## 1 Introduction  
Lignocellulosic agricultural byproducts rich in complex carbohydrates can be used as renewable feed-stocks for the production of monomeric sugars for fermentation by physicochemical and enzymatic degradations [1]. For complete enzymatic hydrolysis, at least three types of cellulases are required; endocellularases, exocellulaases and cellobiases [2]. Endocellularases (EC 3.2.1.4) break the noncovalent interactions present in the amorphous structure of cellulose, exocellulaases (EC 3.2.1.91) hydrolyze chain ends to break the polymer into smaller sugars and cellobiases (EC 3.2.1.21) hydrolyze disaccharides and tetrasaccharides into glucose [3]. The carboymethylcellulose (CMCase) is a type of endocellular, which is the major cellulase in the conversion of cellulose [2]. However, the high cost and low productivity of cellulases are drawbacks to overcome the enzymatic saccharification of lignocellulosic materials [4]. Many studies on the types of strains including recombinants, substrates and cultural conditions for the enhanced production of cellulases have been reported [5; 6].  
Most commercial enzymes are produced in large-scale stirred-tank bioreactors [7; 8]. The oxygen transfer into a bioreactor is one of the most important factors in upscaling [9]. The oxygen transfer rate (OTR) is affected by the aeration rate and agitation speed as well as the inner pressure of the pilot scale bioreactor [7; 10]. The optimal conditions involved in OTR for cell growth are different from those for the production of cellulases [11; 12]. Productions of antibiotic by _Xenorhadus nematophila_ and lipase by _Bacillus subtilis_ were improved with two-stage dissolved oxygen control [13; 14]. The production of CMCase by _Escherichia coli_ KACC 91334P (formerly _E. coli_ JM109/A-53) was enhanced with shifts in the optimal pH and/or temperature from the cell growth to the production of CMCase [15].  
The production of the CMCase by _B. velezensis_ A-68 under optimized conditions was 83.8 U/mL, whereas that by _E. coli_ KACC 91335P was 880.2 U/mL [16]. The production by the recombinant _E. coli_ stain was 10.5 times higher than that by the wild of _Bacillus_ strain. The CMCase produced by _B. velezensis_ A-68 seemed to be essential for its survival, whereas that by _E. coli_ KACC 91335P was not essential for its cell growth. The CMCase produced by _B. velezensis_ A-68 was a growth-associated product, whereas that by _E. coli_ KACC 91335P was a mixed-growth-associated product [16]. The optimal conditions for cell growth of _E. coli_ KACC 91335P were different from its production of CMCase. The optimal conditions of the aeration rate and agitation speed of 7 L bioreactors for the cell growth of _E. coli_ KACC 91335P were 500 rpm and 0.50 vvm, respectively. However, those for the production of CMCase by _E. coli_ KACC 91335P were 416 rpm and 0.95 vvm [16]. For the enhanced production of CMCase, there should be enough cells of _E. coli_ KACC 91335P to participate in the production of CMCase. The enhanced production of mixed-growth-associated products with the conventional process needs at least two bioreactors. The effects of shifts in the optimal conditions of the aeration rate and/or agitation speed of bioreactors from the cell growth to its production of CMCase were investigated for the enhanced production of CMCase by _E. coli_ KACC 91335P on the pilot-scale in this study.