Effect of byproducts in lignocellulose hydrolysates on ethanol fermentation by Issatchenkia orientalis / 生物工程学报

Byproducts in lignocellulose hydrolysates, namely sodium formate (1 to 5 g/L), sodium acetic (2.5 to 8.0 g/L), furfural (0.2-2 g/L), 5-hydroxymethylfurfural (5-HMF, 1 to 1.0 g/L) or vanillin (0.5 to 2 g/L) were used to evaluate their effects on ethanol fermentation by Issatchenkia orientalis HN-1 using single factor test and the response surface central composite experiment. Results showed that most of the byproducts had no obvious inhibition on the production of ethanol, except for the addition of 2 g/L vanillin or 1 g/L of 5-HMF, which reduced the ethanol production by 20.38% and 11.2%, respectively. However, high concentration of some byproducts in lignocellulose hydrolysates, such as sodium formate (1 to 5 g/L), sodium acetic (2.5 to 8.0 g/L), furfural (0.2 to 2 g/L) and vanillin (0.5 to 2 g/L) inhibited the growth of I. orientalis HN-1 significantly. Compared with the control, the dry cell weight of I. orientalis HN-1 decreased by 25.04% to 37.02%, 28.83% to 43.82%, 20.06% to 37.60% and 26.39% to 52.64%, respectively, when the above components were added into the fermentation broth and the fermentation lasted for 36 h. No significant interaction effect of the various inhibitors (sodium formate, sodium acetic, furfural and vanillin) except for vanillin single factor on the ethanol production was observed based on the central composite experiments. The concentrations of byproducts in most lignocellulose hydrolysates were below the initial inhibition concentration on ethanol production by Issatchenkia orientalis HN-1, which indicated that Issatchenkia orientalis HN-1 can be used for ethanol production from lignocellulose hydrolysates.

Butanol production from corn stover hydrolysate with in-situ liquid-liquid extraction / 生物工程学报

Butanol production from corn stover hydrolysates (CSH) with in-situ liquid-liquid extraction was studied to enhance the production and reduce the fermentation cost. Oleyl alcohol was selected as the suitable solvent and added at the initial fermentation time with the ratio of 1:1 (oleyl alcohol: fermentation broth, V/V). Under this condition, butanol and ABE from CSH with 32.1 g/L total sugars were 3.28 and 4.72 g/L, which were 958.1% and 742.9% higher than those of the controls, respectively. Butanol and ABE production from CSH of 49.7 g/L total sugars after detoxification by ion exchange resin D301 coupled with extraction fermentation were 10.34 g/L and 14.72 g/L with an ABE yield of 0.31 g/g (g ABE/g utilized sugar), which were equal to those of glucose and xylose mixture fermentation. The detoxification and extraction fermentation technology of cellulosic butanol production would provide a crucial technical support to the industrialized production of cellulosic butanol.

Comparison of microorganisms fermenting syngas into ethanol / 生物工程学报

To evaluate the ability of microbial mix-culture fermenting syngas into ethanol, we studied the microbial mix-cultures A-fm 4, G-fm 4, Lp-fm 4 and B-fm 4 obtained by enrichment and compared with Clostridium autoethanogenum DSM10061 with 10% and 25% inoculation size. The results show that, with 10% inoculation size, the ethanol production of A-fm 4, G-fm 4, Lp-fm 4, B-fm 4 and C. autoethanogenum were 349.15, 232.16, 104.25, 79.90 and 26.99 mg/L respectively. With 25% inoculation size, the ethanol production were 485.81, 472.73, 348.58, 272.52 and 242.15 mg/L respectively. Higher inoculation size will increase the production of ethanol. The tested mix-culture exhibited a significant yield advantage compared with the maximum production of C. autoethanogenum reported in the literature (259.64 mg/L). This research provided a practical method to improve ethanol production from syngas.

Optimization of corn stover hydrolysis by fed-batch process / 生物工程学报

High-concentration sugars production from stover is an important perspective technology for the cellulosic ethanol industrialization. Fed-batch process is an effective way to achieve this goal in the fermentation industry. In this study, based on fed-batch process, high-concentration sugars were produced from pretreated corn stover by enzymatic hydrolysis. After being pretreated by the dilute sulphuric acid, the impacts of the ratio of solid raw material to liquid culture, the content of supplementary materials and the refilling time on the saccharification rate were investigated. Results showed that the initial ratio of solid raw material to liquid culture was 20% (W/V) and the initial concentrations of enzymes for xylanase, cellulose and pectinase were 220 U, 6 FPU, and 50 U per gram of substrates, respectively. After 24 hours and 48 hours, 8% pretreated corn stovers were added respectively together with the additions of xylanase (20 U) and cellulose (2 FPU) per gram of substrates. After 72 hours, the final concentration of reducing sugar was increased to 138.5 g/L from 48.5 g/L of the non fed-batch process. The rate of enzyme hydrolysis of the raw material was 62.5% of the thoretical value in the fed-batch process. This study demonstrated that the fed-batch process could significantly improve the concentration of reducing sugar.

Screening of high lipid production Trichosporon fermentans mutants by transposon tagging mTn-lacZ/leu2 insertion / 生物工程学报

To improve microbial lipid production, we inserted mTn-lacZ/leu2 into Trichosporon fermentans 2.1368-Leu(-) to obtain high lipid production mutants. By observing the LacZ chromogenic change, the positive reaction between Cerulenin (inhibitor of fatty acid synthase) and phosphate vanillin, a higher lipid-producing mutant 2.1368-Leu(-)-7 grown on corn-stalk hydrolysate was obtained. The lipid content of this mutant reached 38.30% (8.97% higher than that of the control) and the lipid production rate was 8.35% (20.63% higher than that of the control). The rate of sugar utilization was 77%, meaning that 100 g corn-stalk could be converted to 8.32 g lipid. The study provided an effective method for microbial lipid production by using cheap raw materials for biodiesel.

Kinetics of enzymatic hydrolysis of steam-explosion pretreated corn straw / 生物工程学报

In order to learn the enzymatic hydrolysis characteristics of steam-explosion pretreated corn straw by cellulase, the effects of substrate concentration, cellulase concentration and temperature were determined. The kinetics of the hydrolysis reaction could be described with the Michealis-Menten equation, and the hydrolysis reaction obeyed the classical first-order reaction rate in the first three hours. In the condition of 45 degrees C and pH 5.0 and the stirring rate 120 r/min, the Michealis constant (Km) and maximum rate (Vm) for 1.2 FPU/mL of cellulase were 11.71 g/L and 1.5 g/(L x h). The kinetic model, including the parameters such as substrate concentration, enzymatic concentration and temperature, was suit for the hydrolysis reaction under the temperature range from 30 degrees C-50 degrees C.