Surface localization of Helicobacter pylori urease and a heat shock protein homolog requires bacterial autolysis

Abstract

Helicobacter pylori is a gram-negative bacterium which causes chronic gastritis and is associated with peptic ulcer disease, gastric carcinoma, and gastric lymphoma. The bacterium is characterized by potent urease activity, thought to be located on the outer membrane, which is essential for survival at low pH. The purpose of the present study was to investigate mechanisms whereby urease and HspB, a GroEL homolog, become surface associated in vitro. Urease, HspB, and catalase were located almost exclusively within the cytoplasm in fresh log-phase cultures assessed by cryo- immunoelectron microscopy. In contrast, significant amounts of surface-associated antigen were observed in older or subcultured preparations concomitantly with the appearance of significant amounts of extracellular antigen, amorphous debris, and membrane fragments. By use of a variety of biochemical methods, a significant fraction of urease and HspB was associated with the outer membrane in subcultured preparations of H. pylori. Taken together, these results strongly suggest that H. pylori cells undergo spontaneous autolysis during culture and that urease and HspB become surface associated only concomitant with bacterial autolysis. By comparing enzyme sensitivity to flurofamide (a potent, poorly diffusible urease inhibitor) in whole cells with that in deliberately lysed cells, we show that both extracellular and intracellular urease molecules are active enzymatically. Autolysis of H. pylori is an important phenomenon to recognize since it likely exerts significant effects on the behavior of H. pylori. Furthermore, the surface properties of H. pylori must be unique in promoting adsorption of cytoplasmic proteins.