Whole-Genome Sequence ofListeria welshimeriReveals Common Steps in Genome Reduction withListeria innocuaas Compared toListeria monocytogenes

Abstract

We present the complete genome sequence ofListeria welshimeri, a nonpathogenic member of the genusListeria. Listeria welshimeriharbors a circular chromosome of 2,814,130 bp with 2,780 open reading frames. Comparative genomic analysis of chromosomal regions betweenL. welshimeri,Listeria innocua, andListeria monocytogenesshows strong overall conservation of synteny, with the exception of the translocation of an F_oF₁ATP synthase. The smaller size of theL. welshimerigenome is the result of deletions in all of the genes involved in virulence and of “fitness” genes required for intracellular survival, transcription factors, and LPXTG- and LRR-containing proteins as well as 55 genes involved in carbohydrate transport and metabolism. In total, 482 genes are absent fromL. welshimerirelative toL. monocytogenes. Of these, 249 deletions are commonly absent in bothL. welshimeriandL. innocua, suggesting similar genome evolutionary paths from an ancestor. We also identified 311 genes specific toL. welshimerithat are absent in the other two species, indicating gene expansion inL. welshimeri, including horizontal gene transfer. The speciesL. welshimeriappears to have been derived from early evolutionary events and an ancestor more compact thanL. monocytogenesthat led to the emergence of nonpathogenicListeriaspp.