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United States Department of Agriculture

Agricultural Research Service

Research Project: Molecular Biology of Human Pathogens Associated with Food

Location: Produce Safety and Microbiology Research

Title: Hypervariable purine biosynthesis genes contribute to stress response population heterogeneity in Campylobacter jejuni

Authors
item Cameron, Andrew -
item Frirdich, Emilisa -
item Huynh, Steven
item Parker, Craig
item Gaynor, Erin -

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: June 11, 2013
Publication Date: N/A

Technical Abstract: Population heterogeneity gives bacteria a remarkable ability to survive and grow in swiftly changing environments because the generation of cells with variable phenotypes ensures that some will be successful in hostile conditions. Although pure laboratory cultures have historically been assumed to be clonal and homogenous, underlying heterogeneity in bacterial populations can be detected by exposure of the population to various stresses or by single-cell analyses. We observed that the enteric pathogen Campylobacter jejuni, a leading agent of bacterial diarrheal disease, produced progeny that differ from each other in their sensitivity and resistance to osmotic stress. These isolated progeny went on to produce many cells that retain the altered phenotype, but also revertants with the initial sensitivity or resistance observed among the original population. Whole genome sequencing of several isolated osmotic stress sensitive progeny revealed sequence changes occurring solely in two genes of the purine biosynthesis pathway: purF (amidophosphoribosyl tranferase) and apt (adenine phosphoribosyltransferase), which act on the same substrate, phosphoribosyl pyrophosphate. We next sequenced the apt and purF genes from a further 96 single colony isolates from a wildtype, non-stressed population, and found extensive variation in both genes. This included the insertion of large repeats, deletions, and polymorphisms, but no nonsense mutations, thus indicating significant variability with only viable alleles. A purF deletion mutant could not be generated, and an apt deletion mutant was severely impaired for growth and survival. Testing of the 96 colonies for stress phenotypes, such as oxygen survival, revealed that certain allele combinations were associated with stress resistance or sensitivity. This stress response heterogeneity also correlated with the ability of C. jejuni to survive intracellularly in an epithelial cell model of infection. We hypothesize that these hypervariable purine genes affect the stress survival fitness of individual cells and are important for infectious transmission from commensal hosts, and for human disease.

Last Modified: 8/21/2014
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