High frequency genetic variation of purine biosynthesis genes is a mechanism of success in Campylobacter jejuni

Authors: CAMERON, ANDREW - University Of British Columbia; Huynh, Steven; SCOTT, NICHOLLAS - University Of British Columbia; FRIRDRICH, EMILISA - University Of British Columbia; APEL, DMITIRI - University Of British Columbia; FOSTER, LEONARD - University Of British Columbia; Parker, Craig; GAYNOR, ERIN - University Of British Columbia

Submitted to: mBio
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/26/2015
Publication Date: 9/29/2015
Citation: Cameron, A., Huynh, S., Scott, N.E., Frirdrich, E., Apel, D., Foster, L.J., Parker, C., Gaynor, E.C. 2015. High frequency genetic variation of purine biosynthesis genes is a mechanism of success in Campylobacter jejuni. mBio. doi: 10.1128.

Interpretive Summary: Phenotypic variation is prevalent among progeny of the zoonotic pathogen Campylobacter jejuni, the leading agent of enterocolitis in the developed world. Heterogeneity bestows increased survival to bacterial populations because variable phenotypes ensure some cells will be protected against future stress. Exposure to hyperosmotic stress revealed prevalent resistant/sensitive growth differences pre-existing between C. jejuni strain 81-176 colonies. These isolated colonies continued to produce cells with differential phenotypes. Whole-genome sequencing discovered allelic variants of two purine biosynthesis genes, purF and apt, which encode phosphoribosyltransferases that utilize a shared substrate. Genetic analysis determined that purF was essential, while apt was critical for fitness. Population analysis confirmed extensive genetic variation of purF and apt that resulted in viable alleles from in-frame insertion duplications, deletions, or missense polymorphisms. Exposure of purF- and apt-genotyped colonial variants to a variety of niche-relevant stresses determined that alleles were associated with differential stress survival, thus contributing to the total population phenotype distribution. Alleles also contributed to differential intracellular survival in an epithelial cell infection model. Via high-depth amplicon sequencing, the intracellular purF and apt mutant distribution was tracked during infection, and intracellular survival was found to select for stress-fit alleles, as did exposure to oxygen and hyperosmotic stress. Potential DNA-binding sites were identified in purF and apt, and a preliminary DNA-protein affinity screen captured a potential exonuclease that promoted the global spontaneous mutation rate. Taken together, the current study illustrated adaptive properties of high frequency genetic variation of two housekeeping genes, and thus identified a mechanism of pathogen success.

Technical Abstract: Phenotypic variation is prevalent among progeny of the zoonotic pathogen Campylobacter jejuni, the leading agent of enterocolitis in the developed world. Heterogeneity bestows increased survival to bacterial populations because variable phenotypes ensure some cells will be protected against future stress. Exposure to hyperosmotic stress revealed prevalent resistant/sensitive growth differences pre-existing between C. jejuni strain 81-176 colonies. These isolated colonies continued to produce cells with differential phenotypes. Whole-genome sequencing discovered allelic variants of two purine biosynthesis genes, purF and apt, which encode phosphoribosyltransferases that utilize a shared substrate. Genetic analysis determined that purF was essential, while apt was critical for fitness. Population analysis confirmed extensive genetic variation of purF and apt that resulted in viable alleles from in-frame insertion duplications, deletions, or missense polymorphisms. Exposure of purF- and apt-genotyped colonial variants to a variety of niche-relevant stresses determined that alleles were associated with differential stress survival, thus contributing to the total population phenotype distribution. Alleles also contributed to differential intracellular survival in an epithelial cell infection model. Via high-depth amplicon sequencing, the intracellular purF and apt mutant distribution was tracked during infection, and intracellular survival was found to select for stress-fit alleles, as did exposure to oxygen and hyperosmotic stress. Potential DNA-binding sites were identified in purF and apt, and a preliminary DNA-protein affinity screen captured a potential exonuclease that promoted the global spontaneous mutation rate. Taken together, the current study illustrated adaptive properties of high frequency genetic variation of two housekeeping genes, and thus identified a mechanism of pathogen success.