ИСТИНА

Microalgal and cyanobacterial species from locations with harsh environmental conditions such as many Nordic habitats frequently accumulate secondary metabolites such as carotenoids (carotenes and ketocarotenoids) and mycosporin-like amino acids (MAA). The build-up of these compounds conveys the microalgae resilience to stressors such as high light, extreme temperatures and salinities. In human cells, the ketocarotenoid astaxanthin exert anti-aging, anti-inflammatory and other beneficial effects in humans and animals related mostly with its outstanding antioxidative activity. The MAA display a remarkable UV-screening capacity in situ and in vitro. Therefore, these valuable compounds are sought after to produce function food and feed additives, safe colorants, and cosmetics hence the producer strains for the carotenoids and MAA are in high demand for biotechnology. Fourteen microalgal and cyanobacterial lines isolated from different habitats in White Sea region were screened for their capability for accumulation of secondary carotenoids and MAA. The pre-cultures were grown under favorable conditions (BG-11 medium, 50 µmol PAR photons m–2 s–1, 25 °C) in flasks. The 15-mL pre-culture aliquots were transferred to UV-transparent Petri dishes and subjected to stressful irradiances (250 µmol photons m–2 s–1) of different spectral compositions achieved by using three computer-controlled LED light sources in temperature-controlled grow-boxes: white, “W” (standard cold-white LEDs), blue, “B” (λmax = 470 nm, FWHM = 15 nm) and UV-A, “U” (λmax = 365 nm, FWHM = 25 nm). Three spectral compositions were employed (by percentage of total incident irradiance): the “W-B-U” (45% + 45% + 10%), “W-B” (50% + 50% + 0%), and “W-U” (90% + 0% + 10%). After five days of the exposure the cells were harvested, absorption spectra of the suspensions were recorded, and the cells were extracted using the methods by Folch at al. The carotenoid and MAA content and compositions of the cell samples were then screened using gradient HPLC. The highest percentages of secondary carotenoids (1–4% of cell dry weight) were achieved by Bracteacoccus aggregatus BM5/15, Deasonia sp. (45% of β-carotene and 40% of astaxanthin) and Haematococcus pluvialis BM-1 (95% of astaxanthin) under the “W-B-U” treatment. The cyanobacterium Synechococcus sp.1Dp 66E-1 demonstrated the most remarkable induction of MAA (ca. one order of magnitude in comparison with unirradiated control) under the “W-B-U” treatment.