Department of Immunology and Microbiology, University of Colorado Denver Anschutz Medical Campus, 13001 E 17th Pl, Aurora, CO, 80045, USA.
Department of Biology, The City College of New York, 160 Convent Ave, New York, NY, 10031, USA.
Nat Commun. 2020 Dec 7;11(1):6246. doi: 10.1038/s41467-020-20012-7.
Vibrio cholerae is an aquatic microbe that can be divided into three subtypes: harmless environmental strains, localised pathogenic strains, and pandemic strains causing global cholera outbreaks. Each type has a contact-dependent type VI secretion system (T6SS) that kills neighbouring competitors by translocating unique toxic effector proteins. Pandemic isolates possess identical effectors, indicating that T6SS effectors may affect pandemicity. Here, we show that one of the T6SS gene clusters (Aux3) exists in two states: a mobile, prophage-like element in a small subset of environmental strains, and a truncated Aux3 unique to and conserved in pandemic isolates. Environmental Aux3 can be readily excised from and integrated into the genome via site-specific recombination, whereas pandemic Aux3 recombination is reduced. Our data suggest that environmental Aux3 acquisition conferred increased competitive fitness to pre-pandemic V. cholerae, leading to grounding of the element in the chromosome and propagation throughout the pandemic clade.
霍乱弧菌是一种水生微生物，可分为三种亚型：无害的环境菌株、局部致病性菌株和引起全球霍乱暴发的流行菌株。每种类型都有一种依赖接触的六型分泌系统（T6SS），通过转运独特的有毒效应蛋白杀死邻近的竞争者。流行株具有相同的效应物，表明 T6SS 效应物可能影响流行。在这里，我们表明，T6SS 基因簇（Aux3）中的一个存在于两种状态：一小部分环境菌株中的移动、类似噬菌体的元件，以及流行株中特有的和保守的截断 Aux3。环境 Aux3 可以通过位点特异性重组轻易地从基因组中切除并整合，而流行株 Aux3 的重组减少。我们的数据表明，环境 Aux3 的获得赋予了前流行霍乱弧菌更高的竞争适应性，导致该元件在染色体上固定并在整个流行株系中传播。
