title: Salmonella bongori provides insights into the evolution of the Salmonellae.
abstract: The genus Salmonella contains two species, S. bongori and S. enterica. Compared to the well-studied S. enterica there is a marked lack of information regarding the genetic makeup and diversity of S. bongori. S. bongori has been found predominantly associated with cold-blooded animals, but it can infect humans. To define the phylogeny of this species, and compare it to S. enterica, we have sequenced 28 isolates representing most of the known diversity of S. bongori. This cross-species analysis allowed us to confidently differentiate ancestral functions from those acquired following speciation, which include both metabolic and virulence-associated capacities. We show that, although S. bongori inherited a basic set of Salmonella common virulence functions, it has subsequently elaborated on this in a different direction to S. enterica. It is an established feature of S. enterica evolution that the acquisition of the type III secretion systems (T3SS-1 and T3SS-2) has been followed by the sequential acquisition of genes encoding secreted targets, termed effectors proteins. We show that this is also true of S. bongori, which has acquired an array of novel effector proteins (sboA-L). All but two of these effectors have no significant S. enterica homologues and instead are highly similar to those found in enteropathogenic Escherichia coli (EPEC). Remarkably, SboH is found to be a chimeric effector protein, encoded by a fusion of the T3SS-1 effector gene sopA and a gene highly similar to the EPEC effector nleH from enteropathogenic E. coli. We demonstrate that representatives of these new effectors are translocated and that SboH, similarly to NleH, blocks intrinsic apoptotic pathways while being targeted to the mitochondria by the SopA part of the fusion. This work suggests that S. bongori has inherited the ancestral Salmonella virulence gene set, but has adapted by incorporating virulence determinants that resemble those employed by EPEC.
authors.affiliation: Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom.
authors.forename: Maria
authors.initials: M
authors.lastname: Fookes
authors.forename: Gunnar N
authors.initials: GN
authors.lastname: Schroeder
authors.forename: Gemma C
authors.initials: GC
authors.lastname: Langridge
authors.forename: Carlos J
authors.initials: CJ
authors.lastname: Blondel
authors.forename: Caterina
authors.initials: C
authors.lastname: Mammina
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Connor
authors.forename: Helena
authors.initials: H
authors.lastname: Seth-Smith
authors.forename: Georgios S
authors.initials: GS
authors.lastname: Vernikos
authors.forename: Keith S
authors.initials: KS
authors.lastname: Robinson
authors.forename: Mandy
authors.initials: M
authors.lastname: Sanders
authors.forename: Nicola K
authors.initials: NK
authors.lastname: Petty
authors.forename: Robert A
authors.initials: RA
authors.lastname: Kingsley
authors.forename: Andreas J
authors.initials: AJ
authors.lastname: Bäumler
authors.forename: Sean-Paul
authors.initials: SP
authors.lastname: Nuccio
authors.forename: Inés
authors.initials: I
authors.lastname: Contreras
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Santiviago
authors.forename: Duncan
authors.initials: D
authors.lastname: Maskell
authors.forename: Paul
authors.initials: P
authors.lastname: Barrow
authors.forename: Tom
authors.initials: T
authors.lastname: Humphrey
authors.forename: Antonino
authors.initials: A
authors.lastname: Nastasi
authors.forename: Mark
authors.initials: M
authors.lastname: Roberts
authors.forename: Gad
authors.initials: G
authors.lastname: Frankel
authors.forename: Julian
authors.initials: J
authors.lastname: Parkhill
authors.forename: Gordon
authors.initials: G
authors.lastname: Dougan
authors.forename: Nicholas R
authors.initials: NR
authors.lastname: Thomson
mesh_terms: D000818:Animals; D005075:Biological Evolution; D054308:Enteropathogenic Escherichia coli / Q000235:genetics; D005798:Genes, Bacterial; D044404:Genomic Islands / Q000235:genetics; D006801:Humans; D010802:Phylogeny; D012475:Salmonella / Q000235:genetics*; D019779:Salmonella enterica / Q000235:genetics; D017422:Sequence Analysis, DNA; D014178:Translocation, Genetic; D014774:Virulence / Q000235:genetics; D037521:Virulence Factors / Q000235:genetics
chemical_list: D037521:Virulence Factors