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Identifier 000399651
Title Βιοενεργητική στρατηγική βιοαποικοδόμησης της 3,4-διχλωροφαινόλης και παραγωγής H2 από το μικροφύκος Scenedesmus obliquus σε συνθήκες έλλειψης αζώτου
Alternative Title Bioenergetic strategy of biodegradation of 3,4-dichlorophenol and hydrogen production from microalgae Scenedesmus obliquus in nitrogen depletion
Author Κορελίδου, Άννα
Thesis advisor Κοτζαμπάσης, Κυριάκος
Reviewer Γανωτάκης, Δημήτριος
Πυρίντσος, Στέργιος
Abstract Recent publications from our laboratory showed that the unicellular green alga Scenedesmus obliquus invests all its energy reserves in the biodegradation of a particular class of phenolic compounds (one meta-substituted dichlorophenols, dcp) rather than its development. The simultaneous combination of three key metabolic pathways [dcp-biodegradation / photosynthetic H2 production / respiratory procedure] establishes anoxic conditions in a closed system, induces the hydrogenase enzyme and enhances photosynthetic electron flow to hydrogenase yielding large amounts of H2 (Papazi et al., 2012; Papazi and Kotzabasis, 2013). The present work aims to study the distinction of the above mentioned mechanism in nitrogen deficiency conditions. We used 4 treatments: the control cultures (Control), algal cultures in free nitrogen medium ("-N"), algal cultures with dcp ("dcp") and algal cultures in free nitrogen medium with dcp ("dcp-N"). The results from dcp biodegradation and H2 production analyses in "dcp-N" treatment, compared to the corresponding "dcp" treatment, showed that the unicellular green alga gives more energy into biodegradation procedure of dcp and less into hydrogen production, nevertheless dcp is needed even for this relatively low H2 production. To the contrary, "dcp" treatment shows a greater hydrogen production and clearly less quantity of dcp is biodegraded. What appears to be differentiating the final products of these two treatments are the reduced levels of Cytf and thus of the Cytb6f complex in "dcp-N" treatment. This limits the potential flow of electrons from the reduced dcp through PQ and PSI to the hydrogenase enzyme, thereby restricting H2 production. Such restriction gives the possibility to the reduced dcp to choose its biodegradation path (see simplified model). The results of lipid measurements in all treatments indicate that nitrogen deficiency ("-N" and "dcp-N" treatments) leads to increased lipid production. This is because the alga can not use the carbon source available in culture to other paths, therefore triggers lipid biosynthesis. On the other hand, starch quantitation results reveal maximum increase in the "-N" treatment because the inhibition of protein and other macromolecule synthesis leads to the metabolic potential shifting in starch and lipid biosynthesis, where nitrogen is not required. The least starch quantity is noted in "dcp-N" treatment probably because of the considerably enhanced dcp-biodegradation pathway, whereby a big amount of starch in the form of glucose is likely to be used in the required glycosylation of dcp. The lower levels of Cytb6f noted in "dcp-N" treatment, compared to those in "dcp" treamtent, restrict the flow of electrons from the glucose catabolism to PQ and the PSII-independent hydrogen production and enhance dcp-biodegradation and lipid synthesis (see simplified model). The relatively "paradox" fact that emerges from the simplified functional model of basic metabolic processes of the unicellular green alga Scenedesmus obliquus in all 4 treatments is that the levels of Cytb6f are dramatically reduced in the "-N" treatment, inhibiting significantly the photosynthetic electron flow and hence H2 production, whereas significantly high levels of Cytb6f (compared to "-N" treatment) are noted in the "dcp-N" treatment. The proposed differentiation between the two treatments could be explained by the recent decoding of bioenergetic strategy of microalgae (Papazi et al., 2013). When thethe green alga has to face the toxic dcp ("dcp-N" treatment) needs large energy reserves, hence possibly proceeds to catabolism of secondary (and not only) substances. Through this process the alga gains nitrogen along with the required energy (ATP), and that is why in "dcp-N" treatment (compared to "-N" treatment) higher levels of chlorophyll are presentedindicated in this treatment, as opposed to the "-N" handling. 8 All the above highlight specific bioenergetic strategies of microalgae, the understanding of which will set the bases for a new biotechnological approach in the future.
Language Greek
Subject Phenol biodegradation
Βιοαποικοδόμηση φαινόλων
Παραγωγή υδρογόνου
Issue date 2016-03-18
Collection   School/Department--School of Sciences and Engineering--Department of Biology--Post-graduate theses
  Type of Work--Post-graduate theses
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