Abstract
BackgroundListeria monocytogenes is a food-borne pathogen that causes infections with a high-mortality rate and has served as an invaluable model for intracellular parasitism. Here, we report complete genome sequences for two L. monocytogenes strains belonging to serotype 4a (L99) and 4b (CLIP80459), and transcriptomes of representative strains from lineages I, II, and III, thereby permitting in-depth comparison of genome- and transcriptome -based data from three lineages of L. monocytogenes. Lineage III, represented by the 4a L99 genome is known to contain strains less virulent for humans.ResultsThe genome analysis of the weakly pathogenic L99 serotype 4a provides extensive evidence of virulence gene decay, including loss of several important surface proteins. The 4b CLIP80459 genome, unlike the previously sequenced 4b F2365 genome harbours an intact inlB invasion gene. These lineage I strains are characterized by the lack of prophage genes, as they share only a single prophage locus with other L. monocytogenes genomes 1/2a EGD-e and 4a L99. Comparative transcriptome analysis during intracellular growth uncovered adaptive expression level differences in lineages I, II and III of Listeria, notable amongst which was a strong intracellular induction of flagellar genes in strain 4a L99 compared to the other lineages. Furthermore, extensive differences between strains are manifest at levels of metabolic flux control and phosphorylated sugar uptake. Intriguingly, prophage gene expression was found to be a hallmark of intracellular gene expression. Deletion mutants in the single shared prophage locus of lineage II strain EGD-e 1/2a, the lma operon, revealed severe attenuation of virulence in a murine infection model.ConclusionComparative genomics and transcriptome analysis of L. monocytogenes strains from three lineages implicate prophage genes in intracellular adaptation and indicate that gene loss and decay may have led to the emergence of attenuated lineages.
Highlights
Listeria monocytogenes is a food-borne pathogen that causes infections with a high-mortality rate and has served as an invaluable model for intracellular parasitism
Pathogenic listeriae encode several virulence factors that are localized in a virulence gene cluster or Listeria pathogenicity island-1 (LIPI-1) in the genome
Computational multi-virulence-locus sequence typing (MVLST) [22] analysis showed that strain 4b CLIP80459 belongs to epidemic clone ECII and strain 4b F2365 to epidemic clone ECI as previously reported by Nelson and colleagues [15], respectively
Summary
Listeria monocytogenes is a food-borne pathogen that causes infections with a high-mortality rate and has served as an invaluable model for intracellular parasitism. Listeria monocytogenes is a Gram-positive, motile, nonsporulating, rod shaped bacterium It is the causative agent of listeriosis, a food-borne disease, which afflicts both humans and animals. A number of genes required for virulence are not localized in this cluster, including the two internalins inlA and inlB These encode proteins that are expressed on the surface of the bacterium and facilitate the entry of the bacterium into the eukaryotic cell and their incorporation into a membrane-bound vacuole [6,7]. Further pathogenicity islands present in the genus Listeria code for multiple internalins and additional hemolysin genes in species L. ivanovii (LIPI-2) [8] and a subset of strains of lineage I (LIPI-3) [9]
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