Tuesday, May 1, 2012: 2:00 PM
Rhythms Ballroom, 2nd fl (Sheraton New Orleans)
E. coli has been engineered to produce a wide variety of biofuel and biorefinery products. However, it can only produce these products from simple sugars, requiring large amounts of enzymes to depolymerize cellulose into monomer sugars. Engineering E. coli to directly use cellodextrin, the partial hydrolysis product of cellulose, potentially could reduce the requirement of enzyme thereby the overall cost. We have successfully developed a metabolic engineering strategy to engineer microbial cells to use cellodextrin directly. The strategy involves periplasmic expression of a Saccharophagus cellodextrinase with broad substrate specificity, active on cellodextrin with DP of 2-6. The E. coli biocatalyst expressing the enzyme in the periplasm was able to grow, for the first time, on cellodextrin as sole carbon source. Additionally, when expressed in E. coli strains with desired product characteristics, a high yield conversion of cellodextrin to respective products was achieved. The yield of lactic acid and meso-2,3 butanediol (BDO) was 85% and 84%, respectively.
The availability of these cellodextrin-utilizing catalysts is a step closer to consolidated production of chemicals from cellulose. Additional simultaneous saccharification and fermentation (SSF) experiments were carried out to evaluate the feasibility of BDO production from cellulose. The ability to use cellodextrin directly by virtue of cellodextrinase activity was shown to be advantageous, allowing higher conversion yield for BDO from cellulose. Recombinant cellodextrinase expression from the host strain augmented the insufficient glucosidase activities in commercial cellulase cocktails, eliminating the need for supplement. The strategy should generate cost savings and is applicable to other biorefinery products.