Poster Presentation 2-08
Engineering Klebsiella oxytoca for Production of Lactic Acid
from Hexose and Pentose Sugars
Bruce S. Dien,* Terence R. Whitehead, Nancy N.
Nichols and Michael A. Cotta
Fermentation Biotechnology Research Unit
USDA/ARS
Phone: (309)681-6270
Fax: (309)681-6427
E-mail: dienb@ncaur.usda.gov
Lactic acid is used as a feedstock for production of polylactic acid (PLA) based plastics and for production of
ethyl lactate. Currently, lactate is
produced from starch using either lactic acid producing bacteria or the fungus Rhizopus oryzae. Conversion of lignocellulose
to lactic acid requires strains capable of fermenting mixtures of hexose and pentose sugars.
Previously, we have reported on Escherichia
coli strains capable of converting glucose to L-lactic acid with yields up
to 93% of theoretical. We have now
developed Klebsiella oxytoca
bacterium as a host for lactate production from lignocellulosic
biomass.
K. oxytoca is well suited for fermentation
of lignocellulose hydrolysates
because the bacteria naturally grows in paper sulfite streams and ferments a
wide variety of hexoses and pentoses
as well as cellobiose and short xylan
oligomers. We
have transformed and expressed the ldh gene from Streptococcus
bovis into K.
oxytoca strain MA51. The transformed strain produced almost all
L-lactic acid from glucose at maximum yields of 0.82 g/g. The strain also converted cellobiose
and xylose to lactic acid, however, yields were much
lower, only 0.66 g/g and 0.18 g/g, respectively. We are currently seeking to increase the
lactic acid yield on xylose by eliminating production
of other side-products.