Phenotypic modulation by Legionella pneumophila upon infection of macrophages

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.

Temperature Effects on Legionella pneumophila Killing by and Multiplication in Phagocytes of Guinea Pigs

“…4) could grow as well at 42 C as at 37 C. These results suggest that the organism may acquire resistance to 42 C by being phagocytosed. Kwaik et al reported that eleven heat shock proteins of L. pneumophila, including a 60-kDa GroEL-like protein and a 10-kDa GroES-like protein, were induced by phagocytosis by macrophages (11). We also reported that four Legionella proteins (24, 100, 65, and 16 kDa) were induced during intracellular bacterial growth in macrophages (13).…”

The use of differential display‐PCR to isolate and characterize a Legionella pneumophila locus induced during the intracellular infection of macrophages

“…Since many of the MI loci are also induced by stress stimuli (Abu Kwaik et a/., 1993), we examined whether the chromosomal locus represented by the pCS13 insert was also induced by stress stimuli in vitro. The dot blot procedure was performed on RNA isolated from in vitrc-grown bacteria following exposure to heat shock, osmotic shock, acid shock (not shown) or oxidative stress ( Fig.…”

“…Biosynthesis of at least 35 L. pneumophila proteins is induced during logarithmic growth within the macrophage-like U937 cells (Abu Kwaik eta/., 1993). Approximately 1/3 of the macrophage-induced genes (13135) of L. pneumophila are also induced by one or more in vitro stress stimuli (Abu Kwaik et a/., 1993). We believe that the majority of the MI genes that are induced very early in intracellular infection (approximately the first hour) are involved in the bacterial stress response to phagocytosis and to the new intracellular environment.…”

“…The technique of reverse genetics has been used previously to clone one of the MI genes of L. pneumophila (Abu . This technique is limited by the need for an abundant amount of synthesized proteins, which are undetectable during the first few hours of the intracellular infection by L. pneumophila (Abu Kwaik et al, 1993). Therefore, the use of this technique is not possible for examination of bacterial gene expression during the early stages of intracellular infection.…”

Participation of the molecular chaperone DnaK in intracellular growth of Brucella suis within U937‐derived phagocytes

“…Facultatively intracellular bacteria have developed various strategies in order to withstand the bactericidal environment of the phagocyte: (i) escape from the phagosome into the cytoplasm, (ii) inhibition of phagosome maturation, or (iii) resistance to low pH and to the enzymes of the phagolysosome. Salmonella typhimurium and Legionella pneumophila have adapted to the intracellular environment of the macrophage by the selective induction and repression of a multitude of proteins (Buchmeier and Heffron, 1990;Abshire and Neidhardt, 1993;Kwaik et a/., 1993). In salmonellae, virulence-gene transcription is activated by PhoP/PhoQ after phagosome acidification (Aranda et a/., 1992).…”