Environmental DNA adsorption to chitin can promote horizontal gene transfer by natural transformation

Horizontal gene transfer by natural transformation (NT) is induced in <i>Vibrio cholerae</i> upon attachment to chitin surfaces in the aquatic environment. Here, we show that free environmental DNA adsorbs to chitin surfaces under physiologically realistic conditions. Using live-cell imaging and a fluorescent NT reporter, we demonstrate with cellular resolution microscopy that <i>V. cholerae</i> utilizes chitin-bound DNA as a reservoir for genetic exchange. Additionally, we demonstrate that uptake of DNA from this chitin-bound reservoir requires the forceful retraction of competence type IV pili. These findings uncover a role for retraction force in driving pilus-dependent NT and suggest that chitin particle surfaces can act as hotspots for horizontal gene transfer.