Ellison Courtney K, Dalia Triana N, Vidal Ceballos Alfredo, Wang Joseph Che-Yen, Biais Nicolas, Brun Yves V, Dalia Ankur B
Department of Biology, Indiana University, Bloomington, IN, USA.
Biology Department, CUNY Brooklyn College, Brooklyn, NY, USA.
Nat Microbiol. 2018 Jul;3(7):773-780. doi: 10.1038/s41564-018-0174-y. Epub 2018 Jun 11.
Natural transformation is a broadly conserved mechanism of horizontal gene transfer in bacterial species that can shape evolution and foster the spread of antibiotic resistance determinants, promote antigenic variation and lead to the acquisition of novel virulence factors. Surface appendages called competence pili promote DNA uptake during the first step of natural transformation ; however, their mechanism of action has remained unclear owing to an absence of methods to visualize these structures in live cells. Here, using the model naturally transformable species Vibrio cholerae and a pilus-labelling method, we define the mechanism for type IV competence pilus-mediated DNA uptake during natural transformation. First, we show that type IV competence pili bind to extracellular double-stranded DNA via their tip and demonstrate that this binding is critical for DNA uptake. Next, we show that type IV competence pili are dynamic structures and that pilus retraction brings tip-bound DNA to the cell surface. Finally, we show that pilus retraction is spatiotemporally coupled to DNA internalization and that sterically obstructing pilus retraction prevents DNA uptake. Together, these results indicate that type IV competence pili directly bind to DNA via their tip and mediate DNA internalization through retraction during this conserved mechanism of horizontal gene transfer.
自然转化是细菌物种中一种广泛保守的水平基因转移机制，它可以塑造进化并促进抗生素抗性决定因素的传播，促进抗原变异并导致获得新的毒力因子。在自然转化的第一步中，称为感受态菌毛的表面附属物促进DNA摄取；然而，由于缺乏在活细胞中可视化这些结构的方法，它们的作用机制仍不清楚。在这里，我们使用可自然转化的模式物种霍乱弧菌和一种菌毛标记方法，确定了自然转化过程中IV型感受态菌毛介导DNA摄取的机制。首先，我们表明IV型感受态菌毛通过其尖端与细胞外双链DNA结合，并证明这种结合对DNA摄取至关重要。接下来，我们表明IV型感受态菌毛是动态结构，菌毛收缩将尖端结合的DNA带到细胞表面。最后，我们表明菌毛收缩在时空上与DNA内化相关，并且空间上阻碍菌毛收缩会阻止DNA摄取。总之，这些结果表明，IV型感受态菌毛通过其尖端直接与DNA结合，并在这种保守的水平基因转移机制中通过收缩介导DNA内化。
