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Isolation of A Novel Bacillus thuringiensis Phage Representing A New Phage Lineage and Characterization of Its Endolysin.

ABSTRACT: Phages, the parasites of bacteria, are considered as a new kind of antimicrobial agent due to their ability to lyse pathogenic bacteria. Due to the increase of available phage isolates, the newly isolated phage showed increasing genomic similarities with previously isolated phages. In this study, the novel phage vB_BthS_BMBphi, infecting the Bacillus thuringiensis strain BMB171, is isolated and characterized together with its endolysin. This phage is the first tadpole-like phage infecting the Bacillus strains. Genomic analysis shows that the phage genome is dissimilar to all those of previously characterized phages, only exhibiting low similarities with partial regions of the B. thuringiensis prophages. Phylogenetic analysis revealed that the phage was distant from the other Bacillus phages in terms of evolution. The novel genome sequence, the distant evolutionary relationship, and the special virion morphology together suggest that the phage vB_BthS_BMBphi could be classified as a new phage lineage. The genome of the phage is found to contain a restriction modification system, which might endow the phage with immunity to the restriction modification system of the host bacterium. The function of the endolysin PlyBMB encoded by the phage vB_BthS_BMBphi was analyzed, and the endolysin could lyse all the tested Bacillus cereus group strains, suggesting that the endolysin might be used in controlling pathogenic B. cereus group strains. The findings of this study enrich the understanding of phage diversity and provide a resource for controlling the B. cereus group pathogenic bacteria.

SUBMITTER: Yuan Y

PROVIDER: S-EPMC6266608 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundThe recently sequenced 218 kb genome of morphologically atypical Bacillus thuringiensis phage 0305phi8-36 exhibited only limited detectable homology to known bacteriophages. The only known relative of this phage is a string of phage-like genes called BtI1 in the chromosome of B. thuringiensis israelensis. The high degree of divergence and novelty of phage genomes pose challenges in how to describe the phage from its genomic sequences.ResultsPhage 0305phi8-36 and BtI1 are estimated to have diverged 2.0 - 2.5 billion years ago. Positionally biased Blast searches aligned 30 homologous structure or morphogenesis genes between 0305phi8-36 and BtI1 that have maintained the same gene order. Functional clustering of the genes helped identify additional gene functions. A conserved long tape measure gene indicates that a long tail is an evolutionarily stable property of this phage lineage. An unusual form of the tail chaperonin system split to two genes was characterized, as was a hyperplastic homologue of the T4gp27 hub gene. Within this region some segments were best described as encoding a conservative array of structure domains fused with a variable component of exchangeable domains. Other segments were best described as multigene units engaged in modular horizontal exchange. The non-structure genes of 0305phi8-36 appear to include the remnants of two replicative systems leading to the hypothesis that the genome plan was created by fusion of two ancestral viruses. The case for a member of the RNAi RNA-directed RNA polymerase family residing in 0305phi8-36 was strengthened by extending the hidden Markov model of this family. Finally, it was noted that prospective transcriptional promoters were distributed in a gradient of small to large transcripts starting from a fixed end of the genome.ConclusionGenomic organization at a level higher than individual gene sequence comparison can be analyzed to aid in understanding large phage genomes. Methods of analysis include 1) applying a time scale, 2) augmenting blast scores with positional information, 3) categorizing genomic rearrangements into one of several processes with characteristic rates and outcomes, and 4) correlating apparent transcript sizes with genomic position, gene content, and promoter motifs.

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Isolation of A Novel Bacillus thuringiensis Phage Representing A New Phage Lineage and Characterization of Its Endolysin.

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