## 3 Results and Discussion
### Effects of Shifts in Aeration Rate and Agitation Speed on Production of CMCase  
The effects of shifts in the aeration rate and agitation speed on the cell growth of _E. coli_ KACC 91335P and its production of CMCase were examined in 7 L bioreactors. The aeration rate and agitation speed of the 7 L bioreactors for experiments were (1) constant at 0.50 vvm and 500 rpm, (2) shifted in the aeration rate from 0.50 to 0.95 vvm and the agitation speed from 500 to 416 rpm at 24 h, (3) shifted in the aeration rate from 0.50 to 0.95 vvm and the agitation speed from 500 to 416 rpm at 36 h, (4) shifted in the aeration rate from 0.50 to 0.95 vvm and the agitation speed from 500 to 416 rpm at 48 h and (5) constant at 0.95 vvm and 416 rpm. As shown in Figure 3, the maximal cell growth was obtained at the aeration rate of 0.50 vvm and the agitation speed of 500 rpm, which were known as the optimal conditions for the cell growth of _E. coli_ KACC 91335P. However, the highest production of CMCase was obtained with shifts in the aeration rate from 0.50 to 0.95 vvm and the agitation speed from 500 to 416 rpm at 36 h, the mid-log phase of cell growth, which the production of CMCase was 953.2 U/mL. The production of CMCase with shifts in the optimal conditions of the agitation speed and aeration rate from the cell growth of _E. coli_ KACC 91335P to its production of CMCase at the mid-log phase of cell growth was 1.21 times higher than that with the fixed optimal agitation speed and aeration rate for the production of CMCase. As shown in Table 1, the cell growth of _E. coli_ KACC 91335P with shifts in the optimal conditions of the aeration rate and agitation speed at 36 h was also 1.21 times higher than that with the optimal conditions of the aeration rate and agitation speed for the production of CMCase. The production pattern of microbial metabolites can be divided in growth-associated, mixed-growth-associated and non-growth-associated [20]. The formation of mixed-growth-associated products takes place during the log and early stationary phase. In this case, the specific production rate (\(\mathrm{q_{p}}\)) with the specific growth rate (\(\mathrm{\mu_{g}}\)) is given by the following Equation (3):  
\[\mathrm{q_{p}}=\mathrm{\alpha\mu_{g}}+\beta \tag{3}\]  
Figure 2: Effects of shift in agitation speed on (**a**) cell growth and (**b**) production of CMCase by _E. coli_ KACC 91335P (, constant at 500 rpm;, shift in agitation speed from 500 to 416 rpm at 24 h;, shift in agitation speed from 500 to 416 rpm at 36 h;, shift in agitation speed from 500 to 416 rpm at 48 h; and, constant at 416 rpm). The production of CMCase by _E. coli_ KACC 91335P begins with cell growth and continues to the early stationary phase. This is the typical pattern for the mixed-growth-associated production. The shifts in the optimal conditions from the cell growth to those for its production of CMCase after the mid-log phase seemed to result in relatively higher cell growth, which sequentially enhanced the production of CMCase by _E. coli_ KACC 91335P. The CMCase produced by _B. velezensis_ A-53 was a growth-associated product, whereas that by its recombinant, _E. coli_ KACC 91335P, was a mixed-growth associated product [25]. Owing to the difference between the optimal conditions for the cell growth of _E. coli_ KACC 91335P and its production of CMCase, higher cell growth under optimal conditions for cell growth resulted in a lower production of CMCase. However, the production of CMCase by _E. coli_ KACC 91335P with shifts in the optimal conditions of pH and/or temperature from cell growth to its production of CMCase was 1.27 times higher than that with the fixed optimal conditions of pH and/or temperature for the production of CMCase [15].