title: Regulation of type III secretion hierarchy of translocators and effectors in attaching and effacing bacterial pathogens.
abstract: Human enteropathogenic Escherichia coli (EPEC), enterohemorrhagic E. coli (EHEC), and the mouse pathogen Citrobacter rodentium (CR) belong to the family of attaching and effacing (A/E) bacterial pathogens. They possess the locus of enterocyte effacement (LEE) pathogenicity island, which encodes a type III secretion system. These pathogens secrete a number of proteins into culture media, including type III effector proteins and translocators that are required for the translocation of effectors into host cells. Preliminary evidence indicated that the LEE-encoded SepL and Rorf6/SepD may form a molecular switch that controls the secretion of translocators and effectors in CR. Here, we show that SepL and SepD indeed perform this function in A/E pathogens such as EHEC and EPEC. Their sepL and sepD mutants do not secrete translocators but exhibit enhanced secretion of effectors. We demonstrate that SepL and SepD interact with each other and that both SepL and SepD are localized to the bacterial membranes. Furthermore, we demonstrate that culture media influence the type III secretion profile of EHEC, EPEC, and CR and that low-calcium concentrations inhibit secretion of translocators but promote the secretion of effectors, similar to effects on type III secretion by mutations in sepL and sepD. However, the secretion profile of the sepD and sepL mutants is not affected by these culture conditions. Collectively, our results suggest that SepL and SepD not only are necessary for efficient translocator secretion in A/E pathogens but also control a switch from translocator to effector secretion by sensing certain environmental signals such as low calcium.
authors.affiliation: Michael Smith Laboratories, University of British Columbia, 301-2185, East Mall, Vancouver, British Columbia V6T 1Z4, Canada.
authors.forename: Wanyin
authors.initials: W
authors.lastname: Deng
authors.forename: Yuling
authors.initials: Y
authors.lastname: Li
authors.forename: Philip R
authors.initials: PR
authors.lastname: Hardwidge
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Frey
authors.forename: Richard A
authors.initials: RA
authors.lastname: Pfuetzner
authors.forename: Sansan
authors.initials: S
authors.lastname: Lee
authors.forename: Samantha
authors.initials: S
authors.lastname: Gruenheid
authors.forename: Natalie C J
authors.initials: NC
authors.lastname: Strynakda
authors.forename: Jose L
authors.initials: JL
authors.lastname: Puente
authors.forename: B Brett
authors.initials: BB
authors.lastname: Finlay
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000502:physiology; D002118:Calcium / Q000494:pharmacology; D044082:Citrobacter rodentium / Q000378:metabolism* / Q000472:pathogenicity; D004926:Escherichia coli / Q000378:metabolism* / Q000472:pathogenicity; D029968:Escherichia coli Proteins / Q000502:physiology*; D006801:Humans
chemical_list: D001425:Bacterial Outer Membrane Proteins; C087863:EaeB protein, E coli; D029968:Escherichia coli Proteins; C102051:EspA protein, E coli; C474481:EspD protein, E coli; C495684:SepD protein, E coli; C416081:SepL protein, E coli; D002118:Calcium