Increased Hydrogen Production by Genetic Engineering of Escherichia coli - Genetic Engineering: Recent Developments in Applications - page 6

Figure 2. Hydrogen production and anaerobic growth rates of WT and single gene inactivated E. coli strains.
Hydrogen production rate (A, µmol of H2) and anaerobic growth rate (B, A600) by strains W3110 (  ), ZF1
(  ), ZF2 (  ), ZF3 (  ), ZF4 (•) on M9 medium supplemented with 1% (w/v) glucose.
The specific hydrogen yields were determined for W3110 and the gene-inacti-
vated strains at 17 hours following inoculation of M9-glucose medium (Table 2).
All four gene-inactivated strains exhibited 14% to 50% higher specific hydrogen
yields compared to W3110. Strains ZF1 (W3110∆focA) and ZF3 (W3110∆narL)
had specific hydrogen yields of approximately 14 µmols/mg dry cell mass, repre-
senting an increase of about 46% over the yield by W3110. The increased hydro-
gen yield by strain ZF1 (W3110∆focA) is consistent with the hypothesis that an
increase in the level of intracellular formate can either lead to enhanced synthesis
of the FHL polypeptides via the transcriptional activator FhlA, or elevate the
available substrate pool for FHL [29], [30]. The negative effect on growth rates
by the focA deletion might be alleviated if the intracellular formate can be effi-
ciently metabolized by FHL (further described below). The 50% increase in spe-
cific hydrogen yield by strain ZF3 (W3110∆narL) showed that the elimination of
transcriptional repression of nik operon, and of fdhF and pflB genes by the NarL,
results in the increased pyruvate metabolism towards hydrogen [8], [31].