A genome shuffling-generated Saccharomyces cerevisiae isolate that ferments xylose and glucose to produce high levels of ethanol.

Genome shuffling is an efficient approach for the rapid improvement of industrially important microbial phenotypes. This report describes optimized conditions for protoplast preparation, regeneration, inactivation, and fusion using the Saccharomyces cerevisiae W5 strain. Ethanol production was confirmed by TTC (triphenyl tetrazolium chloride) screening and high-performance liquid chromatography (HPLC). A genetically stable, high ethanol-producing strain that fermented xylose and glucose was obtained following three rounds of genome shuffling. After fermentation for 84 h, the high ethanol-producing S. cerevisiae GS3-10 strain (which utilized 69.48 and 100% of the xylose and glucose stores, respectively) produced 26.65 g/L ethanol, i.e., 47.08% higher than ethanol production by S. cerevisiae W5 (18.12 g/L). The utilization ratios of xylose and glucose were 69.48 and 100%, compared to 14.83 and 100% for W5, respectively. The ethanol yield was 0.40 g/g (ethanol/consumed glucose and xylose), i.e., 17.65% higher than the yield by S. cerevisiae W5 (0.34 g/g).

Optimization of xylose fermentation for ethanol production by Candida shehatae HDYXHT-01 / 生物工程学报

Plackett-Burman (PB) design and central composite design (CCD) were applied to optimize of xylose fermentation for ethanol production by Candida shehatae HDYXHT-01. The PB results showed that (NH4)2SO4, KH2PO4, yeast extract and inoculum volume were the main affecting factors. With ethanol productivity as the target response, the optimal fermentation was determined by CCD and response surface analysis (RSM). The optimal fermentation conditions were (NH4)2SO4 1.73 g/L, KH2PO4 3.56 g/L, yeast extract 2.62 g/L and inoculum volume 5.66%. Other fermentation conditions were xylose 80 g/L, MgSO47H20 0.1 g/L, pH 5.0 and 250 mL flask containing 100 mL medium and cultivated at 30 degrees C for 48 h and the agitation speed was 140 r/min. Under this fermentation conditions, ethanol productivity was 26.18 g/L, which was 1.15 times of the initial.

Fermentation optimization by response surface methodology for enhanced production of beta-glucosidase of Aspergillus niger HDF05 / 生物工程学报

In order to obtain high beta-glucosidase productivity, we optimized the fermentation parameters for beta-glucosidase production by Aspergillus niger HDF05. First, we screened the important parameters by Plackeet-Burman design. Second, we used the path of steepest ascent to approach to the biggest response region of parameters affecting beta-glucosidase production. Then, we obtained the optimal parameters by central composite design and response surface analysis. We developed a quadratic polynomial equation for predicting beta-glucosidase production level. The results showed that the important parameters were temperature, packing volume, concentrations of wheat bran and (NH4)2SO4. The optimal fermentation parameters were as follows: temperature 28 degrees C, packing volume 71.4 mL/250 mL, wheat bran 36 g/L and (NH4)2SO4 5.5 g/L. Under the optimal conditions, we obtained the maximum enzyme activity of 60.06 U/mL, with an increase of 23.9% compared to the original fermentation parameters. During enzymatic hydrolysis of acid-pretreated corncob, addition of beta-glucosidase from Aspergillus niger HDF05 greatly reduced the inhibition caused by cellobiose, and the hydrolysis yield was improved from 66.7% to 80.4%.