Natural Transformation in Deinococcus radiodurans : A Genetic Analysis Reveals the Major Roles of DprA, DdrB, RecA, RecF, and RecO Proteins.

Horizontal gene transfer is a major driver of bacterial evolution and adaptation to environmental stresses, occurring notably via transformation of naturally competent organisms. TheDeinococcus radioduransbacterium, characterized by its extreme radioresistance, is also naturally competent. Here, we investigated the role ofD. radioduransplayers 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 bacteriumVibrio cholerae. Then, we studied the involvement of recombination and DNA repair proteins, RecA, RecF, RecO, DprA, and DdrB into the DNA processing steps ofD. radioduranstransformation 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 Delta dprA Delta recF, Delta dprA Delta recO, and Delta dprA Delta ddrBdouble 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 Delta dprAmutant is as resistant as wild type to various doses of gamma-irradiation, suggesting that DprA, and potentially transformation, do not play a major role inD. radioduransradioresistance.