Expression of the Helicobacter pylori ureI gene is required for acidic pH activation of cytoplasmic urease

ureI encodes an integral cytoplasmic membrane protein, It is present in the urease gene cluster of Helicobacter pylori and is essential for infection and acid survival, but its role is unknown, To determine the function of Ur eI protein, we produced H. pylori ureI deletion mutants and measured the pH dependence of urease activity of intact and lysed bacteria and the effect of urea on the membrane potential, We also determined ureI expression, urea se activity, and the effect of urea on membrane potential of several gastri c and nongastric Helicobacter species. ureI was found to be present in the genome of the gastric Helicobacter species and absent in the nongastric Hel icobacter species studied, as determined by PCR. Likewise, Western blot ana lysis confirmed that UreI was expressed only in the gastric Helicobacter sp ecies, When UreI is present, acidic medium pH activation of cytoplasmic ure ase is found, and urea addition increases membrane potential at acidic pH, The addition of a low concentration of detergent raised urease activity of intact bacteria at neutral pH to that of their homogenates, showing that ur ease activity was membrane limited. No acidic pH activation or urea induced membrane potential changes were found in the nongastric Helicobacter speci es. The ureI gene product is probably a pH activated urea transporter or pe rhaps regulates such a transporter as a function of periplasmic pH.