Epigenetic biosensors for bacteriophage detection and phage receptor discrimination

Environmental monitoring of bacteria using phage‐based biosensors has been widely developed for many different species. However, there are only a few available methods to detect specific bacteriophages in raw environmental samples. In this work, we developed a simple and efficient assay to rapidly monitor the phage content of a given sample. The assay is based on the bistable expression of the Salmonella enterica opvAB operon. Under regular growth conditions, opvAB is only expressed by a small fraction of the bacterial subpopulation. In the OpvAB(ON) subpopulation, synthesis of the OpvA and OpvB products shortens the O‐antigen and confers resistance to phages that use LPS as a receptor. As a consequence, the OpvAB(ON) subpopulation is selected in the presence of such phages. Using an opvAB::gfp fusion, we could monitor LPS‐binding phages in various media, including raw water samples. To enlarge our phage‐biosensor panoply, we also developed biosensors able to detect LPS, as well as protein‐binding coliphages. Moreover, the combination of these tools allowed to identify the bacterial receptor triggering phage infection. The epigenetic opvAB::gfp biosensor thus comes in different flavours to detect a wide range of bacteriophages and identify the type of receptor they recognize.