Abstract
Bacteriophages represent a valuable source for studying the mechanisms underlying virus-host interactions. A better understanding of the host-specificity of viruses at the molecular level can promote various phage applications, including bacterial diagnostics, antimicrobial therapeutics, and improve methods in molecular biology. In this study, we describe the isolation and characterization of a novel coliphage, vB_EcoM_VpaE1, which has different host specificity than its relatives. Morphology studies, coupled with the results of genomic and proteomic analyses, indicate that vB_EcoM_VpaE1 belongs to the newly proposed genus Felix01likevirus in the family Myoviridae. The genus Felix01likevirus comprises a group of highly similar phages that infect O-antigen-expressing Salmonella and Escherichia coli (E. coli) strains. Phage vB_EcoM_VpaE1 differs from the rest of Felix01-like viruses, since it infects O-antigen-deficient E. coli strains with an incomplete core lipopolysaccharide (LPS). We show that vB_EcoM_VpaE1 can infect mutants of E. coli that contain various truncations in their LPS, and can even recognize LPS that is truncated down to the inner-core oligosaccharide, showing potential for the control of rough E. coli strains, which usually emerge as resistant mutants upon infection by O-Ag-specific phages. Furthermore, VpaE1 can replicate in a wide temperature range from 9 to 49 °C, suggesting that this virus is well adapted to harsh environmental conditions. Since the structural proteins of such phages tend to be rather robust, the receptor-recognizing proteins of VpaE1 are an attractive tool for application in glycan analysis, bacterial diagnostics and antimicrobial therapeutics.
Highlights
Attachment to cell surface receptors is the first step in phage infection
Natural Escherichia and Salmonella isolates usually contain LPS that consists of: (i) the lipid A, a hydrophobic moiety of the molecule that anchors LPS to the outer membrane (OM); (ii) a phosphorylated, nonrepetitive hetero-oligosaccharide known as the core oligosaccharide; and (iii) the O-antigen side chain polysaccharide (O-PS or O-Ag) that is a polymer of defined repeat units attached to the core OS, and is usually used for serotyping [4]
As the response to a strong selective pressure imposed by a phage infection, bacteria may evade phage attachment by altering the structure of this complex glycolipid through mutations in genes involved in LPS biosynthesis [7,8,9]
Summary
Attachment to cell surface receptors is the first step in phage infection. Phages of Gram-negative bacteria use a variety of cell-associated structures including pili, flagella, outer membrane proteins (Omp) or lipopolysaccharides (LPS) for host cell recognition [1,2,3]. Phage-resistant bacterial strains expressing truncated core LPS can emerge. Costly in terms of reduced growth rate, such a strategy is often employed by bacteria in response to viral attack during phage treatment In this regard, while the use of incomplete LPS-specific phages as auxiliary components of phage cocktails has proved beneficial in biocontrol of pathogenic bacteria [15,16,17], it is surprising that only a very limited number of reports on the isolation and characterization of such viruses have been published far. Bacteriophage VpaE1 described in this study differs from other characterized Felix01-like viruses by its specificity towards deep rough strains of E. coli. To combat the emergence of smooth/rough LPS-specific phage-resistant pathogenic E. coli strains, VpaE1 may be used in phage cocktails
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