THERMOREGULATION IN YERSINIA-ENTEROCOLITICA IS COINCIDENT WITH CHANGES IN DNA SUPERCOILING

Yersinia enterocolitica is a facultative intracellular parasite, displ aying the ability to grow saprophytically or invade and persist intrac ellularly in the mammalian reticuloendothelial system. The transition between such diverse environments requires the co-ordinated regulation of specific sets of genes on both the chromosome and virulence plasmi d. Temperature has a profound pleiotropic effect on gene expression an d phenotypically promotes alterations in cell morphology, outer-membra ne protein synthesis, urease production, lipopolysaccharide synthesis, motility, and synthesis of genes involved in invasion of eukaryotic h ost cells. By examining thermoregulated flagella biosynthesis, we have determined that motility is repressed at 25 degrees C (permissive tem perature) with subinhibitory concentrations of novobiocin. These condi tions also induce virulence gene expression suggesting novobiocin addi tion simulates, at least partially, a high-temperature environment. Fu rthermore, temperature-shift experiments, using Y. enterocolitica cont aining pACYC184 as a reporter plasmid, indicate that thermo-induced al terations of DNA supercoiling coincide with temperature-induced phenot ypic changes. A class of putative DNA gyrase mutant (novobiocin resist ant) likewise demonstrates the 37 degrees C phenotype when cultured at 25 degrees C; it is non-motile, urease negative, calcium growth depen dent, and positive for Yop expression. These results support a model i mplicating DNA topology as a contributing factor of Y. enterocolitica thermoregulation.