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.
Highlights
Bacteriophages are the most abundant entities in the biosphere, and play a pivotal role in contributing to the diversity of many microbial ecosystems through regular interaction with their bacterial hosts (Weitz et al, 2013)
Initial lytic spectrum assessments established that both phages M188 and MC293 shared a strict specificity for L. monocytogenes strains of the 4b and 4e serotypes
Phage MC293 was experimentally determined to be incapable of establishing an infection in any of these three host strains, suggesting that similar secondary bacterial host resistance mechanisms may have been present in these insensitive host strains
Summary
Bacteriophages are the most abundant entities in the biosphere, and play a pivotal role in contributing to the diversity of many microbial ecosystems through regular interaction with their bacterial hosts (Weitz et al, 2013) These phage-host interactions are primarily dependent upon the recognition of a bacterial cell wall constituent by a highly specific sequence on the phage surface known as the receptor binding protein. As a member of the Myoviridae, T4 has a large contractile tail, terminating in a baseplate to which six long tail fibers are attached (Bartual et al, 2010) These fibers (encoded by genes gp34-37) are required for initial recognition and reversible binding of the host’s cell-surface lipopolysaccharides (LPS), which is followed by signal transduction and extension of six shorter tail fibers from the baseplate that bind to the LPS irreversibly (Fokine and Rossmann, 2014). The RBP of the L. lactis phage p2 (encoded by ORF18) has a different structural arrangement consisting of a three-subunit homo-trimer located on the distal end of the tail tube (Spinelli et al, 2006b; Tremblay et al, 2006), and is orthologous to the RBP in phages of other bacteria, including the tail spike protein gp of the B. subtilis phage SPP1 (Vinga et al, 2012), and the gp protein of the Gram-negative E. coli phage T4 (Spinelli et al, 2006b)
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