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Journal of Bacteriology, February 2007, p. 929-939, Vol. 189, No. 3
0021-9193/07/$08.00+0     doi:10.1128/JB.01296-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Characterization of OpdH, a Pseudomonas aeruginosa Porin Involved in the Uptake of Tricarboxylates{triangledown}

Sandeep Tamber,1 Elke Maier,2 Roland Benz,2 and Robert E. W. Hancock1*

Department of Microbiology and Immunology, University of British Columbia, #235 2259 Lower Mall, Lower Mall Research Station, Vancouver, British Columbia, V6T 1Z4 Canada,1 Department of Biotechnology, Biocenter of the University of Würzburg, Am Hubland, D-97074, Würzburg, Germany2

Received 16 August 2006/ Accepted 7 November 2006

The Pseudomonas aeruginosa outer membrane is intrinsically impermeable to many classes of antibiotics, due in part to its relative lack of general uptake pathways. Instead, this organism relies on a large number of substrate-specific uptake porins. Included in this group are the 19 members of the OprD family, which are involved in the uptake of a diverse array of metabolites. One of these porins, OpdH, has been implicated in the uptake of cis-aconitate. Here we demonstrate that this porin may also enable P. aeruginosa to take up other tricarboxylates. Isocitrate and citrate strongly and specifically induced the opdH gene via a mechanism involving derepression by the putative two-component regulatory system PA0756-PA0757. Planar bilayer analysis of purified OpdH demonstrated that it was a channel-forming protein with a large single-channel conductance (230 pS in 1 M KCl; 10-fold higher than that of OprD); however, we were unable to demonstrate the presence of a tricarboxylate binding site within the channel. Thus, these data suggest that the requirement for OpdH for efficient growth on tricarboxylates was likely due to the specific expression of this large-channel porin under particular growth conditions.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, University of British Columbia, #235 2259 Lower Mall, Lower Mall Research Station, Vancouver, British Columbia, V6T 1Z4 Canada. Phone: (604) 822-2682. Fax: (604) 827-5566. E-mail: bob{at}cmdr.ubc.ca.

{triangledown} Published ahead of print on 17 November 2006.

Journal of Bacteriology, February 2007, p. 929-939, Vol. 189, No. 3
0021-9193/07/$08.00+0     doi:10.1128/JB.01296-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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