Engineering phage host range promiscuity

Bacteriophages, viruses that infect bacteria, are the most abundant biological entities on earth and one of the most potent evolution-driving forces in nature due to their capacity to facilitate horizontal gene transfer. Tailed bacteriophages have been studied intensively, and they rely on tail spikes or tail fibres to recognise their cognate host receptors when adsorbing to bacteria. This adsorption step is crucial for the infection process; correspondingly, it is also a key factor dictating host range specificity. Viunalikeviruses are lytic-tailed phages with dsDNA genomes of ~150 kbp that exhibit extensive sequence homologies within the family and generalised transduction capacity. The Viunalikeviruses are virulent phages, and representative examples have been isolated on Gram-negative bacteria, including animal and plant pathogens such as Salmonella, Escherichia, Klebsiella, Shigella and Dickeya. Although there has been limited analysis of Viunalikevirus receptors, the primary receptor of the defining example of this viral group (the Vi01 phage) in Salmonella Typhi has been identified as the Vi capsular polysaccharide (CPS). This study aimed to develop a promiscuous phage receptor expression system allowing infection in a broad range of heterologous hosts. The S. Typhi Vi CPS biosynthetic operon was cloned into a broad host range cosmid and horizontally transferred into a diverse group of Gram-negative species. The expression of the Vi CPS was correlated with the infection of ΦVi01 on all the evaluated species. One of the highlights of this study is the artificial host range extension of ΦVi01 into 19 different species belonging to three different taxonomic Orders. Additionally, the effect of different bacterial defence mechanisms on ΦVi01 virulence was studied. ΦVi01-mediated transduction was observed in most of the analysed hosts, allowing horizontal gene transfer between distantly related hosts. Also, strains expressing the Vi CPS were used to isolate environmental phages recognising this phage receptor in different heterologous hosts. Two new Vi CPS-dependent phages, ΦTKR01 and ΦTKR02, were identified and characterised. This study results are the first description of a synthetic heterologous promiscuous system for phage host range extension. This simple system could have potential applications for genetically engineering non-canonical bacterial species. Additionally, the heterologous expression of this phage receptor serves as a tool for isolating environmental phages capable of recognising this structure.