PHA production is normally triggered through a nutrient
limitation (Haywood et al., 1990), which in our fermentations
was nitrogen. However, it was observed at early time
points in the fermentations (where no nutrient limitation
yet occurred) a surprisingly high PHA accumulation of over
40% CDW (Figs. 1–3). This early high PHA production is
possibly due to the PHA production genes being located
on a plasmid that results in higher gene dosage and
consequently higher gene expression.
Moving forward, the results of high density PHA
production on different oil palm products will be examined
and their effects on copolymer content (e.g., HHx) and on
molecular weight will be determined. The presented fed
batch fermentation strategy using urea as the nitrogen
source offers the possibility for production of P(HB-coHHx)
with a high HHx concentration (19 mol%), which will
allow high cell density fermentation processes with a yield
of 102 g/L PHA. A scale-up of the developed process to
industrial scale is being planned. The design and implementation
of an integrated biorefinery for PHA production
is imaginable. Palm oil mills usually produce excess heat
and electricity by burning waste material (e.g., fruit fiber)
(Basiron, 2007), which could be also used to power a PHA
plant. Hence, the results presented in this study may
contribute to commercialization of biodegradable bioplastics
made from palm oil products, and reduce the
dependency of the plastics industry on fossil fuels.