Comparison of the genome sequences of Listeria monocytogenes and Listeria innocua: clues for evolution and pathogenicity.

Listeria monocytogenes, an invasive opportunistic, food-borne pathogen, remains one of the leading causes of mortality from food-borne infections. The recently determined complete genome sequences of L. monocytogenes strain EGDe and of that of the closely related non-pathogenic species Listeria innocua strain CLIP11262 enhance our knowledge of the genetic basis of the virulence of L. monocytogenes and advance our understanding of the evolution of these Listeria species. Both genomes encode a high number of surface, transport and regulatory proteins. Comparison of the genome organisation revealed a perfect synteny between the two Listeria genomes. Comparison with other closely related bacteria also showed a high conservation in genome organisation among the Listeria, Staphylococcus and Bacillus group of low G+C content bacteria. Distinct G+C content of a number of strain-specific genes suggests intensive lateral gene transfer. The identification of a 55-kb locus encoding proteins with high homology to Salmonella enterica serovar Typhimurium vitamin B(12) synthesis proteins as well as those necessary for degradation of ethanolamine and propanediol further indicates acquisition of a complete metabolic pathway by horizontal gene transfer and a probable role of this locus in anaerobic growth in the host.