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Infection and Immunity, February 2000, p. 470-477, Vol. 68, No. 2
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Expression of the Helicobacter pylori ureI Gene Is Required for Acidic pH Activation of Cytoplasmic Urease

David R. Scott,1,* Elizabeth A. Marcus,1 David L. Weeks,1 Adrian Lee,2 Klaus Melchers,3 and George Sachs1

Department of Physiology, University of California at Los Angeles, and VAGLAHS, Los Angeles, California1; University of New South Wales, Sydney, Australia2; and Byk Gulden, Konstanz, Germany3

Received 9 August 1999/Returned for modification 29 September 1999/Accepted 3 November 1999

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 UreI 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, urease activity, and the effect of urea on membrane potential of several gastric and nongastric Helicobacter species. ureI was found to be present in the genome of the gastric Helicobacter species and absent in the nongastric Helicobacter species studied, as determined by PCR. Likewise, Western blot analysis confirmed that UreI was expressed only in the gastric Helicobacter species. When UreI is present, acidic medium pH activation of cytoplasmic urease 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 urease activity was membrane limited. No acidic pH activation or urea induced membrane potential changes were found in the nongastric Helicobacter species. The ureI gene product is probably a pH activated urea transporter or perhaps regulates such a transporter as a function of periplasmic pH.

* Corresponding author. Mailing address: VAGLAHS, Bldg. 113, Rm. 324, 11301 Wilshire Blvd., Los Angeles, CA 90073. Phone: (310) 268-4672. Fax: (310) 312-9478. E-mail: dscott{at}ucla.edu.

Infection and Immunity, February 2000, p. 470-477, Vol. 68, No. 2
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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