A novel tail fiber protein triggers phage DNA ejection by recognizing lipopolysaccharides of K54 hypervirulent <i>Klebsiella pneumoniae</i>

Phage infection begins with the adsorption of the phage particle to the bacterial cell surface, followed by the injection of the phage genome into the cell. In the encapsulated hypervirulent <i>K. pneumoniae</i> (hv<i>Kp</i>), the capsular polysaccharide (CPS) surrounding the bacterium was assumed to be the adsorption receptor of phage infection. Lipopolysaccharide (LPS) is a common phage receptor in many bacteria. Whether and how CPS and LPS act as receptors simultaneously to initiate the phage infection in hv<i>Kp</i> remains unknown. Here, we demonstrated that bacterial CPS and LPS are both critical determinants for phage infection in hv<i>Kp</i> strain SCNJ1, and mutations in either component confer complete resistance. We revealed that CPS is the primary receptor for phage adsorption, whereas LPS is the secondary receptor for phage injection. Furthermore, we identified a novel tail fiber protein TFP_Y that recognizes host LPS to start phage genome DNA release.