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This study investigates the effect of strategies on poly(3-hydroxybutyrate) [P(3HB)] production in bioreactor. In the production of P(3HB), urea and glucose feeding streams were developed to characterize the fed-batch culture conditions for new Cupriavidus necator NSDG-GG mutant. Feeding urea in repeated fed-batch stage (RFB-I) at 6, and 12 h in cultivation led to insignificant kinetic effect on the cell dry mass (CDM) and P(3HB) accumulation. Feeding glucose in repeated fed-batch stage (RFB-II) demonstrated that the incremental feeding approach of glucose after urea in fill-and-draw (F/D) mode at 24, 30, 36, 42, and 48 h in fermentation increased CDM and P(3HB) concentration. In the 1st cycle in RFB-II, the cumulative CDM reached the value of 26.22 g/L and then it increased with the successive repeated fed-batches to attain biomass of 145 g/L at the end of 5th cycle of RFB-II. The final cumulative P(3HB) concentration at the end of 5th cycle of RFB-II reached 111 g/L with the overall yield of 0.50 g P(3HB) g gluc− 1; the CDM productivity from the RFB-II cycles was in the range of 0.84–1.3 g/(L·h). The RFB-II of glucose in an increment mode produced nearly 2.2 times more increase in CDM and P(3HB) productivities compared to the decrement RFB-II mode. Repeated cultivation had also the advantage of avoiding extra time required for innoculum preparation, and sterilization of bioreactor during batch, thereby it increased the overall industrial importance of the process.

Acetic acid, a potential growth inhibitor, commonly occurs in lignocellulosic hydrolysates. The growth of Cupriavidus necator DSM 545 and production of poly(3-hydroxybutyrate) (PHB) by this bacterium in a glucose-based medium supplemented with various initial concentrations of acetic acid are reported. The bacterium could use both glucose and acetic acid to grow and produce PHB, but acetic acid inhibited growth once its initial concentration exceeded 0.5 g/L. As acetic acid is an unavoidable contaminant in hydrolysates used as sugar sources in commercial fermentations, a mathematical model was developed to describe its impact on growth and the production of PHB. The model was shown to satisfactorily apply to growth and PHB production data obtained in media made with acetic-acid-containing hydrolysates of Napier grass and oil palm trunk as carbon substrates.

Poly-3-hydroxybutyrate (P3HB) is a biopolymer produced by Azotobacter vinelandii. The physicochemical properties and applications of P3HB are strongly influenced by its weight-average molecular mass (Mw), and in A. vinelandii, it could be influenced by the culture conditions. The aim of this study was to evaluate the effect of the P3HB content of the inoculum on the Mw of the polymer produced by A. vinelandii OP in bioreactor cultures. A. vinelandii cells containing 20, 50 and 70% of P3HB were used as inoculum. The P3HB content in the inoculum affected the volumetric P3HB productivity (qP3HB) and the Mw of P3HB. Those cultures inoculated with cells containing 20% of P3HB, achieved the highest qP3HB (0.17±0.018gP3HBL-1h-1); whereas a P3HB content of 70% was reflected as a low qP3HB (0.021±0.002gP3HBL-1h-1). On the other hand, using an inoculum with 70% of polymer content, the Mw of the biopolymer remained stable at values close to 3200kDa; whereas, when an inoculum with 20% of P3HB was used, the Mw decreased drastically during early stages of cultivation. These results show that manipulating the P3HB content of the inoculum is possible to produce biopolymers with a suitable Mw.

Sucrose has several advantages over glucose as a feedstock for bioprocesses, both environmentally and economically. However, most industrial Escherichia coli strains are unable to utilize sucrose. E. coli W can grow on sucrose but stops growing when sucrose concentrations become low. This is undesirable in fed-batch conditions where sugar levels are low between feeding pulses. Sucrose uptake rates were improved by removal of the cscR gene, which encodes a protein that represses expression of the sucrose utilization genes at low sucrose concentrations. Poly-3-hydroxybutyrate (PHB) was used as a model compound in order to assess the effect of improved sugar utilization on bio-production. In the cscR knockout strain, production from sucrose was improved by 50%; this strain also produced 30% more PHB than the wild-type using glucose. This result demonstrates the feasibility of utilizing sucrose as an industrial feedstock for E. coli-based bioprocesses in high cell density culture.