Identification and characterization of the Yersinia enterocolitica gsrA gene, which protectively responds to intracellular stress induced by macrophage phagocytosis and to extracellular environmental stress.

Yersinia enterocolitica is able to resist the microbicidal mechanisms of macrophages and to grow within phagocytic cells. Some bacteria including Y. enterocolitica 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 in intracellular survival of bacteria, we identified and cloned a Y. enterocolitica gene, called 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 a basic, 49,500-Da protein. The GsrA protein shows significant amino acid sequence homology to the HtrA stress protein which was originally identified in Escherichia coli. Furthermore, the genetically defined Y. enterocolitica gsrA mutant was constructed and characterized. The insertional mutation of gsrA resulted in inhibition of growth at temperatures above 39 degrees C and greatly 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 to the intracellular stress in macrophages as well as extracellular environmental stress.