Effects of plasticizer diisobutyl adipate on the Japanese medaka (Oryzias latipes) endocrine system.

Plasticizer pollution of the water environment is one of the world's most serious environmental issues. Phthalate plasticizers can disrupt endocrine function in vertebrates. Therefore, this study analyzed thyroid-related, reproduction-related, and estrogen-responsive genes in Japanese medaka (Oryzias latipes) to determine whether non-phthalate diisobutyl adipate (DIBA) plasticizer could affect endocrine hormone activity or not. Developmental toxicity during fish embryogenesis was also evaluated. At a concentration of 11.57 mg/l, embryonic exposure to DIBA increased the mortality rate. Although abnormal development, including body curvature, edema, and lack of swim bladder inflation, was observed at 3.54 and 11.57 mg/l DIBA, growth inhibition and reduced swimming performance were also observed. In addition, DIBA exposure increased the levels of thyroid-stimulating hormone beta-subunit (tshß) and deiodinase 1 (dio1) but decreased the levels of thyroid hormone receptor alpha (trα) and beta (trß). These results suggest that DIBA has thyroid hormone-disrupting activities in fish. However, kisspeptin (kiss1 and kiss2), gonadotropin-releasing hormone (gnrh1), follicle-stimulating hormone beta (fshß), luteinizing hormone beta (lhß), choriogenin H (chgH), and vitellogenin (vtg1) expression did not change dose-dependently in response to DIBA exposure, whereas gnrh2 and vtg2 expression was elevated. These results indicate that DIBA has low estrogenic activity and does not disrupt the endocrine reproduction system in fish. Overall, this is the first report indicating that non-phthalate DIBA plasticizer is embryotoxic and disrupt thyroid hormone activity in fish.

Claisen Condensation Reaction Mediated Pimelate Biosynthesis via the Reverse Adipate-Degradation Pathway and Its Isoenzymes.

Pimelic acid is an important seven-carbon dicarboxylic acid, which is broadly applied in various fields. The industrial production of pimelic acid is mainly through a chemical method, which is complicated and environmentally unfriendly. Herein, we found that pimelic acid could be biosynthesized by the reverse adipate-degradation pathway (RADP), a typical Claisen condensation reaction that could be applied to the arrangement of C-C bond. In order to strengthen the supply of glutaryl-CoA precursor, PA5530 protein was used to transport glutaric acid. Subsequently, we discovered that the enzymes in the BIOZ pathway are isoenzyme of the RADP pathway enzymes. By combining the isoenzymes of the two pathways, the titer of pimelic acid reached 36.7 mg ⋅ L-1 under the optimal combination, which was increased by 382.9 % compared with the control strain B-3. It was also the highest titer of pimelic acid biosynthesized by Claisen condensation reaction, laying the foundation for the production of pimelic acid and its derivatives.

Rational orthologous pathway and biochemical process engineering for adipic acid production using Pseudomonas taiwanensis VLB120.

Microbial bioprocessing based on orthologous pathways constitutes a promising approach to replace traditional greenhouse gas- and energy-intensive production processes, e.g., for adipic acid (AA). We report the construction of a Pseudomonas taiwanensis strain able to efficiently convert cyclohexane to AA. For this purpose, a recently developed 6-hydroxyhexanoic acid (6HA) synthesis pathway was amended with alcohol and aldehyde dehydrogenases, for which different expression systems were tested. Thereby, genes originating from Acidovorax sp. CHX100 and the XylS/Pm regulatory system proved most efficient for the conversion of 6HA to AA as well as the overall cascade enabling an AA formation activity of up to 48.6 ± 0.2 U gCDW-1. The optimization of biotransformation conditions enabled 96% conversion of 10 mM cyclohexane with 100% AA yield. During recombinant gene expression, the avoidance of glucose limitation was found to be crucial to enable stable AA formation. The biotransformation was then scaled from shaking flask to a 1 L bioreactor scale, at which a maximal activity of 22.6 ± 0.2 U gCDW-1 and an AA titer of 10.2 g L-1 were achieved. The principal feasibility of product isolation was shown by the purification of 3.4 g AA to a purity of 96.1%. This study presents the efficient bioconversion of cyclohexane to AA by means of a single strain and thereby sets the basis for an environmentally benign production of AA and related polymers such as nylon 6,6.

A facile process for adipic acid production in high yield by oxidation of 1,6-hexanediol using the resting cells of Gluconobacter oxydans.

BACKGROUND: Adipic acid (AA) is one of the most important industrial chemicals used mainly for the production of Nylon 6,6 but also for making polyurethanes, plasticizers, and unsaturated polyester resins, and more recently as a component in the biodegradable polyester poly(butylene adipate terephthalate) (PBAT). The main route for AA production utilizes benzene as feedstock and generates copious amounts of the greenhouse gas NO2. Hence, alternative clean production routes for AA from renewable bio-based feedstock are drawing increasing attention. We have earlier reported the potential of Gluconobacter oxydans cells to oxidize 1,6-hexanediol, a potentially biobased diol to AA. RESULTS: The present report involves a study on the effect of different parameters on the microbial transformation of 1,6-hexanediol to adipic acid, and subsequently testing the process on a larger lab scale for achieving maximal conversion and yield. Comparison of three wild-type strains of G. oxydans DSM50049, DSM2003, and DSM2343 for the whole-cell biotransformation of 10 g/L 1,6-hexanediol to adipic acid in batch mode at pH 7 and 30 °C led to the selection of G. oxydans DSM50049, which showed 100% conversion of the substrate with over 99% yield of adipic acid in 30 h. An increase in the concentrations of the substrate decreased the degree of conversion, while the product up to 25 g/L in batch and 40 g/L in fed-batch showed no inhibition on the conversion. Moreover, controlling the pH of the reaction at 5-5.5 was required for the cascade oxidation reactions to work. Cell recycling for the biotransformation resulted in a significant decrease in activity during the third cycle. Meanwhile, the fed-batch mode of transformation by intermittent addition of 1,6-hexanediol (30 g in total) in 1 L scale resulted in complete conversion with over 99% yield of adipic acid (approximately 37 g/L). The product was recovered in a pure form using downstream steps without the use of any solvent. CONCLUSION: A facile, efficient microbial process for oxidation of 1,6-hexanediol to adipic acid, having potential for scale up was demonstrated. The entire process is performed in aqueous medium at ambient temperatures with minimal greenhouse gas emissions. The enzymes involved in catalyzing the oxidation steps are currently being identified.

Sudden death of a 2-year-old child due to alpha-ketoadipic aciduria.

Alpha-ketoadipic acid is one of the metabolic intermediates of lysine and tryptophan, and it is known as the biochemical hallmark of alpha-ketoadipic aciduria (α-KA). α-KA is a rare autosomal recessive disorder. Its pathophysiology is reduced alpha-ketoadipic acid dehydrogenase activity, and that makes it difficult to metabolize lysine and tryptophan. The symptoms of this disease are multiple, e.g., psychomotor retardation, epilepsy, and ataxia, and it can even be asymptomatic. We present a case of sudden death in a 2-year-old boy with alpha-ketoadipic aciduria. Postmortem computed tomography (CT) and autopsy were performed to elucidate the cause of death. No obvious lesions could be identified except for a marked fatty liver. Urinalysis showed elevated excretion of α-ketoadipic acid.

Exploring functionality of the reverse ß-oxidation pathway in Corynebacterium glutamicum for production of adipic acid.

BACKGROUND: Adipic acid, a six-carbon platform chemical mainly used in nylon production, can be produced via reverse ß-oxidation in microbial systems. The advantages posed by Corynebacterium glutamicum as a model cell factory for implementing the pathway include: (1) availability of genetic tools, (2) excretion of succinate and acetate when the TCA cycle becomes overflown, (3) initiation of biosynthesis with succinyl-CoA and acetyl-CoA, and (4) established succinic acid production. Here, we implemented the reverse ß-oxidation pathway in C. glutamicum and assessed its functionality for adipic acid biosynthesis. RESULTS: To obtain a non-decarboxylative condensation product of acetyl-CoA and succinyl-CoA, and to subsequently remove CoA from the condensation product, we introduced heterologous 3-oxoadipyl-CoA thiolase and acyl-CoA thioesterase into C. glutamicum. No 3-oxoadipic acid could be detected in the cultivation broth, possibly due to its endogenous catabolism. To successfully biosynthesize and secrete 3-hydroxyadipic acid, 3-hydroxyadipyl-CoA dehydrogenase was introduced. Addition of 2,3-dehydroadipyl-CoA hydratase led to biosynthesis and excretion of trans-2-hexenedioic acid. Finally, trans-2-enoyl-CoA reductase was inserted to yield 37 µg/L of adipic acid. CONCLUSIONS: In the present study, we engineered the reverse ß-oxidation pathway in C. glutamicum and assessed its potential for producing adipic acid from glucose as starting material. The presence of adipic acid, albeit small amount, in the cultivation broth indicated that the synthetic genes were expressed and functional. Moreover, 2,3-dehydroadipyl-CoA hydratase and ß-ketoadipyl-CoA thiolase were determined as potential target for further improvement of the pathway.

One-Pot Biocatalytic Transformation of Adipic Acid to 6-Aminocaproic Acid and 1,6-Hexamethylenediamine Using Carboxylic Acid Reductases and Transaminases.

Production of platform chemicals from renewable feedstocks is becoming increasingly important due to concerns on environmental contamination, climate change, and depletion of fossil fuels. Adipic acid (AA), 6-aminocaproic acid (6-ACA) and 1,6-hexamethylenediamine (HMD) are key precursors for nylon synthesis, which are currently produced primarily from petroleum-based feedstocks. In recent years, the biosynthesis of adipic acid from renewable feedstocks has been demonstrated using both bacterial and yeast cells. Here we report the biocatalytic conversion/transformation of AA to 6-ACA and HMD by carboxylic acid reductases (CARs) and transaminases (TAs), which involves two rounds (cascades) of reduction/amination reactions (AA → 6-ACA → HMD). Using purified wild type CARs and TAs supplemented with cofactor regenerating systems for ATP, NADPH, and amine donor, we established a one-pot enzyme cascade catalyzing up to 95% conversion of AA to 6-ACA. To increase the cascade activity for the transformation of 6-ACA to HMD, we determined the crystal structure of the CAR substrate-binding domain in complex with AMP and succinate and engineered three mutant CARs with enhanced activity against 6-ACA. In combination with TAs, the CAR L342E protein showed 50-75% conversion of 6-ACA to HMD. For the transformation of AA to HMD (via 6-ACA), the wild type CAR was combined with the L342E variant and two different TAs resulting in up to 30% conversion to HMD and 70% to 6-ACA. Our results highlight the suitability of CARs and TAs for several rounds of reduction/amination reactions in one-pot cascade systems and their potential for the biobased synthesis of terminal amines.

Direct biosynthesis of adipic acid from lignin-derived aromatics using engineered Pseudomonas putida KT2440.

Lignin is one largely untapped natural resource that can be exploited as a raw material for the bioproduction of value-added chemicals. Meanwhile, the current petroleum-based process for the production of adipic acid faces sustainability challenges. Here we report the successful engineering of Pseudomonas putida KT2440 strain for the direct biosynthesis of adipic acid from lignin-derived aromatics. The devised bio-adipic acid route features an artificial biosynthetic pathway that is connected to the endogenous aromatics degradation pathway of the host at the branching point, 3-ketoadipoyl-CoA, by taking advantage of the unique carbon skeleton of this key intermediate. Studies of the metabolism of 3-ketoadipoyl-CoA led to the discovery of crosstalk between two aromatics degradation pathways in KT2440. This knowledge facilitated the formulation and implementation of metabolic engineering strategies to optimize the carbon flux into the biosynthesis of adipic acid. By optimizing pathway expression and cultivation conditions, an engineered strain AA-1 produced adipic acid at 0.76 g/L and 18.4% molar yield under shake-flask conditions and 2.5 g/L and 17.4% molar yield under fermenter-controlled conditions from common aromatics that can be derived from lignin. This represents the first example of the direct adipic acid production from model compounds of lignin depolymerization.

Limited life cycle and cost assessment for the bioconversion of lignin-derived aromatics into adipic acid.

Lignin is an abundant and heterogeneous waste byproduct of the cellulosic industry, which has the potential of being transformed into valuable biochemicals via microbial fermentation. In this study, we applied a fast-pyrolysis process using softwood lignin resulting in a two-phase bio-oil containing monomeric and oligomeric aromatics without syringol. We demonstrated that an additional hydrodeoxygenation step within the process leads to an enhanced thermochemical conversion of guaiacol into catechol and phenol. After steam bath distillation, Pseudomonas putida KT2440-BN6 achieved a percent yield of cis, cis-muconic acid of up to 95 mol% from catechol derived from the aqueous phase. We next established a downstream process for purifying cis, cis-muconic acid (39.9 g/L) produced in a 42.5 L fermenter using glucose and benzoate as carbon substrates. On the basis of the obtained values for each unit operation of the empirical processes, we next performed a limited life cycle and cost analysis of an integrated biotechnological and chemical process for producing adipic acid and then compared it with the conventional petrochemical route. The simulated scenarios estimate that by attaining a mixture of catechol, phenol, cresol, and guaiacol (1:0.34:0.18:0, mol ratio), a titer of 62.5 (g/L) cis, cis-muconic acid in the bioreactor, and a controlled cooling of pyrolysis gases to concentrate monomeric aromatics in the aqueous phase, the bio-based route results in a reduction of CO2 -eq emission by 58% and energy demand by 23% with a contribution margin for the aqueous phase of up to 88.05 euro/ton. We conclude that the bio-based production of adipic acid from softwood lignins brings environmental benefits over the petrochemical procedure and is cost-effective at an industrial scale. Further research is essential to achieve the proposed cis, cis-muconic acid yield from true lignin-derived aromatics using whole-cell biocatalysts.

Fungal community dynamics during degradation of poly(butylene succinate-co-adipate) film in two cultivated soils in Japan.

Fungi play an important role in the degradation of biodegradable plastics (BPs) in soil. However, little is known about their dynamics in the soil during the degradation of BPs. We studied the community dynamics of BP-degrading fungi during poly(butylene succinate-co-adipate) (PBSA) film degradation in two different types of soils using culture-dependent and culture-independent methods. The Fluvisol and the Andosol soils degrade embedded PBSA films at high and low speeds, respectively. The number of PBSA emulsion-degrading fungi that increased in the Fluvisol soil was higher than that in the Andosol soil after embedding with PBSA films. We succeeded in detecting internal transcribed spacer 1 (ITS1) regions those matched that of the fungi by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) in both soils. Our results suggest that fungal community analyses using PCR-DGGE in combination with BP degraders isolation techniques enables the monitoring of BP films-degrading fungi.

Computer-aided engineering of adipyl-CoA synthetase for enhancing adipic acid synthesis.

OBJECTIVE: To enhance adipic acid production, a computer-aided approach was employed to engineer the adipyl-CoA synthetase from Thermobifida fusca by combining sequence analysis, protein structure modeling, in silico site-directed mutagenesis, and molecular dynamics simulation. RESULTS: Two single mutants of T. fusca adipyl-CoA synthetase, E210ßN and E210ßQ, achieved a specific enzyme activity of 1.95 and 1.84 U/mg, respectively, which compared favorably with the 1.48 U/mg for the wild-type. The laboratory-level fermentation experiments showed that E210ßN and E210ßQ achieved a maximum adipic acid titer of 0.32 and 0.3 g/L. In contrast, the wild-type enzyme yielded a titer of 0.15 g/L under the same conditions. Molecular dynamics (MD) simulations revealed that the mutants (E210ßN and E210ßQ) could accelerate the dephosphorylation process in catalysis and enhance enzyme activity. CONCLUSIONS: The combined computational-experimental approach provides an effective strategy for enhancing enzymatic characteristics, and the mutants may find a useful application for producing adipic acid.

Enhancing glutaric acid production in Escherichia coli by uptake of malonic acid.

Glutaric acid is an important organic acid applied widely in different fields. Most previous researches have focused on the production of glutaric acid in various strains using the 5-aminovaleric acid (AMV) or pentenoic acid synthesis pathways. We previously utilized a five-step reversed adipic acid degradation pathway (RADP) in Escherichia coli BL21 (DE3) to construct strain Bgl146. Herein, we found that malonyl-CoA was strictly limited in this strain, and increasing its abundance could improve glutaric acid production. We, therefore, constructed a malonic acid uptake pathway in E. coli using matB (malonic acid synthetase) and matC (malonic acid carrier protein) from Clover rhizobia. The titer of glutaric acid was improved by 2.1-fold and 1.45-fold, respectively, reaching 0.56 g/L and 4.35 g/L in shake flask and batch fermentation following addition of malonic acid. Finally, the highest titer of glutaric acid was 6.3 g/L in fed-batch fermentation at optimized fermentation conditions.

Production of adipic acid by short- and long-chain fatty acid acyl-CoA oxidase engineered in yeast Candida tropicalis.

In this study, to produce adipic acid, mutant strains of Candida tropicalis KCTC 7212 deficient of AOX genes encoding acyl-CoA oxidases which are important in the ß-oxidation pathway were constructed. Production of adipic acid in the mutants from the most favorable substrate C12 methyl laurate was significantly increased. The highest level of production of adipic acid was obtained in the C. tropicalis ΔAOX4::AOX5 mutant of 339.8 mg L-1 which was about 5.4-fold higher level compared to the parent strain. The C. tropicalis ΔAOX4::AOX5 mutant was subjected to fed-batch fermentation at optimized conditions of agitation rate of 1000 rpm, pH 5.0 and methyl laurate of 3% (w/v), giving the maximum level of adipic acid of 12.1 g L-1 and production rate of 0.1 g L-1 h-1.

Multifunctional Nanosystem Based on Graphene Oxide for Synergistic Multistage Tumor-Targeting and Combined Chemo-Photothermal Therapy.

Locating nanomedicines at the active sites plays a pivotal role in the nanoparticle-based cancer therapy field. Herein, a multifunctional nanotherapeutic is designed by using graphene oxide (GO) nanosheets with rich carboxyl groups as the supporter for hyaluronic acid (HA)-methotrexate (MTX) prodrug modification via an adipicdihydrazide cross-linker, achieving synergistic multistage tumor-targeting and combined chemo-photothermal therapy. As a tumor-targeting biomaterial, HA can increase affinity of the nanocarrier toward CD44 receptor for enhanced cellular uptake. MTX, a chemotherapeutic agent, can also serve as a tumor-targeting enhancer toward folate receptor based on its similar structure with folic acid. The prepared nanosystems possess a sheet shape with a dynamic size of approximately 200 nm and pH-responsive drug release. Unexpectedly, the physiological stability of HA-MTX prodrug-decorated GO nanosystems in PBS, serum, and even plasma is more excellent than that of HA-decorated GO nanosystems, while both of them exhibit an enhanced photothermal effect than GO nanosheets. More importantly, because of good blood compatibility as well as reduced undesired interactions with blood components, HA-MTX prodrug-decorated GO nanosystems exhibited remarkably superior accumulation at the tumor sites by passive and active targeting mechanisms, achieving highly effective synergistic chemo-photothermal therapeutic effect upon near-infrared laser irradiation, efficient ablation of tumors, and negligible systemic toxicity. Hence, the HA-MTX prodrug-decorated hybrid nanosystems have a promising potential for synergistic multistage tumor-targeting therapy.

Evidence for functional and regulatory cross-talk between the tricarboxylic acid cycle 2-oxoglutarate dehydrogenase complex and 2-oxoadipate dehydrogenase on the l-lysine, l-hydroxylysine and l-tryptophan degradation pathways from studies in vitro.

Herein are reported findings in vitro suggesting both functional and regulatory cross-talk between the human 2-oxoglutarate dehydrogenase complex (hOGDHc), a key regulatory enzyme within the tricarboxylic acid cycle (TCA cycle), and a novel 2-oxoadipate dehydrogenase complex (hOADHc) from the final degradation pathway of l-lysine, l-hydroxylysine and l-tryptophan. The following could be concluded from our studies by using hOGDHc and hOADHc assembled from their individually expressed components in vitro: (i) Different substrate preferences (kcat/Km) were displayed by the two complexes even though they share the same dihydrolipoyl succinyltransferase (hE2o) and dihydrolipoyl dehydrogenase (hE3) components; (ii) Different binding modes were in evidence for the binary hE1o-hE2o and hE1a-hE2o subcomplexes according to fluorescence titrations using site-specifically labeled hE2o-derived proteins; (iii) Similarly to hE1o, the hE1a also forms the ThDP-enamine radical from 2-oxoadipate (electron paramagnetic resonance detection) in the oxidative half reaction; (iv) Both complexes produced superoxide/H2O2 from O2 in the reductive half reaction suggesting that hE1o, and hE1a (within their complexes) could both be sources of reactive oxygen species generation in mitochondria from 2-oxoglutarate and 2-oxoadipate, respectively; (v) Based on our findings, we speculate that hE2o can serve as a trans-glutarylase, in addition to being a trans-succinylase, a role suggested by others; (vi) The glutaryl-CoA produced by hOADHc inhibits hE1o, as does succinyl-CoA, suggesting a regulatory cross-talk between the two complexes on the different metabolic pathways.

Metabolic engineering of Escherichia coli for producing adipic acid through the reverse adipate-degradation pathway.

Adipic acid is an important dicarboxylic acid mainly used for the production of nylon 6-6 fibers and resins. Previous studies focused on the biological production of adipic acid directly from different substrates, resulting in low yields and titers. In this study, a five-step reverse adipate-degradation pathway (RADP) identified in Thermobifida fusca has been reconstructed in Escherichia coli BL21 (DE3). The resulting strain (Mad136) produced 0.3 g L-1 adipic acid with a 11.1% theoretical yield in shaken flasks, and we confirmed that the step catalyzed by 5-Carboxy-2-pentenoyl-CoA reductase (Tfu_1647) as the rate-limiting step of the RADP. Overexpression of Tfu_1647 by pTrc99A carried by strain Mad146 produced with a 49.5% theoretical yield in shaken flasks. We further eliminated pathways for major metabolites competing for carbon flux by CRISPR/Cas9 and deleted the succinate-CoA ligase gene to promote accumulation of succinyl-CoA, which is the precursor for adipic acid synthesis. The final engineered strain Mad123146, which could achieve 93.1% of the theoretical yield in the shaken flask, was able to produce 68.0 g L-1 adipic acid by fed-batch fermentation. To the best of our knowledge, these results constitute the highest adipic acid titer reported in E. coli.

Mitochondrial oxodicarboxylate carrier deficiency is associated with mitochondrial DNA depletion and spinal muscular atrophy-like disease.

PURPOSE: To understand the role of the mitochondrial oxodicarboxylate carrier (SLC25A21) in the development of spinal muscular atrophy-like disease. METHODS: We identified a novel pathogenic variant in a patient by whole-exome sequencing. The pathogenicity of the mutation was studied by transport assays, computer modeling, followed by targeted metabolic testing and in vitro studies in human fibroblasts and neurons. RESULTS: The patient carries a homozygous pathogenic variant c.695A>G; p.(Lys232Arg) in the SLC25A21 gene, encoding the mitochondrial oxodicarboxylate carrier, and developed spinal muscular atrophy and mitochondrial myopathy. Transport assays show that the mutation renders SLC25A21 dysfunctional and 2-oxoadipate cannot be imported into the mitochondrial matrix. Computer models of central metabolism predicted that impaired transport of oxodicarboxylate disrupts the pathways of lysine and tryptophan degradation, and causes accumulation of 2-oxoadipate, pipecolic acid, and quinolinic acid, which was confirmed in the patient's urine by targeted metabolomics. Exposure to 2-oxoadipate and quinolinic acid decreased the level of mitochondrial complexes in neuronal cells (SH-SY5Y) and induced apoptosis. CONCLUSION: Mitochondrial oxodicarboxylate carrier deficiency leads to mitochondrial dysfunction and the accumulation of oxoadipate and quinolinic acid, which in turn cause toxicity in spinal motor neurons leading to spinal muscular atrophy-like disease.

An Engineered Aro1 Protein Degradation Approach for Increased cis,cis-Muconic Acid Biosynthesis in Saccharomyces cerevisiae.

Muconic acid (MA) is a chemical building block and precursor to adipic and terephthalic acids used in the production of nylon and polyethylene terephthalate polymer families. Global demand for these important materials, coupled to their dependence on petrochemical resources, provides substantial motivation for the microbial synthesis of MA and its derivatives. In this context, the Saccharomyces cerevisiae yeast shikimate pathway can be sourced as a precursor for the formation of MA. Here we report a novel strategy to balance MA pathway performance with aromatic amino acid prototrophy by destabilizing Aro1 through C-terminal degron tagging. Coupling of a composite MA production pathway to degron-tagged Aro1 in an aro3Δ aro4Δ mutant background led to the accumulation of 5.6 g/liter protocatechuic acid (PCA). However, metabolites downstream of PCA were not detected, despite the inclusion of genes mediating their biosynthesis. Because CEN.PK family strains of S. cerevisiae lack the activity of Pad1, a key enzyme supporting PCA decarboxylase activity, chromosomal expression of intact PAD1 alleviated this bottleneck, resulting in nearly stoichiometric conversion (95%) of PCA to downstream products. In a fed-batch bioreactor, the resulting strain produced 1.2 g/liter MA under prototrophic conditions and 5.1 g/liter MA when supplemented with amino acids, corresponding to a yield of 58 mg/g sugar.IMPORTANCE Previous efforts to engineer a heterologous MA pathway in Saccharomyces cerevisiae have been hindered by a bottleneck at the PCA decarboxylation step and the creation of aromatic amino acid auxotrophy through deleterious manipulation of the pentafunctional Aro1 protein. In light of these studies, this work was undertaken with the central objective of preserving amino acid prototrophy, which we achieved by employing an Aro1 degradation strategy. Moreover, resolution of the key PCA decarboxylase bottleneck, as detailed herein, advances our understanding of yeast MA biosynthesis and will guide future strain engineering efforts. These strategies resulted in the highest titer reported to date for muconic acid produced in yeast. Overall, our study showcases the effectiveness of careful tuning of yeast Aro1 activity and the importance of host-pathway dynamics.

Metabolic pathway of 6-aminohexanoate in the nylon oligomer-degrading bacterium Arthrobacter sp. KI72: identification of the enzymes responsible for the conversion of 6-aminohexanoate to adipate.

Arthrobacter sp. strain KI72 grows on a 6-aminohexanoate oligomer, which is a by-product of nylon-6 manufacturing, as a sole source of carbon and nitrogen. We cloned the two genes, nylD 1 and nylE 1 , responsible for 6-aminohexanoate metabolism on the basis of the draft genomic DNA sequence of strain KI72. We amplified the DNA fragments that encode these genes by polymerase chain reaction using a synthetic primer DNA homologous to the 4-aminobutyrate metabolic enzymes. We inserted the amplified DNA fragments into the expression vector pColdI in Escherichia coli, purified the His-tagged enzymes to homogeneity, and performed biochemical studies. We confirmed that 6-aminohexanoate aminotransferase (NylD1) catalyzes the reaction of 6-aminohexanoate to adipate semialdehyde using α-ketoglutarate, pyruvate, and glyoxylate as amino acceptors, generating glutamate, alanine, and glycine, respectively. The reaction requires pyridoxal phosphate (PLP) as a cofactor. For further metabolism, adipate semialdehyde dehydrogenase (NylE1) catalyzes the oxidative reaction of adipate semialdehyde to adipate using NADP+ as a cofactor. Phylogenic analysis revealed that NylD1 should be placed in a branch of the PLP-dependent aminotransferase sub III, while NylE1 should be in a branch of the aldehyde dehydrogenase superfamily. In addition, we established a NylD1/NylE1 coupled system to quantify the aminotransferase activity and to enable the conversion of 6-aminohexaoate to adipate via adipate semialdehyde with a yield of > 90%. In the present study, we demonstrate that 6-aminohexanoate produced from polymeric nylon-6 and nylon oligomers (i.e., a mixture of 6-aminohexaoate oligomers) by nylon hydrolase (NylC) and 6-aminohexanoate dimer hydrolase (NylB) reactions are sequentially converted to adipate by metabolic engineering technology.

New Findings on Aromatic Compounds' Degradation and Their Metabolic Pathways, the Biosurfactant Production and Motility of the Halophilic Bacterium Halomonas sp. KHS3.

The study of the aromatic compounds' degrading ability by halophilic bacteria became an interesting research topic, because of the increasing use of halophiles in bioremediation of saline habitats and effluents. In this work, we focused on the study of aromatic compounds' degradation potential of Halomonas sp. KHS3, a moderately halophilic bacterium isolated from hydrocarbon-contaminated seawater of the Mar del Plata harbour. We demonstrated that H. sp. KHS3 is able to grow using different monoaromatic (salicylic acid, benzoic acid, 4-hydroxybenzoic acid, phthalate) and polyaromatic (naphthalene, fluorene, and phenanthrene) substrates. The ability to degrade benzoic acid and 4-hydroxybenzoic acid was analytically corroborated, and Monod kinetic parameters and yield coefficients for degradation were estimated. Strategies that may enhance substrate bioavailability such as surfactant production and chemotactic responses toward aromatic compounds were confirmed. Genomic sequence analysis of this strain allowed us to identify several genes putatively related to the metabolism of aromatic compounds, being the catechol and protocatechuate branches of ß-ketoadipate pathway completely represented. These features suggest that the broad-spectrum xenobiotic degrader H. sp. KHS3 could be employed as a useful biotechnological tool for the cleanup of aromatic compounds-polluted saline habitats or effluents.