Statistical media optimization studies for growth and PHB production by Ralstonia eutropha

Identification of Oil-Loving Cupriavidus necator BM3-1 for Polyhydroxyalkanoate Production and Assessing Contribution of Exopolysaccharide for Vegetable Oil Utilization

Polyhydroxyalkanoates (PHA) have received attention owing to their biodegradability and biocompatibility, with studies exploring PHA-producing bacterial strains. As vegetable oil provides carbon and monomer precursors for poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P(3HB-co-3HHx)), oil-utilizing strains may facilitate PHA production. Herein, Cupriavidus necator BM3-1, which produces 11.1 g/L of PHB with 5% vegetable oil, was selected among various novel Cupriavidus necator strains. This strain exhibited higher preference for vegetable oils over sugars, with soybean oil and tryptone determined to be optimal sources for PHA production. BM3-1 produced 33.9 g/L of exopolysaccharides (EPS), which was three-fold higher than the amount produced by H16 (10.1 g/L). EPS exhibited 59.7% of emulsification activity (EI24), higher than that of SDS and of EPS from H16 with soybean oil. To evaluate P(3HB-co-3HHx) production from soybean oil, BM3-1 was engineered with P(3HB-co-3HHx) biosynthetic genes (phaCRa, phaARe, and phaJPa). BM3-1/pPhaCJ produced 3.5 mol% of 3HHx and 37.1 g/L PHA. BM3-1/pCB81 (phaCAJ) produced 32.8 g/L PHA, including 5.9 mol% 3HHx. Physical and thermal analyses revealed that P(3HB-co-5.9 mol% 3HHx) was better than PHB. Collectively, we identified a novel strain with high vegetable oil utilization capacity for the production of EPS, with the option to engineer the strain for P(3HB-co-3HHx).

Impact of the environmental parameters on single cell protein production and composition by Cupriavidus necator

Due to the rapid increase in the world's population, many developing countries are facing malnutrition problems, including famine and food insecurity. Particularly, the deficiency of protein sources becomes a serious problem for human and animal nutrition. In this context, Single Cell Proteins, could be exploited as an alternative source of unconventional proteins. The aim of the study was to investigate SCP production and composition by Cupriavidus necator under various environmental conditions, temperature and pH values. A mono-factorial approach was implemented using batch bioreactor cultures under well-controlled conditions. Results were compared in terms of bacterial growth and SCP composition (proteins, nucleic acids, amino acids and elemental formula). Complementary analyses were performed by flow cytometry to study cell morphology, membrane permeability and the presence of Poly(3-hydroxybutyrate) (PHB) production. Our data confirmed the ability of C. necator to produce high amount of proteins (69 %DW at 30 °C and pH7). The results showed that temperature and pH independently impact SCP production and composition. This impact was particularly observed at the highest temperature (40 °C) and also the lowest pH value (pH5) providing lower growth rates, cell elongation, changes in granularity and lower amounts of proteins (down to 44 %DW at pH5) and nucleic acids. These low percentages were related to the production of PHB production (up to 44 %DW at 40 °C) which is the first report of a PHB accumulation in C. necator under nutrient unlimited conditions.

Heterotrophic and autotrophic production of L-isoleucine and L-valine by engineered Cupriavidus necator H16

Advancement in commodity chemical production from carbon dioxide (CO2) offers a promising path towards sustainable development goal. Cupriavidus necator is an ideal host to convert CO2 into high-value chemicals, thereby achieving this target. Here, C. necator was engineered for heterotrophic and autotrophic production of L-isoleucine and L-valine. Citramalate synthase was introduced to simplify isoleucine synthesis pathway. Blocking poly-hydroxybutyrate biosynthesis resulted in significant accumulation of isoleucine and valine. Besides, strategies like key enzymes screening and overexpressing, reducing power balancing and feedback inhibition removing were applied in strain modification. Finally, the maximum isoleucine and valine titers of the best isoleucine-producing and valine-producing strains reached 857 and 972 mg/L, respectively, in fed-batch fermentation using glucose as substrate, and 105 and 319 mg/L, respectively, in autotrophic fermentation using CO2 as substrate. This study provides a feasible solution for developing C. necator as a microbial factory to produce amino acids from CO2.

P3HB from CH4 using methanotrophs: aspects of bioreactor, fermentation process and modelling for cost-effective biopolymer production

P3HB (poly-β-hydroxybutyrate), an energy-storage compound of several microorganisms, can be used as bioplastics material. P3HB is completely biodegradable under aerobic and aerobic conditions, also in the marine environment. The intracellular agglomeration of P3HB was examined employing a methanotrophic consortium. Supplanting fossil, non-degradable polymers by P3HB can significantly reduce the environmental impact of plastics. Utilizing inexpensive carbon sources like CH₄ (natural gas, biogas) is a fundamental methodology to make P3HB production less costly, and to avoid the use of primary agricultural products such as sugar or starch. Biomass growth in polyhydroxyalkanoates (PHA) in general and in Poly (3-hydroxybutyrate) manufacture in specific could be a foremost point, so here the authors focus on natural gas as a proper carbon source and on the selection of bioreactors to produceP3HB, and in future further PHA, from that substrate. CH₄ can also be obtained from biomass, e.g., biogas, syngas methanation or power-to-gas (synthetic natural gas, SNG). Simulation software can be utilized for examination, optimizing and scale-up of the process as shown in this paper. The fermentation systems continuously stirred tank reactor (CSTR), forced-liquid vertical loop bioreactor (VTLB), forced-liquid horizontal tubular loop bioreactor (HTLB), airlift (AL) fermenter and bubble column (BC) fermenter were compared for their methane conversion, kLa value, productivity, advantages and disadvantages. Methane is compared to methanol and other feedstocks. It was discovered that under optimum processing circumstances and using Methylocystis hirsuta, the cells accumulated 51.6% cell dry mass of P3HB in the VTLB setup.

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.

Polyhydroxybutyrate production by Cupriavidus necator in a corn biorefinery concept

The high costs of bioplastics' production may hinder their commercialization. Development of new processes with high yields and in biorefineries can enhance diffusion of these materials. This work evaluated the production of polyhydroxybutyrate (PHB) from the combination of milled corn starchy fraction hydrolysate and crude glycerol as substrates by the strain Cupriavidus necator LPB 1421. After optimization steps, maximum accumulation of 62 % of PHB was obtained, which represents 11.64 g.L^-1 and productivity of 0.162 g.Lh^-1. In a stirred tank bioreactor system with 8 L of operational volume, 70 % of PHB accumulation was reported, representing 14.17 g.L^-1 of the biopolymer with 0.197 g.Lh^-1 productivity. PHB recovery was conducted using a chemical digestion method, reaching >99 % purity. Therefore, the potential application of milled corn as substrate for PHB production was confirmed. The developed bioplastic process could be coupled to a bioethanol producing unit creating the opportunity of a sustainable and economic biorefinery.

Bioconversion of Used Transformer Oil into Polyhydroxyalkanoates by Acinetobacter sp. Strain AAAID-1.5

In this research, the utilisation of used transformer oil (UTO) as carbon feedstock for the production of polyhydroxyalkanoate (PHA) was targeted; with a view to reducing the environmental challenges associated with the disposal of the used oil and provision of an alternative to non-biodegradable synthetic plastic. Acinetobacter sp. strain AAAID-1.5 is a PHA-producing bacterium recently isolated from a soil sample collected in Penang, Malaysia. The PHA-producing capability of this bacterium was assessed through laboratory experiments in a shake flask biosynthesis under controlled culture conditions. The effect of some biosynthesis factors on growth and polyhydroxyalkanoate (PHA) accumulation was also investigated, the structural composition of the PHA produced by the organism was established, and the characteristics of the polymer were determined using standard analytical methods. The results indicated that the bacteria could effectively utilise UTO and produce PHA up to 34% of its cell dry weight. Analysis of the effect of some biosynthesis factors revealed that the concentration of carbon substrate, incubation time, the concentration of yeast extract and utilisation of additional carbon substrates could influence the growth and polymer accumulation in the test organism. Manipulation of culture conditions resulted in an enhanced accumulation of the PHA. The data obtained from GC-MS and NMR analyses indicated that the PHA produced might have been composed of 3-hydroxyoctadecanoate and 3-hydroxyhexadecanoate as the major monomers. The physicochemical analysis of a sample of the polymer revealed an amorphous elastomer with average molecular weight and polydispersity index (PDI) of 110 kDa and 2.01, respectively. The melting and thermal degradation temperatures were 88 °C and 268 °C, respectively. The findings of this work indicated that used transformer oil could be used as an alternative carbon substrate for PHA biosynthesis. Also, Acinetobacter sp. strain AAAID-1.5 could serve as an effective agent in the bioconversion of waste oils, especially UTO, to produce biodegradable plastics. These may undoubtedly provide a foundation for further exploration of UTO as an alternative carbon substrate in the biosynthesis of specific polyhydroxyalkanoates.

Optimization of Growth Conditions to Enhance PHA Production by Cupriavidus necator

The accumulation of polyhydroxyalkanoates (PHAs) by microorganisms usually occurs in response to environmental stress conditions. Therefore, it is advantageous to choose two-step cultivation. The first phase is aimed at maximizing biomass production, and only in the second phase, after setting the suitable conditions, PHA production starts. The aim of this work was to optimize the composition of the minimal propagation medium used for biomass production of Cupriavidus necator DSM 545 using the response surface methodology (RSM). Based on the results from the search for optimization limits, the glucose concentration, the ammonium sulfate concentration and the phosphate buffer molarity were chosen as independent variables. The optimal values were found as follows: the glucose concentration 10.8 g/L; the ammonium sulfate concentration 0.95 g/L; and the phosphate buffer molarity 60.2 mmol/L. The predicted biomass concentration was 4.54 g/L, and the verified value was at 4.84 g/L. Although this work was primarily focused on determining the optimal composition of the propagation medium, we also evaluated the optimal composition of the production medium and found that the optimal glucose concentration was 6.7 g/L; the ammonium sulfate concentration 0.60 g/L; and the phosphate buffer molarity 20 mmol/L. The predicted PHB yield was 54.7% (w/w) of dry biomass, and the verified value was 49.1%.

A novel rotating wide gap annular bioreactor (Taylor-Couette type flow) for polyhydroxybutyrate production by Ralstonia eutropha using carob pod extract

An annular bioreactor (ABR) with wide gap was used for PHB production from Ralstonia eutropha. Hydrodynamic studies demonstrated the uniform distribution of fluid in the ABR due to the Taylor-Couette flow. Thereafter, the ABR was operated at different agitation and sparging rates to study its effect on R. eutropha growth and PHB production. The ABR operated at 500 rpm with air sparge rate of 0.8 vvm yielded a maximum PHB concentration of 14.89 g/L, which was nearly 1.4 times that obtained using a conventional stirred-tank bioreactor (STBR). Furthermore, performances of the bioreactors were compared by operating the reactors under fed-batch mode. At the end of 90 h of operation, the ABR resulted in a very high PHB production of 70.8 g/L. But STBR resulted in a low PHB concentration of 44.2 g/L. The superior performance was due to enhanced oxygen and nutrient mass transfer in the ABR.

Screening for Methane Utilizing Mixed Communities with High Polyhydroxybutyrate (PHB) Production Capacity Using Different Design Approaches

With the adverse environmental ramifications of the use of petroleum-based plastic outweighing the challenges facing the industrialization of bioplastics, polyhydroxyalkanoate (PHA) biopolymer has gained broad interest in recent years. Thus, an efficient approach for maximizing polyhydroxybutyrate (PHB) polymer production in methanotrophic bacteria has been developed using the methane gas produced in the anaerobic digestion process in wastewater treatment plants (WWTPS) as a carbon substrate and an electron donor. A comparison study was conducted between two experimental setups using two different recycling strategies, namely new and conventional setups. The former setup aims to recycle PHB producers into the system after the PHB accumulation phase, while the latter recycles the biomass back into the system after the exponential phase of growth or the growth phase. The goal of this study was to compare both setups in terms of PHB production and other operational parameters such as growth rate, methane uptake rate, and biomass yield using two different nitrogen sources, namely nitrate and ammonia. The newly proposed setup is aimed at stimulating PHB accumulating type II methanotroph growth whilst enabling other PHB accumulators to grow simultaneously. The success of the proposed method was confirmed as it achieved highest recorded PHB accumulation percentages for a mixed culture community in both ammonia- and nitrate-enriched media of 59.4% and 54.3%, respectively, compared to 37.8% and 9.1% for the conventional setup. Finally, the sequencing of microbial samples showed a significant increase in the abundance of type II methanotrophs along with other PHB producers, confirming the success of the newly proposed technique in screening for PHB producers and achieving higher PHB accumulation.

Screening of the strictly xylose-utilizing Bacillus sp. SM01 for polyhydroxybutyrate and its co-culture with Cupriavidus necator NCIMB 11599 for enhanced production of PHB

Polyhydroxybutyrate (PHB) is a biodegradable plastic that can be used as an alternative to petrochemical-based plastics. PHB is produced by various microorganisms such as Ralstonia, Halomonas, and Bacillus species. However, there are very few strains that produce PHB using xylose, an abundant and inexpensive carbon source. In this study, ten xylose-utilizing PHB producers isolated from South Korean marine environments were screened and characterized. Among these isolates, Bacillus sp. SM01, a newly identified strain, produced the highest amount of PHB using xylose. Under optimal conditions, the maximum dry cell weight (DCW) was 3.41 ± 0.09 g/L, with 62% PHB content, and Bacillus sp. SM01 showed Poly (3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer production with propionate; however, the growth of Bacillus sp. SM01 was greatly inhibited by the presence of glucose. Co-culturing Bacillus sp. SM01 with Cupriavidus necator NCIMB 11599 resulted in increased DCW, PHB production, and utilization of glucose and xylose, the main sugar of lignocellulosic biomass, compared with the monoculture. Our results indicated that this co-culture system can be used to increase PHB production and overcome the limitation of sugar consumption associated with Bacillus sp. SM01 and C. necator.

Two-stage enrichment of hydrogen-oxidizing bacteria as biofertilizers

Biofertilizers can replace chemical fertilizers to promote the plant growth without causing any pollution. The study of hydrogen-oxidizing bacteria (HOB) enrichment as biofertilizers from mixed culture is scarce. Our recent study shows that biofertilizing HOB are successfully enriched in a short hydraulic retention time of 10 h. While, the mechanism is unknown. This study intentionally used a two-stage method to enrich biofertilizing HOB specifically with nitrate as nitrogen source in Stage 1 and then 1-aminocyclopropane-1-carboxylate (ACC) as nitrogen source in Stage 2. It was found Pseudomonas (34.46%, reported HOB) predominated in Stage 1, while Azospirillum (59.35%), Azoarcus (36%) were dominant genera and Azospirillum lipoferum strain DSM 1691 (50%), Azoarcus olearius strain DQS-4 (50%) were dominant species in Stage 2. The enriched HOB of Stage 2 showed ACC deaminase activity. Furthermore, they could also fix N₂ and consume Ca₃(PO₄)₂. Thus, the two-stage method can be used as a specific enrichment for HOB as biofertilizers, which extends the application of HOB in agriculture.

Improved fermentation strategies in a bioreactor for enhancing poly(3-hydroxybutyrate) (PHB) production by wild type Cupriavidus necator from fructose

Poly(3-hydroxybutyrate) (PHB) belongs to the family of polyhydroxyalkanoates, biopolymers used for agricultural, industrial, or even medical applications. However, scaling up the production is still an issue due to the myriad of parameters involved in the fermentation processes. The present work seeks, firstly, to scale up poly(3-hydroxybutyrate) (PHB) production by wild type C. necator ATCC 17697 from shaken flasks to a stirred-tank bioreactor with the optimized media and fructose as carbon source. The second purpose is to improve the production of PHB by applying both the batch and fed-batch fermentation strategies in comparison with previous works of wild type C. necator with fructose. Furthermore, thinking of biomedical applications, physicochemical, and cytotoxicity analyses of the produced biopolymer, are presented.

Fed-batch fermentation with an exponential feeding strategy enabled us to achieve the highest values of PHB concentration and productivity, 25.7 g/l and 0.43 g/(l h), respectively. The PHB productivity was 3.3 and 7.2 times higher than the one in batch strategy and shaken flask cultures, respectively. DSC, FTIR, ¹H, and ¹³C NMR analysis led to determine that the biopolymer produced by C. necator ATCC 17697 has a molecular structure and characteristics in agreement with the commercial PHB. Additionally, the biopolymer does not induce cytotoxic effects on the NIH/3T3 cell culture.

Due to the improved fermentation strategies, PHB concentration resulted in 40 % higher of the already reported one for wild type C. necator using other fed-batch modes and fructose as a carbon source. Thus the produced PHB could be attractive for biomedical applications, which generate a rising interest in polyhydroxyalkanoates during recent years.

Light excess stimulates Poly-beta-hydroxybutyrate yield in a mangrove-isolated strain of Synechocystis sp

Poly-β-hydroxybutyrate (PHB) is a biodegradable biopolymer that may replace fossil-based plastics reducing its negative environmental impact. One highly sustainable strategy to produce these biopolymers is the exploitation of photosynthetic microorganisms that use sunlight and CO₂ to produce biomass and subsequently, PHB. Exploring environmental biological diversity is a powerful tool to find resilient microorganisms potentially exploitable to produce bioproducts. In this work, a cyanobacterium (Synechocystis sp.) isolated from a contaminated area close to an important industrial complex was shown to produce PHB under different culture conditions. Carbon, nutrients supply and light intensity impact on biomass and PHB productivity were assessed, showing that the highest yield of PHB achieved was 241 mg L^-1 (31%_dcw) under high light intensity. Remarkably this condition not only stimulated PHB accumulation by 70% compared to other conditions tested but also high cellular duplication rate, maximizing the potential of this strain for PHB production.

Novel external-loop-airlift milliliter scale bioreactors for cell growth studies: Low cost design, CFD analysis and experimental characterization

Many researchers have limited access to fully equipped laboratory-scale batch bioreactors and chemostats due to their relatively high cost. This becomes particularly prohibitive when multiple replicas of the same experiment are required, but not enough bioreactors are available to operate simultaneously. Additionally, experiments using shaken flasks are common but show significant limitations in terms of maintaining homogeneous conditions in liquid cultures or installing instrumentation for monitoring. Here, we proposed to tackle this significant hurdle by providing a route to make available the manufacture of low-cost, milliliter-scale bioreactors. This approach seems plausible for enabling proof-of-concept experiments before moving to a larger scale without significant investments. The conceptually designed systems were based on external-loop bioreactors due to their flexibility, simplicity, and ease of assembling and testing. Designs were initially evaluated in silico with the aid of COMSOL Multiphysics. The successfully evaluated systems were then constructed via additive manufacturing and assembled for hydrodynamics testing via tracer methods. This was enabled by a newly home-made optical absorbance sensor (OAS) for in-line and real-time measurements. Both the in silico and experimental results indicated close to ideal mixing conditions and low shear stress. Cell growth curves were prepared by culturing Escherichia coli and following its cell density in real-time. Our cell growth rate and maximum cell density were similar to those previously obtained in closely related systems. Therefore, the proposed bioreactors are an affordable alternative for batch and continuous cell growth studies rapidly and inexpensively.

Molecular Profiling and Optimization Studies for Growth and PHB Production Conditions in Rhodobacter sphaeroides

In the recent climate change regime, industrial demand for renewable materials to replace petroleum-derived polymers continues to rise. Of particular interest is polyhydroxybutyrate (PHB) as a substitute for polypropylene. Accumulating evidence indicates that PHB is highly produced as a carbon storage material in various microorganisms. The effects of growth conditions on PHB production have been widely studied in chemolithotrophs, particularly in Rhodobacter. However, the results on PHB production in Rhodobacter have been somewhat inconsistent due to different strains and experimental conditions, and it is currently unclear how diverse environmental factors are linked with PHB production. Here, we report optimized growth conditions for PHB production and show that the growth conditions are closely related to reactive oxygen species (ROS) regulation. PHB accumulates in cells up to approximately 50% at the highest level under dark-aerobic conditions as opposed to light aerobic/anaerobic conditions. According to the time-course, PHB contents increased at 48 h and then gradually decreased. When observing the effect of temperature and medium composition on PHB production, 30 °C and a carbon/nitrogen ratio of 9:1 or more were found to be most effective. Among PHB biosynthetic genes, PhaA and PhaB are highly correlated with PHB production, whereas PhaC and PhaZ showed little change in overall expression levels. We found that, while the amount of hydrogen peroxide in cells under dark conditions was relatively low compared to the light conditions, peroxidase activities and expression levels of antioxidant-related genes were high. These observations suggest optimal culture conditions for growth and PHB production and the importance of ROS-scavenging signaling with regard to PHB production.

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.

A closed-loop biorefinery approach for polyhydroxybutyrate (PHB) production using sugars from carob pods as the sole raw material and downstream processing using the co-product lignin

A novel closed-loop biorefinery model using carob pods as the feed material was developed for PHB production. The carob pods were delignified, and as the second step, sugars present in the delignified carob pods were extracted using water. Ralstonia eutropha and Bacillus megaterium were cultivated on the carob pod extract and its performance was evaluated using Taguchi experimental design. R. eutropha outperformed the B. megaterium in terms of its capability to grow at a maximum initial sugar concentration of 40 g L^-1 with a maximum PHB production of 12.2 g L^-1. Finally, the concentrated lignin from the first step was diluted with different proportion of chloroform to extract PHB from the bacterial biomass. The PHB yield and purity obtained were more than 90% respectively using either R. eutropha or B. megaterium. Properties of the PHB produced in this study were examined to establish its application potential.

Preparation and Characterization of Films Based on a Natural P(3HB)/mcl-PHA Blend Obtained through the Co-culture of Cupriavidus Necator and Pseudomonas Citronellolis in Apple Pulp Waste

The co-culture of Cupriavidus necator DSM 428 and Pseudomonas citronellolis NRRL B-2504 was performed using apple pulp waste from the fruit processing industry as the sole carbon source to produce poly(3-hydroxybutyrate), P(3HB) and medium-chain length PHA, mcl-PHA, respectively. The polymers accumulated by both strains were extracted from the co-culture's biomass, resulting in a natural blend that was composed of around 48 wt% P(3HB) and 52 wt% mcl-PHA, with an average molecular weight of 4.3 × 10⁵ Da and a polydispersity index of 2.2. Two melting temperatures (T_m) were observed for the blend, 52 and 174 °C, which correspond to the T_m of the mcl-PHA and P(3HB), respectively. P(3HB)/mcl-PHA blend films prepared by the solvent evaporation method had permeabilities to oxygen and carbon dioxide of 2.6 and 32 Barrer, respectively. The films were flexible and easily deformed, as demonstrated by their tensile strength at break of 1.47 ± 0.07 MPa, with a deformation of 338 ± 19% until breaking, associated with a Young modulus of 5.42 ± 1.02 MPa. This study demonstrates for the first time the feasibility of using the co-culture of C. necator and P. citronellolis strains to obtain a natural blend of P(3HB)/mcl-PHA that can be processed into films suitable for applications ranging from commodity packaging products to high-value biomaterials.

Biokinetics of fed-batch production of poly (3-hydroxybutyrate) using microbial co-culture

A novel fed-batch strategy based on carbon/nitrogen (C/N) ratio in a microbial co-culture production medium broth was carried out in a biocalorimeter for improved production of poly (3-hydroxybutyrate) (PHB). Shake flask study suggested that the C/N ratio of 10 increased the yield of PHB by 2.8 times. Online parameters monitored during the C/N ratio of 10 in biocalorimeter (BioRC1e) indicated that the heat profile was maintained in the fed-batch mode resulting in a PHB yield of 30.3 ± 1.5 g/L. The oxy-calorific heat yield coefficient during the fed-batch strategy was found to be 394.24 ± 18.71 kJ/O₂ due to the oxidative metabolism of glucose. The reported heat-based model adapted for PHB concentration prediction in the present fed-batch mode. The heat-based model has a Nash-Sutcliffe efficiency of 0.9758 for PHB prediction. PHB obtained by fed-batch-mode was characterized using gas chromatography-mass spectrometry (GC-MS) for the monomer-acid analysis, Thermogravimetric analysis (TGA) for thermal stability of PHB, and Fourier transform infrared spectroscopy (FT-IR) for confirmation of functional groups. Here, we establish a favorable C/N ratio for achieving optimal PHB yield and a predictive heat-based model to monitor its production.

Polyhydroxybutyrate Production from Natural Gas in A Bubble Column Bioreactor: Simulation Using COMSOL

In this study, the simulation of microorganism ability for the production of poly-β-hydroxybutyrate (PHB) from natural gas (as a carbon source) was carried out. Based on the Taguchi algorithm, the optimum situations for PHB production from natural gas in the columnar bubble reactor with 30 cm length and 1.5 cm diameter at a temperature of 32 °C was evaluated. So, the volume ratio of air to methane of 50:50 was calculated. The simulation was carried out by COMSOL software with two-dimensional symmetric mode. Mass transfer, momentum, density-time, and density-place were investigated. The maximum production of biomass concentration reached was 1.63 g/L, which shows a 10% difference in contrast to the number of experimental results. Furthermore, the consequence of inlet gas rate on concentration and gas hold up was investigated Andres the simulation results were confirmed to experimental results with less than 20% error.

Production and recovery of poly-3-hydroxybutyrate bioplastics using agro-industrial residues of hemp hurd biomass

The present study describes production and recovery of poly(3-hydroxybutyrate) P(3HB) from agro-industrial residues. Production was conducted using Ralstonia eutropha strain with hemp hurd biomass hydrolysates sugars as a carbon source and ammonium chloride as the nitrogen source. Results show that maximum hydrolysis yield of 72.4% was achieved with total sugar hydrolysate concentration (i.e., glucose and xylose) of 53.0 g/L. Sugar metabolism by R. eutropha showed preference for glucose metabolism over xylose. Under optimum conditions, cells can accumulate P(3HB) polymer in quantity up to 56.3 wt% of the dry cell weight. This corresponds to total production of 13.4 g/L (productivity of 0.167 g/L h). Nitrogen source showed no adverse effect on P(3HB) biosynthesis, but rather on cell growth. Among several examined recovery techniques, ultrasonic-assisted sodium dodecyl sulfate (SDS) recovered bioplastic directly from the broth cell concentrate with P(3HB) content of 92%. Number average molecular weights (M_n) of final recovered bioplastic were in the range of 150-270 kDa with polydispersity index (M_w/M_n) in the range of 2.1-2.4.

Evaluation of culture medium on poly(3-hydroxybutyrate) production by Cupriavidus necator ATCC 17697: application of the response surface methodology

Polyhydroxyalkanoates (PHA), of which polyhydroxybutyrate (PHB) is the most abundant, are polymers of bacterial origin used for various applications in the medical, industrial and agricultural fields. In the present study we worked on the selection, evaluation and improvement of the significant variables of the medium for the production of PHB by Cupriavidus necator ATCC 17697. In order to address the selection of the main factors and optimize the culture medium, a complete factorial experimental design based on the coupled response surface methodology, was presented. The model with the best adjustment of the variables turned out to be quadratic in fructose (C), linear in ammonium sulphate (N) and pH, with interaction in pH and phosphate solution (P), where the pH was the most significant (p < 0.0001) while the micro-elements solution could be neglected. Thus, optimum carbon concentration, adequate nitrogen limitation and interaction between initial pH and phosphate solution concentration are important factors to ensure a high production of PHB. The optimal values of the selected variables were C = 20 g/l, N = 1.5 g/l, P = 8.75 g/l and pH 7.5. A maximum PHB production of 4.6 g/l, obtained under these conditions, increased almost 2.5 times. The polymer accumulated in the cytoplasm of C. necator ATCC 17697 in the form of granules showed an FTIR spectrum corresponding to that of commercial PHB.

Biosynthesis of poly-3-hydroxybutyrate from grass silage by a two-stage fermentation process based on an integrated biorefinery concept

Grass silage as a renewable feedstock for an integrated biorefinery includes nutrients and carbon sources directly available in the press juice (PJ) and in lignocellulosic saccharides from the plant framework. Here, a novel two-stage fed-batch fermentation process for biosynthesis of poly-3-hydroxybutyrate (PHB) by Cupriavidus necator DSM 531 is presented. For bacterial growth, nutrient-rich PJ was employed as a fermentation medium, without any supplements. Saccharides derived from the mechano-enzymatic hydrolysis of the press cake (PC) were subjected to a lactic acid fermentation process, before the fermentation products were fed into the polymer accumulation phase. By combination of pH-stat feeding and cell recycling, the PHB content in 22 g L^-1 total-dry cells reached 39% after 32 h of cultivation. Using mimicked hydrolyzate of diluted PJ artificially supplemented with glucose and xylose, the resulting cell dry weight of 21 g L^-1 contained 42% PHB.

Media studies to enhance the production of verticillins facilitated by in situ chemical analysis

Abstract

Verticillins are a group of epipolythiodioxopiperazine alkaloids that have displayed potent cytotoxicity. To evaluate their potential further, a larger supply of these compounds was needed for both in vivo studies and analogue development via semisynthesis. To optimize the biosynthesis of these secondary metabolites, their production was analyzed in two different fungal strains (MSX59553 and MSX79542) under a suite of fermentation conditions. These studies were facilitated by the use of the droplet-liquid microjunction-surface sampling probe (droplet probe), which enables chemical analysis in situ directly from the surface of the cultures. These experiments showed that the production of verticillins was greatly affected by growth conditions; a significantly higher quantity of these alkaloids was noted when the fungal strains were grown on an oatmeal-based medium. Using these technologies to select the best among the tested growth conditions, the production of the verticillin analogues was increased while concomitantly decreasing the time required for fermentations from 5 weeks to about 11 days. Importantly, where we could previously supply 5–10 mg every 6 weeks, we are now able to supply 50–150 mg quantities of key analogues per month via laboratory scale fermentation.

Graphical abstract

Electronic supplementary material

The online version of this article (10.1007/s10295-018-2083-8) contains supplementary material, which is available to authorized users.

The transcriptional regulator NtrC controls glucose-6-phosphate dehydrogenase expression and polyhydroxybutyrate synthesis through NADPH availability in Herbaspirillum seropedicae

The NTR system is the major regulator of nitrogen metabolism in Bacteria. Despite its broad and well-known role in the assimilation, biosynthesis and recycling of nitrogenous molecules, little is known about its role in carbon metabolism. In this work, we present a new facet of the NTR system in the control of NADPH concentration and the biosynthesis of molecules dependent on reduced coenzyme in Herbaspirillum seropedicae SmR1. We demonstrated that a ntrC mutant strain accumulated high levels of polyhydroxybutyrate (PHB), reaching levels up to 2-fold higher than the parental strain. In the absence of NtrC, the activity of glucose-6-phosphate dehydrogenase (encoded by zwf) increased by 2.8-fold, consequently leading to a 2.1-fold increase in the NADPH/NADP⁺ ratio. A GFP fusion showed that expression of zwf is likewise controlled by NtrC. The increase in NADPH availability stimulated the production of polyhydroxybutyrate regardless the C/N ratio in the medium. The mutant ntrC was more resistant to H₂O₂ exposure and controlled the propagation of ROS when facing the oxidative condition, a phenotype associated with the increase in PHB content.

Improved fed-batch production of high-purity PHB (poly-3 hydroxy butyrate) by Cupriavidus necator (MTCC 1472) from sucrose-based cheap substrates under response surface-optimized conditions

Experimental investigations were carried out for Cupriavidus necator (MTCC 1472)-based improved production of poly-3 hydroxy butyrate (PHB) through induced nitrogen limiting fed-batch cultivation strategies. Initially Plackett-Burman design and response surface methodology were implemented to optimize most influencing process parameters. With optimized process parameter values, continuous feeding strategies ware applied in a 5-l fermenter with table sugar concentration of 100 g/l, nitrogen concentration of 0.12 g/l for fed-batch fermentation with varying dilution rates of 0.02 and 0.046 1/h. To get enriched production of PHB, concentration of the sugar was further increased to 150 and 200 g/l in feeding. Maximum concentrations of PHB achieved were 22.35 and 23.07 g/l at those dilution rates when sugar concentration maintains at 200 g/l in feeding. At maximum concentration of PHB (23.07 g/l), productivity of 0.58 g/l h was achieved with maximum PHB accumulation efficiency up to 64% of the dry weight of biomass. High purity of PHB, close to medical grade was achieved after surfactant hypochlorite extraction method, and it was further confirmed by SEM, EDX, and XRD studies.

Reversal of β-oxidative pathways for the microbial production of chemicals and polymer building blocks

β-Oxidation is the ubiquitous metabolic strategy to break down fatty acids. In the course of this four-step process, two carbon atoms are liberated per cycle from the fatty acid chain in the form of acetyl-CoA. However, typical β-oxidative strategies are not restricted to monocarboxylic (fatty) acid degradation only, but can also be involved in the utilization of aromatic compounds, amino acids and dicarboxylic acids. Each enzymatic step of a typical β-oxidation cycle is reversible, offering the possibility to also take advantage of reversed metabolic pathways for applied purposes. In such cases, 3-oxoacyl-CoA thiolases, which catalyze the final chain-shortening step in the catabolic direction, mediate the condensation of an acyl-CoA starter molecule with acetyl-CoA in the anabolic direction. Subsequently, the carbonyl-group at C3 is stepwise reduced and dehydrated yielding a chain-elongated product. In the last years, several β-oxidation pathways have been studied in detail and reversal of these pathways already proved to be a promising strategy for the production of chemicals and polymer building blocks in several industrially relevant microorganisms. This review covers recent advancements in this field and discusses constraints and bottlenecks of this metabolic strategy in comparison to alternative production pathways.

Growth medium and electrolyte-How to combine the different requirements on the reaction solution in bioelectrochemical systems using Cupriavidus necator

Microbial electrosynthesis is a relatively new research field where microbial carbon dioxide fixation based on the energy supplied by a cathode is investigated. Reaction media used in such bioelectrochemical systems have to fulfill requirements of classical biotechnology as well as electrochemistry. The design and characterization of a medium that enables fast electroautotrophic growth of Cupriavidus necator in microbial electrosynthesis was investigated in detail. The identified chloride-free medium mainly consists of low buffer concentration and is supplied with trace elements. Biotechnologically relevant parameters, such as high-specific growth rates and short lag phases, were determined for growth characterization. Fast growth under all conditions tested, i.e. heterotrophic, autotrophic and electroautotrophic was achieved. The lag phase was shortened by increasing the FeSO₄ concentration. Additionally, electrochemical robustness of the reaction media was proven. Under reductive conditions, no deposits on electrodes or precipitations in the media were observed and no detectable hydrogen peroxide evolved. In the bioelectrochemical system, no lag phase occurred and specific growth rate of C. necator was 0.09 h⁻¹. Using this medium shortens seed train drastically and enables fast electrobiotechnological production processes based on C. necator.

Date seed characterisation, substrate extraction and process modelling for the production of polyhydroxybutyrate by Cupriavidus necator

Poly-3-hydroxybutrate (PHB) is a biodegradable polymer synthesised via bacterial fermentation as a means of storing carbon and energy under unbalanced growth conditions. The production cost of petroleum-based plastics is currently lower than that for biopolymers, and the carbon source is the most significant contributor to biopolymer production cost. A feasibility study to assess the suitability of using a date seed derived media as an alternative for PHB production under various stress conditions was investigated. Results include fructose extraction from date seeds and a mass transfer model to describe the process, demonstrating that the high nutrient content of date seeds makes them a promising raw material for microbial growth and that a meaningful amount of PHB can be produced without supplementation. Maximum dry cell weight and PHB concentrations were 6.3g/l and 4.6g/l respectively, giving a PHB content of 73%, when an initial fructose concentration of 10.8g/l was used.

Production of polyhydroxybutyrate from wheat bran hydrolysate using Ralstonia eutropha through microbial fermentation

The increasing global demand for sustainable resources necessitates the complete utilization of feedstock. Wheat bran consists of significant amount of cellulose and hemicellulose which can be used as a renewable resource for production of fermentable sugars. In this study, alkaline pretreated wheat bran was enzymatically hydrolyzed using cellulase of Trichoderma reesei (37 FPU/g) and β - glucosidase of Aspergillus niger (50 CBU/g). Among the nitrogen sources tested, ammonium sulphate was identified as best nitrogen source for the production of polyhydroxybutyrate (PHB). The overall sugar concentration was about 62.91g/L with the corresponding sugar yield of 629.1mg/g wheat bran and the sugars released were mainly composed of glucose (48.35g/L) and xylose (14.56g/L). The PHB producing mutant strain, Ralstonia eutropha NCIMB 11599 grown in wheat bran hydrolysate produced cell density, PHB and yield of 24.5g/L, 62.5%, and 0.319g/g sugar respectively, with a productivity of 0. 0.255g/L/h. Thus, the results suggested that the wheat bran could be a potential alternative feedstock as it does not require any detoxification due to less inhibitory compounds for production of high cell density with significant amount of polyhydroxybutyrate.

Probing the Kinetic Anabolism of Poly-Beta-Hydroxybutyrate in Cupriavidus necator H16 Using Single-Cell Raman Spectroscopy

Poly-beta-hydroxybutyrate (PHB) can be formed in large amounts in Cupriavidus necator and is important for the industrial production of biodegradable plastics. In this investigation, laser tweezers Raman spectroscopy (LTRS) was used to characterize dynamic changes in PHB content—as well as in the contents of other common biomolecule—in C. necator during batch growth at both the population and single-cell levels. PHB accumulation began in the early stages of bacterial growth, and the maximum PHB production rate occurred in the early and middle exponential phases. The active biosynthesis of DNA, RNA, and proteins occurred in the lag and early exponential phases, whereas the levels of these molecules decreased continuously during the remaining fermentation process until the minimum values were reached. The PHB content inside single cells was relatively homogenous in the middle stage of fermentation; during the late growth stage, the variation in PHB levels between cells increased. In addition, bacterial cells in various growth phases could be clearly discriminated when principle component analysis was performed on the spectral data. These results suggest that LTRS is a valuable single-cell analysis tool that can provide more comprehensive information about the physiological state of a growing microbial population.