Reclassification of the first Bacillus tropicus phage calls for reclassification of other Bacillus temperate phages previously designated as plasmids

Abstract

Bacillus tropicus is a recently identified subspecies of the Bacillus cereus group of bacteria that have been shown to possess genes associated with antimicrobial resistance (AMR) and identified as the causative agent for anthrax-like disease in Chinese soft-shelled turtles. In addition, B. tropicus has demonstrated great potential in the fields of bioremediation and bioconversion. This article describes the comparative genomics of a Bacillus phage vB_Btc-RBClinn15 (referred to as RBClin15) infecting the recently identified B. tropicus AOA-CPS1. RBClin15 is a temperate phage with a putative parABS partitioning system as well as an arbitrium system, which are presumed to enable extrachromosomal genome maintenance and regulate the lysis/lysogeny switch, respectively. The temperate phage RBClin15 has been sequenced however, was erroneously deposited as a plasmid in the NCBI GenBank database. A BLASTn search against the GenBank database using the whole genome sequence of RBClin15 revealed seven other putative temperate phages that were also deposited as plasmids in the database. Comparative genomic analyses shows that RBClin15 shares between 87 and 92% average nucleotide identity (ANI) with the seven temperate phages from the GenBank database. All together RBClin15 and the seven putative temperate phages share common genome arrangements and < 29% protein homologs with the closest phages, including 0105phi7-2. A phylogenomic tree and proteome-based phylogenetic tree analysis showed that RBClin15 and the seven temperate phages formed a separate branch from the closest phage, 0105phi7-2. In addition, the intergenomic similarity between RBClin15 and its closely related phages ranged between 0.3 and 47.7%. Collectively, based on the phylogenetic, and comparative genomic analyses, we propose three new species which will include RBClin15 and the seven temperate phages in the newly proposed genus Theosmithvirus under Caudoviricetes.