Complete genome sequences of bacteriophages Sole and Sato expand the view of the genetic diversity found in the family Tectiviridae

Gillis, Annika [UCL] Hock, Louise [UCL] Mahillon, Jacques [UCL]

Bacteriophages are an important repository of genetic diversity and source of unexplored genes. In the particular case of tectiviruses infecting the Bacillus cereus group, these bacteriophages represent part of the bacterial mobilome and they are, so far, the only ones able to behave as linear plasmids during their lysogenic cycle. Recently, several novel tectiviruses have been found infecting diverse strains belonging to this bacterial lineage (Jalasvuori et al., 2013; Gillis and Mahillon 2014). Among them, partial DNA sequencing of tectiviruses Sole and Sato, isolated from B. cereus sensu lato and emetic B. cereus strains, respectively, uncovered a highly variable region potentially involved in lysogeny maintenance (Jalasvuori et al., 2013). Here, we analyze the complete genome sequences of bacteriophages Sole and Sato. The genome of Sole spans 14,445 bp with 28 putative CDSs, whereas the one of Sato has 14,852 bp comprising 31 putative CDSs. DNA sequence identity comparisons of Sato and Sole against Bacillus virus Bam35 (reference tectivirus) indicated 86 and 89% sequence identity, respectively. Additionally, phylogenetic analyses and genome alignments suggested that both isolates represent novel tectivirus species. Hence, tectiviruses in Gram-positive bacteria have shown to be more diverse than those infecting Gram-negative bacteria, as the latter ones display a very high level of sequence identity. In an effort to assess the host range of Sole and Sato against emetic B. cereus and Bacillus cytotoxicus, two species involved in food poisoning outbreaks, 50 strains of each species devoid of tectiviral-like elements were tested. The results showed that Sole and Sato have a narrow host range, only infecting particular strains. Overall, genome sequencing and comparative analysis of tectiviruses Sole and Sato have expanded the view of the genomic diversity occurring in plasmidial prophages found in members of the B. cereus group.