Enhancement of ethanol production from glycerol in a Klebsiella pneumoniae mutant strain by the inactivation of lactate dehydrogenase

Previously, using gamma-irradiation treatment, we isolated a mutant strain of Klebsiella pneumoniae (named GEM167) that showed high-level ethanol production from glycerol. In the present study, in an effort to enhance ethanol production, we used a deletion of the lactate dehydrogenase gene to engineer a mutant strain incapable of lactate synthesis. In the Delta ldhA mutant of GEM167, the production of ethanol was significantly increased from 21.5 g/l to 28.9 g/l and from 0.93 g/(l h) to 1.2 g/(l h). Introduction of the Zymomonas mobilis pdc and adhlI genes encoding pyruvate decarboxylase and aldehyde dehydrogenase, respectively, further improved the ethanol production level from glycerol to 31.0 g/l; this is the highest level reported to date. (C) 2011 Elsevier Ltd. All rights reserved.