Abstract
Campylobacter jejuni is the leading cause of bacterial food borne illness. While helical cell shape is considered important for C. jejuni pathogenesis, this bacterium is capable of adopting other morphologies. To better understand how helical-shaped C. jejuni maintain their shape and thus any associated colonisation, pathogenicity or other advantage, it is first important to identify the genes and proteins involved. So far, two peptidoglycan modifying enzymes Pgp1 and Pgp2 have been shown to be required for C. jejuni helical cell shape. We performed a visual screen of ∼2000 transposon mutants of C. jejuni for cell shape mutants. Whole genome sequence data of the mutants with altered cell shape, directed mutants, wild type stocks and isolated helical and rod-shaped ‘wild type’ C. jejuni, identified a number of different mutations in pgp1 and pgp2, which result in a change in helical to rod bacterial cell shape. We also identified an isolate with a loss of curvature. In this study, we have identified the genomic change in this isolate, and found that targeted deletion of the gene with the change resulted in bacteria with loss of curvature. Helical cell shape was restored by supplying the gene in trans. We examined the effect of loss of the gene on bacterial motility, adhesion and invasion of tissue culture cells and chicken colonisation, as well as the effect on the muropeptide profile of the peptidoglycan sacculus. Our work identifies another factor involved in helical cell shape.
Highlights
Infection by Campylobacter spp, especially Campylobacter jejuni, is considered to be the most prevalent cause of bacterial diarrhoeal disease worldwide [1]
When isolating helical and rod bacteria from wild type (WT) C. jejuni strains based on colony morphology as described in Esson et al [13], we noticed a colony, which was not quite as grey and flat as the typical rod colony morphology but still distinct from the helical colony morphology, and was composed of bacteria with a loss of curvature (‘kinked rod’ cell morphology, 81176_KR)
In C. jejuni the phase variable region (PVR) are typically homopolymeric tracts (HTs) that are highly susceptible to slipped-strand mispairings, which alter the length of the tracts and generate frameshift mutations during DNA replication and repair [32,33]
Summary
Infection by Campylobacter spp, especially Campylobacter jejuni, is considered to be the most prevalent cause of bacterial diarrhoeal disease worldwide [1]. The bacterium is found in the gastrointestinal tract of healthy animals, especially chickens, destined for human consumption. The helical shape of C. jejuni is believed to be important for the bacteria to colonise chickens and during infection, to move through the mucus layer of the gastrointestinal tract and to ‘corkscrew’ into the cells of a human (or other animal) host. C. jejuni can undergo a transition from helical cells to rod shaped or coccoid forms in older cultures, and under conditions of stress. It is not clear whether C. jejuni can move back and forth between different conformational states during growth. The only genes known to be involved in determination of the helical cell shape of C. jejuni are pgp and pgp2 [5e7], and their protein products are peptidoglycan (PG) peptidases that are important for PG modification [5,6]
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