Comparative transcriptomics of H. pylori strains AM5, SS1 and their hpyAVIBM deletion mutants: possible roles of cytosine methylation

Abstract

Helicobacter pylori is an important human pathogen and one of the most successful chronic colonizers of the human body. H. pylori uses diverse mechanisms to modulate its interaction with the host in order to promote chronic infection and overcome host immune response. Restriction-modification genes are a major part of strain-specific genes present in H. pylori. The role of N(6)--adenine methylation in bacterial gene regulation and virulence is well established but not much is known about the effect of C(5) -cytosine methylation on gene expression in prokaryotes. In this study, it was observed by microarray analysis and RT-PCR, that deletion of an orphan C(5) -cytosine methyltransferase, hpyAVIBM in H. pylori strains AM5and SS1 has a significant effect on the expression of number of genes belonging to motility, adhesion and virulence. AM5ΔhpyAVIBM mutant strain has a different LPS profile and is able to induce high IL-8 production compared to wild-type. hpyAVIBM from strain 26695 is able to complement mutant SS1 and AM5 strains. This study highlights a possible significance of cytosine methylation in the physiology of H. pylori.

Figure 1. hpyAVIAM and hpyAVIBM.

(A) Schematic presentation of operon coding hpyAVIAM and hpyAVIBM. (B) Distribution of hpyAVIBM in symptomatic and asymptomatic strains. P<0.0001.

Figure 2. Variation in dinucleotide repeats in H. pylori clinical isolates.

Arrow indicates the substitution/deletion mutation.

Figure 3. Motility assay.

The photograph shows a BHI 7% FBS soft agar plate after 4 days of incubation. (A) SS1 (B) AM5 (C) Graph showing relative change in the diameter of mutant vs wild-type strain.

Figure 4. Western blotting for CagA and VacA protein levels in H. pylori strainsAM5 and AM5ΔhpyAVIBM.

Figure 5. LPS profiles of hpyAVIBM deletion mutant and wild-type strains.

Lane 1: wild-type strain AM5, lane 2: hpyAVIBM deletion mutant AM5 complemented with hpyAVIBM from strain 26695, lane 3: hpyAVIBM deletion mutant. * highlights the bands different between wild type and mutant.

Figure 6. hpyAVIBM deletion enhances IL-8 production in AGS cell lines.

(1) H. pylori strain AM5/SS1 (2) H. pylori strain AM5ΔhpyAVIBM/SS1ΔhpyAVIBM (3) hpyAVIBM deletion mutant AM5/SS1 complemented with hpyAVIBM from strain 26695.

Figure 7. Natural transformation efficiency of H. pylori strains AM5 and SS1 and their respective hpyAVIBM deletion mutant strains.

Values are calculated as transformants/cfu/mg DNA. P<0.0001.

Figure 8. Survival of a pathogen in host depends upon its ability to modulate the balance between virulence and avirulence.