Comparative and functional genomics of Listeria spp.

The genus Listeria comprises a group of non-sporulating, Gram-positive, soil bacteria belonging to the low G+C group of microorganisms. The genus consists of only six species, L. monocytogenes, L. ivanovii, L. seeligeri, L. innocua, L. welshimeri, and L. grayi. L. monocytogenes and L. ivanovii are the only known pathogens of this group. Comparative whole-genome sequencing of representative strains comprising the entire genus is currently being performed and nearing completion. In the genus Listeria, genome reduction has led to the generation of non-pathogenic species from pathogenic progenitor strains. Indeed, many of the regions absent in the non-pathogenic species represent commonly deleted genes. Speciation and diversity of strains has been achieved by horizontal gene transfer of DNA encoding novel genes probably required for niche specific survival.