ARS | Publication request: Nucleases Encoded by Integrated Elements CJIE2 and CJIE4 Inhibit Natural Transformation of Campylobacter jejuni

Submitted to: Journal of Bacteriology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 7, 2009
Publication Date: February 1, 2010
Repository URL: http://jb.asm.org/cgi/content/full/192/4/936
Citation: Gaasbeek, E.J., Wagenaar, J.A., Guilhabert, M., Van Putten, J.P., Parker, C., Vanderwal, F.J. 2010. Nucleases Encoded by Integrated Elements CJIE2 and CJIE4 Inhibit Natural Transformation of Campylobacter jejuni. Journal of Bacteriology. 192:936-941.

Interpretive Summary: The bacteria Campylobacter jejuni is naturally competent for extracellular DNA uptake. Nevertheless, not every strain is able to acquire foreign DNA since nonnaturally transformable strains do exist. Previously, we showed that many nonnaturally transformable C. jejuni strains express DNase activity. For a subset of strains it was shown that a periplasmic DNase, encoded by dns, inhibits natural transformation in C. jejuni. In the present study, genetic factors coding for DNase activity in absence of dns were identified and characterized in a subset of nonnaturally transformable strains. Comparative genomic hybridization indicated that these nonnaturally transformable dns-negative strains contain DNA/RNA non-specific endonucleases, homologous to the gene products of CJE0566 and CJE1441 from strain RM1221, and are encoded by C. jejuni integrated elements 2 and 4. DNase assays using DNase-negative Escherichia coli and C. jejuni strains, expressing CJE0566 and CJE1441 and a third homologue from strain 07479, indicated that these genes code for DNases. Genetic transfer of these genes to a naturally transformable C. jejuni strain resulted in a decreased efficiency of natural transformation. Overall, the data indicate that, in addition to dns, prophage encoded DNA/RNA non-specific endonucleases affect the natural transformability of C. jejuni through hydrolysis of DNA.

Technical Abstract: The species Campylobacter jejuni displays huge genetic diversity, and is naturally competent for DNA uptake. Nevertheless, not every strain is able to acquire foreign DNA since nonnaturally transformable strains do exist. Previously we showed that many nonnaturally transformable C. jejuni strains express DNase activity. For a subset of strains it was shown that a periplasmic DNase, encoded by dns, inhibits natural transformation in C. jejuni. In the present study, genetic factors coding for DNase activity in absence of dns were identified and characterized in a subset of nonnaturally transformable strains. Comparative genomic hybridization indicated that these nonnaturally transformable dns-negative strains contain DNA/RNA non-specific endonucleases, homologous to the gene products of CJE0566 and CJE1441 from strain RM1221, and are encoded by C. jejuni integrated element 2 and 4. DNase assays using DNase-negative Escherichia coli and C. jejuni strains, expressing CJE0566 and CJE1441 and a third homologue from strain 07479, indicated that these genes code for DNases. Genetic transfer of these genes to a naturally transformable C. jejuni strain resulted in a decreased efficiency of natural transformation. Overall, the data indicate that, in addition to dns, prophage encoded DNA/RNA non-specific endonucleases affect the natural transformability of C. jejuni through hydrolysis of DNA.