Cross talk between type III secretion and flagellar assembly systems in Pseudomonas aeruginosa.
Pseudomonas aeruginosa cytotoxicity is linked to a type III secretion system (T3SS) that delivers effectors into the host cell. We show here that a negative cross-control exists between T3SS and flagellar assembly. We observed that, in a strain lacking flagella, T3SS gene expression, effector secretion, and cytotoxicity were increased. Conversely, we revealed that flagellar-gene expression and motility were decreased in a strain overproducing ExsA, the T3SS master regulator. Interestingly, a nonmotile strain lacking the flagellar filament (DeltafliC) presented a hyperefficient T3SS and a nonmotile strain assembling flagella (DeltamotAB) did not. More intriguingly, a strain lacking motCD genes is a flagellated strain with a slight defect in swimming. However, in this strain, T3SS gene expression was up-regulated. These results suggest that flagellar assembly and/or mobility antagonizes the T3SS and that a negative cross talk exists between these two systems. An illustration of this is the visualization by electron microscopy of T3SS needles in a nonmotile P. aeruginosa strain, needles which otherwise are not detected. The molecular basis of the cross talk is complex and remains to be elucidated, but proteins like MotCD might have a crucial role in signaling between the two processes. In addition, we found that the GacA response regulator negatively affects the T3SS. In a gacA mutant, the T3SS effector ExoS is hypersecreted. Strikingly, GacA was previously reported as a positive regulator for motility. Globally, our data document the idea that some virulence factors are coordinately but inversely regulated, depending on the bacterial colonization phase and infection types.
Soscia
Chantal
C
Laboratoire d'Ingénierie des Systèmes Macromoléculaires (LISM), CNRS-IBSM-UPR9027, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France.
Hachani
Abderrahman
A
Bernadac
Alain
A
Filloux
Alain
A
Bleves
Sophie
S
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D005407:Flagella / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins; D051379:Mice; D020409:Molecular Motor Proteins / Q000235:genetics / Q000378:metabolism*; D011550:Pseudomonas aeruginosa / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D018085:Regulon / Q000502:physiology; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism
D001426:Bacterial Proteins; D002352:Carrier Proteins; C095093:ExsA protein, Pseudomonas aeruginosa; C091100:GacA protein, Bacteria; D036341:Intercellular Signaling Peptides and Proteins; D020409:Molecular Motor Proteins; C506611:PscF protein, Pseudomonas aeruginosa; D011993:Recombinant Fusion Proteins; D015534:Trans-Activators