Indolyl-3-butyric acid effect evaluation on growth and biochemical parameters of microalgae, Isochrysis galbana Parke, 1949

The microalga Isochrysis galbana, due to its nutritional properties, is considered one of important feeds for aquaculture species. Increasing the efficiency of microalgae cultivation with minimal economic costs is the main way to provide live feed and increase profitability of farms. One of the approaches to addressing this issue is the use of phytohormones that have a stimulating effect on the production characteristics and biochemical composition of cultivated microalgae. This study examined the effect of indolyl-3-butyric acid, a phytohormone, at concentrations of 0.1-1 × 10–5 mol. L–1 on the growth of the microalga I. galbana cultivated in an enrichment culture. The duration of the experiment was 7 days. The production characteristics of microalgae were determined by measuring the culture density per 1 mL of the incubation medium as a biomass parameter. Dynamics of cell culture growth were measured using a CytoFLEX flow cytometer. The production characteristics of the culture were also determined on the basis of such parameters as total contents of protein, carbohydrates, lipids, and chlorophyll. The dynamics of the fatty acid composition under the exposure to the phytohormone during cultivation were assessed. The phytohormone at a concentration of 0.4 × 10–5 mol. L–1 was observed to have a stimulating effect on microalgae growth, resulting in a 27% increase over 7 days of cultivation. The effect of indolyl-3-butyric acid at a concentration of 0.4 × 10–5 mol. L–1 on the morphological and biochemical characteristics of the microalgae culture was studied. It was found that the use of the phytohormone resulted in a 57% increase in microalgae cell size compared to the control group. The increase in culture density in the experimental group was accompanied by a 2.6-fold increase in cell aggregates. The increase in protein content after 7 days was 425% in the control group and 538% in the experimental group exposed to the phytohormone. No difference in the carbohydrate content was observed between the control and experimental groups throughout the experiment. Indolyl-3-butyric acid was shown to have a stimulating effect on lipid accumulation. In the exper-imental culture of I. galbana, the total lipid production activity was 1.5-fold higher than in the control culture. An increased contribution of polyunsaturated fatty acids was also noted.