Identification and characterization of novel competence genes comA and exbB involved in natural genetic transformation of Pseudomonas stutzeri.

After transposon mutagenesis we identified a novel gene (comA) of Pseudomonas stutzeri which is essential for natural genetic transformation. The putative amino acid sequence is similar to ComA orthologs of other transformable bacteria including Neisseria gonorrhoeae (ComA), Haemophilus influenzae (Rec-2), Bacillus subtilis (ComEC) and Streptococcus pneumoniae (CelB). Downstream of comA two partially overlapping open reading frames termed exbB and exbD were found coding for putative proteins similar to proteins required for macromolecule uptake in Escherichia coli and present in other Gram-negative bacteria. Insertional inactivation of exbB decreased the transformability to 20% of that of the wild type. The binding of 3H-labeled DNA and its uptake into a DNase-resistant state in the comA and exbB strains were similar to the wild type, suggesting that these proteins are involved in a late step of transformation, presumably in the translocation of DNA from the periplasm into the cytosol. The question of whether the translocation process occurs separately from the step of single-strand formation is discussed.