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

Previously, using γ-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 ΔldhA 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 adhII 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.

► We construed a lactate dehydrogenase gene defective mutant strain of K. pneumoniae GEM167 and expressed Z. mobilis pdc and adhII genes encoding pyruvate decarboxylase and aldehyde dehydrogenase, respectively, in the mutant strain.
► Production level of ethanol from glycerol was remarkably improved by the genetic engineering upto 31.0 g/l.