A Moraxella catarrhalis Two-Component Signal Transduction System Necessary for Growth in Liquid Media Affects Production of Two Lysozyme Inhibitors

Abstract

There are a paucity of data concerning gene products that could contribute to the ability ofMoraxella catarrhalisto colonize the human nasopharynx. Inactivation of a gene (mesR) encoding a predicted response regulator of a two-component signal transduction system inM. catarrhalisyielded a mutant unable to grow in liquid media. ThismesRmutant also exhibited increased sensitivity to certain stressors, including polymyxin B, SDS, and hydrogen peroxide. Inactivation of the gene (mesS) encoding the predicted cognate sensor (histidine) kinase yielded a mutant with the same inability to grow in liquid media as themesRmutant. DNA microarray and real-time reverse transcriptase PCR analyses indicated that several genes previously shown to be involved in the ability ofM. catarrhalisto persist in the chinchilla nasopharynx were upregulated in themesRmutant. Two other open reading frames upregulated in themesRmutant were shown to encode small proteins (LipA and LipB) that had amino acid sequence homology to bacterial adhesins and structural homology to bacterial lysozyme inhibitors. Inactivation of bothlipAandlipBdid not affect the ability ofM. catarrhalisO35E to attach to a human bronchial epithelial cell linein vitro. Purified recombinant LipA and LipB fusion proteins were each shown to inhibit human lysozyme activityin vitroand in saliva. AlipA lipBdeletion mutant was more sensitive than the wild-type parent strain to killing by human lysozyme in the presence of human apolactoferrin. This is the first report of the production of lysozyme inhibitors byM. catarrhalis.