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即使在相同的环境条件下，同基因细菌也能表现出多种表型。这种非遗传的个体性已经在包括分化和应激反应在内的许多生物学过程中得到了观察(1)。一个显著的例子是细菌对抗生素的异质反应，其中一小部分对药物敏感的细菌可以在广泛的抗生素治疗下存活。最近，对持久性现象的重新关注表明，非遗传异质性可能是结核病等感染中抗生素治疗失败的主要原因之一，在结核病中，一个单一的持久性细菌可以重新引发感染(2)。持久性通常是通过监测暴露于抗生素的细菌种群的存活率来观察的。最初对细菌的快速杀灭之后，死亡率显著降低，这表明存在一个持续的亚种群。当从这一持续亚群中生长出来的细胞再次受到抗生素的作用时，得到了相同的双相杀灭曲线，这表明该持续亚群与原种群并无遗传差异。我们之前已经表明，持久性细菌进入表型状态，通过缓慢的生长或休眠来识别，这保护了它们免受抗生素的致命作用(3)。本文研究了持久性对大肠杆菌与噬菌体相互作用的影响。我们专注于两个不同的研究捕食系统:(a)一个噬菌体,存在于每一个细菌的基因组,从而导致细菌死亡,这一过程被称为“前噬菌体感应”和(b)的溶解性噬菌体攻击细菌从外面,感染他们,杀了他们。在这些系统中研究了持久表型的影响，并将得到的实验结果应用于这些相互作用的数学描述(4)。我们使用长期延时显微镜观察了噬菌体裂解启动子下GFP的表达，以及单个感染细菌的细胞命运。我们发现，在抗生素治疗下保护细菌的休眠也能保护它们不受原噬菌体诱导。在低持久性种群和高持久性种群之间进行的竞争实验表明，后者具有明显的优势。这表明，持久性可能是在推进压力的进化压力下进化而来的。有趣的是，我们发现，虽然持久性细菌可以被保护免受原噬菌体诱导，但它们却不能被保护免受裂解性感染。基因表达的定量分析表明，裂解基因在持久性细菌中表达受到抑制。然而，当持久性细菌转变为正常生长时，感染噬菌体恢复基因表达的过程，最终导致细胞裂解。虽然它对种群的短期生存影响不大，但需要考虑到持久性细菌的细胞延迟裂解。利用捕食者-被捕食者相互作用的数学模型，我们发现细菌的非遗传特性可以显著影响种群动态，这可能与理解细菌宿主和噬菌体的共同进化有关。引用1。Rando, O. J. & Verstrepen, K. J.(2007)遗传和表观遗传细胞的时间尺度128,655 -668。2. 斯图尔特·g·R。，罗伯逊，b。《结核病:持久性的问题:微生物学综述》1997 -105。3.Balaban: Q。Merrin, J。印度历的1月,R。Kowalik, L。， & Leibler, S.(2004)细菌持久性作为表型开关科学305,1622 -1625。4. 珍珠,S。Gabay C。Kishony, R。奥本海姆,。， & Balaban, N. Q.(2008)宿主-噬菌体相互作用中的非遗传个体，PLoS Biol 6, e120。
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| 课程简介: |
Isogenic bacteria can exhibit a range of phenotypes, even in homogeneous environmental conditions. Such non-genetic individuality has been observed in a wide range of biological processes, including differentiation and stress response(1). A striking example is the heterogeneous response of bacteria to antibiotics, whereby a small fraction of drug-sensitive bacteria can persist under extensive antibiotic treatments. Recently, a renewed interest in the persistence phenomenon has revealed that non-genetic heterogeneity might be one of the main reasons for the failure of antibiotic treatment in infections such as tuberculosis, where a single persistent bacterium can re-start an infection(2). Persistence is typically observed through the monitoring of the survival fraction of a bacterial population exposed to antibiotics. The initially rapid killing of the bacteria is followed by a significantly reduced killing rate which indicates the presence of a persistent sub-population. When cells grown from this persistent sub-population are subjected again to antibiotics, the same bi-phasic killing curve is obtained, suggesting that the persistent sub-population is not genetically different from the original population. We have previously shown that persistent bacteria enter a phenotypic state, identified by slow growth or dormancy, which protects them from the lethal action of antibiotics(3). Here we studied the effect of persistence on the interaction between Escherichia coli and phage lambda. We focused on two different variations of this well-studied predator-prey system: (a) a phage that is present in the genome of each bacterium and can cause bacterial death by a process called "prophage induction" and (b) a lytic phage that attacks bacteria from the outside, infects them and them kills them. The effect of the persistent phenotype was studied in those systems and the experimental results obtained were then implemented in a mathematical description of these interactions(4). We used long-term time-lapse microscopy to follow the expression of GFP under the phage lytic promoter, as well as cellular fate, in single infected bacteria. We found that dormancy that protects bacteria under antibiotic treatments also protects them against prophage induction. A competition experiment run between a low persistence population and a high persistence one demonstrated a clear advantage to the latter. This suggests that persistence might have evolved under the evolutionary pressure of prophage stress. Intriguingly, we found that, while persistent bacteria are protected from prophage induction, they are not protected from lytic infection. Quantitative analysis of gene expression revealed that the expression of lytic genes is suppressed in persistent bacteria. However, when persistent bacteria switch to normal growth, the infecting phage resumes the process of gene expression, ultimately causing cell lysis. Despite its mild effect on the short-term survival of the population, the delayed cell lysis of persistent bacteria needs to be taken in account. Using a mathematical model for this predator-prey interaction, we found that the bacteria's non-genetic individuality can significantly affect the population dynamics, and might be relevant for understanding the co-evolution of bacterial hosts and phages. References 1. Rando, O. J. & Verstrepen, K. J. (2007) Timescales of genetic and epigenetic inheritance Cell 128, 655-668. 2. Stewart, G. R., Robertson, B. D., & Young, B. D. (2003) Tuberculosis: A problem with persistence Nature Reviews: Microbiology 1, 97-105. 3. Balaban, N. Q., Merrin, J., Chait, R., Kowalik, L., & Leibler, S. (2004) Bacterial persistence as a phenotypic switch Science 305, 1622-1625. 4. Pearl, S., Gabay, C., Kishony, R., Oppenheim, A., & Balaban, N. Q. (2008) Nongenetic individuality in the host-phage interaction PLoS Biol 6, e120.
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