Moraxella catarrhalis phase-variable loci show differences in expression during conditions relevant to disease

• Published in: PloS one Vol. 15; no. 6; p. e0234306
• Main Authors: Tan, Aimee, Blakeway, Luke V, Taha, Yang, Yuedong, Zhou, Yaoqi, Atack, John M, Peak, Ian R, Seib, Kate L
• Format: Journal Article
• Language: English
• Published: San Francisco Public Library of Science 18.06.2020; Public Library of Science (PLoS)
• Subjects: Bacterial infections; Biofilms; Biology and Life Sciences; Chronic obstructive pulmonary disease; Colonization; Comparative analysis; Deoxyribonucleic acid; DNA; DNA methylation; DNA methyltransferase; Gene expression; Genes; Genetic aspects; Genetic diversity; Genomes; Health aspects; Host-bacteria relationships; Identification; Infections; Lung diseases; Medicine and Health Sciences; Microenvironments; Middle ear; Mimicry; Moraxella catarrhalis; Mucosa; Mutation; Nasopharynx; Nucleotide sequence; Obstructive lung disease; Opportunist infection; Otitis media; Pathogens; Permease; Phase variations; Proteins; Respiratory tract; Simple sequence repeats; Vaccines; Virulence; Australia; United Kingdom > UK; Queensland Australia
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0234306

Moraxella catarrhalis is a human-adapted, opportunistic bacterial pathogen of the respiratory mucosa. Although asymptomatic colonization of the nasopharynx is common, M. catarrhalis can ascend into the middle ear, where it is a prevalent causative agent of otitis media in children, or enter the lower respiratory tract, where it is associated with acute exacerbations of chronic obstructive pulmonary disease in adults. Phase variation is the high frequency, random, reversible switching of gene expression that allows bacteria to adapt to different host microenvironments and evade host defences, and is most commonly mediated by simple DNA sequence repeats. Bioinformatic analysis of five closed M. catarrhalis genomes identified 17 unique simple DNA sequence repeat tracts that were variable between strains, indicating the potential to mediate phase variable expression of the associated genes. Assays designed to assess simple sequence repeat variation under conditions mimicking host infection demonstrated that phase variation of uspA1 (ubiquitous surface protein A1) from high to low expression occurs over 72 hours of biofilm passage, while phase variation of uspA2 (ubiquitous surface protein A2) to high expression variants occurs during repeated exposure to human serum, as measured by mRNA levels. We also identify and confirm the variable expression of two novel phase variable genes encoding a Type III DNA methyltransferase (modO), and a conserved hypothetical permease (MC25239_RS00020). These data reveal the repertoire of phase variable genes mediated by simple sequence repeats in M. catarrhalis and demonstrate that modulation of expression under conditions mimicking human infection is attributed to changes in simple sequence repeat length.