## 4 Discussion
The authors reported that the synthesis of \(\beta\)-carotene (7.1 mg/L) was highest in the medium containing 250 mg Zn\({}^{2+}\)/L. At acidic pH, aluminum ions are toxic to both plant and animal cells. Many studies suggest that they increase the peroxidation of phospholipids and proteins in cell membranes and induce oxidative stress in cells [11,24]. It was also indicated that the addition of Al\({}^{3+}\) to the medium at doses from 200 to 300 mg/L resulted in a significant reduction of the biomass yield (Table 3). Among the cations tested in the present study, only aluminum ions increased the content of carotenoids in the cell biomass of the _R. mucilaginousa_ MK1 strain and changed the proportions of \(\beta\)-carotene, torulene, and torularhodin synthesized by the yeast. The share of torulene increased significantly from 31.85% in the control sample to 75.20% in the biomass obtained after cultivation in the medium supplemented with 300 mg Al\({}^{3+}\)/L. A study by [PERSON] et al. [11] showed that the enrichment of the culture medium with aluminum sulfate (0.7 mM) led to an increase in the synthesis of carotenoid pigments and torulene, which confirms the role of aluminum ions in the induction of carotenoid biosynthesis in yeast cells. [PERSON] et al. [25] found that the addition of aluminum ions in the medium resulted in an increase in the activity of malate dehydrogenase and the intracellular accumulation of citric acid by _Rhodotorula taivanensis_ RS1 yeast strain. Manganese is an important trace element that belongs to the group of transition metals. As a cell component, it plays a key role among enzymes involved in various metabolic processes and is also part of an antioxidant--superoxide dismutase, which protects cells by inactivating free radicals. Manganese also acts as an electron store, from where electrons are transferred to reaction sites, and as an activator of many enzymes involved in oxidation, carboxylation, carbohydrate metabolism, and the series of phosphorus and citric acid reactions. Similar to magnesium, this element is involved in the binding of ATP with enzyme complexes (phosphotransferase and phosphokinase) and activates the enzymes taking part in the Krebs cycle, such as dehydrogenase and decarboxylase, as well as RNA polymerase [26]. Hence, this study tested the influence of magnesium on carotenoids biosynthesis by yeast. The results showed no increase in the number of carotenoids in cellular biomass in the control medium, but after cultivation in the medium supplemented with manganese at a dose of 300 mg/L, the proportion of torularhodin in the total pool of carotenoids decreased from 22.8% (control) to 14.1%. Interestingly, [PERSON] et al. [27] observed the opposite effect in their study on carotenoid biosynthesis by _Rhodotorula graminis_ DBVPG 7021 strain, which showed that the presence of manganese ions inhibited the biosynthesis of torulene and torularhodin. The authors hypothesized that manganese cations had a possible negative influence on the activity of desaturases involved in carotenoid biosynthesis by yeast. Similar to micronutrients, B vitamins are critical for the proper functioning and metabolism of yeast cells. For example, biotin is the prosthetic group of acetyl-CoA carboxylase, an enzyme that catalyzes the formation of malonyl-CoA, a substrate in de novo lipid biosynthesis [28]. Riboflavin is essential for the activity of enzymes involved in the TCA cycle, as well as for the electron transport chain, \(\beta\)-oxidation, and various biosynthetic processes [15]. Pantothenic acid (vitamin B\({}_{3}\)) is a metabolic precursor of coenzyme A and many acyl carrier proteins, which are cofactors of many enzymes [12; 13]. Niacin is involved in the biosynthesis of nicotinamide adenine dinucleotide [14]. Due to the significant role played by B vitamins in yeast cell metabolism, this study investigated their influence on carotenoid biosynthesis. To the best of the authors' knowledge, there are no data on this subject in the scientific literature.