related carbon sources or precursors are needed to produce copolymers. For instance,
valeric acid and propionic acid are used to produce copolymers P(3HB-co-3HV).
These precursors are very expensive, and therefore, it limits the production of such
copolymer at an industrial scale. Therefore, the search for novel and cheap carbon
sources is highly required.
Sugars such as glucose, sucrose, fructose, and xylose are structurally unrelated
carbon sources used to produce PHA because they are available at relatively cheaper
rates. As of now, the highest production of P(3HB) was achieved in a recombinant
E. coli containing A. latus PHA biosynthesis genes using glucose as the sole carbon
source (Choi et al. 1998). Besides, recombinant E. coli LS5218 was able to
biosynthesize P(3HB)-based copolymer comprising of 94.6 mol% 3HB and 5.4
mol% mcl-3HA consisting of C 8 , C 10 , C 12 , and C 14 using glucose as the single
carbon source (Hokamura et al. 2015). Interestingly, a wild-type Bacillus cereus fed
with only glucose also has shown to have the ability to polymerize P(3HB-co-3HV)
(Mizuno et al. 2010), suggesting that this microorganism has an intriguing metabolic
versatility of channeling the second monomer using a single carbon source. An
interesting PHA copolymer, P(3HB-co-2-hydroxyalkanoate), with different monomer molar ratio was biosynthesized using recombinant E. coli strain with 20 g/L of
glucose or xylose as the sole carbon source in Luria-Bertani (LB) medium cultivated
at 30
C for 72 h (Mizuno et al. 2018). In LB medium with glucose as the monocarbon source, the strain could store up to 55 wt% of PHA and yield around 10.6 g/L
of dry cell weight. Meanwhile, when xylose was used, about 43 wt% of PHA and
9.6 g/L of the dry cell was obtained. However, when the strain was cultivated under
the same conditions in M9 medium with glucose or xylose as the sole carbon source,
2-hydroxy-3-methylbutyrate (2H3MB) monomer unit in the copolymer could not be
biosynthesized (Fig. 3.2). Cultivation of the recombinant E. coli strain in M9 media
with glucose or xylose also affected the PHA content and dry cell weight. In terms of
PHA content, it was found that about 70 wt% of PHA was obtained for glucose, and
for xylose it declined to 28 wt%. However, for cell dry weight, in both cases, quite a
drastic reduction was noticed.
Next, plant oils and their derivatives are considered as a potential structurally
unrelated carbon source for PHA biosynthesis. An estimate of 0.3–0.4 g of PHA can
be produced using 1 g of glucose (Ryu et al. 1997), meanwhile 0.6–0.8 g of PHA
using 1 g of plant oil (Akiyama et al. 2003). This clarifies that plant oil has more
carbon per weight in comparison to sugar (Akiyama et al. 1992); thus, it is worth
evaluation for PHA biosynthesis. The possibility of corn oil to be a carbon source for
PHA production was demonstrated by Akiyama et al. (Akiyama et al. 1992).
Alcaligenes sp. AK201 fed with 3 g/L of corn oil for 48 h could yield 39 wt% of
PHA and 2.8 g/L of dry cell. Besides, soybean oil is also widely used for PHA
production. The wild type of R. eutropha was shown to yield about 72–76 wt% of P
(3HB) with 118–126 g/L of the dry cell when soybean oil was used as a sole carbon
source (Kahar et al. 2004). Tsuge et al. have also used soybean oil to test for PHA
production in R. eutropha mutants encompassing mutated PhaC (Tsuge et al. 2009).
Twenty recombinant strains of R. eutropha with mutated PhaC were subjected to this
evaluation, and the highest PHA content observed was 57 wt% with 1.6 g/L of dry
64
R. Sivashankari and T. Tsuge
valeric acid and propionic acid are used to produce copolymers P(3HB-co-3HV).
These precursors are very expensive, and therefore, it limits the production of such
copolymer at an industrial scale. Therefore, the search for novel and cheap carbon
sources is highly required.
Sugars such as glucose, sucrose, fructose, and xylose are structurally unrelated
carbon sources used to produce PHA because they are available at relatively cheaper
rates. As of now, the highest production of P(3HB) was achieved in a recombinant
E. coli containing A. latus PHA biosynthesis genes using glucose as the sole carbon
source (Choi et al. 1998). Besides, recombinant E. coli LS5218 was able to
biosynthesize P(3HB)-based copolymer comprising of 94.6 mol% 3HB and 5.4
mol% mcl-3HA consisting of C 8 , C 10 , C 12 , and C 14 using glucose as the single
carbon source (Hokamura et al. 2015). Interestingly, a wild-type Bacillus cereus fed
with only glucose also has shown to have the ability to polymerize P(3HB-co-3HV)
(Mizuno et al. 2010), suggesting that this microorganism has an intriguing metabolic
versatility of channeling the second monomer using a single carbon source. An
interesting PHA copolymer, P(3HB-co-2-hydroxyalkanoate), with different monomer molar ratio was biosynthesized using recombinant E. coli strain with 20 g/L of
glucose or xylose as the sole carbon source in Luria-Bertani (LB) medium cultivated
at 30
C for 72 h (Mizuno et al. 2018). In LB medium with glucose as the monocarbon source, the strain could store up to 55 wt% of PHA and yield around 10.6 g/L
of dry cell weight. Meanwhile, when xylose was used, about 43 wt% of PHA and
9.6 g/L of the dry cell was obtained. However, when the strain was cultivated under
the same conditions in M9 medium with glucose or xylose as the sole carbon source,
2-hydroxy-3-methylbutyrate (2H3MB) monomer unit in the copolymer could not be
biosynthesized (Fig. 3.2). Cultivation of the recombinant E. coli strain in M9 media
with glucose or xylose also affected the PHA content and dry cell weight. In terms of
PHA content, it was found that about 70 wt% of PHA was obtained for glucose, and
for xylose it declined to 28 wt%. However, for cell dry weight, in both cases, quite a
drastic reduction was noticed.
Next, plant oils and their derivatives are considered as a potential structurally
unrelated carbon source for PHA biosynthesis. An estimate of 0.3–0.4 g of PHA can
be produced using 1 g of glucose (Ryu et al. 1997), meanwhile 0.6–0.8 g of PHA
using 1 g of plant oil (Akiyama et al. 2003). This clarifies that plant oil has more
carbon per weight in comparison to sugar (Akiyama et al. 1992); thus, it is worth
evaluation for PHA biosynthesis. The possibility of corn oil to be a carbon source for
PHA production was demonstrated by Akiyama et al. (Akiyama et al. 1992).
Alcaligenes sp. AK201 fed with 3 g/L of corn oil for 48 h could yield 39 wt% of
PHA and 2.8 g/L of dry cell. Besides, soybean oil is also widely used for PHA
production. The wild type of R. eutropha was shown to yield about 72–76 wt% of P
(3HB) with 118–126 g/L of the dry cell when soybean oil was used as a sole carbon
source (Kahar et al. 2004). Tsuge et al. have also used soybean oil to test for PHA
production in R. eutropha mutants encompassing mutated PhaC (Tsuge et al. 2009).
Twenty recombinant strains of R. eutropha with mutated PhaC were subjected to this
evaluation, and the highest PHA content observed was 57 wt% with 1.6 g/L of dry
64
R. Sivashankari and T. Tsuge