The Bacillus phage SPß and its relatives: a temperate phage model system reveals new strains, species, prophage integration loci, conserved proteins and lysogeny management components.

The Bacillus phage SPß has been known for about 50 years, but only a few strains are available. We isolated four new wild-type strains of the SPbeta species. Phage vB_BsuS-Goe14 introduces its prophage into the spoVK locus, previously not observed to be used by SPß-like phages. Sequence data revealed the genome replication strategy and the genome packaging mode of SPß-like phages. We extracted 55 SPß-like prophages from public Bacillus genomes, thereby discovering three more integration loci and one additional type of integrase. The identified prophages resemble four new species clusters and three species orphans in the genus Spbetavirus. The determined core proteome of all SPß-like prophages consists of 38 proteins. The integration cassette proved to be not conserved, even though, present in all strains. It consists of distinct integrases. Analysis of SPß transcriptomes revealed three conserved genes, yopQ, yopR, and yokI, to be transcribed from a dormant prophage. While yopQ and yokI could be deleted from the prophage without activating the prophage, damaging of yopR led to a clear-plaque phenotype. Under the applied laboratory conditions, the yokI mutant showed an elevated virion release implying the YokI protein being a component of the arbitrium system.

Complete genome sequence of the virus isolate vB_BthM-Goe5 infecting Bacillus thuringiensis.

Bacillus thuringiensis (Bt) is non-pathogenic for humans and serves as a biological control agent in agriculture. Understanding its phages will help to prevent industrial production loss of Bt products and will lead to a better understanding of phages in general. The complete genome of the new B. thuringiensis phage isolate vB_BthM-Goe5 (Goe5) was sequenced, revealing a linear 157,804-bp-long dsDNA chromosome flanked by 2579-bp-long terminal repeats. It contains two tRNAs and 272 protein coding regions, 69 of which could be assigned with an annotation. Morphological investigation, using transmission electron microscopy, revealed Myoviridae morphology. The formation of a double baseplate upon tail sheath contraction indicates a link to the group of SPO1-related phages. Comparative genomics with all Bacillus-related viral genomes available in the NCBI genome database during this investigation indicated that Goe5 was a unique isolate, with Bacillus phage Bastille as its closest relative.