Department of Microbiology and Immunology, Life Sciences Centre, The University of British Columbia, Vancouver, British Columbia, Canada.
J Bacteriol. 2012 Nov;194(22):6116-30. doi: 10.1128/JB.01409-12. Epub 2012 Sep 7.
The diarrheal pathogen Campylobacter jejuni and other gastrointestinal bacteria encounter changes in osmolarity in the environment, through exposure to food processing, and upon entering host organisms, where osmotic adaptation can be associated with virulence. In this study, growth profiles, transcriptomics, and phenotypic, mutant, and single-cell analyses were used to explore the effects of hyperosmotic stress exposure on C. jejuni. Increased growth inhibition correlated with increased osmotic concentration, with both ionic and nonionic stressors inhibiting growth at 0.620 total osmol liter(-1). C. jejuni adaptation to a range of osmotic stressors and concentrations was accompanied by severe filamentation in subpopulations, with microscopy indicating septum formation and phenotypic diversity between individual cells in a filament. Population heterogeneity was also exemplified by the bifurcation of colony morphology into small and large variants on salt stress plates. Flow cytometry of C. jejuni harboring green fluorescent protein (GFP) fused to the ATP synthase promoter likewise revealed bimodal subpopulations under hyperosmotic stress. We also identified frequent hyperosmotic stress-sensitive variants within the clonal wild-type population propagated on standard laboratory medium. Microarray analysis following hyperosmotic upshift revealed enhanced expression of heat shock genes and genes encoding enzymes for synthesis of potential osmoprotectants and cross-protective induction of oxidative stress genes. The capsule export gene kpsM was also upregulated, and an acapsular mutant was defective for growth under hyperosmotic stress. For C. jejuni, an organism lacking most conventional osmotic response factors, these data suggest an unusual hyperosmotic stress response, including likely "bet-hedging" survival strategies relying on the presence of stress-fit individuals in a heterogeneous population.
腹泻病原体空肠弯曲菌和其他胃肠道细菌在环境中遇到渗透压变化，通过接触食品加工，以及进入宿主生物体内时，渗透压适应可能与毒力有关。在这项研究中，使用生长曲线、转录组学以及表型、突变体和单细胞分析来探索高渗胁迫暴露对空肠弯曲菌的影响。随着渗透压浓度的增加，生长抑制程度增加，离子和非离子应激物在 0.620 总渗透压升(-1)时抑制生长。空肠弯曲菌适应一系列渗透压应激物和浓度伴随着亚群中严重的丝状化，显微镜观察表明在丝状体内形成隔膜和细胞之间的表型多样性。在盐胁迫平板上，菌落形态分叉为小变体和大变体也说明了种群异质性。携带 GFP 融合到 ATP 合酶启动子的空肠弯曲菌的流式细胞术同样显示在高渗胁迫下存在双峰亚群。我们还在标准实验室培养基上繁殖的克隆野生型群体中发现了频繁的高渗应激敏感变体。高渗上调后的微阵列分析显示热休克基因和编码潜在渗透保护剂合成酶的基因表达增强，氧化应激基因的交叉保护诱导增强。荚膜输出基因 kpsM 也上调，无荚膜突变体在高渗胁迫下生长缺陷。对于空肠弯曲菌来说，这是一种缺乏大多数常规渗透压反应因子的生物体，这些数据表明了一种不寻常的高渗应激反应，包括可能依赖于异质群体中应激适应个体的“赌注避险”生存策略。
