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Journal of Bacteriology, April 2007, p. 3124-3132, Vol. 189, No. 8
0021-9193/07/$08.00+0     doi:10.1128/JB.01677-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Cross Talk between Type III Secretion and Flagellar Assembly Systems in Pseudomonas aeruginosa

Chantal Soscia, Abderrahman Hachani, Alain Bernadac, Alain Filloux, and Sophie Bleves^*

Laboratoire d'Ingénierie des Systèmes Macromoléculaires (LISM), CNRS-IBSM-UPR9027, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France

Received 30 October 2006/ Accepted 31 January 2007

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 (fliC) presented a hyperefficient T3SS and a nonmotile strain assembling flagella (motAB) 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.

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* Corresponding author. Mailing address: Laboratoire d'Ingénierie des Systèmes Macromoléculaires (LISM), CNRS-IBSM-UPR9027, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France. Phone: 33491164126. Fax: 33491712124. E-mail: bleves{at}ibsm.cnrs-mrs.fr

Published ahead of print on 16 February 2007.

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Journal of Bacteriology, April 2007, p. 3124-3132, Vol. 189, No. 8
0021-9193/07/$08.00+0     doi:10.1128/JB.01677-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

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