Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
mBio. 2019 Mar 19;10(2):e02417-18. doi: 10.1128/mBio.02417-18.
Temperate phages play important roles in the physiology of their bacterial hosts and establish a lysogenic relationship with the host through which prophage-expressed genes confer new phenotypes. A key phenotype is prophage-mediated defense against heterotypic viral attack, in which temperate phages collude with their bacterial host to prevent other phages from attacking, sometimes with exquisite specificity. Such defense systems have been described in and phages but are likely widespread throughout the microbial community. Here, we describe a novel prophage-mediated defense system encoded by phage CarolAnn, which defends against infection by unrelated phages grouped in cluster CZ. CarolAnn genes and are coexpressed with the repressor and are necessary and sufficient to confer defense against phage Kita and its close relatives. Kita and these relatives are targeted through Kita gene , a gene that is of unknown function but which is the location of defense escape mutations that overcome CarolAnn defense. Expression of Kita gene is toxic to in the presence of CarolAnn genes and , suggesting that defense may be mediated by an abortive infection type of mechanism. CarolAnn genes and are distant relatives of mycobacteriophage Sbash genes and , respectively, which also confer viral defense but use a different targeting system. Prophage-mediated viral defense systems play a key role in microbial dynamics, as lysogeny is established relatively efficiently, and prophage-expressed genes can strongly inhibit lytic infection of other, unrelated phages. Demonstrating such defense systems in suggests that these systems are widespread and that there are a multitude of different systems with different specificities for the attacking phages.
温和噬菌体在其细菌宿主的生理学中发挥着重要作用，并通过原噬菌体表达的基因赋予新表型与宿主建立溶原关系。一个关键表型是原噬菌体介导的对异型病毒攻击的防御，其中温和噬菌体与其细菌宿主勾结，阻止其他噬菌体攻击，有时具有极高的特异性。这种防御系统在 和 噬菌体中已有描述，但很可能广泛存在于微生物群落中。在这里，我们描述了由 噬菌体 CarolAnn 编码的一种新的原噬菌体介导的防御系统，该系统可防御不相关的噬菌体群簇 CZ 中的噬菌体感染。CarolAnn 的基因 和 与阻遏物共表达，是赋予对噬菌体 Kita 及其近亲防御所必需且充分的。Kita 和这些近亲是通过 Kita 基因 靶向的，该基因的功能未知，但它是克服 CarolAnn 防御的逃避突变的位置。在 CarolAnn 基因 和 的存在下，Kita 基因 的表达对 是有毒的，这表明防御可能是通过一种流产感染类型的机制介导的。CarolAnn 的基因 和 分别是分枝杆菌噬菌体 Sbash 的基因 和 的远亲，它们也赋予病毒防御，但使用不同的靶向系统。原噬菌体介导的病毒防御系统在微生物动力学中起着关键作用，因为溶原性的建立相对有效，并且原噬菌体表达的基因可以强烈抑制其他不相关噬菌体的裂解感染。在 中证明了这种防御系统表明这些系统广泛存在，并且针对攻击噬菌体具有多种不同的特异性系统。
