Legionella pneumophila Catalase-Peroxidases Are Required for Proper Trafficking and Growth in Primary Macrophages

Abstract

Legionella pneumophila, a parasite of aquatic amoebae and pathogen of pulmonary macrophages, replicates intracellularly, utilizing a type IV secretion system to subvert the trafficking of Legionella-containing phagosomes. Defense against host-derived reactive oxygen species has been proposed as critical for intracellular replication. Virulence traits of null mutants in katA and katB, encoding the two Legionella catalase-peroxidases, were analyzed to evaluate the hypothesis that L. pneumophila must decompose hydrogen peroxide to establish a replication niche in macrophages. Phagosomes containing katA or katB mutant Legionella colocalize with LAMP-1, a late endosomal-lysosomal marker, at twice the frequency of those of wild-type strain JR32 and show a decreased frequency of bacterial replication, in similarity to phenotypes of mutants with mutations in dotA and dotB, encoding components of the Type IV secretion system. Quantitative similarity of the katA/B phenotypes indicates that each contributes to virulence traits largely independently of intracellular compartmentalization (KatA in the periplasm and KatB in the cytosol). These data support a model in which KatA and KatB maintain a critically low level of H 2 O 2 compatible with proper phagosome trafficking mediated by the type IV secretion apparatus. During these studies, we observed that dotA and dotB mutations in wild-type strain Lp02 had no effect on intracellular multiplication in the amoeba Acanthamoeba castellanii, indicating that certain dotA/B functions in Lp02 are dispensable in that experimental model. We also observed that wild-type JR32, unlike Lp02, shows minimal contact-dependent cytotoxicity, suggesting that cytotoxicity of JR32 is not a prerequisite for formation of replication-competent Legionella phagosomes in macrophages.

The Quorum Sensing-Dependent Gene katG of Burkholderia glumae Is Important for Protection from Visible Light

“…Pathogenic microorganisms encounter ROS when interacting with host cells during infection (1,3), and catalases are associated with virulence in various bacterial pathogens, including L. pneumophila and Agrobacterium tumefaciens (2,35). KatA of Campylobacter jejuni is essential for its survival in macrophages (5).…”

“…For example, the major catalase KatA of Pseudomonas aeruginosa is important for full virulence (9). KatA and KatB of Legionella pneumophila detoxify the phagosomal milieu to promote intracellular growth of the bacterium (2). In Mycobacterium tuberculosis, KatG is important for survival in ROS-producing macrophages and for virulence in mice (29).…”

Both Inducible Nitric Oxide Synthase and NADPH Oxidase Contribute to the Control of Virulent Phase ICoxiella burnetiiInfections

“…One possibility for the extended doubling times observed in NADPH oxidase and iNOS competent cells is that C. burnetii may devote more energy to up-regulating genes that are necessary to detoxify low levels of reactive nitrogen and oxygen intermediates that may be present in resting macrophages. For example, stationary-phase infectious Legionella pneumophila has been demonstrated to express several virulence traits, including catalase and superoxide dismutase, that are thought to be important for L. pneumophila to establish an infection (10,11,53).…”

Compensatory Functions of Two Alkyl Hydroperoxide Reductases in the Oxidative Defense System ofLegionella pneumophila

“…Since some evidence suggests that L. pneumophila may be faced with an oxidative burst following ingestion by macrophages or amoebae (30,39), protection against ROI may be crucial for pathogenesis. It has been proposed that the L. pneumophila KatA and KatB catalase-peroxidases might provide catalatic activity to detoxify the phagosomal milieu to promote intracellular growth (3). However, L. pneumophila has been shown to be especially susceptible to oxidizing biocides (ozone and H 2 O 2 ) in vitro, indicating that the pathogen might be unusually sensitive to oxidative stress (18,42).…”