## 3 Results and Discussion  
### Effect of Selenium on the Number of Yeast Cells  
Immediately after the introduction of inoculum, the number of _C. utilis_ ATCC 9950 yeast was 4.0-4.9 \(\times\) 10\({}^{7}\) cfu/mL (Figure 1). After 24 h, their number in the control culture increased to 6.1 \(\times\) 10\({}^{8}\) cfu/mL. In the media supplemented with selenium, budding of yeast cells in the log phase was significantly reduced. The literature data presented by [PERSON] et al. [23] and [PERSON] et al. [24] indicate that the inhibitory effect of selenium on yeast cells results from changes in the composition and potential occurring in the cell membranes. The results of the study presented by [PERSON] [25] also confirmed the inhibitory effect of selenium on _Lactobacillus_ growth. The lowest dose of selenium used (4 mg/L) reduced the number of cells to 5.5 \(\times\) 10\({}^{8}\) cfu/mL as compared to the yeast cells grown in the control medium (YPD) after 24 h of cultivation. In all experimental cultures supplemented with increasing doses of selenium (30 and 60 mg/L) after the completion of the logarithmic growth phase, the number of cells was lower than in the control cultures (YPD), and accounted for 3.0 \(\times\) 10\({}^{8}\) and 1.8 \(\times\) 10\({}^{8}\) cfu/mL. In all media supplemented with selenium and in the control medium after 48 h of cultivation, the number of yeast cells decreased and ranged  
Figure 1: Changes in the number of _C. utilis_ yeast cells (Log cfu/mL) after cultivation in the control (YPD) and in the experimental media enriched with selenium in the form of Na\({}_{2}\)SeO\({}_{3}\). \({}^{a-n}\) Means with the same letter did not differ significantly (\(p<\) 0.05). from \(5.4\times 10^{8}\) to \(3.8\times 10^{7}\) cfu/mL. After 72 h of cultivation in the control medium and in medium supplemented with selenium, yeast cells showed signs of having reached the death phase. The lowest number of cells (\(8.3\times 10^{6}\) cfu/mL) was observed after the third day of culturing in the medium containing selenium in an amount of 80 mg/L. [PERSON] et al. [26] reported that the growth of most strains of _Saccharomyces cerevisiae_ was inhibited by a high concentration of selenium (above 125 mg/L) in the culture medium. The investigated _S. cerevisiae_ ATCC 4126 and ATCC 26422 strains exhibited no growth in the medium supplemented with selenium at a dose of 50 mg/L, while the total inhibition of the growth of most yeast strains investigated occurred in the medium supplemented with selenium at a dose of 500 mg/L. The results of the study presented by [PERSON] et al. [27] showed an inhibitory effect of selenium on the number of cells of _Saccharomyces cerevisiae_ yeast (strain 15-6252). The yeasts were subjected to 24 h of cultivation in the YPD medium supplemented with sodium selenite (IV) at a dose between 10 and 50 mg/L. The highest number of yeast cells (\(2.6\times 10^{9}\) cfu/mL) was obtained in the control YPD medium. In terms of sodium selenite (IV) in an amount of 20 and 40 mg/L, the number of yeast cells decreased and accounted for \(1.0\times 10^{9}\) cfu/mL and \(5.3\times 10^{8}\) cfu/mL, respectively. The results of the number of yeast cells obtained in experimental media suggest that the addition of selenium, as well as extension of the cultivation time until the third day, influenced the number of yeast cells. According to [PERSON] et al. [28] and [PERSON] et al. [24], yeasts exhibit the ability to metabolize compounds containing selenium. These processes may lead to a change in the degree of toxicity of this element in yeast cells, which in turn could affect the reduction in the number of yeast cells in the experimental media. The toxic effect of selenium could also be the result of its high chemical similarity to sulfur [29]. Selenium is involved in the metabolic pathway of this element (i.e., sulfur) in the yeast cell structures. It occurs in many proteins, changing their conformational structure and functional activity.