A NOVEL MECHANISM OF UREASE REGULATION IN YERSINIA-ENTEROCOLITICA

Yersinia enterocolitica produces the enzyme urease which hydrolyses ur ea, resulting in the production of carbonic acid and ammonia and a net increase in pH. In the presence of urea, urease enhances survival of Y. enterocolitica in the stomach and presumably in other acidic enviro nments the bacteria encounter during the course of infection. In this study we show that Y. enterocolitica urease is a cytosolic enzyme whic h has a low K-m value (0.15 +/- 0.01 mM urea), suggesting that it func tions at close to maximum velocity even at the low concentrations of u rea available to Y. enterocolitica in gastric fluid and other tissues. Y. enterocolitica urease was active over a wide pH range, but unlike most other bacterial ureases, displayed an optimal activity at pH 3.5- 4.5, suggesting a physiological role in protecting the bacteria from a cid. Higher levels of urease activity were attained al 28 degrees C th an at 37 degrees C, and investigation of the regulation of urease prod uction revealed that the enzyme was not induced by urea, or by nitroge n limitation. Instead maximal activity was attained during the station ary phase of growth which coincides with the period of maximum acid to lerance of the bacteria. This type of regulation has not been describe d for any other ureolytic bacteria and seems to be unique to Y. entero colitica.