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

Abstract

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 Cronobacter sakazakii ATCC 29544 and Escherichia coli MG1655 was isolated. CSP1 showed higher growth inhibition and adsorption rate in E. coli compared to C. sakazakii, and identification of host receptors revealed that CSP1 uses E. coli LamB (LamB_E) as a receptor but that CSP1 requires both C. sakazakii LamB (LamB_C) and lipopolysaccharide (LPS) core for C. sakazakii infection. The substitution of LamB_C with LamB_E in C. sakazakii enhanced CSP1 susceptibility and made C. sakazakii LPS core no more essential for CSP1 infection. Comparative analysis of LamB_C and LamB_E disclosed that the extra proline at amino acid residue 284 in LamB_C made a structural distinction by forming a longer loop and that the deletion of 284P in LamB_C aligns its structure and makes LamB_C function like LamB_E, enhancing CSP1 adsorption and growth inhibition of C. sakazakii. These results suggest that 284P of LamB_C 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 Cronobacter sakazakii 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 C. sakazakii. These results can contribute to a better understanding of the interaction between polyvalent phages and host bacteria for efficient phage application.