Polyhydroxyalkanoates (PHAs) are an important
class of biodegradable polymers synthesized by a few bacteria
under nutrient-limiting conditions. In this study, the
lipase-catalysed degradation of PHA synthesized by
Enterobacter
sp. was monitored. For this, the lipase-encoding
gene from
Bacillus subtilis DI2 was PCR-amplified, cloned
into a T vector system and sequenced. It was expressed in
Escherichia coli
DH5α cells, the recombinant enzyme was
purified 24.25-fold, and its molecular weight was determined
to be around 28 kDa. When PHA biodegradation studies
were carried out with this enzyme, gel permeation chromatography
showed 21.3 and 28.3 % molecular weight
decrease and weight loss, respectively. Further, scanning
electron micrographs revealed alterations in polymer surface
morphology. Changes in molecular vibrations were noticed
in the FTIR spectra. When the chemical shifts in NMR
spectra were studied, a steep reduction in area under the peak
at 1.57 ppm was observed. In the heating range of 30–930 °C
employed during thermogravimetry analysis, the degraded
sample showed a total of 45.82 % weight loss, as against
18.89 %for the native sample. The melting temperature (
Tm)
of the polymer was also brought down from 126.22 to
118.18 °C, as inferred from differential scanning calorimetry.
Lipase-catalysed chain scission reactions could thus be
used to generate low molecular weight functional biopolymers
with wide-ranging pharmaceutical applications, such
as in sustained drug release.
