RNA penetrations into bacteria.

Project Summary Single-stranded RNA bacteriophages (ssRNA phages) are small near-icosahedral viruses that use RNA as genetic material to infect bacteria through retractile pili. Recently >15,000 new ssRNA phages have been identified but their hosts and mechanisms of infection remain unknown. Of the steps during the infection cycle of ssRNA phages, how phages package the genomic RNA and recognize its specific host are only known for model ssRNA coliphages such as MS2 and Qβ; and how RNA is ultimately delivered into the cytosol is obscure. From the preliminary data, the PIs find that the previous paradigm set for the infection mechanism of ssRNA phage based on model coliphages can no longer be applied to other ssRNA phages. Host receptors of ssRNA phages, the retractile pili, are usually involved in the virulence of pathogenic bacteria and the sharing of antibiotic-resistant plasmids. This project will focus on phages PP7 and AP205, which infect Pseudomonas aeruginosa and Acinetobacter spp., respectively, via the Type IV pili (T4P). The overall goal is to determine the mechanisms involved in PP7/AP205 packaging, and RNA penetration into the host, a process which involves both host recognition and RNA entry. Specific aims are to reveal the molecular mechanisms for (1) the packaging of PP7/AP205, (2) the interplay between PP7/AP205 and T4P before RNA entry, and (3) the detachment of T4P during RNA entry. This work will not only reveal insights into the infection mechanism of ssRNA phages but also provide guidelines to engineer ssRNA phages for the following purpose: ssRNA phages will be engineered as means to detach pili of pathogenic bacteria, as an alternative strategy for treating multidrug-resistant bacterial infections. Unlike traditional phage therapy by lysing pathogens, virulence and antibiotic resistance spread are inactivated by breaking pili while leaving the cells to grow, without exerting selective pressure on the host to develop further resistance. Such a method also avoids the release of any unwanted cell contents including DNA, proteins, and toxins into the environment which could interfere with other bacteria or affect human cells. In the future, the proposed project will also provide a basis for developing a method for packaging and delivery of a large number of foreign RNAs into bacterial cells. Due to the short life of RNAs inside the cell, they allow transient regulation of the cells and are less likely to exert long-term genetic effects as in the case of DNA plasmids. In addition, RNA delivery with ssRNA phages does not rely on the artificial preparation of cells competent for heat-shock or electroporation, which is hard to perform in situ.