Two-stage fermentation was normally employed to achieve a high poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] productivity with higher 4HB molar fraction. Here, we demonstrated single-stage fermentation method which is more industrial feasible by implementing mixed-substrate cultivation strategy. Studies on bioreactor scale show a remarkably high PHA accumulation of 73 wt%, contributing to a high PHA concentration and product yield of 8.6 g/L and 2.7 g/g, respectively. This fermentation strategy has resulted in copolymers with wider range of 4HB monomer composition, which ranges from 12 to 55 mol%. These copolymers show a broad range of weight average molecular weight (M w ) from 119.5 to 407.0 kDa. The copolymer characteristics were found to be predominantly affected by the nature of the substrates and the mixture strategies, regardless of the 4HB monomer compositions. This was supported by the determination of copolymer randomness using (13)C-NMR analysis. The study warrants significantly in the copolymer scale-up and modeling at industrial level.
The contribution of microbial depolymerase has received much attention because of its potential in biopolymer degradation. In this study, the P(3HB) depolymerase enzyme of a newly isolated Burkholderia cepacia DP1 from soil in Penang, Malaysia, was optimized using response surface methodology (RSM). The factors affecting P(3HB) depolymerase enzyme production were studied using one-variable-at-a-time approach prior to optimization. Preliminary experiments revealed that the concentration of nitrogen source, concentration of carbon source, initial pH and incubation time were among the main factors influencing the enzyme productivity. An increase of 9.4 folds in enzyme production with an activity of 5.66 U/mL was obtained using optimal medium containing 0.028% N of di-ammonium hydrogen phosphate and 0.31% P(3HB-co-21%4HB) as carbon source at the initial pH of 6.8 for 38 h of incubation. Moreover, the RSM model showed great similarity between predicted and actual enzyme production indicating a successful model validation. This study warrants the ability of P(3HB) degradation by B. cepacia DP1 in producing higher enzyme activity as compared to other P(3HB) degraders being reported. Interestingly, the production of P(3HB) depolymerase was rarely reported within genus Burkholderia. Therefore, this is considered to be a new discovery in the field of P(3HB) depolymerase production.