A family of minimalist bacteriophages, typified by phage Ptero, have evolved to infect diverse bacteria with distinct surface features

The global crisis of antimicrobial resistance (AMR) is driven by the spread of drug-resistant bacteria through human communities, and many species of bacteria are transmitted to people via the environments in which they live. Assessment of bacteria in these environments, ranging from farms and gardens to waterways, maps their spread and provides the possibility of identifying natural predators in the form of bacteriophages (phages). Environmental assessment of a wetland home to a camp of grey-headed flying foxes ( Pteropus poliocephalus ) yielded a local isolate of the bacterium Klebsiella pneumoniae of sequence type ST4919 and its phage predator, Ptero. Structural analysis of the phage virions, biochemical analysis of purified phage proteins and comparative genomics showed Ptero to belong to a set of closely related “minimalist” phages. The minimized architecture of these contractile phages provided a means to understanding the core elements of the phage baseplate, including two virion-associated enzymes carried by each phage to kill specific Klebsiella hosts. We suggest that the simplicity of the 13 related phages characterized here could provide new insight into the mechanisms by which these phages recognize their specific host, dissolve the host cell wall, and penetrate the cytoplasmic membrane of host strains emerging from natural environments.