GROWTH-PHASE AND LOW PH AFFECT THE THERMAL REGULATION OF THE YERSINIA-ENTEROCOLITICA INV GENE

The inv gene encodes the protein invasin, which is the primary invasio n factor for Yersinia enterocolitica in vitro and in vivo. Previous st udies of Yersinia species have shown that inv expression and entry int o mammalian cells are temperature regulated. Invasin production is red uced at the host temperature of 37 degrees C as compared to production at ambient temperature; consequently, this study was initiated to det ermine whether other host environmental signals might induce inv expre ssion at 37 degrees C. An inv::phoA translational fusion was recombine d on to the Y. enterocolitica chromosome by allelic exchange to monito r inv expression. Molecular characterization of expression of the wild -type inv gene and the inv::phoA fusion showed that invasin is not pro duced until early stationary phase in bacteria grown at 23 degrees C. Y. enterocolitica grown at 37 degrees C and pH 5.5 showed levels of in v expression comparable to those observed in bacteria grown at 23 degr ees C. An increase in Na+ ions caused a slight increase in expression at 37 degrees C. However, expression at 37 degrees C was unaffected by anaerobiosis, growth medium, calcium levels, or iron levels. Addition ally, Y. enterocolitica expressed invasin in Peyer's patches two days after being introduced intragastrically into BALB/c mice. These result s suggest that invasin expression in Y. enterocolitica may remain elev ated early during interaction with the intestinal epithelium, a site a t which invasin was shown to be necessary.