The Legionella pneumophila rpoS Gene Is Required for Growth within Acanthamoeba castellanii

Abstract

To investigate regulatory networks in Legionella pneumophila, the gene encoding the homolog of theEscherichia coli stress and stationary-phase sigma factor RpoS was identified by complementation of an E. coli rpoSmutation. An open reading frame that is approximately 60% identical to the E. coli rpoS gene was identified. Western blot analysis showed that the level of L. pneumophila RpoS increased in stationary phase. An insertion mutation was constructed in therpoS gene on the chromosome of L. pneumophila, and the ability of this mutant strain to survive various stress conditions was assayed and compared with results for the wild-type strain. Both the mutant and wild-type strains were more resistant to stress when in stationary phase than when in the logarithmic phase of growth. This finding indicates that L. pneumophila RpoS is not required for a stationary-phase-dependent resistance to stress. Although the mutant strain was able to kill HL-60- and THP-1-derived macrophages, it could not replicate within a protozoan host,Acanthamoeba castellanii. These data suggest that L. pneumophila possesses a growth phase-dependent resistance to stress that is independent of RpoS control and that RpoS likely regulates genes that enable it to survive in the environment within protozoa. Our data indicate that the role of rpoS inL. pneumophila is very different from what has previously been reported for E. coli rpoS.

The autoinducer synthase LqsA and putative sensor kinase LqsS regulate phagocyte interactions, extracellular filaments and a genomic island of Legionella pneumophila

“…In stationary growth phase L. pneumophila is sensitive to sodium chloride, a characteristic that is linked to virulence of the bacteria (Hales and Shuman, 1999). The salt sensitivity of L. pneumophila lacking lqsA or lqsS was assayed by spotting the strains in different dilutions on CYE agar plates either containing 100 mM NaCl or not (Fig.…”

“…The transition proceeds via a 'stringent response' and the production of the second messenger guanosine 3′,5′-bispyrophosphate (ppGpp) by the RelA and SpoT synthases (Hammer and Swanson, 1999;Zusman et al, 2002;Dalebroux et al, 2009). In response to ppGpp the alternative sigma factors RpoS (s S /s 38 ), RpoN (s 54 ) and FliA (s 28 ) control the expression of transmission traits, including contact-dependent cytotoxicity, lysosome evasion, motility and intracellular multiplication (Hales and Shuman, 1999;Hammer et al, 2002;Bachman and Swanson, 2004;Jacobi et al, 2004;Molofsky et al, 2005).…”

The Legionella pneumophila response regulator LqsR promotes host cell interactions as an element of the virulence regulatory network controlled by RpoS and LetA

“…Wild-type L. pneumophila is salt-sensitive, a trait that is intimately linked to virulence, such that avirulent strains are more salt-resistant (Hales and Shuman, 1999). To test whether lqsR affects the salt sensitivity of L. pneumophila, strain JR32 was grown to stationary phase and spotted in different dilutions on CYE agar plates containing 100 mM NaCl.…”

The response regulator LetA regulates the stationary-phase stress response in Legionella pneumophila and is required for efficient infection of Acanthamoeba castellanii

“…The resistance of L. pneumophila strains to acidic stress was determined as described elsewhere [25]. L. pneumophila strains were inoculated into BYE medium and grown at 37 ‡C until stationary phase was reached.…”