Point mutations in the major outer membrane protein drive hypervirulence of a rapidly expanding clone of Campylobacter jejuni.
Infections due to clonal expansion of highly virulent bacterial strains are clear and present threats to human and animal health. Association of genetic changes with disease is now a routine, but identification of causative mutations that enable disease remains difficult. Campylobacter jejuni is an important zoonotic pathogen transmitted to humans mainly via the foodborne route. C. jejuni typically colonizes the gut, but a hypervirulent and rapidly expanding clone of C. jejuni recently emerged, which is able to translocate across the intestinal tract, causing systemic infection and abortion in pregnant animals. The genetic basis responsible for this hypervirulence is unknown. Here, we developed a strategy, termed "directed genome evolution," by using hybridization between abortifacient and nonabortifacient strains followed by selection in an animal disease model and whole-genome sequence analysis. This strategy successfully identified SNPs in porA, encoding the major outer membrane protein, are responsible for the hypervirulence. Defined mutagenesis verified that these mutations were both necessary and sufficient for causing abortion. Furthermore, sequence analysis identified porA as the gene with the top genome-wide signal of adaptive evolution using Fu's Fs, a population genetic metric for recent population size changes, which is consistent with the recent expansion of clone "sheep abortion." These results identify a key virulence factor in Campylobacter and a potential target for the control of this zoonotic pathogen. Furthermore, this study provides general, unbiased experimental and computational approaches that are broadly applicable for efficient elucidation of disease-causing mutations in bacterial pathogens.
Department of Veterinary Microbiology and Preventive Medicine, Iowa State University, Ames, IA 50011;
Zuowei
Z
Wu
Department of Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 119074; Genome Institute of Singapore, Singapore 138672;
Balamurugan
B
Periaswamy
Department of Veterinary Microbiology and Preventive Medicine, Iowa State University, Ames, IA 50011; Department of Veterinary Diagnostic and Production Animal Medicine, Iowa State University, Ames, IA 50011;
Orhan
O
Sahin
Department of Veterinary Pathology, Iowa State University, Ames, IA 50011.
Michael
M
Yaeger
Department of Veterinary Microbiology and Preventive Medicine, Iowa State University, Ames, IA 50011; Department of Veterinary Diagnostic and Production Animal Medicine, Iowa State University, Ames, IA 50011;
Paul
P
Plummer
Genome Institute of Singapore, Singapore 138672;
Weiwei
W
Zhai
Department of Veterinary Microbiology and Preventive Medicine, Iowa State University, Ames, IA 50011;
Zhangqi
Z
Shen
Department of Veterinary Microbiology and Preventive Medicine, Iowa State University, Ames, IA 50011;
Lei
L
Dai
Department of Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 119074; Genome Institute of Singapore, Singapore 138672; zhang123@iastate.edu slchen@gis.a-star.edu.sg.
Swaine L
0000-0002-0107-2861
SL
Chen
Department of Veterinary Microbiology and Preventive Medicine, Iowa State University, Ames, IA 50011; zhang123@iastate.edu slchen@gis.a-star.edu.sg.
Qijing
Q
Zhang
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics*; D002169:Campylobacter Infections / Q000235:genetics* / Q000382:microbiology / Q000635:transmission; D016123:Campylobacter jejuni / Q000235:genetics* / Q000472:pathogenicity; D006801:Humans; D017354:Point Mutation; D018272:Porins / Q000235:genetics*; D012756:Sheep; D012757:Sheep Diseases / Q000235:genetics* / Q000382:microbiology / Q000635:transmission
D001426:Bacterial Proteins; D018272:Porins; C095080:major outer membrane protein, Campylobacter jejuni
Campylobacter; bacterial pathogenesis; clonal expansion; pathogen evolution; population genetics