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Phenotypic modulation by Legionella pneumophila upon infection of macrophages
Y Abu Kwaik1, B I Eisenstein, N C Engleberg
1Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor 48109-0620.
Abstract:
Since many pathogenic bacteria manifest a coordinate regulation of gene expression in response to different environmental stimuli, we examined the phenotypic response of Legionella pneumophila to infection of macrophage-like U937 cells. Intracellular L. pneumophila was radiolabeled, and cell extracts were subjected to two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis. At least 35 Legionella proteins were selectively induced during infection of macrophages, and one of these proteins was not detected in organisms grown in vitro. Expression of at least 32 proteins was selectively repressed during infection of macrophages, and 9 of these proteins were undetectable in intracellularly grown organisms. Thirteen of the macrophage-induced proteins were also induced by one or more of several stress conditions in vitro, and two of these proteins were the heat shock GroEL- and GroES-like proteins. Nineteen of the macrophage-repressed proteins were also repressed by one or more of the stress conditions in vitro. Our data showed that intracellular L. pneumophila manifested a phenotypic modulation and a global stress response to the intracellular environment of the macrophage. The data suggested that multiple regulons are involved in this modulation, which may contribute to the survival of L. pneumophila within alveolar macrophages.
Insights
Legionella pneumophila alters protein expression during macrophage infection, indicating a stress response. This phenotypic modulation aids bacterial survival within host cells.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Cellular Biology
Background:
- Pathogenic bacteria often regulate gene expression in response to environmental changes.
- Understanding bacterial adaptation within host cells is crucial for combating infections.
Purpose of the Study:
- To investigate the phenotypic response of Legionella pneumophila during infection of macrophage-like U937 cells.
- To identify specific protein expression changes indicative of an intracellular stress response.
Main Methods:
- Radiolabeling of intracellular L. pneumophila.
- Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (2D SDS-PAGE) to analyze protein expression.
- Comparison of protein profiles from intracellular bacteria versus in vitro grown bacteria.
Main Results:
- Significant induction (≥35 proteins) and repression (≥32 proteins) of Legionella pneumophila proteins during macrophage infection.
- Identification of unique proteins expressed only intracellularly and proteins undetectable in vitro.
- Correlation of some induced/repressed proteins with in vitro stress conditions, including heat shock proteins (GroEL/GroES).
Conclusions:
- Intracellular L. pneumophila exhibits significant phenotypic modulation and a global stress response within macrophages.
- Multiple bacterial regulons are likely involved in adapting to the intracellular environment.
- This adaptation is critical for the survival of L. pneumophila within alveolar macrophages.