RB49-like Bacteriophages Recognize O Antigens as One of the Alternative Primary Receptors

Abstract

The power of most of the enterobacterial O antigen types to provide robust protection against direct recognition of the cell surface by bacteriophage receptor-recognition proteins (RBP) has been recently recognized. The bacteriophages infecting O antigen producing strains of E. coli employ various strategies to tackle this nonspecific protection. T-even related phages, including RB49-like viruses, often have wide host ranges, being considered good candidates for use in phage therapy. However, the mechanisms by which these phages overcome the O antigen barrier remain unknown. We demonstrate here that RB49 and related phages Cognac49 and Whisky49 directly use certain types of O antigen as their primary receptors recognized by the virus long tail fibers (LTF) RBP gp38, so the O antigen becomes an attractant instead of an obstacle. Simultaneously to recognize multiple O antigen types, LTFs of each of these phages can bind to additional receptors, such as OmpA protein, enabling them to infect some rough strains of E. coli. We speculate that the mechanical force of the deployment of the short tail fibers (STF) triggered by the LTF binding to the O antigen or underneath of it, allows the receptor binding domains of STF to break through the O polysaccharide layer.

Bacterial Virus Forcing of Bacterial O-Antigen Shields: Lessons from Coliphages

“…We also observed a similar effect with an RB49-like phage Whisky49 that selected wzzB-deficient mutants (our unpublished observations) on one of several E. coli strains resulting in an OPS pattern similar to that observed in Salmonella [53]. It is worth noting that Whisky49 phage is also able to recognize the OPS as a primary receptor on some of the host strains it infects ( [51]; also see below)…”

“…Some RB49-like phages have recently been shown to recognize certain types of OPS as a primary receptor. These phages can even behave on some host strains such as E. coli F17 as strategy II viruses, although they are equally capable of infecting rough derivatives of other strains [51]. These findings indirectly indicate that RB49-like viruses activate their baseplate rearrangement before any RBP contact with the immediate OM surface.…”

“…These viruses may also select for two distinct phenotypes of resistant mutants. Finally, some phages may use OPS as one of several alternative primary receptors on a particular host strain [51], so they may also select for rough-resistant clones without being strategy II viruses.…”

“…These findings indirectly indicate that RB49-like viruses activate their baseplate rearrangement before any RBP contact with the immediate OM surface. Interestingly, phage Brandy49, exhibiting the broadest host range within the investigated series of RB49-like viruses, uses some different, as yet unidentified mechanism that apparently allows its LTFs to penetrate different types of OPS to contact some receptor at the OM surface [51]. Regardless of the nature of the receptor recognized by T-even-related phages at the surface of the O-antigen-producing host, the mechanical force of their STF deployment appears to be the mechanism enabling their RBPs to penetrate the OPS barrier for tight phage attachment (Figure 4C).…”

Multireceptor phage cocktail against Salmonella enterica to circumvent phage resistance

“…AKMssTn_001–2 and AKMssTn_115 encode tail spike and tail fibre proteins in phage ssTn LPS , respectively. Both structures have been described as receptor-binding proteins recognizing the LPS of Gram-negative bacteria in myoviruses (Walter et al 2008 , Efimov et al 2022 ). Moreover, AKMssTn_072 gene product was identified as a tail-associated lysozyme in phage ssTn LPS .…”