Polyhydroxyalkanoates are biodegradable
polymer materials that accumulate in numerous bacteria.
The polyhydroxybutyrate is the most common type of
polyhydroxyalkanoates, which potentially serves as precursor
for bioplastic production. The most extensively
studied polyhydroxybutyrate producing bacteria is
Cupriavidus necator
due to its capability to accumulate large
amounts of this biopolymer in simple culture medium.
Accumulation of polyhydroxyalkanoates granules in the
cytoplasm of
C. necator significantly depended on pH,
aeration, carbon sources, nitrogen sources, and minerals in
the culture medium. In the present study, the effect of both
nutritional and physical variables on polyhydroxybutyrate
production was investigated in order to optimize these
conditions. At first, on the basis of one-factor-at-a-time
experiments, fructose and ammonium chloride were found
to be the most suitable sources of carbon and nitrogen for
biopolymer production. Then the most significant factors
affecting granules accumulation were recognized as fructose,
agitation speed, KH
2PO
4, and initial pH using the
Plackett–Burman and central composite design. ANOVA
analysis showed significant interaction between fructose
and agitation speed. After optimization of the medium,
compositions for polyhydroxybutyrate production were
determined as follows: fructose 35 g/L, KH
2PO
4 1.75 g/L,
MgSO
4 7H
2O 1.2 g/L, citric acid 1.7 g/L, trace element
10 mL/L, initial pH = 7, and agitation speed 175 rpm.
Under this optimal culture conditions, the maximum yield
of PHB was 7.48 g/L. The present strategies included in
this study could be used for PHB production by this bacterium.
These results are the highest values of PHB ever
obtained from batch culture of
C. necator reported so far.
