## 3 Results and Analysis
### Optimization of Enzyme Production Conditions for Strain Fermentation  
#### 3.3.1 Single Factor Results  
Effect of Fermentation Time on Enzyme Activity  
Fermentation time significantly affected enzyme activity (\(p<0.05\)). The variation curve of cellulase activity from JZ2 at different fermentation times is shown in Figure 4. Our results showed that enzyme productivity first increased and then decreased, reaching its maximum productivity after 2 d of incubation. The maximum enzyme activity values of  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Appraisal Indicators** & **Appraisal Results** \\ \hline Glucose & + \\ Starch hydrolysis & + \\ Mannitol & - \\ Simon’s citrate & – \\ Power medium & + \\ Nitrate broth & - \\ V-P & + \\ Gelatin medium & + \\ Lysozyme broth & + \\
3\% catalase & + \\ \hline \hline \end{tabular} Note: + indicates a positive result, – indicates a negative result.  
\end{table}
Table 4: Physiological and biochemical characteristics of strain JZ2.  
Figure 2: Morphological characteristics of strain JZ2.  
CMC and FPA for strain JZ2 were 4.282 U/mL and 4.105 U/mL, respectively. After 2 d, enzyme activity began to decrease. The increase in enzyme activity corresponds to the enzyme production stage of the strain. The maximum amount of cellulase was produced by continuously inducing cellulase with the substrate and the extension of fermentation time. The decrease in enzyme activity may be due to the production of other byproducts in the fermentation medium and the depletion of nutrients. These conditions cause bacterial stress, resulting in the inactivation of enzyme secretion [26; 31].  
Figure 5 shows the effect of rotation rate on enzyme activity in strain JZ2. The results showed that the enzyme activity of JZ2 increased with the increased rotation rate (150-180\(\times\)_g_). When the rotation rate was 180\(\times\)_g_, the CMC and FPA enzyme activity values reached 4.066 U/mL and 3.518 U/mL, respectively. The enzyme activity gradually decreased when the rotation rate was <180\(\times\)_g_. According to previous studies, the rotation rate is important because the dissolved oxygen levels it creates in the culture broth affect the cell growth of cellulase-producing microorganisms [32]. However, higher rotation rates  
Figure 4: Effect of fermentation time on enzyme production conditions for JZ2. Different letters (a–c) on same curve in the figure indicate significant differences (_p_ < 0.05) for enzyme activity.  
Figure 3: Phylogenetic tree of strain JZ2.  
also inhibit enzyme activity [26; 33]. This inhibition effect may be due to the impact of high shear forces on JZ2, leading to a decrease in enzyme production capacity.  
Effect of Incubation Temperature on Enzyme Activity  
Figure 6 shows the variation curve of cellulase activity at different temperatures. For JZ2, maximum enzyme activity was achieved after 20 \({}^{\circ}\)C of incubation and decreased after 25 \({}^{\circ}\)C. The CMC and FPA enzyme activity values of strain JZ2 reached a maximum of 4.360 U/mL and 3.165 U/mL, respectively. High temperatures may affect the energy exchange between the strain and the external substance, potentially affecting enzyme production.