A study on the effects of increment and decrement repeated fed-batch feeding of glucose on the production of poly(3-hydroxybutyrate) [P(3HB)] by a newly engineered Cupriavidus necator NSDG-GG mutant in batch fill-and-draw fermentation

Kinetic and stoichiometric parameters in the fed-batch bioreactor production of poly(3-hydroxybutyrate) by Bacillus megaterium using different carbon sources

This study investigates the effects of different strategies on poly(3-hydroxybutyrate)-P(3HB) production in a fed-batch bioreactor by Bacillus megaterium using candy industry effluent (CIE), sucrose, and rice parboiled water (RPW) as carbon sources. In biosynthesis, kinetic and stoichiometric parameters of substrate conversion into products and/or cells, productivity, instantaneous, and specific conversion rates were evaluated. The maximum concentration of P(3HB) was 4.00 g.L-1 (77% of the total dry mass) in 42 h of cultivation in minimal medium/RPW added with a carbon source based on CIE, demonstrating that the fed-batch provided an increase of approximately 22% in the polymer concentration and 32% in the overall productivity in relation to medium based on commercial sucrose. Fed-batch cultivation also had the advantage of avoiding the extra time required for inoculum preparation and sterilization of the bioreactor during the batch, which thereby increased the overall industrial importance of the process. Effluents from the candy, confectionery, and/or rice parboiling industries can be used as alternative substrates for P(3HB) production at a low cost.

One-pot treatment of Saccharophagus degradans for polyhydroxyalkanoate production from brown seaweed

The conventional production of polyhydroxyalkanoate (PHA) from waste biomass requires a pretreatment step (acid or alkali) for reducing sugar extraction, followed by bacterial fermentation. This study aims to find a greener approach for PHA production from brown seaweed. Saccharophagus degradans can be a promising bacterium for simultaneous reducing sugar and PHA production, bypassing the need for a pretreatment step. Cell retention cultures of S. degradans in membrane bioreactor resulted in approximately 4- and 3-fold higher PHA concentrations than batch cultures using glucose and seaweed as carbon sources, respectively. X-ray diffraction, Fourier transform infrared spectroscopy, and nuclear magnetic resonance results revealed identical peaks for the resulting PHA and standard poly(3-hydroxybutyrate). The developed one step process using cell retention culture of S. degradans could be a beneficial process for scalable and sustainable PHA production.

Recent updates to microbial production and recovery of polyhydroxyalkanoates

The increasing use of synthetic polymers and their disposal has raised concern due to their adverse effects on the environment. Thus, other sustainable alternatives to synthetic plastics have been sought, such as polyhydroxyalkanoates (PHAs), which are promising microbial polyesters, mainly due to their compostable nature, biocompatibility, thermostability, and resilience, making this biopolymer acceptable in several applications in the global market. The large-scale production of PHAs by microorganisms is still limited by the high cost of production compared to conventional plastics. This review reports some strategies mentioned in the literature aimed at production and recovery, paving the way for the bio-based economy. For this, some aspects of PHAs are addressed, such as synthesis, production systems, process control using by-products from industries, and advances and challenges in the downstream. The bioplastics properties made them a prime candidate for food, pharmaceutical, and chemical industrial applications. With this paper, it is possible to see that biodegradable polymers are promising materials, mainly for reducing the pollution produced by polymers derived from petroleum.

Minimizing the Lag Phase of Cupriavidus necator Growth under Autotrophic, Heterotrophic, and Mixotrophic Conditions

Cupriavidus necator has the unique metabolic capability to grow under heterotrophic, autotrophic, and mixotrophic conditions. In the current work, we examined the effect of growth conditions on the metabolic responses of C. necator. In our lab-scale experiments, autotrophic growth was rapid, with a short lag phase as the exponential growth stage was initiated in 6 to 12 h. The lag phase extended significantly (>22 h) at elevated O₂ and CO₂ partial pressures, while the duration of the lag phase was independent of the H₂ or N₂ partial pressure. Under heterotrophic conditions with acetate as the organic substrate, the lag phase length was short (<12 h), but it increased with increasing acetate concentrations. When glucose and glycerol were provided as the organic substrate, the lag phase was consistently long (>12 h) regardless of the examined substrate concentrations (up to 10.0 g/L). In the transition experiments, C. necator cells showed rapid transitions from autotrophic to heterotrophic growth in less than 12 h and vice versa. Our experimental results indicate that C. necator can rapidly grow with both autotrophic and heterotrophic substrates, while the lag time substantially increases with nonacetate organic substrates (e.g., glucose or glycerol), high acetate concentrations, and high O₂ and CO₂ partial pressures. IMPORTANCE The current work investigated the inhibition of organic and gaseous substrates on the microbial adaption of Cupriavidus necator under several metabolic conditions commonly employed for commercial polyhydroxyalkanoate production. We also proposed a two-stage cultivation system to minimize the lag time required to change over between the heterotrophic, autotrophic, and mixotrophic pathways.

Enhanced co-production of medium-chain-length polyhydroxyalkanoates and phenazines from crude glycerol by high cell density cultivation of Pseudomonas chlororaphis in membrane bioreactor

Enhanced co-production of medium-chain-length polyhydroxyalkanoates (mcl-PHA) and extracellular phenazines was assessed through a high cell density cultivation of Pseudomonas chlororaphis subsp. aurantiaca (DSM 19603) in a membrane bioreactor using crude glycerol as a fermentative substrate. A maximum dry cell weight (DCW) of 59.25 ± 0.31 g/L was achieved at 90 h of cultivation with a maximum mcl-PHA and extracellular phenazines concentrations of respectively 19.05 ± 0.04 g/L (32.16% of DCW) and 79.42 ± 0.35 mg/L. mcl-PHA concentration achieved through cell retention culture was 28.43-folds higher than that obtained by batch culture. Fourier transform infrared spectroscopy, gas chromatography-mass spectrometry, and ¹H nuclear magnetic resonance analysis identified the produced PHA as a mcl-PHA copolymer of 3-hydroxyhexanoate (0.68%), 3-hydroxyoctanoate (7.76%), 3-hydroxydecanoate (49.18%), 3-hydroxydodecanoate (4.89%), and 3-hydroxytetradecanoate (37.50%). The mcl-PHA exhibited a highly amorphous structure with low crystallinity index (4.19%) and high thermal stability. This is the first report on the enhanced co-production of mcl-PHA and phenazines in a membrane bioreactor.

High cell density culture of Paracoccus sp. LL1 in membrane bioreactor for enhanced co-production of polyhydroxyalkanoates and astaxanthin

A cell retention culture of Paracoccus sp. LL1 was performed in a membrane bioreactor equipped with an internal ceramic filter module to reach high cell density and thus enhance the co-production of polyhydroxyalkanoates (PHA) and astaxanthin as growth-associated products. Cell retention culture results showed that PHA accumulation increased with increasing dry cell weight (DCW), giving rise to a maximum of 113 ± 0.92 g/L of DCW with 43.9 ± 0.91 g/L of PHA (38.8% of DCW) at 48 h. A significant increase in both intracellular and extracellular astaxanthin concentrations was also recorded during fermentation process achieving a maximum of 8.51 ± 0.20 and 10.2 ± 0.24 mg/L, respectively. Amounts of PHA and total astaxanthin produced by cell retention culture were 6.29 and 19.7-folds higher, respectively, than those recorded under batch cultivation. PHA and total astaxanthin productivities by cell retention culture also increased up to 0.914 g/L/h and 0.781 mg/L/h, respectively, which were 3.54 and 11.1-folds higher than those of batch culture. Based on gas chromatography, Fourier transform infrared spectroscopy, and ¹H nuclear magnetic resonance spectroscopy, the extracted PHA was identified as a copolymer of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with a 3-hydroxyvalerate content of 3.78 mol%.

Improved production of D-pantothenic acid in Escherichia coli by integrated strain engineering and fermentation strategies

D-pantothenic acid (D-PA) is an essential vitamin that has been widely used in medicine, food, and animal feed. Microbial production of D-PA from natural renewable resources is attractive and challenging. In this study, both strain improvements and fermentation process strategies were applied to achieve high-level D-PA production in Escherichia coli. First, a D-PA-producing strain was developed through deletion of the aceF and mdh genes combined with the overexpression of the gene ppnk. The obtained engineered E. coli DPA02/pT-ppnk accumulated 6.89 ± 0.11 g/L of D-PA in shake flask fermentation, which was 79.9 % higher than the control strain. Moreover, the cultivation process contributed greatly to D-PA production with respect to titer and productivity by betaine supplementation and dissolved oxygen (DO)-feedback feeding framework. Under optimal conditions, 68.3 g/L of D-PA, the specific productivity of 0.794 g/L h and the yield of 0.36 g/g glucose in 5 L fermenter were achieved. Overall, this research successfully exploited advanced strategies to lay the foundation for bio-based D-PA production in industrial applications.

Response surface methodology optimization of polyhydroxyalkanoate production by Burkholderia cepacia BPT1213 using waste glycerol from palm oil-based biodiesel production

The feasibility of using waste glycerol from the biodiesel industry for biosynthesis of polyhydroxyalkanoate (PHA) by Burkholderia cepacia BPT1213 was evaluated. Culture conditions were optimized by growing B. cepacia BPT1213 in mineral salt medium supplemented with 2% waste glycerol in a 2.5 L bioreactor. Response surface methodology was used to determine the influence of aeration rate (0.6-1.8 vvm), agitation speed (100-300 rpm), and cultivation period (48-72 hr) on PHA production. The optimum conditions for the growth and PHA accumulation were 1.5 vvm, 300 rpm, and 72 hr, with predicted values of 5.08 g/L cell dry weight (CDW), 66.07% PHA content, and 3.35 g/L total PHA concentration. Using these conditions, the experimental system produced 5.63 g/L of CDW with 64.00% wt/wt PHA content, which is threefold higher PHA concentration (3.60 g/L) compared to the non-optimized conditions. The melting temperature (T_m ) of purified PHA was 173.45 ± 1.05°C. In conclusion, the statistical approach was significantly increased the PHA production using waste glycerol as the sole carbon source.