Proffered Papers Australian Society for Microbiology Annual Scientific Meeting 2016

Moraxella catarrhalis ModM: an epigenetic regulator with a potential role in otitis media (#36)

Luke V Blakeway 1 , Aimee Tan 1 , Ben L Schulz 2 , Janessa Pickering 3 , Lea-Ann S Kirkham 3 4 , Deborah Lehmann 4 , Lauren O Bakaletz 5 , Michael P Jennings 1 , Ian R Peak 1 6 , Kate L Seib 1
  1. Institute for Glycomics, Griffith University, Gold Coast, Queensland, Australia
  2. University of Queensland, Brisbane, Queensland, Australia
  3. School of Paediatrics and Child Health, The University of Western Australia, Perth, Western Australia, Australia
  4. Telathon Kids Institute, The University of Western Australia, Perth, Queensland, Australia
  5. Center for Microbial Pathogenesis, Research Institute at Nationwide Children’s Hospital, Columbus, Ohio, USA
  6. School of Medical Science, Griffith University, Gold Coast, QLD, Australia

Introduction

Moraxella catarrhalis is an opportunistic pathogen that causes otitis media (middle ear infection); the most common bacterial infectious disease in first world children1. It expresses a phase variable type III DNA methyltransferase, ModM, which acts as an epigenetic regulator2. Reversible, random, ON/OFF switching of ModM causes differential methylation of the genome, mediating the co-ordinated switching of expression of a set of genes known as a phasevarion (phase variable regulon)3,4.

Methods

The distribution of modM alleles was determined in a panel of M. catarrhalis strains isolated from the nasopharynx of healthy children or middle ear effusates of children with otitis media using multi-plex PCR. The ModM2 and ModM3 methylation target sites were determined using Single Molecule, Real-Time (SMRT) genome sequencing and methylome analysis. Two proteomic techniques, iTRAQ (isobaric Tag for Relative and Absolute Quantitation) and SWATH-MS, were utilized to determine proteins differentially expressed within ModM phasevarions.

Results

Analysis of 97 carriage and 17 otitis media isolates from children found 3 modM alleles that differ in their DNA recognition domain. The distribution of alleles was found to be modM1: 1%, modM2: 82%, and modM3: 17%. modM3 has a statistically significant association with otitis media compared to carriage isolates (p= 0.0022). ModM2 and ModM3 methylate different targets, 5’-GARm6AC-3’ and 5’-ACm6ATC-3’ respectively, and regulate expression of distinct phasevarions (34 and 15 proteins were differentially expressed between ON vs. OFF variants of ModM2 and ModM3, respectively). Several of these proteins are involved in colonization and disease.

Conclusion

ModM alleles are differentially distributed, methylate different target sites and cause switching of expression of distinct sets of proteins. Although modM2 is the most common allele, modM3 is associated with otitis media strains and may play a role in disease progression. This work will aid future vaccine development as proteins regulated by ModM are unsuitable as vaccine candidates due to their variable expression.

 

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