Essential fatty acids in the diet are necessary for the healthy functioning of organisms because humans, as well as other mammals, are unable to synthesize them. Strictly speaking, there are only two primary essential polyunsaturated fatty acids (PUFAs): ALA (α-linolenic, 18:3ω-3) and LA (linoleic, 18:2ω-6) (Nakamura and Nara 2003). They also serve as precursors for substances biologically active in blood clotting, e.g. thromboxane or prostacyclin. Two groups of PUFAs are distinguishable, ω-3 and ω-6. The former are represented for instance by ALA and hexadecatrienoic acid (HDA; 16:3ω-3). The latter include, in particular, LA and γ-linolenic (GLA; 18:3ω-6). ALA belongs to so-called drying-capable vegetable oils. The source of HDA is exclusively photosynthetic microorganisms, mainly marine or freshwater algae, where the content reaches up to tens of percent. These essential substances are necessary as a feed supplement for fish in aquaculture, or zooplankton, which then serves as food for fish (Weylandt et al. 2015).
Oleic acid (OL; 18:1ω-9) occurs in various animal fats and vegetable oils. It is the precursor to the synthesis of essential ALA. PUFAs are the main factor in the favourable influence of the so-called Mediterranean diet. For vegans, vegetarians and for those who lack fish in their diet, these algal and plant products represent an acceptable alternative (Cherif et al.1975).
Fatty acids are valuable products, but usually individual organisms predominantly produce only certain fatty acids. In addition, to cultivate an organism outdoors, it must be able to grow and be resistant to certain technological treatments during cultivation and harvest.
Algae, as a source of FAs, have potential for use in biotechnology because of their high growth rate and the possibility of automated large-scale cultivation. In addition, they can be grown in locations unsuitable for conventional crops because they do not require fertile soil, e.g. in deserts, on roofs of industrial buildings, etc. Outdoor cultivation eliminates the costly supply of heat and light energy. In a temperate climate, however, it is possible to operate outdoor cultivation of algae only for a limited period of the year, when the air temperature and solar radiation is high enough for the growth of these microorganisms. Therefore, there is demand for new organisms with advantageous properties (Lang et al. 2011), e.g. snow algae (Hoham and Remias 2020). Some strains of algae can be used for the production of oils containing high levels of PUFAs, e.g. Monoraphidium sp. for the production of HDA and stearidonic acid (Řezanka et al. 2016, 2017).
However, the correct proportion of ω-6/ω-3 PUFAs is most important and excess is not beneficial for health (Cunnane 2003). Examples of native ratios of ω-6 and ω-3 PUFAs in biotechnologically cultured algae were reported by Lang et al. (2011): for commonly used algae such as Chlorella sp., the ratio of ω-6/ω-3 was 1: 0.40, Parachlorella kessleri (formerly Chlorella kessleri) 1: 0.19, Scenedesmus sp. 1: 0.45. In cyanobacteria, the ratio of these FAs varied from 1: 0.30 by Arthrospira (Spirulina) to cases where cyanobacteria did not produce any ω-3 PUFAs.
Bracteacoccus has been investigated in the bioprospecting of microalgae for biofuel production (Piligaev et al. 2015)d cinnabarinus was shown to grow heterotrophically in medium supplied with sodium or potassium acetate and glucose (Hornung et al. 1977). Subsequently, for B. bullatus, a 10-fold reduction in phosphorus and nitrogen in the nutrient solution resulted in OL, LA and palmitoleic acid (PA; 16:1ω-7) levels reaching 48–64%, 14–24% and 9–13% of total FAs, respectively. The latter alga was cultivated at laboratory scale under constant shaking and saturated with 5% CO2, under irradiance of 160 µmol m–2 s− 1 and 16/8 h photoperiod (Mamaeva et al. 2018). Maltsev et al. (2020) isolated, a new strain of B. bullatus (MZ-Ch32) from soil that produced dry biomass and tFAs to 2.31 g. L− 1 and 55.84%, after 15 days of cultivation. In the total fatty acids, palmitic, hexadecadienic (12.5%), oleic (43.2%) and linoleic acids (23.8%) prevailed. A balanced ratio of ω-6/ω-3 PUFAs makes the strain prospective as food additives and high content of oleic acid for the biofuel production.
About 1100 carotenoids are known (Yabuzaki 2017), and these mainly absorb light at wavelengths from 400–550 nm (violet to green light for use in photosynthesis); they protect chlorophyll from photo-damage. Carotenoids that contain unsubstituted beta-ionone rings (including beta-carotene, alpha-carotene, beta-cryptoxanthin and gamma-carotene) have vitamin A activity and these and other carotenoids can also act as antioxidants. The carotenoid most frequently produced commercially is astaxanthin, whose industrial production is derived from plant- or animal-based and synthetic sources. The main algal source is Haematococcus pluvialis (Borowitzka 2013, Rajesh, et al. 2017). Astaxanthin is also found in yeast, salmon, trout, krill, shrimp, crayfish, crustaceans, and the feathers of some birds.
B. minor has previously been shown to be a promising producer of carotenoids, including astaxanthin diesters comprising 37–42% of total carotenoids, and 53–63% of lipids in dry matter. In this case, a two stage cultivation process was performed, the first (green, 16 days) followed by a second one (red, 11 days, diluted to reduce nitrogen and phosphorus levels), and astaxanthin production was also stimulated by spiking with Na-acetate (Minyuk et al. 2014).
The aim of the current work was to test an isolate of microalga from an extreme mountain snow habitat in order to acquire a producer of valuable fatty acids and carotenoids. The strain should be capable of growing at lower temperatures and light intensities, and thus be adapted to conditions in open pond reactors.