Abstract:
Polyhydroxyalkanoates (PHAs) are internal microbial polyesters that are produced when
there is an abundance of carbon sources and a scarcity of nutrients like nitrogen to function
as energy storage granules and give prokaryotes stress tolerance. These biopolymers
are viable substitutes for carbon-based synthetic polymers and can be obtained from
bacteria growing on putrefied rice. However, their commercialization is constrained by
high production costs. The objective of this work was thus, to isolate and characterize
PHA and PHA-producing bacteria using physical and biochemical processes in order
to synthesize PHA-type biopolymer through a laboratory-scale procedure. A putrefied
rice sample was used to collect the bacteria for this study, and it was then screened
for PHA production. Microscopic staining was done to confirm the presence of PHA
accumulation in the bacteria. When provided with a complex growth medium, bacteria
growing in the medium exhibited diauxic growth. Molecular identification based-on
16srRNA marker gene and Sanger DNA sequencing confirmed the identity of the isolated
PHA producing bacterium as Bacillus tropicus strain MCCC 1A01406. PHA produced
from a cultured bacterial sample was characterized using Raman spectroscopy to confirm
the chemical structure and functional groups present. Results from Raman analysis
confirmed that the PHA produced was a copolymer between 3-hydroxybutyrate (3HB)
and 3-hydroxyvalerate (3HV) units. The diauxic growth together with the production
of a copolymer confirmed that the bacteria used in our study were feeding on more than
one carbon substrate. This study clearly demonstrated that free-living environmental
organisms can be isolated and conveniently used for the purpose of polyhydroxybutyrate
(PHB) bioplastics production.
