Heterogeneity in Levels of Vacuolating Cytotoxin Gene ( vacA ) Transcription among Helicobacter pylori Strains

Abstract

ABSTRACT Broth culture supernatants from Tox + Helicobacter pylori strains induce vacuolation of HeLa cells in vitro and contain VacA in concentrations that are higher than those found in supernatants from Tox − H. pylori strains. To investigate the basis for this phenomenon, we analyzed the transcription of the vacuolating cytotoxin gene ( vacA ) in eight Tox + strains (each with a type s1/m1 vacA genotype) and nine Tox − strains (each with a type s2/m2 vacA genotype). Most of the Tox + and Tox − strains tested used the same vacA transcriptional start point, but Tox + strains yielded significantly stronger primer extension signal intensities than did Tox − strains (mean densitometry values of 15.8 ± 1.9 versus 8.9 ± 1.7, P = 0.0016). Correspondingly, when we introduced vacA :: xylE transcriptional fusions into the chromosomes of a Tox + strain (60190) and a Tox − strain (86-313), the level of XylE activity in 60190 vacA :: xylE was about 30-fold higher than that in 86-313 vacA :: xylE . Sequence analysis and promoter exchange experiments indicated that the different levels of vacA transcription in these two strains cannot be explained solely by a difference in promoter strength. These data indicate that Tox + and Tox − H. pylori strains typically differ not only in the VacA amino acid sequence but also in the level of vacA transcription.