Biomedical Engineering Reference
In-Depth Information
(Lee et al., 1994). The PHB biosynthetic genes of
A. latus
have been used to clone and
produce PHB in
E. coli
(Choi et al., 1998) and resulted in better PHB production in
E.
coli
compared to the PHB biosynthetic genes of
R. eutropha.
In recombinant microorganisms, plasmid stability is of crucial importance for con-
tinued PHB production which is a problem associated with the expression of PHB
biosynthetic gene in bacteria
expression in eukaryotic Cells
Saccharomyces cerivisiae
is the only eukaryotic organism which has been transformed
to accumulate PHB so far with expression of the PHA synthase (phaC
Re
) of
R. eut-
ropha
in the
S. cerivisiae
cytoplasm. In contrast to
E. coli
and plants, yeast does not
require the expression of β-ketothiolase and acetoacetyl-CoA reductase genes for the
PHA accumulation and these steps are catalyzed by the native Erg10 and Fox2 pro-
teins, respectively, which are involved in β-oxidation but functioning as β-ketothiolase
and acetoacetyl-Co A reductase (Leaf et al., 1996).
expression in animal Cells
Expression of PHB biosynthesis genes in animal cells has been achieved in the cells of
insect
Spodoptera frugiperda
and
Trichopulsiani
. In Spodoptera, an alternative path-
way for the biosynthesis of PHB is created. The dehydratase domain mutant rat fatty
acid synthase cDNA and phaC
Re
were expressed simultaneously which resulted into
PHB synthesis (Williams et al., 1996). A baculovirus,
Autographa californica
nuclear
polyhedrosis virus system has been also used to express PhaC
Re
in
Trichopulsiani
cells.
These cells accumulated PHB synthase in 50% of the total cell protein.
expression in Plants
The PHA biosynthesis genes from microorganisms have been successfully expressed
in
Arabidopsis thaliana
(Nawrath et al., 1994; Poirier et al., 1992),
Brassica napus
(Valentin et al., 1999),
Gossypium hirsutum
(John and Keller, 1996),
Nicotiana
tabacum
(Nakashita et al., 1999),
Solanum tuberosum
(Mittendorf et al., 1998) and
Zea mays
(Hahn et al., 1999). However, transgenic plants are impaired. For PHA bio-
synthesis in plants, phaC
Re
and phaB
Re
alone or together with phaA
Re
have been used.
Sometimes, phaA expression is not required because it is present in plants. Replace-
ment of phaA
Re
by bkt B
Re
in plants enabled them to accumulate co-polymers (Slater
et al., 1998; Valentin et al., 1999). Transgenic plants harbour PHB synthesis gene and
found to accumulate PHB in various compartments of plant cells and tissues such as
nucleus, vacuoles and cytoplasm. However, in case of transgenic plant,
B. napus,
PHB
accumulation occurred in leucoplasts (Valentin et al., 1999).
Transgenic plant may prove cost effective PHB producer because PHB are pro-
duced from carbon dioxide, water and sunlight. If efforts are concentrated on im-
proving this process, it may be possible to see bioplastic agriculture in the future and
agricultural bioplastic products may appear in the market.
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