Enhancement of Biogas Yield of Poplar Leaf by High-Solid Codigestion with Swine Manure.

The aim of this work was to examine the improvement of anaerobic biodegradability of organic fractions of poplar leaf from codigestion with swine manure (SM), thus biogas yield and energy recovery. When poplar leaf was used as a sole substrate, the cumulative biogas yield was low, about 163 mL (g volatile solid (VS))(-1) after 45 days of digestion with a substrate/inoculum ratio of 2.5 and a total solid (TS) of 22 %. Under the same condition, the cumulative biogas yield of poplar leaf reached 321 mL (g VS)(-1) when SM/poplar leaf ratio was 2:5 (based on VS). The SM/poplar leaf ratio can determine C/N ratio of the cosubstrate and thus has significant influence on biogas yield. When the SM/poplar leaf ratio was 2:5, C/N ratio was calculated to be 27.02, and the biogas yield in 45 days of digestion was the highest. The semi-continuous digestion of poplar leaf was carried out with the organic loading rate of 1.25 and 1.88 g VS day(-1). The average daily biogas yield was 230.2 mL (g VS)(-1) and 208.4 mL (g VS)(-1). The composition analysis revealed that cellulose and hemicellulose contributed to the biogas production.

Expression of heterogenous pyruvate carboxylase in Escherichia coli with lactose as inducer and its effect on succinate production / 生物工程学报

Escherichia coli strain DC1515, deficient in glucose phosphotransferase (ptsG), lactate dehydrogenase (ldhA) and pyruvate:formate lyase (pflA), is a promising candidate for the fermentative production of succinate. To further improve the succinate producing capability of DC1515, we constructed plasmid pTrchisA-pyc with heterogenous pyruvate carboxylase (pyc) from Bacillus subtilis 168 under the Trc promoter and introduced it into DC1515. We used lactose as a substitute of IPTG to induce pyc. We optimized the culture conditions such as the lactose addition time, the lactose concentration and the culture temperature after induction for succinate production. We also explored the effect of lactose supplement during the fermentation. The results showed that pyc can be expressed under lactose induction in the fermentative medium with 15 g/L glucose due to the deficient of ptsG in DC1515. Under optimized conditions, the final succinate concentration reached to 15.17 g/L, which was 1.78-fold higher than that of control strain. If complementing lactose twice to the concentration of 1 g/L during the fermentation, the final succinate concentration could further reach to 17.54 g/L. This work might provide valuable information for gene expression in E. coli strains using lactose as inducer for succinate production in a glucose-medium. Due to the reduced cost, E. coli is becoming a more promising strain for succinate production through fermentation.