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Journal of Bacteriology, November 1999, p. 6977-6986, Vol. 181, No. 22
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

A Novel Lipolytic Enzyme Located in the Outer Membrane of Pseudomonas aeruginosa

Susanne Wilhelm,1 Jan Tommassen,2 and Karl-Erich Jaeger1,*

Lehrstuhl Biologie der Mikroorganismen, Ruhr Universität, D-44780 Bochum, Germany,1 and Department of Molecular Microbiology and Institute of Biomembranes, Utrecht University, NL-3584 CH Utrecht, The Netherlands2

Received 13 July 1999/Accepted 8 September 1999

A lipase-negative deletion mutant of Pseudomonas aeruginosa PAO1 still showed extracellular lipolytic activity toward short-chain p-nitrophenylesters. By screening a genomic DNA library of P. aeruginosa PAO1, an esterase gene, estA, was identified, cloned, and sequenced, revealing an open reading frame of 1,941 bp. The product of estA is a 69.5-kDa protein, which is probably processed by removal of an N-terminal signal peptide to yield a 67-kDa mature protein. A molecular mass of 66 kDa was determined for 35S-labeled EstA by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography. The amino acid sequence of EstA indicated that the esterase is a member of a novel GDSL family of lipolytic enzymes. The estA gene showed high similarity to an open reading frame of unknown function located in the trpE-trpG region of P. putida and to a gene encoding an outer membrane esterase of Salmonella typhimurium. Amino acid sequence alignments led us to predict that this esterase is an autotransporter protein which possesses a carboxy-terminal beta -barrel domain, allowing the secretion of the amino-terminal passenger domain harboring the catalytic activity. Expression of estA in P. aeruginosa and Escherichia coli and subsequent cell fractionation revealed that the enzyme was associated with the cellular membranes. Trypsin treatment of whole cells released a significant amount of esterase, indicating that the enzyme was located in the outer membrane with the catalytic domain exposed to the surface. To our knowledge, this esterase is unique in that it exemplifies in P. aeruginosa (i) the first enzyme identified in the outer membrane and (ii) the first example of a type IV secretion mechanism.

* Corresponding author. Mailing address: Ruhr Universität Bochum, Lehrstuhl Biologie der Mikroorganismen, Universitätsstrasse 150, D-44780 Bochum, Germany. Phone: 49 234 322 3101. Fax: 49 234 321 4425. E-mail: karl-erich.jaeger{at}ruhr-uni-bochum.de.

Journal of Bacteriology, November 1999, p. 6977-6986, Vol. 181, No. 22
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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