Novel Host Recognition Mechanism of the K1 Capsule-Specific Phage of Escherichia coli : Capsular Polysaccharide as the First Receptor and Lipopolysaccharide as the Secondary Receptor

Abstract

K1 capsule-specific phages of Escherichia coli have been reported in recent years, but the molecular mechanism involved in host recognition of these phages remains unknown. In this study, the interactions between PNJ1809-36, a new K1-specific phage and its host bacteria E. coli DE058, were investigated. A transposon mutation library was used to screen for receptor-related genes. Gene deletion, lysis curve determination, plaque formation test, adsorption assay and inhibition assay of phage by lipopolysaccharide (LPS) showed that capsular polysaccharide (CPS) was the first receptor for the initial adsorption of PNJ1809-36 to E. coli DE058 and LPS was a secondary receptor for the irreversible binding of the phage. The penultimate galactose in the outer core was identified as the specific binding region on LPS. Through antibody blocking assay, fluorescence labeling and high-performance gel permeation chromatography (HPGPC), the tail protein ORF261 of phage PNJ1809-36 was identified as the receptor binding protein on CPS. Given these findings, we propose a model for the recognition process of phage PNJ1809-36 on E. coli DE058: The phage PNJ1809-36 tail protein ORF261 recognizes and adsorbs to the K1 capsule; then the K1 capsule is partially degraded, exposing the active site of LPS which is recognized by phage PNJ1809-36. This model provides insight into the molecular mechanisms between K1-specific phages and their host bacteria. IMPORTANCE It has been speculated that CPS is the main receptor of K1-specific phages belonging to Siphoviridae . In recent years, a new type of K1-specific phage belonging to Myoviridae has been reported, but its host recognition mechanisms remain unknown. Here, we studied the interactions between PNJ1809-36, a new type of K1 phage, and its host bacteria E. coli DE058. Our research showed that the phage initially adsorbed to the K1 capsule mediated by ORF261 and then bound to the penultimate galactose of LPS to begin the infection process.

Characterization and Comparative Genomics Analysis of a New Bacteriophage BUCT610 against Klebsiella pneumoniae and Efficacy Assessment in Galleria mellonella Larvae

“…The phage BUCT610 is not a temperate phage, its genome cannot integrate into the K1119 genome, although it can only lyse K. pneumoniae K1119. According to reports related to the recognition mechanism of phages and hosts, the lipopolysaccharides (LPS) and capsular polysaccharide (CPS) of bacteria play an important role in phage adsorption, which is an important factor in determining the host range of phages [ 30 , 31 ]. Therefore, we speculate that the specific capsule type of K1119 is one of the main reasons for the phage BUCT610 to specifically lyse K. pneumoniae K1119.…”

Genome-wide phage susceptibility analysis inAcinetobacter baumanniireveals capsule modulation strategies that determine phage infectivity

“…Fully-glycosylated LOS may thus act as a steric barrier decreasing phage binding efficiency. This barrier may impede interactions with membrane-proximal parts of the capsule, or, alternatively, with internal LOS sugars providing a putative secondary receptor, as seen with other phage-bacteria pairs [73]. Mutation of lpxA , which completely prevents LOS production, was reported to also block Loki adsorption [40].…”

RpoE Facilitates Stress-Resistance, Invasion, and Pathogenicity of Escherichia coli K1

“…Capsular staining [ 38 ] was performed using a capsular staining kit (Solarbio, Beijing, China). Staining was performed according to the manufacturer’s instructions.…”