Sunday, July 24, 2011
Grand Ballroom, 5th fl (Sheraton New Orleans)
Homo-fermentative production of ethanol in Escherichia coli has been well illustrated by heterologous expression of pyruvate decarboxylase (PDC) and alcohol dehydrogenase II (ADH) from Zymomonas mobilis. To increase the metabolite channeling in the two sequential reactions, a bifunctional enzyme was created by in-frame fusion of Z. mobilis PDC (ZmPDC) with ADH (ZmPDC-ADH) or vice versa (ADH-ZmPDC). With 4% glucose, E. coli strain expressing unfused ZmPDC and ADH (control strain) could produce around 2% ethanol within 20 h. In contrast, 1.4% ethanol was obtained for E. coli expressing ZmPDC-ADH whereas the strain with ADH-ZmPDC produced little ethanol. A linker was then introduced to separate the two fusion domains. However, it gave no improvement in ethanol yield for the strain with the bifunctional enzyme. Furthermore, ZmPDC in the chimeric enzyme was replaced by PDC of Zymobacter palmae (ZpPDC) and of Acetobacter pasteurianus (ApPDC), giving ZpPDC-ADH and ApPDC-ADH, respectively. As a result, E. coli strain with ApPDC-ADH was able to produce a theoretical yield of ethanol from either 4% glucose or 4% xylose. For the control strain in xylose fermentation, ethanol production reached only 70% of the theoretical yield. This result indicates the enhanced utilization of metabolites by the bifunctional enzyme in the pathway.