A tail of two phages: genomic and functional analysis of Listeria monocytogenes phages vB_LmoS_188 and vB_LmoS_293 reveal the receptor-binding proteins involved in host specificity

Abstract

The physical characteristics of bacteriophages establish them as viable candidates for downstream development of pathogen detection assays and biocontrol measures. To utilize phages for such purposes, a detailed knowledge of their host interaction mechanisms is a prerequisite. There is currently a wealth of knowledge available concerning Gram-negative phage-host interaction, but little by comparison for Gram-positive phages and Listeria phages in particular. In this research, the lytic spectrum of two recently isolated Listeria monocytogenes phages (vB_LmoS_188 and vB_LmoS_293) was determined, and the genomic basis for their observed serotype 4b/4e host-specificity was investigated using comparative genomics. The late tail genes of these phages were identified to be highly conserved when compared to other serovar 4-specific Listeria phages. Spontaneous mutants of each of these phages with broadened host specificities were generated. Their late tail gene sequences were compared with their wild-type counterparts resulting in the putative identification of the products of ORF 19 of vB_LmoS_188 and ORF 20 of vB_LmoS_293 as the receptor binding proteins of these phages. The research findings also indicate that conserved baseplate architectures and host interaction mechanisms exist for Listeria siphoviruses with differing host-specificities, and further contribute to the current knowledge of phage-host interactions with regard to Listeria phages.

Genomic Diversity of Common Sequence Types of Listeria monocytogenes Isolated from Ready-to-Eat Products of Animal Origin in South Africa

“…Listeria phages as previously reported in other studies [42,[49][50][51]. The identified phages in the present study are commonly found in Listeria strains globally and have been associated with the survival evolution and persistence of L. monocytogenes in food-processing facilities [42,52].…”

Molecular Basis of Bacterial Host Interactions by Gram-Positive Targeting Bacteriophages

“…SV 4b/4e specific phages M188 and MC293 are members of the same cluster of temperate phages as A118, A500, and A006, with high conservation of their tail morphogenesis sub-module [ 103 ] ( Figure 2 ). As SV 4b/e specific phages, their RBPs are proposed to require terminal GlcNAc at position C4 of the RhoP backbone for attachment ( Figure 5 ).…”

“…As SV 4b/e specific phages, their RBPs are proposed to require terminal GlcNAc at position C4 of the RhoP backbone for attachment ( Figure 5 ). Continued exposure of both phages to an insensitive SV 4c L. monocytogenes strain generated spontaneous mutants, 188_Mut and 293_Mut, with expanded host ranges including SV 4a and 4c strains as well as SV 4b/e strains [ 103 ]. Sequence analysis of their baseplate encoding genes revealed extensive mutation within gp19 of phage 118_Mut and gp20 of 293_Mut.…”

“…Sequence analysis of their baseplate encoding genes revealed extensive mutation within gp19 of phage 118_Mut and gp20 of 293_Mut. For instance, the latter retained only 82% nucleotide sequence identity (49/238 residues mutated) to parental MC293 gp20 [ 103 ]. Based on HHpred analysis and relative position within the tail morphogenesis sub-module, M188 gp19 and MC293 gp20 were identified as RBPs with structural homology to the RBP (gp49) of TP901-1 [ 103 ].…”

Diversity, specificity and molecular evolution of the lytic arsenal of Pseudomonas phages: in silico perspective

“…Traditional phage therapy is known as being host-specific, property that is determined by the tropism exhibited by the virion structural proteins to bacterial receptors (pilus, flagella, capsule compounds, membrane proteins, etc.) at adsorption step (Casey et al, 2015;Harvey et al, 2018). This property was also believed to be retained at some degree by the endolysins of phages infecting Gram-positive bacteria (Schmelcher et al, 2012) however, to the best of author's knowledge, there are no systematic in silico studies or experimental testing of hostspecificity at intra-genus level.…”