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Applied and Environmental Microbiology, November 2008, p. 6980-6986, Vol. 74, No. 22
0099-2240/08/$08.00+0     doi:10.1128/AEM.01117-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Mechanisms of Cation Exchange by Pseudomonas aeruginosa PAO1 and PAO1 wbpL, a Strain with a Truncated Lipopolysaccharide{triangledown}

J. Shephard,1 A. J. McQuillan,1 and P. J. Bremer2*

Department of Chemistry, University of Otago, Dunedin, New Zealand,1 Department of Food Science, University of Otago, Dunedin, New Zealand2

Received 18 May 2008/ Accepted 17 September 2008

The ability of bacterial cells to sequester cations is well recognized, despite the fact that the specific binding sites and mechanistic details of the process are not well understood. To address these questions, the cation-exchange behavior of Pseudomonas aeruginosa PAO1 cells with a truncated lipopolysaccharide (LPS) (PAO1 wbpL) and cells further modified by growth in a magnesium-deficient medium (PAO1 wbpL – Mg2+) were compared with that of wild-type P. aeruginosa PAO1 cells. P. aeruginosa PAO1 cells had a negative surface charge (zeta potential) between pH 11 and 2.2, due to carboxylate groups present in the B-band LPS. The net charge on PAO1 wbpL cells was increasingly positive below pH 3.5, due to the influence of NH3+ groups in the core LPS. The zeta potentials of these cells were also measured in Na+, Ca2+, and La3+ electrolytes. Cells in the La3+ electrolyte had a positive zeta potential at all pH values tested. Growing P. aeruginosa PAO1 wbpL in magnesium-deficient medium (PAO1 wbpL – Mg2+) resulted in an increase in its zeta potential in the pH range from 3.0 to 6.5. In cation-exchange experiments carried out at neutral pH with either P. aeruginosa PAO1 or PAO1 wbpL, the concentration of bound Ca2+ was found to decrease as the pH was reduced from 7.0 to 3.5. At pH 3.5, the bound Mg2+ concentration decreased sharply, revealing the activity of surface sites for cation exchange and their pH dependence. Infrared spectroscopy of attached biofilms suggested that carboxylate and phosphomonoester functional groups within the core LPS are involved in cation exchange.

* Corresponding author. Mailing address: Department of Food Science, University of Otago, P.O. Box 56, Dunedin, New Zealand. Phone: 643-479-5468. Fax: 643-479-7567. E-mail: phil.bremer{at}otago.ac.nz

{triangledown} Published ahead of print on 26 September 2008.

Applied and Environmental Microbiology, November 2008, p. 6980-6986, Vol. 74, No. 22
0099-2240/08/$08.00+0     doi:10.1128/AEM.01117-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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