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Journal of Bacteriology, September 2007, p. 6695-6703, Vol. 189, No. 18
0021-9193/07/$08.00+0     doi:10.1128/JB.00023-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

The Autotransporter Esterase EstA of Pseudomonas aeruginosa Is Required for Rhamnolipid Production, Cell Motility, and Biofilm Formation

Susanne Wilhelm,¹ Aneta Gdynia,¹ Petra Tielen,^2, Frank Rosenau,^1* and Karl-Erich Jaeger¹

Institute For Molecular Enzyme Technology, Heinrich Heine University Duesseldorf, Research Centre Juelich, D-52426 Juelich, Germany,¹ Biofilm Centre, University Duisburg-Essen, Geibelstr. 41, D-47057 Duisburg, Germany²

Received 5 January 2007/ Accepted 2 July 2007

Pseudomonas aeruginosa PAO1 produces the biodetergent rhamnolipid and secretes it into the extracellular environment. The role of rhamnolipids in the life cycle and pathogenicity of P. aeruginosa has not been completely understood, but they are known to affect outer membrane composition, cell motility, and biofilm formation. This report is focused on the influence of the outer membrane-bound esterase EstA of P. aeruginosa PAO1 on rhamnolipid production. EstA is an autotransporter protein which exposes its catalytically active esterase domain on the cell surface. Here we report that the overexpression of EstA in the wild-type background of P. aeruginosa PAO1 results in an increased production of rhamnolipids whereas an estA deletion mutant produced only marginal amounts of rhamnolipids. Also the known rhamnolipid-dependent cellular motility and biofilm formation were affected. Although only a dependence of swarming motility on rhamnolipids has been known so far, the other kinds of motility displayed by P. aeruginosa PAO1, swimming and twitching, were also affected by an estA mutation. In order to demonstrate that EstA enzyme activity is responsible for these effects, inactive variant EstA* was constructed by replacement of the active serine by alanine. None of the mutant phenotypes could be complemented by expression of EstA*, demonstrating that the phenotypes affected by the estA mutation depend on the enzymatically active protein.

Published ahead of print on 13 July 2007.

Present address: Institute for Microbiology, Technical University Braunschweig, D-38023 Braunschweig, Germany.

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