|Miller, William - Bill|
Submitted to: Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2004
Publication Date: 1/20/2005
Citation: Miller, W.G., Pearson, B.M., Wells, J.M., Kapitonov, V.V., Mandrell, R.E. 2005. Diversity of campylobacter jejuni type i restriction-modification loci. Microbiology. 151:337-351.
Interpretive Summary: Campylobacter jejuni is a human gastrointestinal pathogen. Studies of this organism are hindered by the presence of multiple restriction-modification systems. These systems effectively degrade any DNA introduced into these bacteria. Several restriction-modification systems exist in Campylobacter but only one, the Type I system, is universal among all strains. This study analyzed the Campylobacter Type I systems of several poultry, livestock and clinical Campylobacter strains. It found that the Type I system has several unique features and is remarkably diverse. This incredible diversity will make it difficult to bypass the Type I system through inactivation. However, this same diversity will enhance our knowledge of the evolution of this species.
Technical Abstract: The Type I restriction-modification (hsd) systems of 62 Campylobacter jejuni strains were characterized according to DNA and amino-acid sequences, and/or gene organization. The closely related organism Helicobacter pylori has three Type I systems; however, no evidence was found that C. jejuni strains contain multiple Type I systems, although hsd loci are present in at least two different chromosomal locations. Also, unlike H. pylori, intervening open reading frames are present, in some strains, between hsdR and hsdS and between hsdS and hsdM. No definitive function can be ascribed to these ORFs, designated here as rloA-H (R linked ORF) and mloA-B (M linked ORF). Based on parsimony analysis of amino-acid sequences to assess character relatedness, the C. jejuni Type I R-M systems are assigned to one of three families: 'IAB', 'IC', or 'IF'. Our study confirms that HsdM proteins within a family are highly conserved but share little homology with HsdM proteins from other families. The 'IC' hsd loci are >99% identical, as are the 'IF' hsd loci. Additionally, whereas the nucleotide sequences of the 'IAB' hsdR and hsdM genes show a high degree of similarity, the nucleotide sequences of the 'IAB' hsdS and rlo genes vary considerably. This diversity suggests that recombination between 'IAB' hsd loci would lead not only to new hsdS alleles but also to the exchange of rlo genes; five C. jejuni hsd loci are presumably the result of such recombination. Finally, we present evidence that hsdS transcription in C. jejuni is induced by the addition of exogenous genomic DNA. Transcription of NCTC 11168 hsdS, however, is not induced by 11168 genomic DNA, suggesting that induction is not a result of the addition of DNA, per se, but the addition of heterologously methylated DNA. The importance of these findings with regard to the evolution and regulation of C. jejuni Type I R-M systems is discussed.