differs from other spp. in codon usage.

spp. are important enteric pathogens in a wide range of vertebrates including humans. Previous comparative analysis revealed conservation in genome composition, gene content, and gene organization among spp., with a progressive reductive evolution in metabolic pathways and invasion-related proteins. In this study, we sequenced the genome of zoonotic pathogen and conducted a comparative genomic analysis. While most intestinal species have similar genomic characteristics and almost complete genome synteny, fewer protein-coding genes and some sequence inversions and translocations were found in the genome. The genome exhibits much higher GC content (39.6 %) than other species (24.3-32.9 %), especially at the third codon position (GC3) of protein-coding genes. Thus, has a different codon usage, which increases the use of less energy costly amino acids (Gly and Ala) encoded by GC-rich codons. While the tRNA usage is conserved among species, consistent with its higher GC content, uses a unique tRNA for GTG for valine instead of GTA in other species. Both mutational pressures and natural selection are associated with the evolution of the codon usage in spp., while natural selection seems to drive the codon usage in . Other unique features of the genome include the loss of the entire traditional and alternative electron transport systems and several invasion-related proteins. Thus, the preference for the use of some less energy costly amino acids in may lead to a more harmonious parasite-host interaction, and the strengthened host-adaptation is reflected by the further reductive evolution of metabolism and host invasion-related proteins.