M P Sory

The Yersinia yop regulon.

Growth of yersiniae is restricted at 37°C in the absence of calcium ions. This phenomenon correlates with the massive release of a set of proteins called Yops. Growth restriction and Yops production are governed by a 70 kb plasmid called pYV. yop genes are distributed throughout pYV and constitute a thermoactivated regulon controlled by the gene virF. The transcription activator VirF is a member of a new family of regulators including those of the arabinose and rhamnose operons as well as a regulator of enteric colonization pili. The role of calcium ions on the release of Yops remains largely unknown.

Genetic analysis of the plasmid region controlling virulence in Yersinia enterocolitica 0:9 by Mini-Mu insertions and lac gene fusions.

Enteropathogenic strains of Yersinia enterocolitica harbor a virulence plasmid (pYVe plasmid) of 70 kilobases (kb) which specifies, at 37 degrees C, a calcium requirement for growth, autoagglutinability, resistance to the bactericidal activity of human serum, and the expression of outer membrane proteins (OMP). Some mutations suppress the calcium requirement for growth while others make the bacteria unable to grow at 37 degrees C, even in the presence of calcium. To analyse the genes involved in these latter phenotypes, the plasmid of a serogroup 0:9 strain was subjected to transposon mutagenesis with a Mini-Mu (Kan, lac) element. The mapping of 15 insertions and the analysis of transcription showed that at least four transcription units, spanning 22 kb, are involved in the phenomenon of calcium dependence. Mutations in two divergent units (virA and virB) suppressed the requirement for calcium at 37 degrees C. When insertions occurred in the other units (virC and virD), the Y. enterocolitica host became thermosensitive for growth. VirA, B and C mutants did no longer express the pYVe dependent OMPs. VirD mutants expressed and released these proteins save two of mol. wt 37,400 and 40,800 daltons. Transcription of the lac genes in the four groups of mutants was dependent on temperature.

Yersinia enterocolitica O:9 as a potential live oral carrier for protective antigens.

Yersinia enterocolitica has the capacity to invade the intestinal tissue and to resist the primary host resistance. The former is chromosome coded while the second largely depends on the presence of a 70 kb plasmid called pYV. This plasmid directs the conditional synthesis of high amounts of proteins (YOPs) that are secreted and inserted in the outer membrane. In order to evaluate Y. enterocolitica W22703 as a potential live carrier for immunization, three strains expressing beta-galactosidase (GZ), were tested for their ability to induce an antibody response to this antigen in mice. The first strain contained plasmid pGC1256, a mutated pYV plasmid containing lacZ transcribed from a yop gene promoter. This strain produced high amounts of GZ instead of a YOP protein and was shown to be hypovirulent. The other strains tested were W22703 pYV+ and pYV- containing a derepressed lac operon carried on an independent plasmid. Immunoblot analysis of sera of mice having received by oral inoculation, W22703(pGC1256) or the pYV+ GZ producing strain revealed the presence of antibodies to GZ. The response to GZ after inoculation of W22703(pGC1256) was shown by ELISA to be only slightly inferior to that obtained by subcutaneous injection of GZ. No response was obtained after oral inoculation of the pYV-GZ producing strain. This showed that the presence of pYV was necessary to obtain an antibody response in this system.

Genetics of YOP Production in Yersinia Enterocolitica

Y. enterocolitica is a common human pathogen which causes gastrointestinal syndromes of various severities, ranging from mild diarrhoea to mesenteric adenitis evoking an appendicitis, systemic involvement is unusual with Y. enterocolitica but arthritis and erythema nodosum are common complications.