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Identifier

000451955

Title

Συγκριτική μελέτη της βιοενεργητικής απόκρισης του χλωροφύκους Chlorella vulgaris σε διαφορετικές συνθήκες καλλιέργειας – Βιοτεχνολογικές προοπτικές

Alternative Title

Comparative study of the bioenergetic response of Chlorella vulgaris in different growth conditions – Biotechnological perspectives

Author

Μολοχίδου, Μαρία Ν.

Thesis advisor

Κοτζαμπάσης, Κυριάκος

Reviewer

Μόσχου, Παναγιώτης
Σαρρής, Παναγιώτης

Abstract

In this thesis, the differentiation of the molecular structure and function of the photosynthetic mechanism (using JIP-test) of the unicellular green alga Chlorella vulgaris was studied in different growth conditions (autotrophic and mixotrophic) and in different atmospheres (oxygenic, anoxic enriched or not with CO₂). In addition, a comparative study was carried out between cultivation conditions for biotechnological applications. The microalgae were cultivated in closed systems at a constant temperature (25^oC) and irradiation (10 μmol m^-2 s^-1) under different culture conditions with respect to the growth medium (autotrophic medium [BBM]; glucose-added [GBBM]; peptone-added [PBBM]; glucose- and peptone-added [GPBBM]) and the atmosphere composition (air [AIR]; air enriched with 30% CO₂ [30% CO₂ in AIR]), nitrogen atmosphere [N₂]; nitrogen atmosphere enriched with 30% CO₂ [30% CO₂ in N₂]). The presence of glucose in the growth medium in air atmosphere [GBBM_ AIR] showed from the first day an improved state of the photosynthetic mechanism compared to that of the control [BBM], although when the mixotrophic culture was exposed to an atmosphere of extreme CO₂ concentration [GBBM 30 % CO₂], it showed limited stress. The addition of 30 % CO₂ to the atmosphere did not modulate growth, because it is probably the maximum that the photosynthetic mechanism can handle under the given light conditions (10 μmol m^-2 s^-1). The corresponding treatment in nitrogen atmosphere [GBBM_ N₂] did not give measurable values in the JIP-test and this may be related to the production of hydrogen (H₂).) using the PSII-independent electron transport pathway. From the study of photosynthetic and respiratory activity under different culture conditions, it was shown that the microalga treats them in a rational way. Indicatively, the addition of an exogenous carbon source ([GBBM]) led to increased O₂ consumption (due to respiratory activity) and reduced photosynthetic activity. Respiration-photosynthesis feedback in anoxic conditions allows survival, but limits biomass production. The experimental results clearly showed that the mixotrophic culture conditions favour microalgae at various levels, both in terms of photosynthetic mechanism and biomass levels, as well as its biochemical composition. When glucose is added to the culture medium (GBBM manipulation), the microalgae invests primarily in growth. In addition, glucose contributes to the production of high value bioproducts under specific atmospheric conditions. On the one hand, it leads to the production of photosynthetic hydrogen (H₂).) when grown under anoxic nitrogen conditions (handling [GBBM_N₂]) and, on the other hand, it enables the production of fatty acids desired for biodiesel production, regardless of the atmosphere ([GBBM] and [GPBBM]). The addition of peptone to the culture medium [PBBM] favours the maintenance of high levels of PUFA, ω-3 and ω-6 fatty acids, while the production of MUFA is reduced, so under these conditions the microalgae is primarily recommended for pharmaceutical and nutritional use. Therefore, Chlorella vulgaris is a biological system that can adapt its bioenergetic strategy according to growth conditions and opens new perspectives for its use in Green Biotechnology.

Language

Greek

Subject

Biodiesel

Biofuels

Biohydrogen

Βιοκαύσιμα

Βιοντίζελ

Βιουδρογόνο

Χλωροφύκος

Issue date

2022-11-25