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Étude des mécanismes physiologiques et moléculaires de la filamentation de Sphaerotilus natans, bactérie modèle du foisonnement invasif en boues activées

Abstract : Filamentous bulking is a widespread problem in many activated sludge wastewater treatment plants. The objective of this study is to improve the understanding of physiological and molecular mechanisms of filamentation, in order to define strategies for future treatments against bulking. Sphaerotilus natans, which is able to grow reversibly as single-cell or filament, has been used as a model within this work. Different types of culture experiments, as well as cFDA/SE staining and flow cytometry analysis have showed that different strains of S. natans have various behaviours and that filaments grow by a chain of cell divisions instead of a reassembly of single cells. RT-QPCR analysis shows that sthA gene expression increases strongly after induction of filamentation and then stays at high level. LC-MS-MS analysis of protein expression from filamentous and single-cell forms of S. natans allows the identification of enzymes involved in filamentation and especially in sheath synthesis. Intracellular rRNA concentration, measured by RT-QPCR, varies strongly during S. natans and other microorganism growth, leading to an important decrease in the FISH signal intensity, measured by flow cytometry. The efficiency of bacterial quantification using FISH, especially in complex matrix such as activated sludge is therefore questioned. The hypothesis of filament lysis when growth conditions return to normal, deduced from FISH quantification, is also weakened.
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Submitted on : Tuesday, September 13, 2011 - 5:07:17 PM
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Sébastien Lacroix. Étude des mécanismes physiologiques et moléculaires de la filamentation de Sphaerotilus natans, bactérie modèle du foisonnement invasif en boues activées. Microbiologie et Parasitologie. AgroParisTech, 2008. Français. ⟨NNT : 2008AGPT0022⟩. ⟨pastel-00623223⟩

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