Enzymatic activity and protein expression of cellulase from rice straw produced by Trichoderma reesei in the presence of oxygen vectors

Oxygen mass transfer is one of the most essential factors affecting microbial cell growth and cellulase fermentation. In this study, an effective approach capable of improving oxygen mass transfer was developed by adding oxygen vectors into the fermentation broth by Trichoderma reesei. With the addition of 1% (v/v) n-dodecane, the volumetric mass transfer coefficient (kLa) was increased from 142 h−1 to 185 h−1 at the beginning of the fermentation. In response to the improved oxygen transfer, 44.6% higher FPase activity, 29.2% higher xylanase activity and 42.5% higher saccharification yield of rice straw were obtained. The scanning electron microscopy showed that the addition of n-dodecane did not cause obvious variations on the cell morphology, whereas the comparative proteomics analysis identified 30 protein spots with different expression levels. Among them, exoglucanases (CBH I, CBH II), endoglucanase (EG VI), xylanases (Xyn I, Xyn II, Xyn III), acetyl xylan esterase, swollenin and cellulose induced protein (Cip1) were highly expressed after the addition of n-dodecane, whereas more EG III and β-xylosidase were produced without the addition of n-dodecane. The present study indicated that the addition of n-dodecane was advantageous for cellulase fermentation by T. reesei.