Studies on the Bacterial Stress Proteins as Virulence Fctors

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Yersinia enterocolitica is a facultative intracellular pathogen which is able to resist the microbicidal mechanisms of macrophages and to grow within phagocytic cells. Some bacteria including Y.enterocolitical have been shown to respond to the hostile environment in macrophages by producing a set of stress proteins which are also induced by environmental stresses. To understand the role of stress proteins on the intracellular survival of bacteriawe identified and cloned a Y.enterocolitica gene, celled gsrA (global stress requirement). The gsrA gene was identified because its insertional inactivation by a transposon resulted in the inability of the organism to grow at an elevated temperature and to survive within macrophages after phagocytosis. The gsrA gene was sequenced and shown to encode for a basic, 49500 Da protein. The GsrA protein shows significant amino acid sequence homology to the HtrA stress protein which was originally indentified in Escherichia coli. Furthermore, the genetically defined Y.enterocolitica gsrA mutant was constructed and characterized. The insertional mutation of gsrA resulted in the inhibition of growth at temperatures above 39ﾟC and the grealty increased susceptibility to oxidative and osmotic stresses. The mutant additionally lost the ability to survive and replicate within macrophages. These results, taken together, indicate that the gsrA gene is an essential component of the protection mechanism employed by Y.enterocolitica, allowing it to respond against the intracellular stress found in macrophages as well as extracellular environmental stress.