Identification of amino acid residue in the LamB responsible for the receptor compatibility of polyvalent coliphage CSP1.

Unlabelled: Polyvalent bacteriophages show the feature of infecting bacteria across multiple species or even orders. Infectivity of a polyvalent phage is variable depending on the host bacteria, which can disclose differential inhibition of bacteria by the phage. In this study, a polyvalent phage CSP1 infecting both ATCC 29544 and MG1655 was isolated. CSP1 showed higher growth inhibition and adsorption rate in compared to , and identification of host receptors revealed that CSP1 uses LamB (LamB) as a receptor but that CSP1 requires both LamB (LamB) and lipopolysaccharide (LPS) core for infection. The substitution of LamB with LamB in enhanced CSP1 susceptibility and made LPS core no more essential for CSP1 infection. Comparative analysis of LamB and LamB disclosed that the extra proline at amino acid residue 284 in LamB made a structural distinction by forming a longer loop and that the deletion of 284P in LamB aligns its structure and makes LamB function like LamB, enhancing CSP1 adsorption and growth inhibition of . These results suggest that 284P of LamB plays a critical role in determining the CSP1-host bacteria interaction. These findings could provide insight into the elucidation of molecular determinants in the interaction between polyvalent phages and host bacteria and help us to understand the phage infectivity for efficient phage application.

Importance: Polyvalent phages have the advantage of a broader host range, overcoming the limitation of the narrow host range of phages. However, the limited molecular biological understanding on the host bacteria-polyvalent phage interaction hinders its effective application. Here, we revealed that the ability of the polyvalent phage CSP1 to infect ATCC 29544 is disturbed by a single proline residue in the LamB protein and that lipopolysaccharide is used as an auxiliary receptor for CSP1 to support the adsorption and the subsequent infection of . These results can contribute to a better understanding of the interaction between polyvalent phages and host bacteria for efficient phage application.