Cj0011c, a Periplasmic Single- and Double-Stranded DNA-Binding Protein, Contributes to Natural Transformation in Campylobacter jejuni

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Abstract
Campylobacter jejuni is an important bacterial pathogen causing gastroenteritis in humans. C. jejuni is capable of natural transformation, which is considered a major mechanism mediating horizontal gene transfer and generating genetic diversity. Despite recent efforts to elucidate the transformation mechanisms of C. jejuni, the process of DNA binding and uptake in this organism is still not well understood. In this study, we report a previously unrecognized DNA-binding protein (Cj0011c) in C. jejuni that contributes to natural transformation. Cj0011c is a small protein (79 amino acids) with a partial sequence homology to the C-terminal region of ComEA in Bacillus subtilis. Cj0011c bound to both single- and double-stranded DNA. The DNA-binding activity of Cj0011c was demonstrated with a variety of DNAs prepared from C. jejuni or Escherichia coli, suggesting that the DNA binding of Cj0011c is not sequence dependent. Deletion of the cj0011c gene from C. jejuni resulted in 10- to 50-fold reductions in the natural transformation frequency. Different from the B. subtilis ComEA, which is an integral membrane protein, Cj0011c is localized in the periplasmic space of C. jejuni. These results indicate that Cj0011c functions as a periplasmic DNA receptor contributing to the natural transformation of C. jejuni.