BIOSYNTHESIS OF FATS AND THEIR REGULATION IN MICROALGAE CELLS UNDER STRESS CONDITIONS

ABSTRACT

In this study, it was found that the equivalent of energy-rich substances and carbohydrates produced during photosynthesis is mainly used in the biosynthesis of nitrogen-free reserve compounds, TAGs (triacylglycerols). In the process of growth, it was found that the concentration of NaCl in the nutrient medium affects the formation of microelement lipids in the cell. The effect of NaCl salts and medium pH at various concentrations on lipid biosynthesis was studied.

АННОТАЦИЯ

В данной статье, изучаются, что эквивалент богатых энергией веществ и углеводов, образующихся при фотосинтезе, в основном используется в биосинтезе безазотистых резервных соединений, ТАГ (триацилглицерыдов). В процессе роста установлено, что концентрация NaCl в питательной среде влияет на образование микроэлементных липидов в клетке. Исследовано влияние солей NaCl и рН среды в различных концентрациях на биосинтез липидов.

Keywords: microalgae, stress, lipid, biomass, photoassimilation, fat, population, incubation, concentration, triacylglycerol.

Ключевые слова: микроводоросли, стресс, липид, биомасса, фотоассимиляция, масел, популяция, инкубация, концентрация, триацилглицерид.

INTRODUCTION.

It is known that under the influence of various stress conditions of nature, algae belonging to the class Chlorophyta undergo quantitative changes in the synthesis of triatselglecerol (TAG) and membrane lipids, ie TAG accumulates as a reserve for photosynthesis under unfavorable conditions [1,2]. Microbes become stressed during nitrogen deficiency, in which case TAG accumulation increases for protection, and the lack of nitrogen in the nutrient content reduces their viability [3,4]. Algae living in a population have been found to accumulate large amounts of free fatty acids under stress conditions, so it is important to study the response of microflora to nitrogen deficiency conditions [5]. In industry, intensive cultivation of cultures is important for the production of saturated and unsaturated fatty acids from microalgae [6]. However, light intensity, extreme temperature changes, and nitrogen deficiency have a significant effect on changes in pigment and lipid metabolism in microflora [7]. According to the results obtained, in this case, the amount of TAG in the cell of algae was increased by 2-3 times [8].

The aim of our research is to study the effect of stress conditions on the lipid biosynthesis processes of local microflora strains.

MATERIALS AND METHODS

2.1 Strains of Microalgae The objects of study used were strains of unicellular green algae genera Scenedesmus, Stichococcus, Chlorococcum, Ankistrodesmus, Chlamydomonas, Chlorella, Coelastrum and Pediastrum, isolated from water sources in Uzbekistan [9].

2.2 Growth Condition Cultures of microalgae were grown under sterile conditions in “Chu- 13” medium for 14 days, with a supply of carbon dioxide by blowing air containing 2% CO2 and with continuous illumination by fluorescent white light (200 μmol photons m²⋅s^-1) [10.,11].

RESULTS AND DISCUSSION

Accumulative cultures of microalgae were obtained from water samples collected in Uzbekistan (Fig. 1).  As noted in previous articles, the microalgae used in the experiment were isolated from freshwater basins in Uzbekistan [12]. For the experiments, biomass of local microflora grown under optimal conditions for 14 days in the Chu-13 nutrient medium was obtained and grown for up to 5 hours in the Chu-13 nutrient medium containing 400 and 600 mM NaCl salts. The process of lipid formation of microflora in a nutrient medium with a salt of 400 mM NaCl showed that when strains of micronutrients of the genus Scenedesmus were grown for 1 hour incubation relative to the initial concentration of total intracellular lipids (22.5-24.7-28.8%). an increase in the amount of fats (3-8%) was observed. An increase in total lipids in the cells was found to be proportional to the increase in culturing timeAt 5 hours of growth, the amount of fat in the cells almost doubled compared to the initial concentration and amounted to 39.2-38.5-43.5%. Chlorococcum-derived microalgae synthesized lipids (60.8–66.3%) to the maximum extent when grown in a Chu-13 nutrient medium containing 400 mM of NaCl, which was 18–20% higher than the initial concentration. Ankistrodesmus angustus UT15, Ankistradesmus falcatus UT18 and Chlorella sp 2, Pediastrum sp.6 microalgae strains showed a similar process in Scenedesmus and Chlorococcum microalgae, with Ankistrodesmus angustus UT15 at 14.9% of the 5th hour of growth. falcatus UT8 - 12.6%, Chlorella sp.2 4.7% and pediastrum sp 6-17.1% maximal total lipid synthesis was observed. When microalgaes strains were cultured for 3 h in a medium containing 600 mM NaCl, the total average lipid synthesis of microalgae was accelerated by 8.19% compared to those grown in a medium containing 400 mM NaCl. However, when microalgae strains were grown in a nutrient medium with a concentration of 600 mM of NaCl, a decrease in total lipid synthesis was observed at the end of the 5th hour. 

Figure. 1. The process of preparing microalgae for planting:

Scenedesmus sp 29(a), S.quadricauda UT4 (b), Ankistrodesmus folkotus UT8 (c), Ankistrodesmus angustus UT15 (d), Chlorella sp.4 (e), Chlorococcum sp.14 (f), Coelastrum sp.16 (i) and Pediastrum sp.6 (j).

Table 1.

The ability of local microalgae to form lipids over time under conditions of salinity with NaCl.

These results show that the total lipid content of microflora grown at low salinity concentrations increased steadily and the 5-hour time interval did not act as a fatal stress for them, while at high concentrations of NaCl all microflora strains grew more than 3 hours. causes cell death and a decrease in total lipid content. 

When studying the formation of lipids in the cells of microflora strains and the effect of the pH environment on the regulation of fats in them, microflora strains of the genus Scenedesmus increased for 5 hours when the pH was reduced to 4.0 by adding hydrochloric acid to the Chu-13 nutrient medium (pH 7.5). total lipid synthesis was observed to increase by 12–14% compared to the variant, and a decrease in total fat content by 6–9% was observed at 7 h of growth (Table 2). It should be noted that the same situation was repeated in the strain of Ch. a sharp decrease in fat content was found to be 14.3%.

However, Ank. angustus UT15, Ank. the ability of falcatus UT20 strains to form high total lipids when grown in an acidic pH environment corresponds to 5 hours of the incubation period, and they produced lipids ranging from 33.8–35.6%, respectively. Separately,  chlorella sp.2, and pediastrum tetras. It should be noted that the maximum rate of lipid formation in pediastrum sp 6  microalgae strains covered a shorter period of time than in the above-mentioned microalgae. Chlorella sp.2 and pediastrum sp 6 observed a decrease in total fat content when the growth time exceeded 3 h. Almost no change was observed in the 7-hour dynamics compared to the control variant grown in conditions where the nutrient medium "Chu-13" with alkaline micronutrients was equal to pH-9.0.

Table 2.

The lipid-forming property of microalgae strains over time under stress conditions with pH -4.0 and pH-9.0.

CONCLUSION

Thus, stress factors affecting microalgae directly affect their overall lipid regulation over a period of time, causing them to increase or decrease. This means that all the physiological processes in the cell are directed to the fatty acid-forming system to form active lipids over a period of time as a result of stress and the accumulation of lipids as a reserve substance. The results of the study showed that the nutrient medium with a pH of 9.0 for local microalgae strains is not a stress factor and that such an environment does not affect the physiological processes in the cells of microflora strains.

Analysis of the results of the study showed that incubation of microalgae at stress intervals for a certain period of time to increase the efficiency of obtaining large amounts of lipids for biotechnological processes determines the productivity of the product.

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