ABSTRACT
In our effort to improve the efficiency and yield of xylose-to-ethanol bioconversion in Pichia stipitis, the transaldolase (TAL) in the pentose phosphate pathway was identified as a rate-limiting enzyme for improvement. A mutant containing the Q263R change was first obtained by directed evolution with 5-fold increase of activity, which was then incorporated into P. stipitesvia the pYDS vector to produce a genetically stable strain for fermentation on xylose. In comparison with the parental strain, TAL-Q263R(+) increases ethanol prodcution by 36% and 100% as measured by volumetric production rate and specific production rate, respectively. Thus improving the transaldolase activity in P. stipitis can significantly increase the rate and yield of xylose conversion to ethanol.
Subject(s)
Ethanol/metabolism , Pichia/enzymology , Protein Engineering , Transaldolase/metabolism , Ethanol/chemistry , Molecular Conformation , Pichia/metabolism , Transaldolase/genetics , Xylose/chemistry , Xylose/metabolismABSTRACT
The production of bioethanol by the conversion of lignocellulosic waste has attracted much interest in recent years because of its low cost and great potential availability. However, the high cost of the enzyme required for this conversion is often considered to be the major bottleneck in the commercial lignocellulosic ethanol industry. In this work, the hydrolysis of rice straw by free and entrapped lignocellulolytic enzymes (cellulase, xylanase and laccase) was carried out at pH 5.5 and 37°C. The hydrolysis of rice straw by enzymes entrapped in a membrane produced a higher monosaccharide content: 601.05 mg/g rice straw for entrapped enzymes vs. 465.46 mg/g rice straw for free enzymes. This study has shown that enzyme entrapment is an important technique for the efficient use and reuse of enzymes in industrial applications and also for the rapid separation of saccharide products from the reaction medium, thus improving the remaining enzymatic activities.
