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Table 3.
The fermentation products of strains W3110, ZF1 (W3110
∆
focA) and ZF3 (W3110
∆
narL).
the effect of Multi-copy Gene expression on Hydrogen
Yields
Recent reports have described improvements in fermentative hydrogen yields
in E. coli through the modification of the specific transcriptional activator, and
repressor proteins of the FHL system, FhlA and HycA, respectively [22]. The
three global regulators Fnr, ArcAB and IhfAB modulate the expression of mul-
tiple genes involved in the anaerobic metabolism of pyruvate in E. coli [9], [15],
[19], [27], [28]. The impact on fermentative hydrogen yields by the over-produc-
tion of the Fnr, ArcAB, and IhfAB proteins, and of ModE which is the second-
ary transcriptional activator of the hycoperon, was examined in strains W3110
and ZF1 (W3110
∆
focA). Strain ZF1 (W3110
∆
focA) was selected because an
increased level of cellular formate, combined with the over-expression of formate-
metabolizing genes might have a synergistic effect on hydrogen formation. The
specific hydrogen yields following induction of the plasmid-bearing strains are
shown in Table 4. Strain ZF7, over-expressing of the fnr gene in W3110 back-
ground, exhibited an approximately 5.5-fold increase in specific hydrogen yield
compared to the control strain ZF6 (containing the plasmid without promoter-
driven gene expression). Over-expression of the fnr gene in the
∆
focA genetic
background (strain ZF13) resulted in the generation of 10 µmol of H
2
/mg of
dry cell mass compared to 6 µmol of H
2
/mg of dry cell mass obtained with over-
expression of the fnr gene in the wild-type W3110 background (strain ZF7) in
TYP medium. When induced in M9-glucose medium for 8 hours, strains ZF7
and ZF13 accumulated approximately 24 µmol of H2/mg of dry cell mass and 34
µmol of H2/mg of dry cell mass, respectively (data not shown). Over-expression
of the global regulators ArcAB and IhfAB, and of the secondary transcriptional
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