Expression dynamics of the CfrBI restriction-modification system in single cells and theimpact on restriction of phage infection for the bacterial population

多重耐药细菌是现代医疗机构面临的日益严重的问题。因此，认为有必要促进研究新的方法来对抗病原菌。噬菌体是细菌特异性病毒，并且由于其高宿主特异性和裂解细菌细胞的效率而成为有前途的工具。然而，细菌也可以获得对抗生素的抗性，而抗生素可以克服细菌的抗性。需要研究来加深我们对噬菌体抗性的协同进化过程和机制的理解。细菌用于对抗由细菌引起的感染的最广泛和移动的机制之一是质粒编码的限制性修饰（R-M）系统。这些系统识别特定的DNA序列，并且由甲基转移酶（MT）和限制性内切核酸酶（RE）组成，其在结合到识别序列时，分别甲基化或切割DNA。甲基化导致DNA对相应RE的抗性。在获得这种基于质粒的R-M系统期间，MT和RE编码基因的及时协调表达是建立保护和防止病毒DNA修饰的关键，所述病毒DNA修饰将使系统无功能，导致产生抗性噬菌体后代，所述抗性噬菌体后代将威胁整个细菌群体的存活。虽然R-M系统的体外调控机制研究取得了进展，但对体内调控动力学的研究却知之甚少。以下建议旨在增加我们对R-M系统在体内的调节、它们在单细胞中建立期间的动力学、涉及的因素以及它们对细菌细胞和群体的保护功能的后果的理解。最终，知识的获得将有助于我们进一步了解细菌和细菌的相互作用和共同进化以及细菌感染的噬菌体治疗的前景。

Multiple drug-resistant bacteria are an increasing problem for modern health care institutions. It is therefore deemed necessary to facilitate the research in novel approaches to combat pathogenic bacteria. Bacteriophages are bacteria-specific viruses and a promising tool due to their high host-specificity and efficiency to lyse bacterial cells. However, bacteria can also acquire resistances against phages and phages can overcome bacterial resistances. Studies are needed to deepen our understanding of the co-evolutionary processes and mechanisms of phage resistance. One of the most widespread and mobile mechanisms bacteria use to combat infections by phages are plasmid-encoded restriction modification (R-M) systems. These systems recognize a specific DNA sequence and consist of a methyltransferase (MT) and a restriction endonuclease (RE) that, upon binding to the recognition sequence, methylate or cleave the DNA, respectively. Methylation leads to resistance of the DNA against the corresponding RE. During the acquisition of such a plasmid-based R-M system, the timely orchestrated expression of the MT- and RE-encoding genes is key to establish protection and to prevent modification of virus DNA that would render the system non-functional, leading to the production of resistant phage progenies that would threaten the survival of the whole bacterial population. While progress has been made in the study of the regulatory mechanism of R-M systems in vitro, little is known about the regulatory dynamics in vivo. The following proposal aims to increase our understanding about the regulation of R-M systems in vivo, their dynamics during their establishment in single cells, involved factors and the consequences for their protective function of bacterial cells and populations. Eventually, the gain in knowledge will help to progress our understanding of the interaction and co-evolution of bacteria and phages and the prospect of phage therapy for bacterial infections.