Abstract
Bacteria of the genus Listeria (phylum Firmicutes) include both human and animal pathogens, as well as saprophytic strains. A common component of Listeria spp. genomes are plasmids, i.e., extrachromosomal replicons that contribute to gene flux in bacteria. This study provides an in-depth insight into the structure, diversity and evolution of plasmids occurring in Listeria strains inhabiting various environments under different anthropogenic pressures. Apart from the components of the conserved plasmid backbone (providing replication, stable maintenance and conjugational transfer functions), these replicons contain numerous adaptive genes possibly involved in: (i) resistance to antibiotics, heavy metals, metalloids and sanitizers, and (ii) responses to heat, oxidative, acid and high salinity stressors. Their genomes are also enriched by numerous transposable elements, which have influenced the plasmid architecture. The plasmidome of Listeria is dominated by a group of related replicons encoding the RepA replication initiation protein. Detailed comparative analyses provide valuable data on the level of conservation of these replicons and their role in shaping the structure of the Listeria pangenome, as well as their relationship to plasmids of other genera of Firmicutes, which demonstrates the range and direction of flow of genetic information in this important group of bacteria.
Highlights
The genus Listeria (Firmicutes) comprises 26 species, but studies have mainly focused on only one, L. monocytogenes, a pathogenic bacterium causing rare but severe food poisoning that can be fatal to unborn children and individuals with a compromised immune system [1]
This study indicated that plasmids are common in this species (54% of tested strains harbored such replicons), their distribution varied greatly depending on the L. monocytogenes sequence type (ST) and lineage
We gathered a large collection of Listeria spp. strains, isolated from various environments, that are subject to different anthropogenic pressures
Summary
The genus Listeria (Firmicutes) comprises 26 species, but studies have mainly focused on only one, L. monocytogenes, a pathogenic bacterium causing rare but severe food poisoning that can be fatal to unborn children and individuals with a compromised immune system [1]. Many genes that may contribute to the ability of Listeria spp. to colonize various environments have been identified within mobile genetic elements, mainly plasmids These genes can confer resistance to antibiotics [6,7], sanitizers [8,9], heavy metals [10,11,12] or elevated temperatures [13]. Combined with data available in GenBank and from our previous studies, we analyzed a set of 113 complete plasmid sequences from different Listeria species to provide an in-depth insight into their diversity, genetic load and potential contribution to the stress responses of these bacteria, as well as the impact of transposable elements (TEs) on the evolution of these replicons
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