The stimulating effects of exometabolites of microalgae chlorella vulgaris on the lactic acid bacteria bacillus coagulans

This study aimed to determine the stimulating effect of exometabolites of microalgae Chlorella Vulgaris IPPAS C-2 — indole compounds that are cultured on wastewater model solution. The purification process of a model wastewater solution with Chlorella Vulgaris microalgae obtained biomass of microalgae with a high lipid content (up to 50%), whereas the residual concentrations of pollutants in the solution were ammonium cations of 1.5 mg/l and phosphate anions of 3.5 mg/l. The residual concentration of microorganisms in the purified model sample of wastewater does not exceed 0.3 million CFU/ml. Growth factors of indole nature, which are external metabolites of microalgae, were also found in the solution. Purified effluents were used in the microbiological synthesis of lactic acid to confirm the stimulating effect of accumulated metabolites. The control sample was a nutrient medium based on malt germ extract. The glucose concentration in all samples is the same and is 140 g/l. A strain of lactic acid bacteria Bacillus coagulans B-10468 was used as a test culture. The highest concentration of lactic acid bacteria (100 million cells/ml) was observed in a sample containing microalgae metabolites. This concentration is 1.7 times higher than in the control sample. In the future, the growth rate of Bacillus coagulans cells slowed down since the concentration of lactic acid reached the limit values of 30–50 g/l on the 3rd day, which contributed to the bacterial cell growth inhibition. The use of a growth stimulator based on treated wastewater by microalgae in the cultivation of bacteria of the species Bacillus coagulans B-10468 increases the specific rate of accumulation of bacterial biomass (0.27 day^–1), which is 26% more than in the control sample; increases the yield of lactic acid (120 g/l) by 25% compared with the traditional stimulant — malt sprouts. The lactic acid production using growth stimulants from wastewater treatment with microalgae will reduce the cost of its production. The use of this technological solution will provide an opportunity to reduce the cost of polymer, polylactide, which is one of the main materials for additive technologies.