2.6 Analytical Methods
The optical density at 600 nm (OD600) was measured in a
1.5-mL cuvette (1 cm light path length) with a spectrophotometer
(UV-16-1, Shimazu). One unit of OD600 was equivalent to
0.534 g/L cell dry weight. Glucose in the fermentation broth samples was
determined with a YSI 2300 glucose analyzer (Yellow Spring, OH). All
metabolites including acetone, butanol, ethanol, acetic acid, and
butyric acid in the fermentation broth samples were analyzed, after
removing cells by centrifugation or microfiltration using 0.2-µm syringe
filters and acidified with phosphoric acid (1% v/v), with a gas
chromatograph (GC-2014, Shimadzu) following the method described
elsewhere (Xu et al., 2015).