The Genome of Erysipelothrix rhusiopathiae, the Causative Agent of Swine Erysipelas, Reveals New Insights into the Evolution of Firmicutes and the Organism's Intracellular Adaptations

Erysipelothrix rhusiopathiaeis a Gram-positive bacterium that represents a new class,Erysipelotrichia, in the phylumFirmicutes. The organism is a facultative intracellular pathogen that causes swine erysipelas, as well as a variety of diseases in many animals. Here, we report the first complete genome sequence analysis of a member of the classErysipelotrichia. TheE. rhusiopathiaegenome (1,787,941 bp) is one of the smallest genomes in the phylumFirmicutes. Phylogenetic analyses based on the 16S rRNA gene and 31 universal protein families suggest thatE. rhusiopathiaeis phylogenetically close toMollicutes, which comprisesMycoplasmaspecies. Genome analyses show that the overall features of theE. rhusiopathiaegenome are similar to those of other Gram-positive bacteria; it possesses a complete set of peptidoglycan biosynthesis genes, two-component regulatory systems, and various cell wall-associated virulence factors, including a capsule and adhesins. However, it lacks many orthologous genes for the biosynthesis of wall teichoic acids (WTA) and lipoteichoic acids (LTA) and thedltABCDoperon, which is responsible ford-alanine incorporation into WTA and LTA, suggesting that the organism has an atypical cell wall. In addition, likeMollicutes, its genome shows a complete loss of fatty acid biosynthesis pathways and lacks the genes for the biosynthesis of many amino acids, cofactors, and vitamins, indicating reductive genome evolution. The genome encodes nine antioxidant factors and nine phospholipases, which facilitate intracellular survival in phagocytes. Thus, theE. rhusiopathiaegenome represents evolutionary traits of bothFirmicutesandMollicutesand provides new insights into its evolutionary adaptations for intracellular survival.