Abstract
AbstractThe bacterial genusKingellaincludes two pathogenic species, namelyKingella kingaeandKingella negevensis, as well as strictly commensal species. BothK. kingaeandK. negevensissecrete a toxin called RtxA that is absent in the commensal species. Here we present a phylogenomic study of the genusKingella, including new genomic sequences for 88 clinical isolates, genotyping of another 131 global isolates, and analysis of 52 available genomes. The phylogenetic evidence supports that the toxin-encoding operonrtxCAwas acquired by a common ancestor of the pathogenicKingellaspecies, and that a preexisting type-I secretion system was co-opted for toxin export. Subsequent genomic reorganization distributed the toxin machinery across two loci, with 30-35% ofK. kingaestrains containing two copies of thertxAtoxin gene. ThertxAduplication is largely clonal and is associated with invasive disease. Assays with isogenic strains show that a single copy ofrtxAis associated with reduced cytotoxicity in vitro. Thus, our study identifies key steps in the evolutionary transition from commensal to pathogen, including horizontal gene transfer, co-option of an existing secretion system, and gene duplication.
Publisher
Springer Science and Business Media LLC
Subject
General Physics and Astronomy,General Biochemistry, Genetics and Molecular Biology,General Chemistry,Multidisciplinary