Oral Presentation BacPath 13: Molecular Analysis of Bacterial Pathogens Conference 2015

ModM DNA methyltransferase methylome analysis reveals a potential role for Moraxella catarrhalis phasevarions in otitis media (#25)

Luke V. Blakeway 1 , Peter M. Power 1 , Freda E.-C. Jen 1 , Sam R. Worboys 1 , Matthew Boitano 2 , Tyson A. Clark 2 , Jonas Korlach 2 , Lauren O. Bakaletz 3 , Michael P. Jennings 1 , Ian R. Peak 1 4 , Kate L. Seib 1
  1. Institute for Glycomics, Griffith University, Gold Coast, QLD, Australia
  2. Pacific Biosciences, Menlo Park, CA, United States
  3. Center for Microbial Pathogenesis, Research Institute at Nationwide Children’s Hospital, Columbus, OH, United States
  4. School of Medical Science, Griffith University, Gold Coast, QLD, Australia

Moraxella catarrhalis is an opportunistic pathogen that causes otitis media and exacerbations of chronic obstructive pulmonary disease. M. catarrhalis expresses a type III DNA methyltransferase, ModM, that is phase variable. The reversible ON/OFF switching of ModM expression determines whether methylation is present or absent within the ModM recognition sequence throughout the genome. DNA methylation regulates gene expression by altering the affinity of regulatory proteins for DNA, and differential methylation caused by phase variation of ModM mediates the co-ordinated switching of expression of multiple genes, known as a phasevarion (phase variable regulon). This results in two distinct phenotypes within a population, one of which may have an advantage to survival in a particular niche. Three modM alleles have been identified (modM1-3) that differ in their DNA recognition domain, causing methylation of a different site and regulation of a different phasevarion depending on the allele present. Using single-molecule, real-time (SMRT) genome sequencing and methylome analysis, we have determined that the ModM2 methylation target is 5’-GARm6AC-3’ and the ModM3 methylation target is 5’-ACm6ATC-3’. Using two proteomic techniques, isobaric tag for relative and absolute quantitation (iTRAQ) and SWATH-MS analysis, proteins important in colonization and disease were found to be differentially expressed between the ON and OFF variants of ModM2 and ModM3. Investigation of the distribution of modM alleles in a panel of M. catarrhalis strains, isolated from the nasopharynx of healthy children or middle ear effusions of children with otitis media, revealed that modM1 is rare, modM2 is the most common allele, and modM3 is intermediate. Additionally, a statistically significant association of modM3 with otitis media associated isolates was observed. The modulation of gene expression via the ModM phasevarions, and the significant association of the modM3 allele with otitis media isolates suggests a key role for ModM phasevarions in the pathogenesis of M. catarrhalis.