Development of a structured dynamic model for the production of polyhydroxybutyrate (PHB) in Azohydromonas lata cultures

Modeling the bioconversion of starch to P(HB-co-HV) optimized by experimental design using Bacillus megaterium BBST4 strain

Poly(hydroxybutyrate-co-hydroxyvalerate) (P(HB-co-HV)) is a prominent biopolymer as a potential candidate for use in the biomedical area. Several Bacillus spp. strains show promising characteristics in the use of several carbon sources and are an interesting alternative for the production of P(HB-co-HV). Sewage from the agricultural and food processing industries can be used to obtain abundantly starch as a carbon source for PHA production. The aim of the present study was to optimize by response surface methodology and desirability, the production of PHA by a Bacillus megaterium strain using starch as the sole carbon source. Two optimal conditions were determined without sporulation and were used to perform new experiments to calibrate and validate a mechanistic model, developed to simulate the dynamics of PHA and biomass production. The developed model successfully represents the kinetics of the microorganism. Employing different characterization techniques, it was determined that the PHA produced by the strain is a copolymer composed of different HB:HV proportions. Using starch as the sole carbon source in a minimal salt medium, this work shows the first reports in the literature of: 1) a mathematical model for predicting growth kinetic and PHA production for B. megaterium strain and 2) a Bacillus spp. producing P(HB-co-HV) copolymer.

Application of process system engineering tools to the fed-batch production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) from a vinasses-molasses Mixture

Fed-batch production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer using vinasses-molasses mixture is carried out in this work by implementing different process systems engineering tools. Two fed-batch strategies are tested experimentally at 5 L scale, considering only offline information: (1) offline optimizing control and (2) exponential feeding. Application of these strategies showed that different feeding profiles result in different dynamic behaviour, influencing both, yield and biopolymer properties. As offline-based feeding strategies do not consider information of the culture status, they cannot deal with uncertainties. Therefore, a closed loop control strategy was implemented, which uses biomass and substrate information predicted online by soft-sensors. Results demonstrated the technical feasibility to produce biopolymer using a 75/25%vol. vinasses-molasses mixture. Successful implementation of the soft-sensor-based control strategy was evidenced at pilot plant scale, where sugar concentration was kept almost constant for 14 h, while obtaining the desired copolymer. Thus, proposed control strategy could be of interest at industrial-scale.

Model-based intensification of a fed-batch microbial process for the maximization of polyhydroxybutyrate (PHB) production rate

An integrated metabolic-polymerization-macroscopic model, describing the microbial production of polyhydroxybutyrate (PHB) in Azohydromonas lata bacteria, was developed and validated using a comprehensive series of experimental measurements. The model accounted for biomass growth, biopolymer accumulation, carbon and nitrogen sources utilization, oxygen mass transfer and uptake rates and average molecular weights of the accumulated PHB, produced under batch and fed-batch cultivation conditions. Model predictions were in excellent agreement with experimental measurements. The validated model was subsequently utilized to calculate optimal operating conditions and feeding policies for maximizing PHB productivity for desired PHB molecular properties. More specifically, two optimal fed-batch strategies were calculated and experimentally tested: (1) a nitrogen-limited fed-batch policy and (2) a nitrogen sufficient one. The calculated optimal operating policies resulted in a maximum PHB content (94% g/g) in the cultivated bacteria and a biopolymer productivity of 4.2 g/(l h), respectively. Moreover, it was demonstrated that different PHB grades with weight average molecular weights of up to 1513 kg/mol could be produced via the optimal selection of bioprocess operating conditions.