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Characterization of Phenotypic Changes Involved in the Uptake of Weakly Soluble Hydrocarbons by Pseudomonas Aeruginosa

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Nguyen, Thanh-Thuy (2017). Characterization of Phenotypic Changes Involved in the Uptake of Weakly Soluble Hydrocarbons by Pseudomonas Aeruginosa Thèse. Québec, Université du Québec, Institut national de la recherche scientifique, Doctorat en biologie, 337 p.

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Résumé

Petroleum products like linear alkanes (e.g. hexadecane, octadecane, etc.) and polycyclic aromatic hydrocarbons (e.g. naphthalene, phenanthrene, etc.) are very important pollutants in the environment because of their abundance, toxicity, weak solubility, and persistence due to their poor bioavailability, the limitation of biodegradation pathways and a high tendency to the sorption to other hydrophobic organic matters. There are different types of treatments applied in the polluted environments, including chemical, physical and biological methods. The chemical and physical treatments can cause a secondary pollution, and are expensive. In contrast, the continuous exposure to the contaminants has led to the evolution of microorganisms that are able to grow on hydrocarbons, degrade and utilize the polluted hydrocarbons as their carbon sources, and this inspired the development of biological treatment methods. Thus, the ability of microbial-degrading hydrocarbons is a potential key element in the clean-up strategy of polluted sites. Many different microorganisms, including algae, fungi and bacteria, have been reported to possess the capability of degrading a wide variety of the polluted persistent organic compounds. Among these bacteria, different members of the Pseudomonas genus, which also possess the capacity to degrade weakly soluble hydrocarbons such as linear alkanes, polycyclic aromatic compounds (PAHs), etc., have already been isolated for studying mechanisms involving the effective biodegradation of polluted hydrocarbons by these microorganisms.

Pseudomonas aeruginosa bacteria are found in a wide variety of environments, such as soil, water or in association with plants and animals as well as inside of the human body. These bacteria can also grow on hydrophobic carbon substrates such as long-chain linear alkanes and PAHs. The ability to grow in various unfavorable conditions of these bacteria, such as on the petroleum-related products in the polluted environments, relies on their high adaptabilities. In response to the environmental stimuli, bacteria can use different second messengers to regulate various cellular processes for their survival and adaptive development.

At the time this project was started, it was known that the second messenger bis-(3'-5')-cyclic dimeric guanosine monophosphate (cyclic di-GMP or c-di-GMP) plays a key role in the bacterial biofilm development, including the P. aeruginosa species. c-di-GMP was shown to be overproduced in various P. aeruginosa rough small colony variants(SCVs) derived from different clinical isolates. This cell type possesses high abilities to grow and form biofilms in unfavorable conditions. The formation of rough SCVs of P.aeruginosa strain 57RP on dextrose in biofilm or in static liquid cultures was also observed in previous experiments in the laboratory of Prof. Richard Villemur. Strain 57RP and several other P. aeruginosa strains were also able to grow and form biofilm on hexadecane, other n-alkanes and PAHs used as a whole carbon source. We hypothesized that the 57RP rough SCVs, which shared some common phenotypic behaviors with the clinical rough SCVs, also overproduce c-di-GMP. However, to which extent this second messenger would influence the appearance of SCVs and the capacity of degrading linear alkanes and/or PAHs was still unclear. Several studies carried out on the growth of certain oil-degrading bacteria growing on different substrates revealed that hexadecane induced a large change in gene expression of biofilm cells compared to the cells growing on pyruvate {Sabirova, 2006 #10585}{Sabirova, 2011 #10578} or to the planktonic cells growing on acetate {Vaysse, 2009 #10584}. Many up-regulated proteins were found in different cell compartments such as the outer membrane, periplasm, inner membrane and cytoplasm. Question to which extent of different modulation of gene expression would be seen between the 57RP cells growing on hexadecane and the 57RP cells growing on other substrates, such as glucose, requires some proteomic studies to be carried out for a better understanding of the physiological adaptation of 57RP cells to the hydrophobic substrate.

The principal aim of this project was to characterize the phenotypic changes of a P.aeruginosa strain 57RP, previously isolated from a hydrocarbon-polluted site in Canada by our laboratory, and capable of using several weakly soluble hydrocarbons, such as hexadecane, as the sole carbon source for its growth. The present study was carried out to further investigate the previously suggested important role of c-di-GMP in the phenotypic switching of the bacterial cell states and characterize initially the components of the cell envelope of 57RP SCV grown on hexadecane.

Type de document: Thèse Thèse
Directeur de mémoire/thèse: Villemur, Richard
Mots-clés libres: -
Centre: Centre INRS-Institut Armand Frappier
Date de dépôt: 02 sept. 2018 20:16
Dernière modification: 02 sept. 2018 20:16
URI: http://espace.inrs.ca/id/eprint/7496

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