THE EFFECT OF ENVIRONMENTAL PH ON THE PROTON MOTIVE FORCE OF HELICOBACTER-PYLORI

Background & Aims: Responses of the proton motive farce (the driving f orce for protons) in Helicobacter pylori to varying medium pH may expl ain gastric colonization. The aim of this study was to determine the e ffect of external pH (pH(out)) on the proton motive force, the sum of the pH gradient, and the potential difference across the bacterial mem brane. Methods: Intracellular pH (pH(in)) was measured by bis-carboxye thyl-carboxyfluorescein fluorescence and transmembrane potential diffe rence (PD) by fluorescent quenching of 3,3'-dipropyl thiadicarbocyanin e iodide at differing pH(out) and was correlated with survival, Result s: PD was -131 +/- 0.36 mV (n = 3), and pH(in) was about 8.4 at loadin g pH(out) 7.0. PD increased as pH(out) was increased from 4.0 to 8.0, giving a constant proton motive force of about -220 mV. Outside these limits, PD collapsed irreversibly to zero, Addition of 5 mmol/l urea t o weak buffer at pH 3.0 or 3.5 prevented irreversible collapse of PD b y elevation of pH(out) caused by NH3 production, Urea addition to weak buffer at pH 7.0 collapsed the PD as urease activity increased the pH (out) to about 8.4, Survival was also limited to this range of pH(out) . Conclusions: H. pylori survives over the range of pH(out) where it m aintains a proton motive force. The effect of urease activity on pH(ou t), while allowing gastric survival in acidic media, may limit surviva l in nonacidic media.