The role of EmhABC efflux pump in Pseudomonas fluorescens LP6a

• Author / Creator

  Adebusuyi, Abigail A

• 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.

• Subjects / Keywords

  • Pseudomonas fluorescens
  • Physico-chemical factors
  • RND efflux pumps
  • Membrane fatty acids
  • Polycyclic aromatic hydrocarbons
  • Membrane modification
  • EmhABC
  • Membrane permeability
  • Environmental pollutants
  • Biodegradation

• Graduation date

  Fall 2012

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3ZD3T

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.