Stepanov S. Assimilation pathways of С1-2 monohydric alcohols by Chlamydomonas reinhartdii cells

The aim of the dissertation is to establish the mechanism of growth stimulating unicellular green alga Chlamydomonas reinhardtii by addition of С1-2 monohydric alcohols. The growth, photosynthetic activity, metabolism and energy transformation of C. reinhardtii cells in batch culture at Kessler's mineral medium have been investigated in the present work. It has been shown that the small concentrations of methanol (20-120 мМ) stimulated the growth of culture. The stimulating effect of methanol didn't induce the change in efficiency of energy transformation in photosystems I and II. Though the functional state of the photosynthetic apparatus improved in the presence of exogenous methanol, it had no effect on the rate of net СО2 fixation. Intracellular chlorophyll content decreased after methanol addition without any change in chlorophyll a/b ratio. The intracellular content of NADH was increased after addition of 50 mM methanol. Without illumination, NADН content increased only slightly. The total protein and free amino acids content was determined as a possible consequence of increasing intracellular NADН content due to methanol addition. Changing in amino acids percentage occurred: glutamate, glutamine, alanine, serine, tyrosine content was increased and content of methionine was decreased. The results of cytochemical study showed that catalase is localized in mitochondria and suggested its involvement in methanol elimination. Methanol-induced quantitative changes in ultrastructure of C. reinhardtii cells were detected: the volume of C. reinhardtii cells and partial volume of chloroplasts decreased, partial volumes of vacuoles, mitochondria, and plastoglobules increased. Methanol addition has also resulted in increase in catalase activity of the mitochondria. Obtained data confirmed the assumption that carbon from methanol can be utilized in the reactions of C1 metabolism and photorespiration. New hypothesis explaining growth stimulation by methanol has been confirmed. According to this hypothesis the growth of algal culture is stimulated due to additional NADH formation and the cellular redox potential changes in result of methanol catabolism.