Grant: Project Grant

The use of lytic viruses called bacteriophages (or simply phages) to kill multidrug resistant bacteria such as the human pathogen Clostridioides difficile (Cdif) represents an exciting alternative to antibiotics. The manipulation of the microbiome with genetically engineered phages to restore health is also very attracting. However, despite 100 years of phage research, important gaps still exist in our understanding of the molecular steps leading to a successful viral infection. Filling these gaps is essential for the future development and approval of phage-based biotherapeutics. The most critical step of a phage infection cycle is recognition of a bacterial receptor. This lock-and-key interaction is highly specific, the lock being a bacterial surface component and the key being a phage protein. We recently identified SlpA, the main protein composing the outer layer of Cdif cells, as an important phage receptor. Using bioinformatics and cryo-electronic microscopy (cryo-EM) reconstruction of whole phage particles, we also identified phage proteins involved in SlpA recognition. Most importantly, we successfully engineered a phage tail to make it bind to and infect a different host in a SlpA-dependent manner. Finally, diverse bacterial factors and antiphage systems can interfere with phage infection, but these are often overlooked in phage therapy protocols. Our goal is to describe with an unprecedent level of detail phage-host interactions in Cdif, with emphasis on the molecular interactions between phage tail proteins and SlpA, as well as the impact of host defenses on infection. To achieve this goal, we will use bacterial and phage genomics, microscopy, genetic engineering, phage functional assays, and a mouse model of Cdif infection. These exciting results will deepen our global understanding of phage-host interactions and, ultimately, will pave the way to the rational design of therapeutic phages to fight Cdif infections.