Poster Presentation Australian Society for Microbiology Annual Scientific Meeting 2014

Phasevarion mediated epigenetic virulence gene regulation in Helicobacter pylori (#435)

Yogitha N Srikhanta 1 , Rebecca J Gorrell 2 , Peter M Power 3 , Jonas Korlach 4 , Elizabeth L Hartland 1 , Michael P Jennings 3 , Terry Kwok 2
  1. Microbiology and Immunology, The University of Melbourne, Melbourne, Victoria, Australia
  2. Department of Biochemistry and Molecular Biology, Monash University, Melbourne, Victoria, Australia
  3. Institute for Glycomics, Griffith University, Gold Coast, Queensland, Australia
  4. Pacific Biosciences, San Francisco, California, USA

Many host-adapted bacterial pathogens contain type III DNA methyltransferases (mod genes) that are subject to phase variable expression (high-frequency reversible ON/OFF switching of gene expression). Our previous studies have identified phase variable N6-adenosine type III DNA methyltransferases in several clinically important pathogens that can control the random switching of expression of multiple genes 1 2  . These systems constitute phase variable regulons called phasevarions. We recently observed that phasevarions exist in the persistent, cancer-causing human pathogen Helicobacter pylori 3 . Until then a role in virulence for any H. pylori DNA methyltransferase had not been ascribed. The phase variable type III DNA methyltransferase of H. pylori (ModH) is highly conserved in all strains, but contains a variable DNA recognition domain. We have observed 17 modH alleles to date and reported that modH5, the most abundant allele, controls at least 2 key virulence genes with important roles in colonization. A motility assay further supports a role for the ModH5 phasevarion in colonization. Proteomic analysis of heat-extracted surface-associated proteins identified AmiE, an aliphatic amidase important for H. pylori survival in the acidic gastric environment, which was up-regulated in expression in the ModH5 mutant. The target site recognised and methylated by ModH5 has not previously been determined. We identified the ModH5 methylation target site (5’-GAm6CC-3’) using the cutting-edge technology single molecule real time DNA sequencing. The 4 bp site is atypical of type III DNA methyltransferases. Analysis of the distribution of the modified site showed association with the intergenic regions of genes controlled by the ModH5 phasevarion. Transcriptional mutational studies confirmed the target site. Our data verifies that phasevarions exist in H. pylori and may have major implications for H. pylori vaccine development and host:pathogen interactions.

  1. Srikhanta YN, Maguire TL, Stacey KJ, Grimmond SM & Jennings MP (2005). The phasevarion: A genetic system controlling coordinated, random switching of expression of multiple genes. Proc Natl Acad Sci USA. 102 (15):5547-5551
  2. Srikhanta YN, Dowideit SJ, Edwards, JL, Falsetta ML, Wu H-J, Harrison OB, Fox KL, Seib KL Maguire TL, Wang A-J, Maiden MC, Grimmond SM, Apicella MA & Jennings MP (2009). Phasevarions mediate random switching of gene expression in pathogenic Neisseria. PloS Pathogens 5(4):e1000400
  3. Srikhanta YN, Gorrell RJ, Steen JA, Gawthorne JA, Kwok T, Grimmond SM, Robins-Browne RM & Jennings MP (2011). Phasevarion mediated epigenetic gene regulation in Helicobacter pylori. PLoS One 6(12):e27569