mgr inż. Jan Cichoński
The topic of my dissertation is: „The influence of salicylates and variable illumination periods on the biosynthesis of carotenoids and phenolic compounds in the cells of green microalgae.”
Microalgae are unicellular photosynthetic organisms that are a source of many valuable substances: pigments, enzymes, carbohydrates, phenolic compounds, and lipids 1. Under stress conditions, induced by e.g. intensive light and nutrients deficiency, microalgae overproduce beneficial metabolites 2. Phytohormones also influence the increase in the production of metabolites, such as phenolic compounds and carotenoids in microalgae. Kozlova et al. (2017) prove that abscisic acid, 24-epibrassinolide, brassinolide and indoleacetic acid improve carotenogenesis in cells, while 24-epibrassinolide influenced carotenoids overproduction the most 3. Moreover, Kováčik et al. (2010) have shown, that microalgae treated with salicylic acid produce more phenolic acids, compared to untreated cultures. The important factor that modulates the photosynthesis process, and the profile of cellular compounds, is the length of light and dark phases during the microalgal culture. Yusof et al. (2021) demonstrated that in microalgae grown under constant illumination, the concentration of carotenoids is higher, compared to their yield in microalgae grown under 12-hour irradiance (12h light: 12h dark) 4. Up to date, the publications were mainly demonstrating the accumulation of metabolites in microalgal cells, and they have minutely described the biosynthesis.
The overproduction of valuable metabolites by microalgae is a crucial element in biological and biotechnological research. Worldwide, there is a continuous growth of interest in microalgal production of high value foods, nutraceuticals and sources of biofuels. However, the biosynthesis of compounds such as carotenoids and phenolic compounds (given their enormous potential in medicine and many other industries), may be even more valuable than the use of algae as sources of biofuels, especially in the times of replacing combustion engines. Therefore, broadening the knowledge about the biosynthesis of carotenoids and phenolic compounds by green microalgae under stress conditions induced by salicylic acid, methyl salicylate, and variable photoperiod represents both the cognitive and practical aspects of the conducted research.
Thus, the aim of the study is to determine the influence of salicylates and variable illumination period on the growth, biosynthesis of phenolic compounds and carotenoids, and the level/activity of chosen biosynthetic pathways enzymes of studied compounds.
During the proposed research, microalgal cultures will be carried out in photobioreactors under different illumination lengths (photoperiods) and treated with phytohormones 5. First, the secondary metabolites of the algae (carotenoids and phenolic compounds) will be extracted and the total concentration of carotenoids will be evaluated using a spectrophotometric method 6. Carotenoids and phenolic compounds will be analyzed using UPLC-Q/TOF-MS and UPLC-PDA assays 7,8. Furthermore, activity and levels of key enzymes of the biosynthetic pathways of carotenoids (PSY, PDS) and phenolic compounds (PAL/TAL, CHS/CHI) under stress conditions will be determined 8. Moreover, the influence of the studied conditions on the generation of oxidative stress and the antioxidative response will be assessed. These studies will consist of determining free radical levels (hydrogen peroxide, superoxide radical) 8, evaluating oxidative damage to macromolecules (proteins, lipids, DNA) 9, and assessing the antioxidant response for generated respiratory burst, by determining the activities of antioxidative enzymes (SOD, CAT) 10.
The results of these studies will broaden the knowledge of cell biology and microalgal biochemistry. The integration of knowledge about the profiles of secondary metabolites in microalgal cells, related to the activity of biosynthetic enzymes, will allow to obtain more detailed molecular picture of salicylates and photoperiod influence on the biochemistry of green algae. This knowledge will be supplied by the effect of stress conditions on the generation of oxidative stress and the antioxidant response of cells. The discovery of molecular relationships between stress conditions and the growth and productivity of microalgae will also improve the knowledge of the biochemical ecology of these organisms. The basic research character of these studies does not exclude the utilization of gathered results in the creation of new methods of microalgal cultures optimization, to improve the yield of valuable metabolites in microalgae.
PSY – phytoene synthase
PDS – phytoene desaturase
PAL – L-phenylalanine ammonia-lyase
TAL – L-tyrosine ammonia-lyase
CHS – chalcone synthase
CHI – chalcone isomerase
SOD – superoxide dismutase
CAT – catalase
- Koller, M., Muhr, A. & Braunegg, G. Microalgae as versatile cellular factories for valued products. Algal Res. 6, 52–63 (2014).
- Sun, X.-M., Ren, L.-J., Zhao, Q.-Y., Ji, X.-J. & Huang, H. Microalgae for the production of lipid and carotenoids: a review with focus on stress regulation and adaptation. Biotechnol. Biofuels 11, 272 (2018).
- Kozlova, T. A., Hardy, B. P., Krishna, P. & Levin, D. B. Effect of phytohormones on growth and accumulation of pigments and fatty acids in the microalgae Scenedesmus quadricauda. Algal Res. 27, 325–334 (2017).
- Yusof, N. S. et al. Photoperiod influenced the growth and antioxidative responses of Chlorella vulgaris, Isochrysis galbana, and Tetraselmis chuii. J. Appl. Pharm. Sci. (2021) doi:10.7324/JAPS.2021.110415.
- Szpyrka, E. et al. A Non-Vector Approach to Increase Lipid Levels in the Microalga Planktochlorella nurekis. Molecules 25, 270 (2020).
- Lichtenthaler, H. K.  Chlorophylls and carotenoids: Pigments of photosynthetic biomembranes. in Methods in Enzymology vol. 148 350–382 (Academic Press, 1987).
- O’Neil, C. A. & Schwartz, S. J. Chromatographic analysis of cis/trans carotenoid isomers. J. Chromatogr. A 624, 235–252 (1992).
- Czerniewicz, P., Sytykiewicz, H., Durak, R., Borowiak-Sobkowiak, B. & Chrzanowski, G. Role of phenolic compounds during antioxidative responses of winter triticale to aphid and beetle attack. Plant Physiol. Biochem. 118, 529–540 (2017).
- Sytykiewicz, H., Łukasik, I., Goławska, S. & Chrzanowski, G. Aphid-Triggered Changes in Oxidative Damage Markers of Nucleic Acids, Proteins, and Lipids in Maize (Zea mays L.) Seedlings. Int. J. Mol. Sci. 20, 3742 (2019).
- Czerniewicz, P. & Chrzanowski, G. The Effect of Santolina chamaecyparissus and Tagetes patula Essential Oils on Biochemical Markers of Oxidative Stress in Aphids. Insects 12, 360 (2021).
Microalgae, Carotenoids, Phenolic compounds, Salicylates, Photoperiod, Oxidative stress