0, containing 5 mM β-mercaptoethanol and 1 mM EDTA) at 4 °C overnight. The gel was then transferred onto a glass plate, sealed in film, and incubated at 50 °C for 4 h. The gel was stained in a solution of 0.25% Congo red for 5 min and destained in
1 M NaCl for 1 h. Fermentations were performed as described previously (Jeon et al., 2009). The yeast strains were grown to active exponential phase at 30 °C and 200 r.p.m. in 800 mL of SD medium in 1-L Erlenmeyer flasks for 48 h. The cells were collected by centrifugation, washed twice with sterile distilled water and inoculated into minimal medium (6.7 g L−1 YNB and 1.3 g L−1 Trp drop-out amino acid) to remove any residual carbon source. After incubation at 30 °C for 1 h, the cells were harvested by centrifugation and inoculated into 20 mL selleck chemicals llc fermentation medium (CMC medium) in 50-mL closed bottles. Fermentations were performed at 30 °C
with mild agitation at 100 r.p.m. Ethanol concentrations were determined by GC (model GC7890; Agilent) as described previously (Jeon et al., 2009) with an DB-WAXetr column (50.0 m × 0.32 mm) at an oven temperature of 120 °C and with a flame this website ionization detector at 250 °C. The ethanol standards were prepared using commercial grade ethanol. Helium with a flow rate of 40 mL min−1 was used as the carrier gas. We have previously reported the expression of endoglucanase CelE (previously called EgE) and β-glucosidase Bgl1 in S. cerevisiae (Jeon
et al., 2009). In that study, we successfully transformed these endoglucanase and β-glucosidase genes into S. cerevisiae and confirmed that the recombinant yeast strain could efficiently express and secrete CelE and Bgl1. To assemble the minicellulosome via scaffolding protein CbpA from C. cellulovorans, we constructed a chimeric endoglucanase CelE containing the catalytic domain of CelE fused with a tandem-aligned dockerin domain of C. cellulovorans Acetophenone EngB (Fig. 1a). This was done because the cohesin–dockerin interaction was shown to be species-specific in different bacterial species (Fierobe et al., 2005). The gene encoding chimeric CelE was fused to the gene coding for the secretion signal sequence of the α-mating factor from S. cerevisiae and expressed under the constitutive control of the ADH1 promoter. To confirm whether each transformant had endoglucanase production potential, a plate assay was carried out using 1 g L−1 CMC as a substrate, according to the Congo red staining method (Den Haan et al., 2007). The yeast cells harboring the plasmids encoding chimeric CelE (pADH-α-CelE and pADHαcCelEmCbpA) and their concentrated supernatants hydrolyzed the substrate, and a clear halo was observed. However, no halo appeared around the colony of the control strain harboring the control plasmid pADHα (Fig. 3).