Microalga Euglena gracilis is able to photosynthesis and can also absorb different organic substrates from the environment both under the light conditions and in the darkness. In comparison with autotrophy, mixotrophic cultivation of E. gracilis with ethanol as carbon source has a significant influence on the metabolic characteristics of the microalgal cells. For most microalgae ethanol is toxic, but due to the unique biochemical organization, E. gracilis cells are able to effectively utilize ethanol with accumulation of the storage polysaccharide paramylon. Ethanol as a source of easily digestible carbon retards the light-dependent formation of the photosynthetic apparatus of the microalgal cells. Analysis of photosynthetic pigments at different light intensities showed that E. gracilis microalga is a shade-tolerant organism with a special way to adapt to shade. Light intensity also changes the rate of organic substrates uptake, which can affect the growth rate of a culture and the content of pigments in the cells. Effect of three variants of light intensities on the cultures of E. gracilis, which were grown mixotrophically in the presence of ethanol and ethanol and glutamate in nutrition medium, was investigated in this work. Autotrophic culture was the control variant. The density of the cultures and the content of photosynthetic pigments (chlorophylls and carotenoids) in the cells were fixed in every 3 days during 20 days of the investigation. At the stationary growth phase the maximal cell concentration was registered in the culture with ethanol and sodium glutamate under illumination 100 mmol/(m2 · s). Decreased chlorophylls content in the cells of mixotrophic cultures in comparison with autotrophic cultures at the beginning of exponential growth phase can be explained by catabolic repression of photosynthetic pigments synthesis. It was shown that chlorophylls and carotenoids content, chlorophylls a/b ratio increased with duration of mixotrophic cultures growth.
Keywords: Euglena gracilis, microalga, mixotrophy, ethanol, growth rate, light intensity, chlorophylls, carotenoids
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1. Mokrosnop, V.M., Polishuk, A.V. & Zolotareva, E.K. (2015). Functional state of the photosynthetic apparatus of cells of Euglena gracilis during mixotrophic cultivation. Dop. NAN Ukraine, 10, pp. 77-84 [in Ukrainian].
2. Mokrosnop, V.M. (2016). Dynamics of chlorophyll and paramylon accumulation in Euglena gracilis cells at mixotrophic cultivation. Biol Studii, 10, No. 2, pp. 141-148. https://doi.org/10.30970/sbi.1002.483
3. Rodriguez-Zavala, J. S., Ortiz-Cruz, M. A., Mendoza-Hernanderz, G. & Moreno-Sanchez, R. (2010). Increased synthesis of a-tocopherol, paramylon and tyrosine by Euglena gracilis under conditions of high biomass production. J. Appl. Microbiol, 109, pp. 2160-2172. https://doi.org/10.1111/j.1365-2672.2010.04848.x
4. Yoval-Sanchez, B., Jasso-Chavez, R., Lira-Silva, E., Moreno-Sanchez, R. & Rodriguez-Zavala, J. S. (2011). Novel mitochondria alcohol metabolizing enzymes of Euglena gracilis. J. Bioenerg. Biomembr, 43, pp. 519-530. https://doi.org/10.1007/s10863-011-9373-4
5. Rikin, A. & Schwartzbach, S.D. (1989). Regulation by light and ethanol of the synthesis of the light harvesting chlorophyll a/b binding protein of photosystem II in Euglena. Planta, 178, pp. 76-83. https://doi.org/10.1007/BF00392529
6. Nicolas, P., Freyssinet, G. & Nigon, V. (1980). Effect of light on glucose utilization by Euglena gracilis. Plant Physiol, 65, pp. 631-634. https://doi.org/10.1104/pp.65.4.631
7. Brody, M. (1986). Chlorophyll studies. In The biology of Euglena. Vol II. Biochemistry (Ed. D.E. Buetow). New York: Academic Press, Inc.
8. Beneragama, C.K. & Goto, K. (2010). Chlorophyll a:b ratio increases under low-light in "shade-tolerant" Euglena gracilis. Trop. agricult. res., 22, No. 1, pp. 12-25.
9. Andersen, R.A. (2005). Algal Culturing Techniques. London: Elsevier Academic Press.
10. Lichtenthaler, H.K. & Welburn, A.R. (1983). Determination of total carotenoids and chlorophyll a and b of leaf extracts in different solvents. Biochemical Society Transactions, 603, pp. 591-593. https://doi.org/10.1042/bst0110591
11. Garlaschi, F.M., Garlaschi, A.M., Lombardi, A. & Forti, G. (1974). Effect of ethanol on the metabolism of Euglena gracilis. Plant Sci. Lett., 2, pp. 29-39. https://doi.org/10.1016/0304-4211(74)90035-2
12. Niki, E., Noguchi, N., Tsuchihashi, H. & Gotoh, N. (1995). Interaction among vitamin C, vitamin E, and beta-carotene. Amer. J. clin. nutr., 62, No. 6, pp. 1322S-1326S. https://doi.org/10.1093/ajcn/62.6.1322S