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

Abstract

The Bacillus phage SP{beta} has been known for about 50 years, but only a few strains are avalible. 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 SP{beta}-like phages. We could also reveal the SP{beta}-like phage genome replication strategy, the genome packaging mode, and the phage genome opening point. We extracted 55 SP{beta}-like prophages from public Bacillus genomes, thereby discovering three more integration loci and one additional type of integrase. The identified prophages resembled four new species clusters and three species orphans in the genus Spbetavirus. The determined core proteome of all SP{beta}-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 SP{beta} 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.