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Role of microbial adhesion in phenanthrene biodegradation by Pseudomonas fluorescens LP6a Open Access


Other title
microbial adhesion, Pseudomonas fluorescens, Hydrophobicity, biodegradation, dodecanol
Type of item
Degree grantor
University of Alberta
Author or creator
Abbasnezhad, Hassan
Supervisor and department
Murray R. Gray (Chemical and Materials Engineering, University of Alberta)
Examining committee member and department
Xu, Zhenghe (Chemical and Materials Engineering, University of Alberta)
Daugulis, Andrew (chemical Engineering, Queen's University)
Yeung, Toney (Chemical and Materials Engineering, University of Alberta)
Foght M, Julia (Biological Sciences, University of Alberta)
Department of Chemical and Materials Engineering

Date accepted
Graduation date
Doctor of philosophy
Degree level
Biodegradation of poorly water soluble hydrocarbons, such as n-alkanes and polycyclic aromatic hydrocarbons (PAHs) is often limited by the low availability of the pollutant to microbes. Adhesion of microorganisms to the oil-water interface can influence this availability. Our approach was to study a range of compounds and mechanisms to promote the adhesion of a hydrophilic PAH degrading bacterium, Pseudomonas fluorescens LP6a, to an oil-water interface and examine the effect on biodegradation of phenanthrene by the bacteria. The cationic surfactants cetylpyridinium chloride (CPC), poly-L-lysine and chlorhexidine gluconate (CHX) and the long chain alcohols 1-dodecanol, 2-dodecanol and farnesol increased the adhesion of P. fluorescens LP6a to n-hexadecane from ca. 30% to ca. 90% of suspended cells adhering. The alcohols also caused a dramatic change in the oil-water contact angle of the cell surface, increasing it from 24° to 104°, whereas the cationic compounds had little effect. In contrast, cationic compounds changed the electrophoretic mobility of the bacteria, reducing the mean zeta potential from –23 to –7 mV in 0.01M potassium phosphate buffer, but the alcohols had no effect on zeta potential. This results illustrate that alcohols acted through altering the cell surface hydrophobicity, whereas cationic surfactants changed the surface charge density. Phenanthrene was dissolved in heptamethylnonane and introduced to the aqueous growth medium, hence forming a two phase system. Introducing 1-dodecanol at concentrations of 217, 820 or 4100 mg/L resulted in comparable increases in phenanthrene biodegradation of about 30% after 120 h incubation with non-induced cultures. After 100 h of incubation with LP6a cultures induced with 2-aminobenzoate, 4.5% of the phenanthrene was mineralized by cultures versus more than 10% by the cultures containing initial 1-dodecanol or 2-dodecanol concentrations of 120 or 160 mg/L. The production and accumulation of metabolites in the aqueous phase responded similarly to the addition of 1-dodecanol. Further experiments showed that the positive influence of the alcohols could not be attributed to the changes in surface and interfacial tension or increase in biomass concentration. The results suggest that enhanced adhesion of bacterial cells to the oil-water interface was the main factor responsible for the observed increase in phenanthrene biodegradation by P. fluorescens LP6a.
License granted by Hassan Abbasnezhad ( on 2009-08-28T15:47:37Z (GMT): 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 the above terms. The author reserves all other publication and other rights in association with the copyright in the thesis, and except as herein 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.
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