Biochemical Engineering for Biomass Refinery
Lots of extreme microorganisms utilize carbohydrate components of plant cell walls,including celluslose and hemicelluloses,facilitated by a diverse set of glycoside hydrolases (GHs).From a biomass into fermentable sugars.Exploring the glycoside hydrolases (GHs) of extreme microorganisms may give a potential way for overcoming the high cost of plant cell wall pretreatment and hydrolysis.
Anaerobic thermophilic bacterium Caldicellulosiruptor provides an effective way for converting biomass to biofuels through consolidated bioprocessing. In our research,genes encoding thermophilic GHs in genome DNA of Caldicellulosiruptor were screened and analyzed.The transcription of the genes for biomass degradation and metabolism was assayed through microarray when Caldicellulosiruptor cultured in different carbohydrates.Some extreme enzymes having potential for industry application were cloned,heterologously expressed,and biochemically characterized.The domain constitutions of GHs were analyzed by heterologously expression of different truncations,xylanase with different domains was biochemically characterized. A nonel GH11 xylanase(Xyn11) with a catalytic domain(GH-CD) and a carbohydrate binding module(CBM6) was first heterologously expressed. The recombinant Xyn11A is active in a wide temperature range from 40 to 95℃ with the highest activity at 75℃. In addition, novel xylanolytic enzymes, GH10 endo-β-1,4-xylosidase(Coxy1 A),encoded in one gene cluster of Caldicellulosiruptor were biochemically characterized. The intracellular enzymes provide a potential way for xylan degradation in vitro.
Succinic acid has a huge potential market with wide applications in chemical,food.medicine industry, and many more. Bio-basee succinate production has attracted much attention in recent years for many reasons such as low price,low pollution or renewable resources. However, compared to the petrol-chemical synthesis process, the biotechnological process using microbial cell biocatalysts usually encounters product inhibition characterized by low succinic acid concentration and productivity. In situ product removal (ISPR) strategy was applied to improve the succinic acid fermentation process in order to dismiss the product inhibition and enhance the succinic acid produvtion. In our work, wild E. coli W 1485 was chosen as the original strain for metabolic pathway reconstruction. The supply of HCO3- was enhanced for succinate synthesis by overexpressing a heterogeneous carbonic anhydrase (CA) encoded by Cyanobacterium anabaena sp.7120 ecaA gene. An integarated fermentation process for the production of succinic acid by A. succinogenes BE-1 with high concentration, yield and productivity was developed by applying ISPR strategy through a coupled expanded bed assorption (EBA) system. The cost of the novel coupled process was much lower than those traditional processes in which the fermentation an purification were separated. Taking operation cost as an example, it was 60%-70% at a discount. Total unit production cost reduced to 1.187 $/kg.