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Two small ncRNAs jointly govern virulence and transmission in Legionella pneumophila
Author(s) -
Sahr Tobias,
Brüggemann Holger,
Jules Matthieu,
Lomma Mariella,
AlbertWeissenberger Christiane,
Cazalet Christel,
Buchrieser Carmen
Publication year - 2009
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2009.06677.x
Subject(s) - virulence , legionella pneumophila , repressor , biology , rpos , microbiology and biotechnology , mutant , flagellum , psychological repression , bacteria , transcription factor , genetics , gene , gene expression , promoter
Summary To transit from intra‐ to extracellular environments, Legionella pneumophila differentiates from a replicative/non‐virulent to a transmissive/virulent form using the two‐component system LetA/LetS and the global repressor protein CsrA. While investigating how both regulators act co‐ordinately we characterized two ncRNAs, RsmY and RsmZ, that link the LetA/LetS and CsrA regulatory networks. We demonstrate that LetA directly regulates their expression and show that RsmY and RsmZ are functional in Escherichia coli and are able to bind CsrA in vitro . Single mutants have no (Δ rsmY ) or a little (Δ rsmZ ) impact on virulence, but the Δ rsmYZ strain shows a drastic defect in intracellular growth in Acanthamoeba castellanii and THP‐1 monocyte‐derived macrophages. Analysis of the transcriptional programmes of the Δ letA , Δ letS and Δ rsmYZ strains revealed that the switch to the transmissive phase is partially blocked. One major difference between the Δ letA , Δ letS and Δ rsmYZ strains was that the latter synthesizes flagella. Taken together, LetA activates transcription of RsmY and RsmZ, which sequester CsrA and abolish its post‐transcriptional repressive activity. However, the RsmYZ‐CsrA pathway appears not to be the main or only regulatory circuit governing flagella synthesis. We suggest that rather RpoS and LetA, by influencing LetE and probably cyclic‐di‐GMP levels, regulate motility in L. pneumophila .

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