## 3 Results and Discussion
### Yield and Synthesis Efficiency of BC  
One of the most critical parameters of the cellulose production process is the efficiency of its synthesis. In the medium containing sucrose with hydrolysis disaccharide, yeast's \(\beta\)-D-fructofuranosidase, the yield and efficiency of biopolymer synthesis were comparable to standard HS media. Different enzyme unit numbers did not influence the yield, which amounted to approximately 4.0 g/L (Figure 3a). A significant quantity of BC was also obtained from the control cultures without enzyme addition, but with a much lower yield, 1.5 g/L, compared to standard HS and medium with the enzyme. The BC synthesis efficiency was approximately 40% (Figure 3d), while for medium with enzymatically undegraded sucrose, approximately 7%. The obtained efficiency of BC synthesis was on a very good level, comparable to or better than earlier reports of the use of _K. xylinus_ strain with a modified HS medium [6]. The second product of sucrose splitting by \(\beta\)-D-Fru is fructose, which can also be used as an effective carbon source for BC synthesis. However, its uptake by _K. xylinus_ cells and then use in BC synthesis requires additional energy for transportation across the cell membranes and conversion to glucopyranose. Therefore, bacterial cells use fructose as a secondary carbon source when glucose is present in a cultivation medium [36]. It is also worth highlighting the relatively significant amount of cellulose obtained from the control medium with sucrose and the omission of the \(\beta\)-D-Fru. It suggests that the analysed strain of _K. xylinus_ may produce enzymes with \(\beta\)-D-fructofuranosidase activity. The available literature confirms the possibility of genes for these kinds of enzymes in some species from the genus Acetobacter sp., which partially confirms this hypothesis [37]. From the cultures cultivated in a medium with lactose and 12 U/mL of the \(\beta\)-Gal, the highest BC yield of 5.15 g/L was obtained. The cultures with the addition of 6.0 U/mL of enzyme resulted in 4.75 g/L for 3 U/mL; 3.83 g/L of BC yield was reached. Surprisingly, in the cultures with the highest amount of enzyme added (60 U/mL), a significant yield reduction was recorded, reaching 2.87 g/L (Figure 3b). Only a minor amount of BC was obtained in the control without enzyme, 0.2 g/L. The efficiency of BC synthesis by _K. xylinus_ in the HS medium containing lactose and the enzyme \(\beta\)-Gal was also high. Cultures with 3, 6, and 12 U/mL of enzyme amounted to 38%, 48%, and even 52%, respectively (Figure 3e). It may be assumed that bacterial cells used most of the glucose released from lactose for BC synthesis. The high value of the BC synthesis effectiveness is astonishing, considering that the second product of lactose hydrolysis is galactose, and it cannot be included in the metabolism of both BC synthesis and biomass production [10]. Moreover, the lower acidification of cultivation media was not recorded, which could partially explain the high effectiveness. The cultures with the initial amount of enzyme at 60 U/mL were less effective in BC synthesis, with 27% efficiency (Figure 3e). \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Enzyme**} & **Initial Amount of** & **Remaining Activity \({}^{*}\)** \\  & **Enzyme in Medium (U/mL)** & **(\%)** \\ \hline  & 1.6 & 34.04 \(\pm\) 14.35 \({}^{\times}\) \\ \(\beta\)-D-Fru & 3.2 & 29.50 \(\pm\) 14.04 \\  & 4.8 & 38.05 \(\pm\) 16.66 \\  & 6.2 & 48.20 \(\pm\) 19.91 \\ \hline  & 3.0 & 12.59 \(\pm\) 9.43 \\ \(\beta\)-Gal & 6.0 & 7.37 \(\pm\) 5.19 \\  & 12 & 3.93 \(\pm\) 2.07 \\  & 60 & 1.66 \(\pm\) 1.90 \\ \hline  & 5.0 & 14.15 \(\pm\) 2.77 \\  & 10 & 23.60 \(\pm\) 6.86 \\ GLA & 20 & 32.69 \(\pm\) 3.12 \\  & 40 & 50.96 \(\pm\) 6.44 \\ \hline \hline \end{tabular} \({}^{*}\)The activity was measured in residual medium obtained after 6 days of _K. xylinus_ cultivation. The medium’s initial enzyme activity unit number was treated as 100%. \({}^{\times}\)\(\pm\)—standard deviation.  
\end{table}