title: Induction of the Yersinia type 3 secretion system as an all-or-none phenomenon.
abstract: Pathogenic Yersinia spp. possess a protein secretion system, designated as type 3, that plays a clear role in promoting their survival vis-à-vis the macrophage. Inductive expression of the Yersinia type 3 secretion system (T3SS), triggered either by host cell contact, or, in the absence of host cells, by a reduction in extracellular calcium ion levels, is accompanied by a withdrawal from the bacterial division cycle. Here, we analyzed Ca(2+)-dependent induction of the T3SS at the single-cell level to understand how Yersinia coordinates pro-survival and growth-related activities. We utilized a novel high-throughput quantitative microscopy approach as well as flow cytometry to determine how Ca(2+) levels, T3SS expression, and cellular division are interrelated. Our analysis showed that there is a high degree of homogeneity in terms of T3SS expression levels among a population of Y. pseudotuberculosis cells following the removal of Ca(2+), and that T3SS expression appears to be independent of the cellular division cycle. Unexpectedly, our analysis showed that Ca(2+) levels are inversely related to the initiation of inductive T3SS expression, and not to the intensity of activation once initiated, thus providing a basis for the seemingly graded response of T3SS activation observed in bulk-level analyses. The properties of the system described here display both similarities to and differences from that of the lac operon first described 50 years ago by Novick and Weiner.
authors.affiliation: Department of Microbiology and Immunology, Miller School of Medicine, University of Miami, Miami, FL 33136, USA.
authors.forename: David J
authors.initials: DJ
authors.lastname: Wiley
authors.forename: Roland
authors.initials: R
authors.lastname: Rosqvist
authors.forename: Kurt
authors.initials: K
authors.lastname: Schesser
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002455:Cell Division / Q000502:physiology*; D005434:Flow Cytometry / Q000379:methods; D015964:Gene Expression Regulation, Bacterial; D008853:Microscopy / Q000379:methods; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015007:Yersinia / Q000166:cytology / Q000502:physiology*