Investigating the Impact of Cultivation Regimes on the Antibacterial Properties of Non-Polar Extracts of Chlorella sorokiniana and Anabaena sphaerica.

The study tested the hypothesis that cultivation conditions and additional exposure to light radiation influence the magnitude of the antibacterial effect of non-polar metabolites extracted from the cells of the microalgae Chlorella sorokiniana and the cyanobacteria Anabaena sphaerica. It was found that non-polar extracts of the microalgae Chlorella sorokiniana and the cyanobacteria Anabaena sphaerica extracted with petroleum ether have an inhibitory effect on the growth of Gram-positive bacteria of the genus Bacillus. The most promising antibacterial agents are extracts of microalgae and cyanobacteria obtained from cell biomass grown at the level of photosynthetically active radiation 100 ± 10 µmol photons/(m²s) and temperature - 36 ± 0.1 °C. At the same time, the non-polar extract of the microalgae Chlorella sorokiniana has an inhibitory effect only when the system is additionally exposed to light (100 ± 10 µmol photons/(m²·s)) (the minimum inhibitory concentration of the extract is ≈ 125 µg/ml), whereas the non-polar extract of the cyanobacteria Anabaena sphaerica shows antimicrobial activity both with and without additional light radiation (the minimum inhibitory concentration of the extract is 72 µg/ml and 830 µg/ml, respectively). For these extracts, IC₅₀ concentration values for the HEK293 cell line and SI selectivity indices for Chlorella sorokiniana (IC₅₀ = 260 µg/ml, SI ('light') = 2.08) and Anabaena sphaerica (IC₅₀ = 220 µg/ml, SI = 3.06/0.27 ('light'/'dark')) were determined.