The genus Klebsiella is a significant contributor to bacterial infections in humans and is known to have a diverse environmental presence, encompassing many species and serotypes. Antimicrobial resistance (AMR) is of growing concern, with AMR strains from livestock and hospital settings spilling over into environmental reservoirs1. Bacteriophages hold potential for controlling Klebsiella strains, both in clinical infections and environmental reservoirs. These viruses are found in the same niches as their bacterial prey, including waterway environments where they are commonly sourced2.
The Klebsiella capsule polysaccharide acts as a barrier to entry for most phage, requiring the hydrolase or lyase function of an enzyme to recognise and degrade the capsule. In the phage field, these enzymes are commonly called depolymerases and have been found to be highly specific to a capsule type though only few have as yet been structurally characterized.
In collaboration with the Bunurong Traditional Owners, we aimed to study Klebsiella and Klebsiella bacteriophages in waterways across the Melbourne Catchment region. We sampled a waterway associated with a migratory grey-headed flying fox colony, characterising a Klebsiella pneumoniae strain associated with strains isolated from bat guano, ST49194. This strain possesses a K61 capsule type, not typically associated with clinical isolates of Klebsiella. Phage Ptero was isolated against this strain and found to share a lineage with another local bacteriophage called Merri-merri-uth nyilam marra-natj5.
Bacteriophage Ptero has a depolymerase protein specific to K61 polysaccharide and is the first depolymerase found to be reliant on the presence of cations for enzymatic function. Using a combination of electron microscopy, mass spectrometry, Alphafold3 and FoldSeek we have identified in the virions a baseplate protein with a putative transglycosylase domain. This domain is not present in previously solved baseplate structures and was determined to be highly conserved across the Jameshumphriesvirinae subfamily. Further work will evaluate this domain’s enzymatic function and its role in this distinctive bacteriophage–host environment.