Abstract
A 98.1 Kb genomic region from B. pumilus 15.1, a strain isolated as an entomopathogen toward C. capitata, the Mediterranean fruit fly, has been characterised in search of potential virulence factors. The 98.1 Kb region shows a high number of phage-related protein-coding ORFs. Two regions with different phylogenetic origins, one with 28.7 Kb in size, highly conserved in Bacillus strains, and one with 60.2 Kb in size, scarcely found in Bacillus genomes are differentiated. The content of each region is thoroughly characterised using comparative studies. This study demonstrates that these two regions are responsible for the production, after mitomycin induction, of a phage-like particle that packages DNA from the host bacterium and a novel phage for B. pumilus, respectively. Both the phage-like particles and the novel phage are observed and characterised by TEM, and some of their structural proteins are identified by protein fingerprinting. In addition, it is found that the phage-like particle shows bacteriocin activity toward other B. pumilus strains. The effect of the phage-like particles and the phage in the toxicity of the strain toward C. capitata is also evaluated.
Highlights
We found that part of the 98.1 Kb region showed a genomic organisation and structure similar to B. subtilis PBSX particles
During characterisation of the strain B. pumilus 15.1 [2], we observed that under some culture conditions (such as elevated temperatures (45–50 ◦ C) or oxygen depletion), a phagelike lysis process occurred, as the optical density of the cultures suddenly dropped after a normal initial growth phase
This observation reminded us of the behaviour of the induction of the lytic cycle of a temperate phage and led us to hypothesise the presence of a prophage in the genome of B. pumilus 15.1
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Bacillus pumilus 15.1, a natural bacterium isolated from a partially decomposed common reed plant as a strain active against larvae of the Mediterranean fruit fly (Ceratitis capitata) [1], has been extensively characterised in our research group for the last 10 years. B. pumilus 15.1 is a motile bacterium, shows the high capability of metabolising a wide range of compounds, and can form biofilms [2]. The strain contains a 7.8 Kb cryptic plasmid, with 33 copies per chromosome [3], and at least one uncharacterised megaplasmid. The strain genome has been previously described [4] and is publicly available
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