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The role of EmhABC efflux pump in Pseudomonas fluorescens LP6a Open Access


Other title
Membrane fatty acids
Pseudomonas fluorescens
Membrane modification
RND efflux pumps
Environmental pollutants
Polycyclic aromatic hydrocarbons
Membrane permeability
Physico-chemical factors
Type of item
Degree grantor
University of Alberta
Author or creator
Adebusuyi, Abigail A
Supervisor and department
Foght, Julia (Biological Sciences)
Examining committee member and department
Turner, Raymond (Biological Sciences, University of Calgary)
Gray, Murray (Chemical and Materials Engineering)
Foght, Julia (Biological Sciences)
Dennis, Jonathan (Biological Sciences)
Pukatzki, Stefan (Medical Microbiology and Immunology)
Department of Biological Sciences
Microbiology and Biotechnology
Date accepted
Graduation date
Doctor of Philosophy
Degree level
Efflux pumps belonging to the resistance-nodulation-division (RND) superfamily in bacteria are involved in antibiotic resistance and solvent tolerance but have an unknown physiological role. EmhABC, a RND-type efflux pump in the hydrocarbon-degrading bacterium Pseudomonas fluorescens LP6a, extrudes hydrophobic antibiotics, dyes and polycyclic aromatic hydrocarbons (PAHs) including phenanthrene and anthracene but not naphthalene. Because PAH substrates of EmhABC are also carbon sources for LP6a, the authentic physiological role of this pump in LP6a was determined. The effects of physico-chemical factors such as temperature or antibiotics on the activity and expression of EmhABC were examined in order to deduce its authentic role(s) in LP6a. Based on expression studies, efflux assays and membrane fatty acid analysis, induction of EmhABC expression by physico-chemical factors is linked to modulation of membrane fatty acids. Physico-chemical factors such as variation in incubation temperature, pH and increased Mg2+ concentration induced the expression of EmhABC, whereas pump substrates such as phenanthrene and chloramphenicol did not. The active efflux of phenanthrene decreased the efficiency of phenanthrene degradation by LP6a but the presence of EmhABC was important for efficient degradation of naphthalene. This suggests that the activity of EmhABC in LP6a has implications for bioremediation and biocatalytic transformation of PAHs and heterocycles. The deleterious effect of an antibiotic or other compound on cell membrane integrity and fatty acid composition may be the signal that initiates the induction of the EmhABC efflux pump, and inducers of bacterial efflux pumps may include environmental factors rather than the substrates per se. For effective treatment of bacterial infections, the factors affecting a bacterial pathogen in its environment and the effect of the antibiotic on the membrane should be considered. These observations suggest that the EmhABC efflux pump may be involved in the management of membrane stress. Efflux of fatty acids replaced as a result of membrane damage or phospholipid turnover may be the authentic physiological role of the EmhABC efflux pump in P. fluorescens LP6a.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
 Adebusuyi AA, Foght JM (2011) An alternative physiological role for the EmhABC efflux pumps in Pseudomonas fluorescens cLP6a. BMC Microbiol 11:252 Adebusuyi AA, Smith AY, Gray MR, Foght JM (2012) The EmhABC efflux pump decreases efficiency of phenanthrene biodegradation by Pseudomonas fluorescens strain LP6a. Appl Microbiol Biotechnol doi:10.1007/s00253-012-3932-4

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