DNA uptake in bacteria

Natural competence is widespread among bacterial species. The mechanism of DNA uptake in both gram-positive and gram-negative bacteria is reviewed. Th e transformation pathways are discussed, with attention to the fate of dono r DNA as it is processed by the competent cell. The proteins involved in me diating various steps in these pathways are described, and models for the t ransformation mechanisms are presented. Uptake of DNA across the inner memb rane is probably similar in grampositive and gram-negative bacteria, and at least some of the required proteins are orthologs. The initial transformat ion steps differ, as expected, from the presence of an outer membrane only in the gram-negative organisms. The similarity of certain essential compete nce proteins to those required for the assembly of type-4 pili and for type -2 protein secretion is discussed. Finally several hypotheses for the biolo gical role of transformation are presented and evaluated.