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Abstract
Phase-variable restriction-modification systems are a feature of a diverse range of bacterial species. Stochastic, reversible switches in expression of the methyltransferase produces variation in methylation of specific sequences. Phase-variable methylation by both Type I and Type III methyltransferases is associated with altered gene expression and phenotypic variation. One phase-variable gene of Campylobacter jejuni encodes a homologue of an unusual Type IIG restriction-modification system in which the endonuclease and methyltransferase are encoded by a single gene. Using both inhibition of restriction and PacBio-derived methylome analyses of mutants and phase-variants, the cj0031c allele in C. jejuni strain NCTC11168 was demonstrated to specifically methylate adenine in 5΄CCCGA and 5΄CCTGA sequences. Alterations in the levels of specific transcripts were detected using RNA-Seq in phase-variants and mutants of cj0031c but these changes did not correlate with observed differences in phenotypic behaviour. Alterations in restriction of phage growth were also associated with phase variation (PV) of cj0031c and correlated with presence of sites in the genomes of these phages. We conclude that PV of a Type IIG restriction-modification system causes changes in site-specific methylation patterns and gene expression patterns that may indirectly change adaptive traits.
Highlights
Campylobacter jejuni is a major cause of food-borne gastroenteritis in humans with more than 400 million cases of Campylobacteriosis reported annually worldwide [1]
phase variation (PV) mediated by alterations in the repeat tract are predicted to simultaneously abrogate both activities, i.e. methylation and restriction, reducing the toxic effects associated with inactivation of other Type II restriction modification (RM) systems
Orthologues of Cj0031 were found in several other species including a distant association with a putative RM system of the cyanobacteria, Microcystis aeruginosa
Summary
Campylobacter jejuni is a major cause of food-borne gastroenteritis in humans with more than 400 million cases of Campylobacteriosis reported annually worldwide [1]. Campylobacters are present in a very high fraction of farmed chickens with significant numbers of bacteria in each colonized bird [4,5]. Rapid microevolution may be a major mechanism that facilitates persistent colonization of and rapid transmission between individual birds. Most of phase-variable genes of C. jejuni encode surface proteins or enzymes that modify host surface structures [7]. One of these phase-variable genes encodes a restriction modification (RM) system that has the potential to act as a stochastically-regulated modifier of expression of other genes or mediate alternation between phage susceptible and resistant states [8]
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