title: Identification of gene products involved in the oxidative stress response of Moraxella catarrhalis.
abstract: Moraxella catarrhalis is subjected to oxidative stress from both internal and environmental sources. A previous study (C. D. Pericone, K. Overweg, P. W. Hermans, and J. N. Weiser, Infect. Immun. 68:3990-3997, 2000) indicated that a wild-type strain of M. catarrhalis was very resistant to killing by exogenous hydrogen peroxide (H₂O₂). The gene encoding OxyR, a LysR family transcriptional regulator, was identified and inactivated in M. catarrhalis strain O35E, resulting in an increase in sensitivity to killing by H₂O₂ in disk diffusion assays and a concomitant aerobic serial dilution effect. Genes encoding a predicted catalase (KatA) and an alkyl hydroperoxidase (AhpCF) showed dose-dependent upregulation in wild-type cells exposed to H₂O₂. DNA microarray and real-time reverse transcription-PCR (RT-PCR) analyses identified M. catarrhalis genes whose expression was affected by oxidative stress in an OxyR-dependent manner. Testing of M. catarrhalis O35E katA and ahpC mutants for their abilities to scavenge exogenous H₂O₂ showed that the KatA catalase was responsible for most of this activity in the wild-type parent strain. The introduction of the same mutations into M. catarrhalis strain ETSU-4 showed that the growth of a ETSU-4 katA mutant was markedly inhibited by the addition of 50 mM H₂O₂ but that this mutant could still form a biofilm equivalent to that produced by its wild-type parent strain.
authors.affiliation: Department of Internal Medicine, Pulmonary and Critical Care Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
authors.forename: Todd C
authors.initials: TC
authors.lastname: Hoopman
authors.forename: Wei
authors.initials: W
authors.lastname: Liu
authors.forename: Stephanie N
authors.initials: SN
authors.lastname: Joslin
authors.forename: Christine
authors.initials: C
authors.lastname: Pybus
authors.forename: Chad A
authors.initials: CA
authors.lastname: Brautigam
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Hansen
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002374:Catalase / Q000235:genetics / Q000378:metabolism; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008969:Molecular Sequence Data; D001936:Moraxella catarrhalis / Q000187:drug effects* / Q000378:metabolism*; D018384:Oxidative Stress / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; D006861:Hydrogen Peroxide; D002374:Catalase