Wu Zuowei, Periaswamy Balamurugan, Sahin Orhan, Yaeger Michael, Plummer Paul, Zhai Weiwei, Shen Zhangqi, Dai Lei, Chen Swaine L, Zhang Qijing
Department of Veterinary Microbiology and Preventive Medicine, Iowa State University, Ames, IA 50011;
Department of Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 119074; Genome Institute of Singapore, Singapore 138672;
Proc Natl Acad Sci U S A. 2016 Sep 20;113(38):10690-5. doi: 10.1073/pnas.1605869113. Epub 2016 Sep 6.
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.
高毒力细菌菌株的克隆扩增所导致的感染对人类和动物健康构成了明显且现实的威胁。基因变化与疾病的关联如今已属常规，但确定导致疾病的致病突变仍然困难。空肠弯曲菌是一种重要的人畜共患病原体，主要通过食源途径传播给人类。空肠弯曲菌通常定殖于肠道，但最近出现了一种高毒力且迅速扩张的空肠弯曲菌克隆，它能够穿过肠道，导致怀孕动物发生全身感染和流产。导致这种高毒力的遗传基础尚不清楚。在此，我们开发了一种称为“定向基因组进化”的策略，通过致流产菌株和非致流产菌株之间的杂交，随后在动物疾病模型中进行筛选并进行全基因组序列分析。该策略成功鉴定出编码主要外膜蛋白的porA基因中的单核苷酸多态性（SNP）与高毒力有关。明确的诱变验证了这些突变对于导致流产既是必要的也是充分的。此外，序列分析使用Fu's Fs（一种用于近期种群大小变化的群体遗传指标）将porA鉴定为全基因组适应性进化信号最强的基因，这与克隆“羊流产”的近期扩张一致。这些结果确定了空肠弯曲菌中的一个关键毒力因子以及控制这种人畜共患病原体的一个潜在靶点。此外，本研究提供了通用的、无偏见的实验和计算方法，广泛适用于有效阐明细菌病原体中的致病突变。
