoxin (STX) and analogues (paralytic shellfish poison, PSP) in South America (encoded by sxt genetic cluster) and none of them in Africa. Nevertheless, this particular geographic pattern is usually overlooked in current hypotheses about the species dispersal routes. Here, we combined genomics, phylogenetic analyses, toxicity data and a literature survey to unveil the evolutionary history and spread of the species. Phylogenies based on 354 orthologous genes from all the available genomes and ribosomal ITS sequences of the taxon showed two well-defined clades: the American, having the PSP producers; and the Oceania/Europe/Asia, including the CYL producers. We propose central Africa as the original dispersion center (non-toxic populations), reaching North Africa and North America (in former Laurasia continent). The ability to produce CYL probably took place in populations that advanced to sub-Saharan Africa and then to Oceania and South America. According to the genomic context of the sxt cluster found in PSP-producer strains, this trait was acquired once by horizontal transfer in South America, where the ability to produce CYL was lost.
拉菲尔藻（柱孢鱼腥藻）是一种分布广泛的蓝藻，能产生细胞毒素 cylindrospermopsin（CYL），主要分布在大洋洲、亚洲和欧洲，或者产生神经毒素石房蛤毒素（STX）和类似物（麻痹性贝类毒素，PSP），主要分布在南美洲（由 sxt 基因簇编码），在非洲则没有。然而，目前关于该物种传播途径的假说通常忽略了这一特定的地理模式。在这里，我们结合基因组学、系统发育分析、毒性数据和文献综述，揭示了该物种的进化历史和传播。基于来自所有可用基因组的 354 个直系同源基因和该分类群的核糖体 ITS 序列构建的系统发育树显示出两个明确的分支：一个是包含 PSP 生产者的美洲分支，另一个是包含 CYL 生产者的大洋洲/欧洲/亚洲分支。我们提出中非是最初的扩散中心（非毒性种群），随后扩散到北非和北美（前劳亚大陆）。产生 CYL 的能力可能发生在向撒哈拉以南非洲，然后向大洋洲和南美洲扩散的种群中。根据在 PSP 生产者菌株中发现的 sxt 簇的基因组背景，这种特性是在南美洲通过水平转移获得的，而在南美洲，产生 CYL 的能力已经丧失。
