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Open Access Research article

Interaction between extracellular lipase LipA and the polysaccharide alginate of Pseudomonas aeruginosa

Petra Tielen14*, Hubert Kuhn2, Frank Rosenau35, Karl-Erich Jaeger3, Hans-Curt Flemming1 and Jost Wingender1

Author Affiliations

1 Department of Aquatic Microbiology, University of Duisburg-Essen, Faculty of Chemistry, Biofilm Centre, Universitätsstrasse 5, D-45141, Essen, Germany

2 University of Duisburg-Essen, CAM-D Technologies GmbH, Schützenbahn 70, D-45117, Essen, Germany

3 Institute for Molecular Enzyme Technology, Heinrich-Heine-University of Duesseldorf, Research Centre Juelich, Stetternicher Forst, D-52425, Juelich, Germany

4 Current adress: Institute for Microbiology, Technische Universität Braunschweig, Spielmannstrasse 7, D-38106, Braunschweig, Germany

5 Current adress: Institute for Pharmaceutical Biotechnology/ Ulm Centre for Peptide Pharmaceuticals, University Ulm, Albert-Einstein-Allee 11, D-89081, Ulm, Germany

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BMC Microbiology 2013, 13:159  doi:10.1186/1471-2180-13-159

Published: 13 July 2013

Abstract

Background

As an opportunistic human pathogen Pseudomonas aeruginosa is able to cause acute and chronic infections. The biofilm mode of life significantly contributes to the growth and persistence of P. aeruginosa during an infection process and mediates the pathogenicity of the bacterium. Within a biofilm mucoid strains of P. aeruginosa simultaneously produce and secrete several hydrolytic enzymes and the extracellular polysaccharide alginate. The focus of the current study was the interaction between extracellular lipase LipA and alginate, which may be physiologically relevant in biofilms of mucoid P. aeruginosa.

Results

Fluorescence microscopy of mucoid P. aeruginosa biofilms were performed using fluorogenic lipase substrates. It showed a localization of the extracellular enzyme near the cells. A microtiter plate-based binding assay revealed that the polyanion alginate is able to bind LipA. A molecular modeling approach showed that this binding is structurally based on electrostatic interactions between negatively charged residues of alginate and positively charged amino acids of the protein localized opposite of the catalytic centre. Moreover, we showed that the presence of alginate protected the lipase activity by protection from heat inactivation and from degradation by the endogenous, extracellular protease elastase LasB. This effect was influenced by the chemical properties of the alginate molecules and was enhanced by the presence of O-acetyl groups in the alginate chain.

Conclusion

We demonstrate that the extracellular lipase LipA from P. aeruginosa interacts with the polysaccharide alginate in the self-produced extracellular biofilm matrix of P. aeruginosa via electrostatic interactions suggesting a role of this interaction for enzyme immobilization and accumulation within biofilms. This represents a physiological advantage for the cells. Especially in the biofilm lifestyle, the enzyme is retained near the cell surface, with the catalytic centre exposed towards the substrate and is protected from denaturation and proteolytic degradation.

Keywords:
Biofilm; Lipase; Polysaccharide; Interaction; Enzyme stability; Molecular modeling