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Journal of Bacteriology, February 1999, p. 973-980, Vol. 181, No. 3
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Effect of wzx (rfbX) Mutations on A-Band and B-Band Lipopolysaccharide Biosynthesis in Pseudomonas aeruginosa O5

Lori L. Burrows and Joseph S. Lam*

Department of Microbiology, University of Guelph, Guelph, Ontario, Canada N1G 2W1

Received 15 July 1998/Accepted 17 November 1998

The wbp cluster of Pseudomonas aeruginosa O5 encodes a number of proteins involved in biosynthesis of the heteropolymeric and Wzy-dependent B-band O antigen, including Wzy, the O-antigen polymerase, and Wzz, the regulator of O-antigen chain length. A gene (formerly wbpF), contiguous with wzy in the wbp cluster, is predicted to encode a highly hydrophobic protein with multiple membrane-spanning domains. This secondary structure is consistent with that of Wzx (RfbX), the putative O-antigen unit translocase or "flippase." Insertion of a Gmr cassette at two separate sites within the putative wzx gene led in both cases to the loss of B-band lipopolysaccharide (LPS) O-antigen production. To our knowledge, this is the first report of the successful generation of chromosomal wzx gene replacement mutations. Surprisingly, inactivation of wzx also led to a marked delay in production of the ATP-binding cassette-transporter-dependent, D-rhamnose homopolymer, A-band LPS. This effect on A-band LPS synthesis was alleviated by supplying multiple copies of WbpL in trans. WbpL, a WecA (Rfe) homologue, was shown recently to be essential for the initiation of both A-band and B-band LPS synthesis in P. aeruginosa O5 (H. L. Rocchetta, L. L. Burrows, J. C. Pacan, and J. S. Lam, Mol. Microbiol. 28:1103-1119, 1998). These results suggest that the delay in A-band LPS production may arise from insufficient access to WbpL when the completed B-band O unit is not successfully translocated to the periplasm. Without adequate WbpL, A-band LPS synthesis is delayed. A subset of wzx mutants appeared to have accumulated second-site mutations which either restored the normal expression of A-band LPS or abolished A-band expression completely. Complementation studies showed that all of the additional mutations affecting LPS synthesis that were characterized in this study were located within the B-band LPS genes.

* Corresponding author. Mailing address: Department of Microbiology, University of Guelph, Guelph, Ontario, Canada N1G 2W1. Phone: (519) 824-4120, ext. 3823. Fax: (519) 837-1802. E-mail: jlam{at}uoguelph.ca.

Journal of Bacteriology, February 1999, p. 973-980, Vol. 181, No. 3
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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