Abstract
This report describes the morphological characterization and genome analysis of an induced prophage (PLg-TB25) from a dairy strain of Lactococcus garvieae. The phage belongs to the Siphoviridae family and its morphology is typical of other lactococcal phages. A general analysis of its genome did not reveal similarities with other lactococcal phage genomes, confirming its novelty. However, similarities were found between genes of its morphogenesis cluster and genes of Gram-positive bacteria, suggesting that this phage genome resulted from recombination events that took place in a heterogeneous microbial environment. An in silico search for other prophages in 16 L. garvieae genomes available in public databases, uncovered eight seemingly complete prophages in strains isolated from dairy and fish niches. Genome analyses of these prophages revealed three novel L. garvieae phages. The remaining prophages had homology to phages of Lactococcus lactis (P335 group) suggesting a close relationship between these lactococcal species. The similarity in GC content of L. garvieae prophages to the genomes of L. lactis phages further supports the hypothesis that these phages likely originated from the same ancestor.
Highlights
Bacterial viruses are considered the most abundant and diverse biological entities in our biosphere
The L. garvieae temperate phage PLg-TB25 is a new member of the Siphoviridae family
The recent isolation of a lytic phage infecting a strain of L. garvieae with significant similarities to dairy L. lactis phages belonging to the c2 and Q54 groups[14], raised the question of whether the same was true for temperate L. garvieae phages and prophages
Summary
Bacterial viruses (phages) are considered the most abundant and diverse biological entities in our biosphere. Once the genome of a temperate phage is injected into the cytoplasm of its bacterial host, depending on the metabolic state of the cell, the phage genes involved in the lysogenic cycle may be expressed to favour this lifestyle. Temperate phages carry genes coding for toxins, regulatory and effector proteins, adhesins, exonucleases and superantigens These sequences are often flanked by a specific transcriptional promoter and terminator, allowing gene expression during the lysogenic cycle[6]. The presence of a new prophage in a bacterial strain may lead to the so-called “lysogenic conversion”, where a non-pathogenic strain is converted into a pathogen by the integration of a temperate phage genome carrying genes coding for toxin or virulence factors. We searched for prophages in 16 L. garvieae genomes available in public databases, leading to the identification of three novel prophages
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