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Journal of Bacteriology, September 1998, p. 4442-4451, Vol. 180, No. 17
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

The Pseudomonas aeruginosa rhlG Gene Encodes an NADPH-Dependent beta -Ketoacyl Reductase Which Is Specifically Involved in Rhamnolipid Synthesis

Jesús Campos-García,1 Alma Delia Caro,1 Rebeca Nájera,1 Raina M. Miller-Maier,2 Ragheb A. Al-Tahhan,2 and Gloria Soberón-Chávez1,*

Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos 62250, México,1 and Department of Soil and Water Science, University of Arizona, Tucson, Arizona 857212

Received 6 April 1998/Accepted 9 June 1998

A Pseudomonas aeruginosa gene homologous to the fabG gene, which encodes the NADPH-dependent beta -ketoacyl-acyl carrier protein (ACP) reductase required for fatty acid synthesis, was identified. The insertional mutation of this fabG homolog (herein called rhlG) produced no apparent effect on the growth rate and total lipid content of P. aeruginosa cells, but the production of rhamnolipids was completely abrogated. These results suggest that the synthetic pathway for the fatty acid moiety of rhamnolipids is separate from the general fatty acid synthetic pathway, starting with a specific ketoacyl reduction step catalyzed by the RhlG protein. In addition, the synthesis of poly-beta -hydroxyalkanoate (PHA) is delayed in this mutant, suggesting that RhlG participates in PHA synthesis, although it is not the only reductase involved in this pathway. Traits regulated by the quorum-sensing response, other than rhamnolipid production, including production of proteases, pyocyanine, and the autoinducer butanoyl-homoserine lactone (PAI-2), were not affected by the rhlG mutation. We conclude that the P. aeruginosa rhlG gene encodes an NADPH-dependent beta -ketoacyl reductase absolutely required for the synthesis of the beta -hydroxy acid moiety of rhamnolipids and that it has a minor role in PHA production. Expression of rhlG mRNA under different culture conditions is consistent with this conclusion.

* Corresponding author. Mailing address: Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apdo. Postal 510-3, Cuernavaca, Morelos 62250, Mexico. Phone: (52) (73) 291634. Fax: (52) (73) 172388. E-mail: gloria{at}ibt.unam.mx.

Journal of Bacteriology, September 1998, p. 4442-4451, Vol. 180, No. 17
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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