Characterization of Parageobacillus Bacteriophage vB_PtoS_NIIg3.2-A Representative of a New Genus within Thermophilic Siphoviruses.

A high temperature-adapted bacteriophage, vB_PtoS_NIIg3.2 (NIIg3.2), was isolated in Lithuania from compost heaps using Parageobacillus toebii strain NIIg-3 as a host for phage propagation. Furthermore, NIIg3.2 was active against four strains of Geobacillus thermodenitrificans, and it infected the host cells from 50 to 80 °C. Transmission electron microscopy analysis revealed siphovirus morphology characterized by an isometric head (~59 nm in diameter) and a noncontractile tail (~226 nm in length). The double-stranded DNA genome of NIIg3.2 (38,970 bp) contained 71 probable protein-encoding genes and no genes for tRNA. In total, 29 NIIg3.2 ORFs were given a putative functional annotation, including those coding for the proteins responsible for DNA packaging, virion structure/morphogenesis, phage-host interactions, lysis/lysogeny, replication/regulation, and nucleotide metabolism. Based on comparative phylogenetic and bioinformatic analysis, NIIg3.2 cannot be assigned to any genus currently recognized by ICTV and potentially represents a new one within siphoviruses. The results of this study not only extend our knowledge about poorly explored thermophilic bacteriophages but also provide new insights for further investigation and understanding the evolution of Bacilllus-group bacteria-infecting viruses.

Geobacillus Bacteriophages from Compost Heaps: Representatives of Three New Genera within Thermophilic Siphoviruses.

We report a detailed characterization of five thermophilic bacteriophages (phages) that were isolated from compost heaps in Vilnius, Lithuania using Geobacillus thermodenitrificans strains as the hosts for phage propagation. The efficiency of plating experiments revealed that phages formed plaques from 45 to 80 °C. Furthermore, most of the phages formed plaques surrounded by halo zones, indicating the presence of phage-encoded bacterial exopolysaccharide (EPS)-degrading depolymerases. Transmission Electron Microscopy (TEM) analysis revealed that all phages were siphoviruses characterized by an isometric head (from ~63 nm to ~67 nm in diameter) and a non-contractile flexible tail (from ~137 nm to ~150 nm in length). The genome sequencing resulted in genomes ranging from 38,161 to 39,016 bp. Comparative genomic and phylogenetic analysis revealed that all the isolated phages had no close relatives to date, and potentially represent three new genera within siphoviruses. The results of this study not only improve our knowledge about poorly explored thermophilic bacteriophages but also give new insights for further investigation of thermophilic and/or thermostable enzymes of bacterial viruses.