Abstract

Naturally competent bacteria encode sophisticated protein machinery for the uptake and translocation of exogenous DNA into the cell. If this DNA is integrated into the bacterial genome, the bacterium is said to be naturally transformed. Most competent bacterial species utilise type IV pili for the initial DNA uptake step. These proteinaceous cell-surface structures are composed of thousands of pilus subunits (pilins), designated as major or minor according to their relative abundance in the pilus. Here, we show that the minor pilin FimT plays an important role in the natural transformation of Legionella pneumophila. We use NMR spectroscopy, in vitro DNA binding assays and in vivo transformation assays to understand the molecular basis of FimT’s role in this process. FimT binds to DNA via an electropositive patch, rich in arginines, several of which are well-conserved and located in a conformationally flexible C-terminal tail. FimT orthologues from other Gammaproteobacteria share the ability to bind to DNA. Our results suggest that FimT plays an important role in DNA uptake in a wide range of competent species.

Highlights

  • Competent bacteria encode sophisticated protein machinery for the uptake and translocation of exogenous DNA into the cell

  • Natural transformation is an important mode of horizontal gene transfer with widespread consequences for bacterial evolution

  • The first step of this process involves DNA uptake mediated by T4P9, which has only been studied in a handful of competent species

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Summary

Introduction

Competent bacteria encode sophisticated protein machinery for the uptake and translocation of exogenous DNA into the cell If this DNA is integrated into the bacterial genome, the bacterium is said to be naturally transformed. Most competent bacterial species utilise type IV pili for the initial DNA uptake step These proteinaceous cell-surface structures are composed of thousands of pilus subunits (pilins), designated as major or minor according to their relative abundance in the pilus. Studies of several competent bacteria have shown that their T4P (or their pilins) can directly interact with DNA15,25–29 This function was attributed to specialised minor pilins or pilin-like proteins in Neisseria species (ComP)[27,28], Vibrio cholerae (VC0858 and VC0859)[15], and Thermus thermophilus (ComZ)[29], a major pilin (PilA4) has been suggested to contribute in the latter[30]. In addition to these proteins, the minor pilin FimT has been implicated in natural transformation, as its loss leads to a reduction in transformation efficiency in Acinetobacter baylyi[35]

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