Tuesday, May 3, 2011
A mutant strain of Klebsiella pneumoniae, termed GEM167, was obtained by g-ray irradiation, in which glycerol metabolism was dramatically affected on exposure to g rays. Levels of metabolites of the glycerol reductive pathway, 1,3-propanediol and 3-hydroxypropionic acid, were decreased in the GEM167 strain compared to a control strain, whereas the levels of metabolites derived from the oxidative pathway, 2,3-butanediol, ethanol, lactate, and succinate, were increased. Notably, ethanol production was greatly enhanced upon fermentation by the mutant strain using crude glycerol derived from biodiesel industry, to a maximum production level of 21.5 g/l, with a productivity of 0.93 g/l/h. In an effort to enhance ethanol production, we engineered a mutant strain incapable of lactate formation (lactate is a major metabolite competing with ethanol for reducing equivalents) by deleting the lactate dehydrogenase gene. Production of ethanol was significantly increased in an DldhA mutant of GEM167 (28.9 g L-1 and 1.2 g L-1 h-1). 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-1; this is the highest level reported to date. These results suggested that the recombinant K. pneumoniae strain was valuable for development of industrial process to produce ethanol using waste by-product.