Genome organization and the evolution of the virulence gene locus in Listeria species

The chromosomal region of Listeria monocytogenes harboring the gene cluster prfA-plcA-hly-mpl-actA-plcB (virulence gene cluster; vgc) harbors virulenc e genes critical for the survival of the bacteria following infection. Prev ious studies have implicated it as an ancestral pathogenicity island, deriv atives of which are present in the species L. ivanovii and L. seeligeri, bu t absent in nonpathogenic species such as L. innocua. We cloned the corresp onding region from L. innocua and L. welshimeri and compared its sequences to those from L. monocytogenes, L. ivanovii and L. seeligeri. The analysis allowed exact determination of delineation and size of the vgc and suggests that these genes may have been acquired by bacteriophage transduction. Thu s, here we present an alternative view of the evolution of Listeria spp. an d suggest that L. monocytogenes may be the primordial species of this genus .