EFFECT OF GROWTH-PHASE AND ACID SHOCK ON HELICOBACTER-PYLORI CAGA EXPRESSION

Helicobacter pylori strains possessing cagA are associated with peptic ulceration. To understand the regulation of expression of cagA, picB, associated with interleukin-8 induction, and ureA, encoding the small urease subunit, we created gene fusions of cagA, ureA, and picB of st rain 3401, using a promoterless reporter (xylE). Expression of XylE af ter growth in broth culture revealed that basal levels of expression o f cagA and ureA in H. pylori were substantially greater than for picB. For cagA expression in stationary-phase cells, brief exposure to acid pH caused a significant increase in xylE expression compared with neu tral pH. In contrast, expression of xylE in ureA or picB decreased aft er parallel exposure to acid pH (pH 7 > 6 > 5 > 4), regardless of the growth phase. Expression of the CagA protein varied with growth phase and pH exposure in parallel with the observed transcriptional variatio n, The concentration of CagA in a cell membrane-enriched fraction afte r growth at pH 6 was significantly higher than after growth at pH 5 or 7. We conclude that the promoterless reporter xylE is useful for stud ying the regulation of gene expression in H. pylori and that regulatio n of CagA production occurs mainly at the transcriptional level.