Abstract Submittal Form - 27th Symposium on Biotechnology ... - EERE

dactylonomyskittlesBiotechnology

Feb 12, 2013 (4 years and 2 months ago)

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Poster Presentation 5
-
23


Homo
-
Ethanol Fermentation by a Novel M
utant of
Escherichia
c
oli


Youngnyun Kim
, L.O. Ingram and K.T. Shanmugam*


Department of Microbiology and Cell Science,

University of Florida, Gainesville, FL32611
,

Phone:
352
-
846
-
0965

em
ail:
shan@ufl.edu



We have previously described an ethanologenic
Escherichia coli
, strain KO11, that ferments all the
sugars in biomass to ethanol, carrying the pyruvate decarboxylase and alcohol dehydrogenase genes from
Zymomonas mobilis
. As a continuat
ion of these studies, a non
-
recombinant
E. coli
, strain SE2378, that
also ferments both glucose and xylose to ethanol was constructed by introducing appropriate mutations in
the various enzymes responsible for the metabolism of pyruvate. Strain SE2378 was
derived from a
double mutant, AH242,

that lacks both lactate dehydrogenase and pyruvate formate lyase, the two
enzymes that are responsible for production of lactate and acetyl
-
CoA (further metabolized to acetate and
ethanol) during the mixed
-
acid fermenta
tion of sugars by wild type
E. coli
. Strain AH242 (

ldh
,

pfl
) is
anaerobic minus due to its inability to reoxidize NADH generated during glycolysis. A mutant derivative
of this double mutant that can grow anaerobically was obtained after mutagenesis and t
his mutant, strain
SE2378, produced ethanol as the major fermentation product at a yield of 85% (mol/mol) from glucose
and 79% (mol/mol) from xylose. Two mutations were mapped in
pdhR
, the gene that controls the
expression of the genes encoding pyruvate de
hydrogenase. Apparently, the mutant PdhR supported the
production of active pyruvate dehydrogenase (PDH) complex in the anaerobic cell and the acetyl
-
CoA
produced by the PDH was reduced by the native alcohol dehydrogenase to ethanol.