Branched Lateral Tail Fiber Organization in T5-Like Bacteriophages DT57C and DT571/2 is Revealed by Genetic and Functional Analysis

Abstract

The T5-like siphoviruses DT57C and DT571/2, isolated from horse feces, are very closely related to each other, and most of their structural proteins are also nearly identical to T5 phage. Their LTFs (L-shaped tail fibers), however, are composed of two proteins, LtfA and LtfB, instead of the single Ltf of bacteriophage T5. In silico and mutant analysis suggests a possible branched structure of DT57C and DT571/2 LTFs, where the LtfB protein is connected to the phage tail via the LtfA protein and with both proteins carrying receptor recognition domains. Such adhesin arrangement has not been previously recognized in siphoviruses. The LtfA proteins of our phages are found to recognize different host O-antigen types: E. coli O22-like for DT57C phage and E. coli O87 for DT571/2. LtfB proteins are identical in both phages and recognize another host receptor, most probably lipopolysaccharide (LPS) of E. coli O81 type. In these two bacteriophages, LTF function is essential to penetrate the shield of the host’s O-antigens. We also demonstrate that LTF-mediated adsorption becomes superfluous when the non-specific cell protection by O-antigen is missing, allowing the phages to bind directly to their common secondary receptor, the outer membrane protein BtuB. The LTF independent adsorption was also demonstrated on an O22-like host mutant missing O-antigen O-acetylation, thus showing the biological value of this O-antigen modification for cell protection against phages.

Riding the wave of genomics to investigate aquatic coliphage diversity and activity

“…The gene encoding MAR003J3_00081 is an orthologue of ltfA in phage DT57C and DT571/2 which with l tfB encode for L‐shaped tail fibres that allow attachment to different O‐antigen types. This arrangement of two genes encoding the L‐shaped tail fibres is different from T5, which encodes the L‐shaped tail fibres in a single gene (Golomidova et al, ; Nobrega et al, ). vB_Eco_mar003J3 contains orthologues of both ltfA and ltfB , suggesting that it too uses two gene products for L‐shaped tail fibres, whereas vB_Eco_mar004NP2 only contains an orthologue of ltfB (MAR004NP2_00162) and does not contain an orthologue of the single gene used by T5 ( ltf ).…”

The Presence of Two Receptor-Binding Proteins Contributes to the Wide Host Range of Staphylococcal Twort-Like Phages

“…The E. coli lytic myovirus phi92 has at least five different tail spikes and tail fiber proteins identified by cryoelectron microscopy, allowing it to infect a wide range of E. coli and Salmonella strains (54). Two different RBPs, LtfA and LtfB of the T5-like siphoviruses DT57C and DT571/2, recognize different O antigens, i.e., the O22 or O87 type and the O81 type, respectively (55). Two different carbohydrate-binding modules have been identified in Lactococcus lactis phage Tuc2009; the first is in a classical bona fide RBP (BppL), and the other is in an accessory protein, BppA (56).…”

Function of bacteriophage G7C esterase tailspike in host cell adsorption

“…It has been recently shown that the presence of acetyl groups on the O-antigen protects E. coli 4s from infection of certain T5-like bacteriophages. These viruses (e.g., DT571/2 and fibreless mutants of phage DT57C) possess long non-contractile tails and recognize membrane proteins, but not LPS, on the cell surface (Golomidova et al, 2016). They cannot infect WT 4s but grow well on E. coli 4sI or 4sR that carry a non-acetylated O-antigen or no O-antigen at all (Golomidova et al, 2016).…”

“…These viruses (e.g., DT571/2 and fibreless mutants of phage DT57C) possess long non-contractile tails and recognize membrane proteins, but not LPS, on the cell surface (Golomidova et al, 2016). They cannot infect WT 4s but grow well on E. coli 4sI or 4sR that carry a non-acetylated O-antigen or no O-antigen at all (Golomidova et al, 2016). The mechanism of this effect is unclear, but one can speculate that the O-acetyl groups enhance the interaction between the neighboring O-antigen chains thus creating a less penetrable surface layer.…”