In order to determine dry cell weight, the turbidity in the fermentation broth
was measured with a spectrophotometer (DU-70 Beckman Inc., Fullerton, CA) at
660 nm. According to the method of Oh et al. [28], dry weight cell concentration
was calculated from OD660 nm using the following conversion equation: Dry cell
weight (g/l) = 0.747
×
OD660 nm + 0.494. The concentrations of glucose and SOD activities
were determined by the F006 and A001-1 kit, respectively (Nanjing JianCheng
Biothech Institute, China). Production of -carotene was quantified by measuring
the absorption of the acetone-extracted -carotene at 450 nm [29,30]. Catalase
activities were determined according to our previous study [31]. One unit of catalase
activity is defined as the amount that decomposes 1 mol H2O2 per min. The amount
of protein in the cell extract was measured using the Coomassie blue method [32].