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Identifier 000419530
Title Μελέτη της βιοαποικοδόμησης φαινολικών ενώσεων από μικροοργανισμούς
Alternative Title A study of the biodegradation of phenolic compounds by microorganisms
Author Νάζος, Θεοχάρης Θ
Thesis advisor Γανωτάκης, Δημήτριος
Reviewer Κατερινόπουλος, Χαράλαμπος
Κοτζαμπάσης, Κυριάκος
Μελής, Αναστάσιος
Παυλίδης, Ιωάννης
Τσιώτης, Γεώργιος
Χανιωτάκης, Νικόλαος
Abstract The main objective of this study was elucidation of the biodegradation mechanism of phenolic compounds by two different photosynthetic microorganisms. More specifically, the model organism Chlamydomonas reinhardtii and a novel green microalga that was isolated from a contaminated site of the river Giofyros (city of Heraklio) were used. Through this study it was shown that the biodegradation of phenolic compounds by the green microalga Chlamydomonas reinhardtii is a bioenergetic process. In the absence of an alternative carbon source, Chlamydomonas was found to biodegrade phenol in order to obtain carbon reserves. At the same time the biodegradation of high initial concentrations of phenol proved to be an aerobic, photoregulated process. Chlamydomonas uses an aerobic pathway with a catechol intermediate implicated. The microalga was able to biodegrade phenol in the dark only when the cultures were supplied with oxygen exogenously. The presence of an alternative carbon source affected significantly the biodegradation process. The presence of carbon dioxide eliminated the ability of the microorganism to biodegrade phenol, while the presence of acetic acid assisted Chlamydomonas in the biodegradation of high initial concentrations of phenol effectively, resulting in biomass increase and alleviation of the impacts of xenobiotics on the photosynthetic apparatus of the alga. When culture growth was inhibited, phenol biodegradation pushed microalgae into a maintenance and survival mode. The determining step in the biodegradation of phenol proved to be the catechol ring cleavage. Chlamydomonas reinhardtii was found to be able to biodegrade partially a series of monosubstituted methylphenols. The relative position of the substituents in combination with the presence or absence of an alternative carbon source regulated the biodegradation percentage. Ortho and meta isomers exhibited resistance in biodegradation compared to the para isomer. Once again, the role of acetic acid as an alternative carbon source was demonstrated. Biodegradation studies of phenol by immobilized Chlamydomonas reinhardtii in calcium alginate beads showed that immobilized cells are able to biodegrade phenol as well. Photosynthetic efficiency measurements proved that the polymeric matrix protected the cells from phenol inhibitory effects. Cells remained matabolically active for a period of 15 days while only the cells immobilized at the outer surface of the beads contributed to the 16 biodegradation process. Cell release depended on the initial concentration of the alginate solution as well as the culture conditions such as the presence or absence of phenol. In the final part of this thesis, a green microalga from the Giofyros river was isolated and studied. The presence of a pronounced extracellular matrix around the cell wall of this alga was found to play an important role in the protection of this microorganism from some inhibitors such as antibiotics and DCMU. The cells were able to grow in the presence of these inhibitors and keep the function of the photosynthetic apparatus active, compared to the microalga Chlamydomonas reinhardtii, which was significantly inhibited. Phenol was found not to have a measurable effect on the microalga from the river Giofyros due to the protective role of the extracellular matrix. This microorganism was found be able to biodegrade phenol only in the absence of an alternative carbon source from the culture medium. The main conclusion of this thesis is that the biodegradation of phenol by photosynthetic microorganisms is a bioenergetic process depending on the culture conditions and the structural and cell wall characteristics of each particular strain. Photosynthetic microorganisms act like bioenergetic machines that manage with the most profitable way their energy reserves by finding the best bioenergetic balance between growth, stress and the biodegradation of phenolic compounds.
Language Greek
Subject Alginate beads
Chlamydomonas reinhardtii
Σφαιρίδια αλγινικού ασβεστίου
Issue date 2018-10-01
Collection   School/Department--School of Sciences and Engineering--Department of Chemistry--Doctoral theses
  Type of Work--Doctoral theses
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