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卫生保健机构日益严重的问题。因此，有必要促进研究对抗致病菌的新方法。噬菌体是一种细菌特异性的病毒，由于其对宿主的高特异性和高效的裂解细菌细胞而成为一种很有前途的工具。然而，细菌也可以获得对噬菌体的耐药性，而噬菌体可以克服细菌的耐药性。研究需要加深我们对噬菌体耐药性的共同进化过程和机制的理解。细菌用来对抗噬菌体感染的最广泛和可移动的机制之一是质粒编码限制性修饰（R-M）系统。这些系统识别特定的DNA序列，由甲基转移酶（MT）和限制性内切酶（RE）组成，它们与识别序列结合后，分别甲基化或切割DNA。甲基化导致DNA对相应的RE产生抗性。在获得这种基于质粒的R-M系统期间，及时协调MT和RE编码基因的表达是建立保护和防止病毒DNA修饰的关键，这种修饰会使系统失去功能，导致抗性噬菌体后代的产生，从而威胁整个细菌群体的生存。虽然对R-M系统的体外调控机制的研究取得了进展，但对其在体内的调控动力学知之甚少。以下建议旨在增加我们对R-M系统在体内的调节，其在单细胞中建立过程中的动态，涉及的因素及其对细菌细胞和群体的保护功能的后果的理解。最终，这些知识的获得将有助于我们进一步了解细菌和噬菌体的相互作用和共同进化，以及噬菌体治疗细菌感染的前景。

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.