Abstract

Horizontal gene transfer is a major driver of bacterial evolution and adaptation to environmental stresses, occurring notably via transformation of naturally competent organisms. The Deinococcus radiodurans bacterium, characterized by its extreme radioresistance, is also naturally competent. Here, we investigated the role of D. radiodurans players involved in different steps of natural transformation. First, we identified the factors (PilQ, PilD, type IV pilins, PilB, PilT, ComEC-ComEA, and ComF) involved in DNA uptake and DNA translocation across the external and cytoplasmic membranes and showed that the DNA-uptake machinery is similar to that described in the Gram negative bacterium Vibrio cholerae. Then, we studied the involvement of recombination and DNA repair proteins, RecA, RecF, RecO, DprA, and DdrB into the DNA processing steps of D. radiodurans transformation by plasmid and genomic DNA. The transformation frequency of the cells devoid of DprA, a highly conserved protein among competent species, strongly decreased but was not completely abolished whereas it was completely abolished in ΔdprA ΔrecF, ΔdprA ΔrecO, and ΔdprA ΔddrB double mutants. We propose that RecF and RecO, belonging to the recombination mediator complex, and DdrB, a specific deinococcal DNA binding protein, can replace a function played by DprA, or alternatively, act at a different step of recombination with DprA. We also demonstrated that a ΔdprA mutant is as resistant as wild type to various doses of γ-irradiation, suggesting that DprA, and potentially transformation, do not play a major role in D. radiodurans radioresistance.

Highlights

  • Natural transformation is a mode of horizontal gene transfer which contributes to the acquisition of new properties and to genome evolution

  • D. radiodurans is classified as a Gram positive bacterium, it was shown that cells contain two membranes (Thompson and Murray, 1981)

  • We investigate the involvement of different Deinococcal proteins in natural transformation and propose a model showing their role at the three stages of the process: DNA internalization, DNA protection and DNA establishment into the host cell (Figure 9)

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Summary

Introduction

Natural transformation is a mode of horizontal gene transfer which contributes to the acquisition of new properties and to genome evolution. Since the discovery of natural transformation of Streptococcus pneumoniae (Griffith, 1928), more than 85 species have been shown to be naturally transformable (Johnston et al, 2014). This mechanism can be divided into three steps: Functions Involved in Deinococcus Transformation (1) External double-stranded DNA (dsDNA) capture followed by the translocation of single-stranded DNA (ssDNA) into the cytosol. Single-stranded DNA binding proteins (SSB) protect internalized ssDNA from degradation by nucleases and limit the loading of the RecA recombinase. DprA, a member of the recombination mediator proteins (RMP) family dedicated to natural bacterial transformation, interacts with naked and SSB-coated ssDNA and protects DNA (Mortier-Barriere et al, 2007; Quevillon-Cheruel et al, 2012)

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