Biomedical Engineering Reference
In-Depth Information
overexpression of the ketoisovalerate decarboxylase and alcohol dehydrogenase
genes and optimizing the fermentation conditions. The engineered strain produced
0.6 g/L isobutanol after 36 h. The team led by Xue-Li Zhang of Tianjin Institute of
Industrial Biotechnology engineered E. coli for isobutanol production (Two patents,
CN201110155176.0 and CN201120096157.0, have been applied). The native fer-
mentation pathways of E. coli competing for pyruvate (lactate dehydrogenase,
pyruvate-formate lyase, alcohol dehydrogenase, fumarate reductase) were firstly
deleted, and the essential genes of the isobutanol synthetic pathway were then
integrated into the chromosome of the engineered strain. Expression of these
essential genes was further fine-tuned to obtain the optimal strength for isobutanol
production. Since NADPH is required for isobutanol production and NADH is
produced during glycolysis, cofactor engineering was utilized to obtain the maxi-
mum yield for anaerobic isobutanol production. After an engineered strain coupling
isobutanol production with cell growth had been obtained, metabolic evolution was
utilized to improve both the anaerobic cell growth and isobutanol production.
A previous report showed that 3-methyl-1-butanol was identified in a small
quantity in the fusel alcohols produced by Saccharomyces cerevisiae during
ethanol fermentation [ 55 ]. Compared with the wild-type cells producing 3-methyl
-1-butanol at 92.3 mg/L at 24 h, the mutant showed a 1.8-2.3-fold increase in
production. In 2008, Liao's group [ 28 ] demonstrated the production of 3-methyl
-1-butanol in E. coli. They engineered an E. coli strain to produce 3-methyl
-1-butanol from glucose via the host's amino acid biosynthetic pathways [ 28 ].
Recently, they further improved the 3-methyl-1-butanol production by random
mutagenesis of L -leucine biosynthesis and two-phase fermentation and obtained
9.5 g/L 3-methyl-1-butanol after 60 h with a yield of 0.11 g/g glucose, showing
promise in using E. coli as a host for 3-methyl-1-butanol biofuel production [ 56 ].
Microbial production of 3-methyl-1-butanol and 2-methyl-1-butanol in China has
not been reported yet. A preliminary study is currently being conducted in the
authors' laboratory.
5 Concluding Remarks
Although R & D into microbial production of BCHAs in China is relatively weak,
the lag is not significant, since the worldwide research in this area is still in its
infancy. Driven by the energy requirements and environmental concerns, more
efforts devoted to fundamentals and technological innovations will enable our
next-generation biofuels to be more competitive in the market, and contribute to
the sustainability of the country's economic and social development.
Acknowledgements This work was supported by the National Knowledge Innovation Project
of the Chinese Academy of Sciences (KSCX2-YW-G-064) and the National Basic Research
Program
(973
Program,
2011CBA00806
and
2011CBA00807).
X.-L.Z.
and
Q.-H.W.
are
supported by the Bairenjihhua Program of the Chinese Academy of Sciences.
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