## 3 Results and Discussion
### Impact on the Growth and Fermentation Kinetics
Bluer and darker blue shades indicate higher initial thiamine in the cultivation medium, while pinker and darker pink shades indicate higher initial biotin in the cultivation medium. such a disparity in regard to biotin biosynthesis capacity. There is, however, an overall consensus of past and present findings regarding the essential role assumed by biotin in yeast growth and viability, its significance being, as such, asserted. In contrast to biotin, thiamine appeared to exert an effect solely on fermentation kinetics and had no impact on the considered growth parameters (Table 3, Figure 1, Supplementary Table S1). Interestingly, the significance of thiamine in regard to fermentation does not appear to be dose-related in a linear fashion, since distinctive differences in the fermentation rates only appeared between the yeasts cultivated in 50 \(\upmu\)g/L and 250 \(\upmu\)g/L of thiamine, the total absence of the vitamin rather standing as an intermediate, and highly versatile condition. While rising concentrations of the initial thiamine in the medium allowed for dose-dependent decreases in the duration of the fermentation process, this dose-dependent trend did not appear in the fermentation rates, since yeasts fermented in 50 \(\upmu\)g/L appeared to display the lowest fermentation rates at any given biotin level. The intermediate fermentation rates resulting from the complete absence of thiamine in the cultivation medium might result from the establishment, by the yeast, of a survival strategy to resist the inadequate growth conditions. It has indeed been shown that, when grown in the complete absence of thiamine, _S. cerevisiae_ displays thiamine synthesis-related proteins Thi4 and Thi5 as amongst its most abundant proteins [33], both acting as suicide enzymes to maintain thiamine levels [34]. Interestingly, _THI4_ expression has been positively correlated to the _S. cerevisiae_ fermentation rate [35], as well as negatively correlated to the thiamine concentration in the medium [36]. Overall, the overexpression of _THI4_ has been proven to improve glucose fermentation and the resulting ethanol production [37]; as such, it could be envisioned that, in the absence of thiamine, a metabolic balancing system is established within the yeast as a response to the deficiency, allowing it to maintain the sufficient fermentative capacity that has been observed here. Surprisingly, however, these findings regarding the role exerted by thiamine on both _S. cerevisiae_ growth kinetics do not agree with previous conclusions found on the matter by [PERSON] and colleagues; as such, notable decreases in _S. cerevisiae_ EC1118 growth rates have been noted in thiamine limitation conditions, with significant effects observed for doses lower than 125 \(\upmu\)g/L [38], while thiamine, whether absent or as low as 50 \(\upmu\)g/L, did not induce any growth impairment here. Although these findings regarding the impact held by thiamine on the yeast growth do not concur, the research conducted by [PERSON] and colleagues does agree with the present results, that conclude in the essential character of thiamine for alcoholic fermentation [38]. A difference in fermentative behavior in regard to thiamine does, however, appear since increases in thiamine have led to rather proportional increases in the yeast fermentation capacity in the work conducted by [PERSON] [38], rather than inducing a maintained fermentation state in complete absence of thiamine, as observed here. Such diverging findings might be an expression of individual differences between the different strains used, or might reflect the differences in physiological states of the yeasts at inoculation; as such, the fermentations conducted by [PERSON] and colleagues relied on thiamine-starved, pre-cultivated yeasts, rather than directly rehydrated commercial ADY that were used in the present experiment, and specifically chosen to