期刊
JOURNAL OF INDUSTRIAL MICROBIOLOGY & BIOTECHNOLOGY
卷 29, 期 5, 页码 221-227出版社
SPRINGER HEIDELBERG
DOI: 10.1038/sj.jim.7000299
关键词
catabolite repression; lactic acid production; xylose fermentation; Escherichia coli
Conversion of lignocellulose,to lactic acid requires strains capable of fermenting sugar mixtures of glucose and xylose. Recombinant Escherichia coli strains were engineered to selectively produce L-lactic acid and then used to ferment sugar mixtures. Three of these strains were catabolite repression mutants (ptsG(-)) that have the ability to simultaneously ferment glucose and xylose. The best results were obtained for ptsG- strain FBR19. FBR19 cultures had a yield of 0.77 (g lactic acid/g added sugar) when used to ferment a 100 g/l total equal mixture of glucose and xylose. The strain also consumed 75% of the xylose. In comparison, the ptsG(+) strains had yields of 0.47-0.48 g/g and consumed 18-22% of the xylose. FBR19 was subsequently used to ferment a variety of glucose (0-40 g/l) and xylose (40 g/l) mixtures. The lactic acid yields ranged from 0.74 to 1.00 g/g. Further experiments were conducted to discover the mechanism leading to the poor yields for ptsG(+) strains. Xylose isomerase (XI) activity, a marker for induction of xylose metabolism, was monitored for FBR19 and a ptsG+ control during fermentations of a sugar mixture. Crude protein extracts prepared from FBR19 had 10-12 times the specific XI activity of comparable samples from ptsG(+) strains. Therefore, higher expression of xylose metabolic genes in the ptsG(-) strain may be responsible for superior conversion of xylose to product compared to the ptsG(+) fermentations.
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