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Polyhydroxyalkanoates (PHAs) are emerging as alternatives to plastics by replacing fossil fuels with renewable raw substrates. Herein, we present the construction of engineered Escherichia coli strains to produce short-chain-length PHAs (scl-PHAs), including the monomers 4-hydroxyvalerate (4HV) and 3-hydroxyvalerate (3HV) produced from levulinic acid (LA). First, an E. coli strain expressing genes (lvaEDABC) from the levulinic acid metabolic pathway of Pseudomonas putida KT2440 was constructed to generate 4HV-CoA and 3HV-CoA. Second, both PhaAB enzymes from Cupriavidus necator H16 were expressed to supply 3-hydroxybutyrate (3HB)-CoA from acetyl-CoA. Finally, PHA synthase (PhaCCv) from Chromobacterium violaceum was introduced for the subsequent polymerization of these three monomers. The resulting E. coli strains produced four PHAs (w/w% of dry cell weight): 9.1 wt% P(4HV), 1.7 wt% P(3HV-co-4HV), 24.2 wt% P(3HB-co-4HV), and 35.6 wt% P(3HB-co-3HV-co-4HV).

In this study, a phaCR gene encoding PHA synthase was identified in Rhodoligotrophos defluvii which was adjacent to β-ketothiolase encoded by phaAR gene and acetoacetyl-CoA reductase encoded by phaBR gene. Amino acid comparison of PhaCR showed the highest homology of 65.98% with PhaC of R. appendicifer, while its homology with typical class I PHA synthase in Cupriavidus necator was only 42.54%. PHA synthesis genes were then transformed into E. coli harboring phaCABR and phaCRABC which were cultured with 15 g/L glucose respectively, and 20.46 wt% and 16.95 wt% of CDW for poly(3-hydroxybutyrate) (PHB) were accumulated respectively. To further explore the effect of substrate specificity for PHA production, the ptsG gene was then deleted and 15 g/L glucose and 1.5 g/L propionate were co-employed as carbon sources, which enabled the synthesis of poly(3HB-co-3HV) copolymer. As a result, poly(3HB-co-3HV) was accumulated up to 24.74 wt% of CDW, and the highest content of 3-hydroxyvalerate (3HV) was 10.86 mol%. The Td5 was 260 °C, which implied that it possessed good thermal stability, and the Mw of GPC in recombinant strains were between 22 and 26 × 104 g/mol, and the highest PDI was 3.771. The structure of poly (3HB-co-3HV) copolymer was determined through 1H NMR analysis.

Polyhydroxyalkanoates are attractive alternatives to traditional plastics. However, although polyhydroxybutyrate (PHB) is produced in large quantities by Cupriavidus necator H16, its properties are far from ideal for the manufacture of plastic products. These properties may be improved through its coproduction with 3-hydroxypropionate (3HP), which leads to the formation of the copolymer poly(3-hydroxybutyrate-co-3-hydroxypropionate) (poly(3HB-co-3HP). To achieve this, a pathway was designed to enable C. necator H16 to convert β-alanine to 3HP. The initial low levels of incorporation of 3HP into the copolymer were overcome by the overproduction of the native propionyl-CoA transferase together with PHA synthase from Chromobacterium sp. USM2. Following optimization of 3HP incorporation into the copolymer, the molar fraction of 3HP could be controlled by cultivation in medium containing different concentrations of β-alanine. Between 0 and 80 mol % 3HP could be achieved. Further supplementation with 2 mM cysteine increased the maximum 3HP molar fraction to 89%. Additionally, the effect of deletions of the phaA and phaB1 genes of the phaCAB operon on 3HP molar fraction were investigated. A phaAB1 double knockout resulted in a copolymer containing 91 mol % 3HP without the need for cysteine supplementation.

Marine macroalgae are potential renewable feedstocks for valuable biomaterials. Among them, alginate is a primary component in brown algae that can be nonenzymatically converted and enzymatically degraded by alginate lyases to 4-deoxy- l -erythro-5-hexoseulose uronic acid (DEH). Here, we constructed alginolytic enzyme complexes comprising two different alginate lyases for synergistic alginate degradation. The complexes showed good thermostability with 60% of the residual activity at high temperature (60 °C). Furthermore, they produced 0.85 and 0.18 mg/mL DEH from alginate and natural brown algae as substrates, respectively. The enzyme complex successfully decomposed brown algal biomass, resulting in a 3.15-fold improvement in DEH when compared to free enzymes. The Ralstonia eutropha strain with alginolytic enzyme complexes on the cell surface showed higher Polyhydroxybutyrate (PHB) production and produced 2.58 g/L PHB from alginate. After the use of alginate, remaining biomass such as fucoidan and laminaran can also be used in the future for high value ingredients in nutritional, medical device, skincare and dermatological products. These results demonstrate that it is possible to create more efficient strategies for producing biodegradable PHB and functional polysaccharides from brown algal substrates.

Poly(ethylene terephthalate) (PET) is a widely used plastic in bottles and fibers; its waste products pollute the environment owing to its remarkable durability. Recently, Ideonella sakaiensis 201-F6 was isolated as a unique bacterium that can degrade and assimilate PET, thus paving the way for the bioremediation and bioconversion of PET waste. We found that this strain harbors a poly(hydroxyalkanoate) (PHA) synthesis gene cluster, which is highly homologous with that of Cupriavidus necator, an efficient PHA producer. Cells grown on PET accumulated intracellular PHA at high levels. Collectively, our findings in this study demonstrate that I. sakaiensis can mediate the direct conversion of non-biodegradable PET into environment-friendly plastic, providing a new approach for PET recycling.

Consensus design (CD) is a representative sequence-based protein design method that enables the design of highly functional proteins by analyzing vast amounts of protein sequence data. This study proposes a partial consensus design (PCD) of a protein as a derivative approach of CD. The method replaces the target protein sequence with a consensus sequence in a secondary-structure-dependent manner (i.e., regionally dependent and divided into α-helix, β-sheet, and loop regions). In this study, we generated several artificial partial consensus l-threonine 3-dehydrogenases (PcTDHs) by PCD using the TDH from Cupriavidus necator (CnTDH) as a target protein. Structural and functional analysis of PcTDHs suggested that thermostability would be independently improved when consensus mutations are introduced into the loop region of TDHs. On the other hand, enzyme kinetic parameters (kcat/Km) and average productivity would be synergistically enhanced by changing the combination of the mutations-replacement of one region of CnTDH with a consensus sequence provided only negative effects, but the negative effects were nullified when the two regions were replaced simultaneously. Taken together, we propose the hypothesis that there are protein regions that encode individual protein properties, such as thermostability and activity, and that the introduction of consensus mutations into these regions could additively or synergistically modify their functions.

Polyhydroxybutyrate (PHB) is a biodegradable plastic with physical properties similar to petrochemically derived plastics. Here, Shewanella marisflavi BBL25 was engineered by inserting the pLW487 vector containing polyhydroxyalkanoates synthesis genes from Ralstonia eutropha H16. Under optimal conditions, the engineered S. marisflavi BBL25 produced 1.99 ± 0.05 g/L PHB from galactose. The strain showed high tolerance to various inhibitors and could utilize lignocellulosic biomass for PHB production. When barley straw hydrolysates were used as a carbon source, PHB production was 3.27 ± 0.19 g/L. In addition, PHB production under the microbial fuel cell system was performed to confirm electricity coproduction. The maximum electricity current output density was 1.71 mA/cm2, and dry cell weight (DCW) and PHB production were 11.4 g/L and 6.31 g/L, respectively. Our results demonstrated PHB production using various lignocellulosic biomass and the feasibility of PHB and electricity production, simultaneously, and it is the first example of PHB production in engineered Shewanella.

Purpose To synthesize and investigate polyhydroxyalkanoates (PHAs) with different monomer composition and percentages and polymer films prepared from them. Results Various PHAs: homopolymer poly-3-hydroxybutyrate P(3HB) and 2-, 3-, and 4-component copolymers comprising various combinations of 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV), 4-hydroxybutyrate (4HB), and 3-hydroxyhexanoate (3HHx) monomers were synthesized under specialized conditions. Relationships were found between the monomer composition of PHAs and their molecular-weight and thermal properties and degree of crystallinity. All copolymers had decreased weight average molecular weights, Mw (to 390–600 kDa), and increased values of polydispersity (3.2–4.6) compared to the P(3HB). PHA copolymers showed different thermal behavior: an insignificant decrease in Tmelt and the presence of the second peak in the melting region and changes in parameters of crystallization and glass transition. At the same time, they retained thermostability, and the difference between Tmelt and Tdegr was at least 100–120 °C. Incorporation of 4HB, 3HV, and 3HHx monomer units into the 3-hydroxybutyrate chain caused changes in the amorphous to crystalline ratio and decreased the degree of crystallinity (Cx) to 20–40%. According to the degree to which the monomers reduced crystallinity, they were ranked as follows: 4HB – 3HHx – 3HV. A unique set of films was produced; their surface properties and physical/mechanical properties were studied as dependent on PHA composition; monomers other than 3-hydroxybutyrate were found to enhance hydrophilicity, surface development, and elasticity of polymer films. Conclusion An innovative set of PHA copolymers was synthesized and solution-cast films were prepared from them; the copolymers and films were investigated as dependent on polymer chemical composition. Results obtained in the present study contribute to the solution of a critical issue of producing degradable polymer materials.

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.

Terpenoids have an impressive structural diversity and provide valuable substances for a variety of industrial applications. Among terpenes, the sesquiterpenes (C15 ) are the largest subclass with bioactivities ranging from aroma to health promotion. In this article, we show a gram-scale production of the sesquiterpene α-humulene in final aqueous concentrations of 2 g L-1 with the recombinant strain Cupriavidus necator pKR-hum in a fed-batch mode on fructose as carbon source and n-dodecane as an extracting organic phase for in situ product removal. Since C. necator is capable of both heterotrophic and autotrophic growth, we additionally modeled the theoretically possible yields of a heterotrophic versus an autotrophic process on CO2 in industrially relevant quantities. We compared the cost-effectiveness of both processes based on a production of 10 t α-humulene per year, with both processes performing equally with similar costs and gains. Furthermore, the expression and activity of 3-hydroxymethylglutaryl-CoA reductase (hmgR) from Myxococcus xanthus was identified as the main limitation of our constructed C. necator pKR-hum strain. Thus, we outlined possible solutions for further improvement of our production strain, for example, the replacement of the hmgR from M. xanthus by a plant-based variant to increase α-humulene production titers in the future.

Polyhydroxyalkanoates (PHAs) are polyesters of significant interest due to their biodegradability and properties similar to petroleum-derived plastics, as well as the fact that they can be produced from renewable sources such as by-product streams. In this study, brewer’s spent grain (BSG), the main by-product of the brewing industry, was subjected to a set of physicochemical pretreatments and their effect on the release of reducing sugars (RS) was evaluated. The RS obtained were used as a substrate for further PHA production in Burkholderia cepacia, Bacillus cereus, and Cupriavidus necator in liquid cultures. Although some pretreatments proved efficient in releasing RS (acidthermal pretreatment up to 42.1 gRS L-1 and 0.77 gRS g-1 dried BSG), the generation of inhibitors in such scenarios likely affected PHA production compared with the process run without pretreatment (direct enzymatic hydrolysis of BSG). Thus, the maximum PHA accumulation from BSG hydrolysates was found in the reference case with 0.31 ± 0.02 g PHA per g cell dried weight, corresponding to 1.13 ± 0.06 g L-1 and a PHA yield of 23 ± 1 mg g-1 BSG. It was also found that C. necator presented the highest PHA accumulation of the tested strains followed closely by B. cepacia, reaching their maxima at 48 h. Although BSG has been used as a source for other bioproducts, these results show the potential of this by-product as a no-cost raw material for producing PHAs in a waste valorization and circular economy scheme.

The present study focuses on sustainable production of biodegradable polymers by Cupriavidus necator DSMZ 545 using glycerol as substrate. The batch growth and biopolymer production kinetics were established in a 7-L bioreactor, which resulted in a total biomass of 8.88 g L–1 and poly(3-hydroxybutyrate) (PHB) accumulation of 6.76 g L–1. The batch kinetic and independently acquired substrate inhibition data were then used to develop a mathematical model for PHB production process. This was eventually used to design different nutrient feeding strategies under constant feed rate, decreasing feed rate, and pseudo steady state of substrate (glycerol) to optimize the PHB production during fed-batch cultivation. Among all the fed-batch cultivation strategies, the highest PHB accumulation and productivity of 13.12 g L–1 and 0.27 g L–1 h–1, respectively, was achieved in fed-batch bioreactor cultivation where a pseudo steady state with respect to glycerol was maintained. This work is licensed under a Creative Commons Attribution 4.0 International License.

LysR-type transcription regulators (LTTRs) comprise one of the largest families of transcriptional regulators in bacteria. They are typically homo-tetrameric proteins and interact with promoter DNA of ~ 50-60 bp. Earlier biochemical studies have suggested that LTTR binding to promoter DNA bends the DNA and, upon inducer binding, the bend angle of the DNA is reduced through a quaternary structure change of the tetrameric LTTR, leading to the activation of transcription. To date, crystal structures of full-length LTTRs, DNA-binding domains (DBD) with their target DNAs, and the regulatory domains with and without inducer molecules have been reported. However, these crystal structures have not provided direct evidence of the quaternary structure changes of LTTRs or of the molecular mechanism underlying these changes. Here, we report the first crystal structure of a full-length LTTR, CbnR, in complex with its promoter DNA. The crystal structure showed that, in the absence of bound inducer molecules, the four DBDs of the tetrameric CbnR interact with the promoter DNA, bending the DNA by ~ 70°. Structural comparison between the DNA-free and DNA-bound forms demonstrates that the quaternary structure change of the tetrameric CbnR required for promoter region-binding arises from relative orientation changes of the three domains in each subunit. The mechanism of the quaternary structure change caused by inducer binding is also discussed based on the present crystal structure, affinity analysis between CbnR and the promoter DNA, and earlier mutational studies on CbnR. DATABASE: Atomic coordinates and structure factors for the full-length Cupriavidus necator NH9 CbnR in complex with promoter DNA are available in the Protein Data Bank under the accession code 7D98.

Poly (3-hydroxybutyrate) (PHB) is a good alternative to petroleum-based plastics due to its biodegradable and biocompatible properties. In the present work, Cupriavidus necator ATCC 25207 was used for the first time to produce PHB using fructose, glucose, and acid or enzyme hydrolyzed molasses, a cheap carbon source. The bacterium produced highest PHB with 4.99 g/L, 3.94 g/L, and 15.28 g/L using fructose, glucose, and acid hydrolyzed molasses, respectively. Sulfuric acid and invertase treated molasses yielded 1288% and 529% more PHB than untreated molasses. In addition, acid treated molasses resulted in 151% more PHB but 34.04% less cell growth than enzyme hydrolyzed molasses. This novel finding could have applications in fermentations using molasses in growth or production media. The utilization of glucose by the bacterium was increased by 67.03% through spontaneous mutagenesis. The characterizations of the produced polymers were carried out using FTIR, NMR, XRD, DSC, TGA, and GPC. The molecular weights of PHB samples from acid hydrolyzed molasses and fructose are 3.84 $$\times $$ 105 and 1.43 $$\times $$ 106 g/mol, respectively. This study shows that C. necator ATCC 25207 has a potential to be used in PHB production using acid hydrolyzed molasses.

An astonishing variety of functions has been attributed to polyphosphate (polyP) in prokaryotes. Besides being a reservoir of phosphorus, functions in exopolysaccharide formation, motility, virulence and in surviving various forms of stresses such as exposure to heat, extreme pH, oxidative agents, high osmolarity, heavy metals and others have been ascribed to polyP. In this contribution, we will provide a historical overview on polyP, will then describe the key proteins of polyP synthesis, the polyP kinases, before we will critically assess of the underlying data on the multiple functions of polyP and provide evidence that – with the exception of a P-storage-function – most other functions of polyP are not relevant for survival of Ralstonia eutropha, a biotechnologically important beta-proteobacterial species.

Oil extracted from spent coffee grounds (SCG) [yield 16.8 % (w/w)] was discovered to be a highly suitable carbon substrate for the biosynthesis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3 HV)] copolymers by Cupriavidus necator DSM 545 in the absence of any traditional 3 HV precursors. Cells cultivated in a 3 L bioreactor (batch) reached a total biomass concentration of 8.9 g L−1 with a P(3HB-co-3 HV) (6.8 mol% 3 HV) content of 89.6 % (w/w). In contrast, cells grown on sunflower oil reached a total biomass concentration of 9.4 gL−1 with a P(3HB-co-3 HV) (0.2 mol% 3 HV) content of 88.1 % (w/w). It is proposed that the organism could synthesize 3 HV monomers from succinyl CoA, an intermediate of the tricarboxylic acid (TCA) cycle, via the succinate-propionate metabolic pathway.

Chemolithoautotrophic bacterium Ralstonia eutropha is a versatile host for production of various useful compounds including polyhydroxyalkanoates (PHAs) under both heterotrophic and autotrophic conditions. In this bacterium, Calvin–Benson–Bassham (CBB) cycle is functional even under heterotrophic conditions on sugars and reutilizes CO2 emitted through sugar metabolisms into PHA, leading to increase in yield of the storage polyester. This study focused on isopropanol production from glucose by engineered strains of R. eutropha. The isopropanol-producing strains were constructed by introduction of codon-optimized genes of acetoacetate decarboxylase (adc) and primary-secondary alcohol dehydrogenase (adh) from clostridia into glucose-utilizing and PHA-negative (ΔphaC1) strain of R. eutropha. Several genetic modifications showed that high expression of the isopropanol synthesis genes by using a strong synthetic promoter and deletion of NAD+-dependent (S)-3-hydroxybutyryl-CoA dehydrogenase genes (paaH1 and had) in addition to NADPH-dependent acetoacetyl-CoA reductase genes (phaB1 and phaB3) were effective for improving isopropanol production with low by-production of acetone. Isopropanol titer of 4.13 g/L was achieved by two-stage cultivation of the strain IP-007/pBj5c2-adh-adc, corresponding to overall yield of 0.6 mol mol-glucose−1. The fixation of sugar-derived CO2 during isopropanol synthesis was evaluated by 13C-labelling of the isopropanol produced from [1–13C]-glucose. The 13C-abundance in isopropanol synthesized by the engineered strain was significantly increased up to 4.8%, demonstrating actual reassimilation of CO2 emitted from glucose moiety by decarboxylation and potential contribution towards increase in the carbon yield of isopropanol on glucose.

The study addresses the growth of the wild-type strain Cupriavidus necator B-10646 and synthesis of polyhydroxyalkanoates by this strain on media containing plant oils with different compositions of fatty acids: palm, Siberian oilseed, and refined and unrefined sunflower seed oils. The study showed that the best carbon substrate was palm oil. Comparison of fatty acid compositions of the starting oils and unutilized residual substrates showed that C. necator B-10646 cells consumed the fatty acids from palm oil evenly while in experiments with other oils, they utilized polyenoic fatty acids first. Higher production parameters of the culture were obtained by preparation of emulsified oil medium using Tween 80 and sodium cocoyl glutamate as emulsifiers. All polyhydroxyalkanoate specimens were terpolymers that contained 3-hydroxybutyrate as the major component and minor amounts of 3-hydroxyvalerate (0.9–1.9 mol%) and 3-hydroxyhexanoate (0.5–1.1 mol%). Molecular weight of polyhydroxyalkanoate specimens depended on the type of plant oil and emulsifier.

The acyl-CoA dehydrogenase (FadE) and (R)-specific enoyl-CoA hydratase (PhaJ) are functionally related to the degradation of fatty acids and the synthesis of polyhydroxyalkanoates (PHAs). To verify this, a recombinant Cupriavidus necator H16 harboring the plasmid -pMPJAS03- with fadE from Escherichia coli strain K12 and phaJ1 from Pseudomonas putida strain KT2440 under the arabinose promoter (araC-PBAD) was constructed. The impact of co-expressing fadE and phaJ genes on C. necator H16/pMPJAS03 maintaining the wild-type synthase on short-chain-length/medium-chain-length PHA formation from canola or avocado oil at different arabinose concentrations was investigated. The functional activity of fadEE.c led to obtaining higher biomass and PHA concentrations compared to the cultures without expressing the gene. While high transcriptional levels of phaJ1P.p, at 0.1% of arabinose, aid the wild-type synthase to polymerize larger-side chain monomers, such as 3-Hydroxyoctanoate (3HO) and 3-Hydroxydecanoate (3HD). The presence of even small amounts of 3HO and 3HD in the co-polymers significantly depresses the melting temperature of the polymers, compared to those composed of pure 3-hydroxybutyrate (3HB). Our data presents supporting evidence that the synthesis of larger-side chain monomers by the recombinant strain relies not only upon the affinity of the wild-type synthase but also on the functionality of the intermediate supplying enzymes.

Objective The rapid accumulation of crude-oil based plastics in the environment is posing a fundamental threat to the future of mankind. The biodegradable and bio-based polyhydroxyalkanoates (PHAs) can replace conventional plastics, however, their current production costs are not competitive and therefore prohibiting PHAs from fulfilling their potential. Results Different low-quality animal by-products, which were separated by thermal hydrolysis into a fat-, fat/protein-emulsion- and mineral-fat-mixture- (material with high ash content) phase, were successfully screened as carbon sources for the production of PHA. Thereby, Ralstonia eutropha Re2058/pCB113 accumulated the short- and medium-chain-length copolymer poly(hydroxybutyrate-co-hydroxyhexanoate) [P(HB-co-HHx)]. Up to 90 wt% PHA per cell dry weight with HHx-contents of 12–26 mol% were produced in shake flask cultivations. Conclusion In future, the PHA production cost could be lowered by using the described animal by-product streams as feedstock. Graphical abstract

Coupling recent advancements in genetic engineering of diverse microbes and gas-driven fermentation provides a path towards sustainable commodity chemical production. Cupriavidus necator H16 is a suitable species for this task because it effectively utilizes H2 and CO2 and is genetically tractable. Here, we demonstrate the versatility of C. necator for chemical production by engineering it to produce three products from CO2 under lithotrophic conditions: sucrose, polyhydroxyalkanoates (PHAs), and lipochitooligosaccharides (LCOs). We engineered sucrose production in a co-culture system with heterotrophic growth 30 times that of WT C. necator. We engineered PHA production (20-60% DCW) and selectively altered product composition by combining different thioesterases and phaCs to produce copolymers directly from CO2. And, we engineered C. necator to convert CO2 into the LCO, a plant growth enhancer, with titers of ~1.4 mg/L-equivalent to yields in its native source, Bradyrhizobium. We applied the LCOs to germinating seeds as well as corn plants and observed increases in a variety of growth parameters. Taken together, these results expand our understanding of how a gas-utilizing bacteria can promote sustainable production.

The valorization of agricultural waste is a sustainable way of how to utilize renewable resources wisely. Grape pomace is a by-product of the manufacturing of the must. The potential of Cupriavidus necator, Halomonas halophila and Halomonas organivorans to produce poly(3-hydroxybutyrate) (PHB) by using oil and fermentable sugars derived from grape pomace has been studied. C. necator proved to be the best producer of PHB when utilizing grape pomace extract as a carbon source. After 29.5 h of fermentation of C. necator in 2-L bioreactor, PHB titers reached 8.3 g l−1 and 63 % PHB content in bacteria cell dry mass. The average molecular weight and the polydispersity of accumulated polymer was 512.2 kDa and 1.2, respectively. In addition to fermentable sugars, this work indicates that oil, pigments, phenolics, lignin and cellulose can be isolated from seeds and the rest of the grape pomace to support the cascading utilization of agricultural waste and natural valuable resources recovery.

Films were prepared from 2% solutions of biodegradable poly-3-hydroxybutyrate [P(3HB)] and investigated. The polymer was synthesized by the Cupriavidus necator B-10646 bacterium cultivated using various carbon sources (glucose and glycerol of different degrees of purity, containing 0.3 to 17.93% impurities). Glycerol as the substrate influenced molecular-weight properties and crystallinity of the polymer without affecting its temperature characteristics. The P(3HB) specimens synthesized from glycerol had reduced Mw (300–400 kDa) and degree of crystallinity (50–55%) compared to the specimens synthesized from glucose (860 kDa and 76%, respectively). The low-crystallinity P(3HB) specimens, regardless of the degree of purity of glycerol, produced a beneficial effect on the properties of polymer films, which had a better developed folded surface and increased hydrophilicity. The values of the highest roughness (Ra) of the films synthesized from glycerol were 1.8 to 4.0 times lower and the water angles 1.4–1.6 times smaller compared to the films synthesized from glucose (71.75 nm and 87.4°, respectively). Those films performed better as cell scaffolds: the number of viable NIH fibroblasts was 1.7–1.9 times higher than on polystyrene (control) or films of P(3HB) synthesized from glucose.

Waste paper as a resource for polyhydroxyalkanoate (PHA) production through anaerobic digestion is a low-cost strategy to produce bioplastic. In this study, volatile fatty acids (VFAs) produced from waste paper, one of the significant constituents of municipal solid waste, was utilized as a feedstock for polyhydroxyalkanoate (PHA) production. PHA production from synthetic VFAs by Cupriavidus necator was initially optimized under different VFAs concentrations, VFAs ratios, and nitrogen sources. VFAs concentration of 10 g/L, 5:1:4 ratio of acetic, propionic, and butyric acids (HAc:HPr:HBu) and NaNO3 as nitrogen source were considered the optimum conditions with 56.98% PHA and 0.31 g/g yield. Anaerobic digestion of shredded office paper (OP/S) produced the maximum VFAs (521.50 mg/L) after 15 days of incubation and were utilized for PHA synthesis. Almost 2.24-fold increase in the yield of PHA was achieved with limited nutrient medium compared to nutrient contained medium with a PHA content of 53.50 and 23.88%, respectively. PHA production using anaerobic effluent of waste paper is a promising approach where a series of pretreatment processes, the expensive enzymatic hydrolysis, and detoxification were no longer required, suggesting an environmentally friendly way of biopolymer production.

Among the various types of polyhydroxyalkanoate (PHA), poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] [P(3HB-co-3HHx)] has a high potential to serve as commercial bioplastic due to its striking resemblance to petroleum-based plastics. In this study, five different genotypes of Cupriavidusnecator transformants harbouring the phaCBP-M-CPF4 gene (including PHB¯4/pBBR1-CBP-M-CPF4) were developed to evaluate the efficiency of 3HHx monomer incorporation. The fraction of 3-hydroxyhexanoate (3HHx) monomer that was incorporated into the PHA synthesized by these C. necator transformants using palm oil as the sole carbon source, was examined. Overall, co-expression of enoyl-CoA hydratase gene (phaJ1) from Pseudomonas aeruginosa, along with PHA synthase (PhaC), increased the 3HHx composition in the PHA copolymer. The differences in the enzyme activities of β-ketothiolase (PhaACn) and NADPH-dependent acetoacetyl-CoA reductase (PhaBCn) of the C. necator mutant hosts used in this study, were observed to alter the 3HHx composition and molecular weight of the PHA copolymer produced. The 3HHx fractions in the P(3HB-co-3HHx) produced by these C. necator transformants ranged between 1 and 18 mol%, while the weight-average molecular weight ranged from 0.7 × 106 to 1.8 × 106 Da. PhaCBP-M-CPF4 displayed a typical initial lag-phase and a relatively low synthase activity in the in vitro enzyme assay, which is thought to be the reason for the higher molecular weights of PHA obtained in this study.

Hydrolysate cassava peel obtained from agro-industrial residues was used as a carbon source in the production of polyhydroxyalkanoates (PHAs) by Cupriavidus necator. The optimum culture conditions were pH 9, a C/N ratio of 11, and a C/P ratio of 7. Characterization of the PHA polymers by FTIR, DSC and GC–MS revealed copolymers consisting of 3HB and 3HV monomers with melting temperatures (Tm) between 100 and 150 °C. Random and aligned microfibers with average diameters of 1.56 ± 0.41 μm and 1.72 ± 0.52 μm, respectively, were produced by electrospinning. In general, it was possible to obtain PHAs from cassava peel, and PHAs could be applied to produce fibers by electrospinning. The above strategy is an alternative use of agro-industrial cassava waste and opens up potential applications in the manufacture of biopolymers for their use in industry and biomedicine.

Significance The Calvin cycle is the most important carbon fixation pathway in the biosphere. However, its carboxylating enzyme Rubisco also accepts oxygen, thus producing 2-phosphoglycolate. Phosphoglycolate salvage pathways were extensively studied in photoautotrophs but remain uncharacterized in chemolithoautotrophs using the Calvin cycle. Here, we study phosphoglycolate salvage in the chemolithoautotrophic model bacterium Cupriavidus necator H16. We demonstrate that this bacterium mainly reassimilates 2-phosphoglycolate via the glycerate pathway. Upon disruption of this pathway, a secondary route, which we term the malate cycle, supports photorespiration by completely oxidizing 2-phosphoglycolate to CO2. While the malate cycle was not previously known to metabolize 2-phosphoglycolate in nature, a bioinformatic analysis suggests that it may support phosphoglycolate salvage in diverse chemoautotrophic bacteria., Carbon fixation via the Calvin cycle is constrained by the side activity of Rubisco with dioxygen, generating 2-phosphoglycolate. The metabolic recycling of phosphoglycolate was extensively studied in photoautotrophic organisms, including plants, algae, and cyanobacteria, where it is referred to as photorespiration. While receiving little attention so far, aerobic chemolithoautotrophic bacteria that operate the Calvin cycle independent of light must also recycle phosphoglycolate. As the term photorespiration is inappropriate for describing phosphoglycolate recycling in these nonphotosynthetic autotrophs, we suggest the more general term “phosphoglycolate salvage.” Here, we study phosphoglycolate salvage in the model chemolithoautotroph Cupriavidus necator H16 (Ralstonia eutropha H16) by characterizing the proxy process of glycolate metabolism, performing comparative transcriptomics of autotrophic growth under low and high CO2 concentrations, and testing autotrophic growth phenotypes of gene deletion strains at ambient CO2. We find that the canonical plant-like C2 cycle does not operate in this bacterium, and instead, the bacterial-like glycerate pathway is the main route for phosphoglycolate salvage. Upon disruption of the glycerate pathway, we find that an oxidative pathway, which we term the malate cycle, supports phosphoglycolate salvage. In this cycle, glyoxylate is condensed with acetyl coenzyme A (acetyl-CoA) to give malate, which undergoes two oxidative decarboxylation steps to regenerate acetyl-CoA. When both pathways are disrupted, autotrophic growth is abolished at ambient CO2. We present bioinformatic data suggesting that the malate cycle may support phosphoglycolate salvage in diverse chemolithoautotrophic bacteria. This study thus demonstrates a so far unknown phosphoglycolate salvage pathway, highlighting important diversity in microbial carbon fixation metabolism.

Enzymatic conversion of nitriles to carboxylic acids by nitrilases has gained significance in the green synthesis of several pharmaceutical precursors and fine chemicals. Although nitrilases from several sources have been characterized, there exists a scope for identifying broad spectrum nitrilases exhibiting higher substrate tolerance and better thermostability to develop industrially relevant biocatalytic processes. Through genome mining, we have identified nine novel nitrilase sequences from bacteria and evaluated their activity on a broad spectrum of 23 industrially relevant nitrile substrates. Nitrilases from Zobellia galactanivorans, Achromobacter insolitus and Cupriavidus necator were highly active on varying classes of nitriles and applied as whole cell biocatalysts in lab scale processes. Z. galactanivorans nitrilase could convert 4-cyanopyridine to achieve yields of 1.79 M isonicotinic acid within 3 h via fed-batch substrate addition. The nitrilase from A. insolitus could hydrolyze 630 mM iminodiacetonitrile at a fast rate, effecting 86 % conversion to iminodiacetic acid within 1 h. The arylaliphatic nitrilase from C. necator catalysed enantioselective hydrolysis of 740 mM mandelonitrile to (R)-mandelic acid in 4 h. Significantly high product yields suggest that these enzymes would be promising additions to the suite of nitrilases for upscale biocatalytic application.

CO2 has been electrochemically reduced to the intermediate formate, which was subsequently used as sole substrate for the production of the polymer polyhydroxybutyrate (PHB) by the microorganism Cupriavidus necator. Faradaic efficiencies (FE) up to 54 % have been reached with Sn‐based gas‐diffusion electrodes in physiological electrolyte. The formate containing electrolyte can be used directly as drop‐in solution in the following biological polymer production by resting cells. 56 mg PHB L−1 and a ratio of 34 % PHB per cell dry weight were achieved. The calculated overall FE for the process was as high as 4 %. The direct use of the electrolyte as drop‐in media in the bioconversion enables simplified processes with a minimum of intermediate purification effort. Thus, an optimal coupling between electrochemical and biotechnological processes can be realized., Drop of a life: This study presents the concept of a drop‐in electrolysis: CO2 has been electrochemically reduced to the intermediate formate and was subsequently used as sole substrate for the production of the polymer polyhydroxybutyrate (PHB) by the microorganism Cupriavidus necator without downstream processes to combine both conversions.

Nonionic surfactant-based cloud point extraction of polyhydroxyalkanoate from fermentation broth was implemented in a modified rotating disc contactor. The effect of rotor speed and phase flowrates...

Polyhydroxyalkanoates (PHAs) are polymers of hydroxy derived fatty acids synthesized by various organisms. These polymers can be effectively used as a biocompatible and biodegradable alternative to the chemically synthesized plastic. PHA cost, however, still limits the increase in PHA production. One of the ways to reduce PHA cost is to use inexpensive carbon sources such as fatty acids. The aim of this work was to study the effect of various concentrations of oleic acid (5-50 g/L) on the growth of the Cupriavidus necator B-10646 bacterium, polymer synthesis and properties. Cells were grown for 48 h in Schlegel mineral medium at 30°C and 200 rpm on an incubator shaker. The content and the composition of the polymer were determined by chromatography of fatty acid methyl esters using a chromatographymass spectrometer. The molecular weight distribution of the polymer was determined using gel permeation chromatography. Thermal analysis was performed using a differential scanning calorimeter. The maximum yield of biomass (6.4-6.7 g/L) and the highest polymer content (64- 71% of the weight of dry biomass) were obtained from 10-20 g/L of oleic acid after 48 hours of cultivation. In addition to 3-hydroxybutyrate, which is the dominant monomer (more than 98 mol.%), 3-hydroxyvalerate (0.7-1.7 mol.%) and 3-hydroxyhexanoate (0.1-0.4 mol.%) were identified in the polymer synthesized by the bacterium. As the concentration of oleic acid was increased, both the weight average and the number average molecular weights decreased (from 803 to 381 kDa and from 292 to 94 kDa, respectively) but polydispersity of the polymers increased (from 2.8 to 4.1). The results obtained in the present study provide the basis for the next stage of scaling up the process of PHA synthesis from oleic acid

Microbial polyhydroxyalkanoates (PHAs) are biopolyesters produced by microorganisms as intracellular granules under nutrient stress. Due to non-toxic and biodegradable behavior these polyesters are a sustainable source of wide range of biomaterials such as bioplastics. As a result of excellent polymeric properties such as melting temperatures (Tm), glass transition temperature (Tg), crystallinity, Young’s modulus and stress to break ratio these polyesters are capable of replacing the synthetic plastics. Bioplastics produced using PHAs as biomass source can be used for packaging material and disposable products on the other hand biofuels can also be generated using PHAs. PHAs find countless applications in industry, agriculture, pharmaceuticals and health. A large number of bacterial, microalgal and fungal species can produce these polyesters. Bacterial species such as Bacillus megaterium, Pseudomonas aeruginosa, P. oleovorans, P. stutzeri and Cupriavidus necator are some highly studied microorganisms for PHA production. This review summarizes the most important aspects of PHAs, crystalline and granular structure of PHA biosynthesizing genes and their relevant proteins. Thermal and physical properties, sources, extraction, purification methods of PHAs are briefly discussed. Applications of PHAs, phylogenetic analysis of Pseudomonas sp. in term of its PHAs synthesizing genes, future prospects and possible outcomes are discussed.

Polyhydroxyalkanoates (PHA) are biopolymer synthesized as storage granules by microbes in the cell’s cytoplasm under excess carbon and limited nitrogen conditions. This study aims to examine the production and optimization of PHA from Ceiba pentandra oil, a non-edible feedstock, by Cupriavidus necator. Response surface methodology was used to optimize the concentrations of carbon, nitrogen, and inoculum for the production of PHA. To improve the physical, mechanical, and thermal properties of PHA, it was blended with polylactic acid (PLA) which possesses high bio-compatibility and bio-absorbability. Furthermore, batch mode cultivation of PHA in a 3-L bioreactor was performed under the optimized conditions (Ceiba pentandra oil—17.13 g/L, urea—1.34 g/L, and inoculum—53.42 mL/L), and 8.51 g/L (0.47 g PHA/g of Ceiba pentandra oil) of PHA product was obtained. The PHA was characterized by FTIR and the presence of functional groups such as C=O, OH, and CH were observed. 1H and 13C NMR spectroscopy revealed the existence of hydroxy valerate (HV) and hydroxybutyrate (HB), and maximal decomposition temperature was identified to be 217.7 °C from TGA analysis. Therefore, Ceiba pendantra oil appears to be an attractive alternate carbon source for PHA production.

Early Access; International audience; A methodology for plasmid expression level monitoring of eGFP expression suitable for dynamic processes was assessed during fermentation. This technique was based on the expression of a fluorescent biosensor (eGFP) encoded on a recombinant plasmid coupled to single-cell analysis. Fluorescence intensity at single-cell level was measured by flow cytometry. We demonstrated that promoter evaluation based on single-cell analysis versus classic global analysis brings valuable insights. Single-cell analysis pointed out the fact that intrinsic fluorescence increased with the strength of the promoter up to a threshold. Beyond that, cell permeability increases to excrete the fluorescent protein in the medium. The metabolic load due to the increase in the eGFP production in the case of strong constitutive promoters leads to slower growth kinetics compared with plasmid-free cells. With the strain Cupriavidus necator Re2133, growth rate losses were measured from 3% with the weak constitutive promoter P-lac to 56% with the strong constitutive promoter P-j5. Through this work, it seems crucial to find a compromise between the fluorescence intensity in single cells and the metabolic load; in our conditions, the best compromise found was the weak promoter P-lac. The plasmid expression level monitoring method was tested in the presence of a heterogeneous population induced by plasmid-curing methods. For all the identified subpopulations, the plasmid expression level heterogeneity was significantly detected at the level of fluorescence intensity in single cells. After cell sorting, growth rate and cultivability were assessed for each subpopulation. In conclusion, this eGFP biosensor makes it possible to follow the variations in the level of plasmid expression under conditions of population heterogeneity. Key Points center dot Development of a plasmid expression level monitoring method at the single-cell level by flow cytometry. center dot Promoter evaluation by single-cell analysis: cell heterogeneity and strain robustness. center dot Reporter system optimization for efficient subpopulation detection in pure cultures.

International audience; A bioreactor was designed to provide high gas mass transfer to reach cell and product titres in the g L-1 level from CO2 for realistic, laboratory scale, engineered autotrophic strain evaluation. The design was based on independent CO2, H-2 and air inputs and the ability to operate at high pressures. The bioreactor configuration and cultivation strategy enabled growth of Cupriavidus necator strains for long periods, to reach over 3 g L-1 dry cell weight. No negative impact of the high pressure was observed on viability of the strains up to more than 4 bar overpressure. The cultivation was then carried out using an engineered isopropanol producing strain; in this case, 3.5 g L-1 isopropanol was obtained from CO2 as the sole carbon source. This is the first reported demonstration of a successful production from engineered bacteria of product in the g L-1 range on CO2 , raising the prospect of future development of CO2-based bioprocesses.

Hydrogenases (H2 ase) catalyze the oxidation of dihydrogen and the reduction of protons with remarkable efficiency, thereby attracting considerable attention in the energy field due to their biotechnological potential. For this simple reaction, [NiFe] H2 ase has developed a sophisticated but intricate mechanism with the heterolytic cleavage of dihydrogen, where its Ni-Fe active site exhibits various redox states. Recently, new spectroscopic and crystal structure studies of [NiFe] H2 ases have been reported, providing significant insights into the catalytic reaction mechanism, hydrophobic gas-access tunnel, proton-transfer pathway, and electron-transfer pathway of [NiFe] H2 ases. In addition, [NiFe] H2 ases have been shown to play an important role in biofuel cell and solar dihydrogen production. This concept provides an overview of the biocatalytic reaction mechanism and biochemical application of [NiFe] H2 ases based on the new findings.

Significance We constructed simple cells (SimCells) whose native chromosomes were removed and replaced by synthetic genetic circuits. The chromosome-free SimCells can process designed DNA and express target genes for an extended period of time. The strategy of SimCell generation is applicable to most bacteria, creating a universal platform for reprogramming bacteria. We demonstrated that SimCells can be designed as safe agents for bacterial therapy through synthesis and delivery of a potent anticancer drug against a variety of cancer cell lines. This showed that the nonreplicating and programmable property of SimCells is advantageous for applications in sensitive environments. The results of this work will both improve our understanding of natural living systems and simultaneously lay the foundations for future advances in synthetic biology., A type of chromosome-free cell called SimCells (simple cells) has been generated from Escherichia coli, Pseudomonas putida, and Ralstonia eutropha. The removal of the native chromosomes of these bacteria was achieved by double-stranded breaks made by heterologous I-CeuI endonuclease and the degradation activity of endogenous nucleases. We have shown that the cellular machinery remained functional in these chromosome-free SimCells and was able to process various genetic circuits. This includes the glycolysis pathway (composed of 10 genes) and inducible genetic circuits. It was found that the glycolysis pathway significantly extended longevity of SimCells due to its ability to regenerate ATP and NADH/NADPH. The SimCells were able to continuously express synthetic genetic circuits for 10 d after chromosome removal. As a proof of principle, we demonstrated that SimCells can be used as a safe agent (as they cannot replicate) for bacterial therapy. SimCells were used to synthesize catechol (a potent anticancer drug) from salicylic acid to inhibit lung, brain, and soft-tissue cancer cells. SimCells represent a simplified synthetic biology chassis that can be programmed to manufacture and deliver products safely without interference from the host genome.

Phenoxyalkanoic acid (PAA) herbicides are mainly metabolized by microorganisms in soils, but the degraders that perform well under alkaline environments are rarely considered. Herein, we report Cupriavidus oxalaticus strain X32, which showed encouraging PAA-degradation abilities, PAA tolerance, and alkali tolerance. In liquid media, without the addition of exogenous carbon sources, X32 could completely remove 500 mg/L 2,4-dichlorophenoxyacetic acid (2,4-D) or 4-chloro-2-methylphenoxyacetic acid within 3 days, faster than that with the model degrader Cupriavidus necator JMP134. Particularly, X32 still functioned at pH 10.5. Of note, with X32 inoculation, we observed 2,4-D degradation in soils and diminished phytotoxicity to maize (Zea mays). Furthermore, potential mechanisms underlying PAA biodegradation and alkali tolerance were then analyzed by whole-genome sequencing. Three modules of tfd gene clusters involved in 2,4-D catabolism and genes encoding monovalent cation/proton antiporters involved in alkali tolerance were putatively identified. Thus, X32 could be a promising candidate for the bioremediation of PAA-contaminated sites, especially in alkaline surroundings.

Tuna condensate, an organic-rich by-product from the tuna canning industry, was assessed as a substrate for polyhydroxyalkanoate (PHA) production using Cupriavidus necator TISTR 1095. The effect of cultivation parameters on PHA accumulation was studied, including substrate concentration, carbon to nitrogen (C/N) ratio, initial pH-value control and fermentation strategies. For the bacterium, a biomass of 3.8 ± 0.1 g/L, PHA of 1.64 ± 0.1 g/L with PHA productivity of 0.027 g/L.h were obtained under batch cultivation using 100% tuna condensate with a C/N ratio of 88:1 and no control of pH. However, the PHA production was increased 1.3-fold when repeated-batch cultivation was applied. The highest biomass (7.5 ± 0.1 g/L) and PHA (3.8 ± 0.1 g/L) with 0.063 g/L.h of PHA productivity were achieved after the third cycle of repeated-batch cultivation. High chemical oxygen demand (COD) removal efficiency of 70% under the optimal condition was also demonstrated. The polymers generated by C. necator TISTR 1095 were characterised. The size of polymer granules was in the range of 0.7-0.8 μm. The polymer produced in the optimal medium under batch and repeated-batch cultivation was identified as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with a 20 mol% of 3-hydroxyvalerate. The molecular mass (Mn) and polydispersity of the polymer were 2 × 106 Da and 2.5, respectively. The results demonstrated that tuna condensate could be used as a cheap substrate for PHA production on an industrial scale.

Due to their advantageous properties, polyhydroxyalkanoates are a promising alternative to conventional petroleum-based plastics. Currently, high production costs in upstream and downstream have to be reduced to make the plastic material competitive. As most of the PHA producing organisms metabolize a wide range of substrates upstream cost can be reduced using carbon rich waste material. For large scale application sophisticated control approaches based on mathematical models can help to further increase the productivity. In the present work, a hybrid cybernetic model approach is presented, which is adapted to experiments with fructose and acetate feeding, respectively. Furthermore, the validated model was used to qualitatively predict the effect of co-substrate feeding.

A novel polyhydroxyalkanoate (PHA)-producing bacterium, Jeongeupia sp. USM3 (JCM 19920) was isolated from the limestone soil at Gua Tempurung, Perak, Malaysia. This is the first report on the complete genome sequence for the genus Jeongeupia. This genome consists of a circular chromosome with a size of 3,788,814 bp and contains 3557 genes. Two PHA synthase (phaC) genes encoding for the key enzyme in the polymerization of PHA monomers and other PHA-associated genes were identified from the genome. Phylogenetic analysis of the PhaC protein sequences has revealed that both PhaC1 and PhaC2 of Jeongeupia sp. USM3 are categorized as Class I PHA synthases with 56% similarity to each other. Both of the PHA synthase genes of this isolate were cloned and heterologously expressed in a PHA mutant strain Cupriavidus necator PHB−4. The ability of the transformants to accumulate PHA showed that both PhaC1 and PhaC2 were functional.

Process stability is a key operational issue when operating dark fermentation with mixed microbial cultures for hydrogen production. This study aimed at mitigating the instability of hydrogen production by separately adding exogenous pure strains suspected to have key roles in fermentative cultures. Among them, Clostridium acetobutylicum, Clostridium pasteurianum and Lactobacillus bulgaris which became predominant within the mixed culture strongly reduced the spectrum of produced metabolites and H2 production variability. Interestingly, Escherichia coli and Cupriavidus necator, which remained in minor abundance, maintained a high and stable H2 production while lowering the metabolic variability. 16S rRNA revealed that this could correlate to a simplification of the microbial diversity and the non-emergence of spore-forming competitors such as Sporolactobacillus sp. These results illustrate the potential beneficial role of minor OTUs as keystone species on H2-producing complex ecosystem and support the possibility of using them to engineer the ecosystem and maintain high and stable performances.

Cupriavidus necator H16 is an ideal strain for polyhydroxybutyrate (PHB) production from CO(2). Low-oxygen stress can induce PHB synthesis in C. necator H16 while reducing bacterial growth under chemoautotrophic culture. The optimum growth and PHB synthesis of C. necator H16 cannot be achieved simultaneously, which restricts PHB production. The present study was initiated to address the issue through comparative transcriptome and gene function analysis. First, the comparative transcriptome of C. necator H16 chemoautotrophically cultured under low-oxygen stress and nonstress conditions was studied. Three types of genes were discovered to have differential levels of transcription: those involving PHB enzymatic synthesis, PHB granulation, and regulators. Under low-oxygen stress conditions, acetoacetyl-coenzyme A (CoA) reductase gene phaB2, PHB synthase gene phaC2, phasins genes phaP1 and phaP2, and regulator genes uspA and rpoN were upregulated 3.0-, 2.5-, 1.8-, 2.7-, 3.5-, and 1.6-fold, respectively. Second, the functions of upregulated genes and their applications in PHB synthesis were further studied. It was found that the overexpression of phaP1, phaP2, uspA, and rpoN can induce PHB synthesis under nonstress conditions, while phaB2 and phaC2 have no significant effect. Under the optimum conditions, the PHB percentage content in C. necator H16 was increased by 37.2%, 28.4%, 15.8%, and 41.0%, respectively, with overexpression of phaP1, phaP2, uspA, and rpoN, and the corresponding PHB production increased by 49.8%, 42.9%, 47.0%, and 77.5%, respectively, under nonstress chemoautotrophic conditions. Similar promotion by phaP1, phaP2, uspA, and rpoN was observed in heterotrophically cultured C. necator H16. The PHB percentage content and PHB production were increased by 54.4% and 103.1%, respectively, with the overexpression of rpoN under nonstress heterotrophic conditions. IMPORTANCE Microbial fixation of CO(2) is an effective way to reduce greenhouse gases. Some microbes, such as C. necator H16, usually accumulate PHB when they grow under stress. Low-oxygen stress can induce PHB synthesis when C. necator H16 is autotrophically cultured with CO(2), H(2), and O(2), while under stress, growth is restricted, and total PHB yield is reduced. Achieving the optimal bacterial growth and PHB synthesis at the same time is an ideal condition for transforming CO(2) into PHB by C. necator H16. The present study was initiated to clarify the molecular basis of low-oxygen stress promoting PHB accumulation and to realize the optimal PHB production by C. necator H16. Genes upregulated under nonstress conditions were identified through comparative transcriptome analysis and overexpression of phasin, and regulator genes were demonstrated to promote PHB synthesis in C. necator H16.

Many homologous genes encoding β-oxidation enzymes have been found in the genome of Cupriavidus necator H16 (synonym Ralstonia eutropha H16). By proteome analysis, the degradation of adipic acid was investigated and showed differences from the degradation of hexanoic acid. During β-oxidation of adipic acid, activation with coenzyme A (CoA) is catalyzed by the two-subunit acyl-CoA ligase encoded by B0198 and B0199. The operon is completed by B0200 encoding a thiolase catalyzing the cleavage of acetyl-CoA at the end of the β-oxidation cycle. C. necator ΔB0198-B0200 strain showed improved growth on adipic acid. Potential substitutes are B1239 for B0198-B0199 and A0170 as well as A1445 for B0200. A deletion mutant without all three thiolases showed diminished growth. The deletion of detected acyl-CoA dehydrogenase encoded by B2555 has an altered phenotype grown with sebacic acid but not adipic acid. With hexanoic acid, acyl-CoA dehydrogenase encoded by B0087 was detected on two-dimensional (2D) gels. Both enzymes are active with adipoyl-CoA and hexanoyl-CoA as substrates, but specific activity indicates a higher activity of B2555 with adipoyl-CoA. 2D gels, growth experiments, and enzyme assays suggest the specific expression of B2555 for the degradation of dicarboxylic acids. In C. necator H16, the degradation of carboxylic acids potentially changes with an increasing chain length. Two operons involved in growth with long-chain fatty acids seem to be replaced during growth on medium-chain carboxylic acids. Only two deletion mutants showed diminished growth. Replacement of deleted genes with one of the numerous homologous is likely. IMPORTANCE The biotechnologically interesting bacterium Cupriavidus necator H16 has been thoroughly investigated. Fifteen years ago, it was sequenced entirely and annotated (A. Pohlmann, W. F. Fricke, F. Reinecke, B. Kusian, et al., Nat Biotechnol 24:1257–1262, 2006, https://doi.org/10.1038/nbt1244). Nevertheless, the degradation of monocarboxylic fatty acids and dicarboxylic acids has not been elucidated completely. C. necator is used to produce value-added products from affordable substrates. One of our investigations' primary targets is the biotechnological production of organic acids with different and specific chain lengths. The versatile metabolism of carboxylic acids recommends C. necator H16 as a candidate for producing value-added organic products. Therefore, the metabolism of these compounds is of interest, and, for different applications in industry, understanding such central metabolic pathways is crucial.