Mechanism of tartaric acid mediated dissipation and biotransformation of tetrabromobisphenol A and its derivatives in soil.

Biotransformation is a major dissipation process of tetrabromobisphenol A and its derivatives (TBBPAs) in soil. The biotransformation and ultimate environmental fate of TBBPAs have been widely studied, yet the effect of root exudates (especially low-molecular weight organic acids (LMWOAs)) on the fate of TBBPAs is poorly documented. Herein, the biotransformation behavior and mechanism of TBBPAs in bacteriome driven by LMWOAs were comprehensively investigated. Tartaric acid (TTA) was found to be the main component of LMWOAs in root exudates of Helianthus annus in the presence of TBBPAs, and was identified to play a key role in driving shaping bacteriome. TTA promoted shift of the dominant genus in soil bacteriome from Saccharibacteria_genera_incertae_sedis to Gemmatimonas, with a noteworthy increase of 24.90-34.65% in relative abundance of Gemmatimonas. A total of 28 conversion products were successfully identified, and ß-scission was the principal biotransformation pathway for TBBPAs. TTA facilitated the emergence of novel conversion products, including 2,4-dibromophenol, 3,5-dibromo-4-hydroxyacetophenone, para-hydroxyacetophenone, and tribromobisphenol A. These products were formed via oxidative skeletal cleavage and debromination pathways. Additionally, bisphenol A was observed during the conversion of derivatives. This study provides a comprehensive understanding about biotransformation of TBBPAs driven by TTA in soil bacteriome, offering new insights into LMWOAs-driven biotransformation mechanisms.

Tartrate fermentation with H2 production by a new member of Sporomusaceae enriched from rice paddy soil.

In rice paddies, soil and plant-derived organic matter are degraded anaerobically to methane (CH4), a powerful greenhouse gas. The highest rate of methane emission occurs during the reproductive stage of the plant when mostly dicarboxylic acids are exudated by the roots. The emission of methane at this stage depends largely on the cooperative interaction between dicarboxylic acid-fermenting bacteria and methanogenic archaea in the rhizosphere. The fermentation of tartrate, one of the major acids exudated, has been scarcely explored in rice paddy soils. In this work, we characterized an anaerobic consortium from rice paddy soil composed of four bacterial strains, whose principal member (LT8) can ferment tartrate, producing H2 and acetate. Tartrate fermentation was accelerated by co-inoculation with a hydrogenotrophic methanogen. The assembled genome of LT8 possesses a Na+-dependent oxaloacetate decarboxylase and shows that this bacterium likely invests part of the H2 produced to reduce NAD(P)+ to assimilate C from tartrate. The phylogenetic analysis of the 16S rRNA gene, the genome-based classification as well as the average amino acid identity (AAI) indicated that LT8 belongs to a new genus within the Sporomusaceae family. LT8 shares a few common features with its closest relatives, for which tartrate degradation has not been described. LT8 is limited to a few environments but is more common in rice paddy soils, where it might contribute to methane emissions from root exudates.IMPORTANCEThis is the first report of the metabolic characterization of a new anaerobic bacterium able to degrade tartrate, a compound frequently associated with plants, but rare as a microbial metabolite. Tartrate fermentation by this bacterium can be coupled to methanogenesis in the rice rhizosphere where tartrate is mainly produced at the reproductive stage of the plant, when the maximum methane rate emission occurs. The interaction between secondary fermentative bacteria, such as LT8, and methanogens could represent a fundamental step in exploring mitigation strategies for methane emissions from rice fields. Possible strategies could include controlling the activity of these secondary fermentative bacteria or selecting plants whose exudates are more difficult to ferment.

Deciphering the stereo-specific catalytic mechanisms of cis-epoxysuccinate hydrolases producing L(+)-tartaric acid.

Microbial epoxide hydrolases, cis-epoxysuccinate hydrolases (CESHs), have been utilized for commercial production of enantiomerically pure L(+)- and D(-)-tartaric acids for decades. However, the stereo-catalytic mechanism of CESH producing L(+)-tartaric acid (CESH[L]) remains unclear. Herein, the crystal structures of two CESH[L]s in ligand-free, product-complexed, and catalytic intermediate forms were determined. These structures revealed the unique specific binding mode for the mirror-symmetric substrate, an active catalytic triad consisting of Asp-His-Glu, and an arginine providing a proton to the oxirane oxygen to facilitate the epoxide ring-opening reaction, which has been pursued for decades. These results provide the structural basis for the rational engineering of these industrial biocatalysts.

Enantioselectivity in the enzymatic dehydration of malate and tartrate: Mirror image specificities of structurally similar dehydratases.

Malate (2-hydroxysuccinic acid) and tartrate (2,3-dihydroxysuccinic acid) are chiral substrates; the former existing in two enantiomeric forms (R and S) while the latter exists as three stereoisomers (R,R; S,S; and R,S). Dehydration by stereospecific hydrogen abstraction and antielimination of the hydroxyl group yield the achiral products fumarate and oxaloacetate, respectively. Class-I fumarate hydratase (FH) and L-tartrate dehydratase (L-TTD) are two highly conserved enzymes belonging to the iron-sulfur cluster hydrolyase family of enzymes that catalyze reactions on specific stereoisomers of malate and tartrate. FH from Methanocaldococcus jannaschii accepts only (S)-malate and (S,S)-tartrate as substrates while the structurally similar L-TTD from Escherichia coli accepts only (R)-malate and (R,R)-tartrate as substrates. Phylogenetic analysis reveals a common evolutionary origin of L-TTDs and two-subunit archaeal FHs suggesting a divergence during evolution that may have led to the switch in substrate stereospecificity preference. Due to the high conservation of their sequences, a molecular basis for switch in stereospecificity is not evident from analysis of crystal structures of FH and predicted structure of L-TTD. The switch in enantiomer preference may be rationalized by invoking conformational plasticity of the amino acids interacting with the substrate, together with substrate reorientation and conformer selection about the C2C3 bond of the dicarboxylic acid substrates. Although classical models of enzyme-substrate binding are insufficient to explain such a phenomenon, the enantiomer superposition model suggests that a minor reorientation in the active site residues could lead to the switch in substrate stereospecificity.

Evaluating anti-viral effect of Tylvalosin tartrate on porcine reproductive and respiratory syndrome virus and analyzing the related gene regulation by transcriptomics.

BACKGROUND: Porcine reproductive and respiratory syndrome virus (PRRSV) is an economically important pathogen, characterized by its genetic and antigenic variation. The PRRSV vaccine is widely used, however, the unsatisfied heterologic protection and the risk of reverse virulence raise the requirement to find some new anti-PRRSV strategies for disease control. Tylvalosin tartrate is used to inhibit PRRSV in the field non-specifically, however, the mechanism is still less known. METHODS: The antiviral effects of Tylvalosin tartrates from three producers were evaluated in a cell inoculation model. Their safety and efficacy concentrations, and effecting stage during PRRSV infection were analyzed. And, the Tylvalosin tartrates regulated genes and pathways which are potentially related to the anti-viral effect were further explored by using transcriptomics analysis. Last, the transcription level of six anti-virus-related DEGs was selected to confirm by qPCR, and the expression level of HMOX1, a reported anti-PRRSV gene, was proved by western blot. RESULTS: The safety concentrations of Tylvalosin tartrates from three different producers were 40 µg/mL (Tyl A, Tyl B, and Tyl C) in MARC-145 cells and 20 µg/mL (Tyl A) or 40 µg/mL (Tyl B and Tyl C) in primary pulmonary alveolar macrophages (PAMs) respectively. Tylvalosin tartrate can inhibit PRRSV proliferation in a dose-dependent manner, causing more than 90% proliferation reduction at 40 µg/mL. But it shows no virucidal effect, and only achieves the antiviral effect via long-term action on the cells during the PRRSV proliferation. Furthermore, GO terms and KEGG pathway analysis was carried out based on the RNA sequencing and transcriptomic data. It was found that the Tylvalosin tartrates can regulate the signal transduction, proteolysis, and oxidation-reduction process, as well as some pathways such as protein digestion and absorption, PI3K-Akt signaling, FoxO signaling, and Ferroptosis pathways, which might relate to PRRSV proliferation or host innate immune response, but further studies still need to confirm it. Among them, six antivirus-related genes HMOX1, ATF3, FTH1, FTL, NR4A1, and CDKN1A were identified to be regulated by Tylvalosin tartrate, and the increased expression level of HMOX1 was further confirmed by western blot. CONCLUSIONS: Tylvalosin tartrate can inhibit PRRSV proliferation in vitro in a dose-dependent manner. The identified DEGs and pathways in transcriptomic data will provide valuable clues for further exploring the host cell restriction factors or anti-PRRSV target.

C4-dicarboxylate metabolons: interaction of C4-dicarboxylate transporters of Escherichia coli with cytosolic enzymes.

Metabolons represent the structural organization of proteins for metabolic or regulatory pathways. Here, the interaction of fumarase FumB, aspartase AspA, and L-tartrate dehydratase TtdAB with the C4-dicarboxylate (C4-DC) transporters DcuA, DcuB, DcuC, and the L-tartrate transporter TtdT of Escherichia coli was tested by a bacterial two-hybrid (BACTH) assay in situ, or by co-chromatography using mSPINE (membrane Streptavidin protein interaction experiment). From the general C4-DC transporters, DcuB interacted with FumB and AspA, DcuA with AspA, whereas DcuC interacted with neither FumB nor AspA. Moreover, TtdT did not interact with TtdAB. The fumB-dcuB, the dcuA-aspA, and the ttdAB-ttdT genes encoding the respective proteins colocalize on the genome and each pair of genes forms cotranscripts, whereas the dcuC gene lies alone. The data suggest the formation of DcuB/FumB and DcuB/AspA metabolons for the uptake of L-malate, or L-aspartate, and their conversion to fumarate for fumarate respiration and excretion of the product succinate. The DcuA/AspA metabolon catalyzes uptake and conversion of L-aspartate to fumarate coupled to succinate excretion. The DcuA/AspA metabolon provides ammonia at the same time for nitrogen assimilation (ammonia shuttle). On the other hand, TtdT and TtdAB are not organized in a metabolon. Reasons for the formation (DcuA/AspA, DcuB/FumB, and DcuB/AspA) or nonformation (DcuC, TtdT, and TtdAB) of metabolons are discussed based on their metabolic roles.

Structural insights into a new substrate binding mode of a histidine acid phosphatase from Legionella pneumophila.

MapA is a histidine acid phosphatase (HAP) from Legionella pneumophila that catalyzes the hydroxylation of a phosphoryl group from phosphomonoesters by an active-site histidine. Several structures of HAPs, including MapA, in complex with the inhibitor tartrate have been solved and the substrate binding tunnel identified; however, the substrate recognition mechanism remains unknown. To gain insight into the mechanism of substrate recognition, the crystal structures of apo-MapA and the MapAD281A mutant in complex with 5'-AMP were solved at 2.2 and 2.6 Å resolution, respectively. The structure of the MapAD281A/5'-AMP complex reveals that the 5'-AMP fits fully into the substrate binding tunnel, with the 2'-hydroxyl group of the ribose moiety stabilized by Glu201 and the adenine moiety sandwiched between His205 and Phe237. This is the second structure of a HAP/AMP complex solved with 5'-AMP binding in a unique manner in the active site. The structure presents a new substrate recognition mechanism of HAPs.

d-Tartrate utilization correlates with phylogenetic subclade in Pseudomonas cichorii.

Pseudomonas cichorii is divided into two subclades based on the 16S ribosomal RNA gene sequence and core genome multilocus sequence typing. It was shown that subclade 2 strains utilize d-tartrate as a sole carbon source, whereas subclade 1 strains do not. Draft genome sequencing was performed with P. cichorii strains to identify d-tartrate utilization genes. By genome comparative and homology search studies, an ∼7.1-kb region was identified to be involved in d-tartrate utilization. The region is subclade 2 specific, and contains tarD and dctA genes, which encode a putative enzyme and transporter of d-tartrate, respectively. When the region was introduced into subclade 1 strains, the transformants were able to utilize d-tartrate. Partial fragments of tarD and dctA were amplified from all subclade 2 strains tested in this study by PCR using gene-specific primers, but not from subclade 1 strains. This is the first report on the genetic analysis of biochemical characteristics corresponding to a specific phylogenetic group in P. cichorii.

Use of grape racemes from Grillo cultivar to increase the acidity level of sparkling base wines produced with different Saccharomyces cerevisiae strains.

The most important oenological characteristics of high-quality sparkling wines are aromatic aspect, taste persistence, perlage, high levels of acidity and low pH. Due to hot climate and reduced rainfall that characterize Sicily region, white grape varieties such as Grillo cultivar cultivated in this area are characterized by very low concentrations of malic and tartaric acids. Grillo cultivar is characterized by an intense production of raceme grapes with low pH and high content of tartaric and malic acids. These fruits possess the chemical properties useful to increase the amounts of acids in the final wines. With this in mind, the present research was carried out to test the ability of four Saccharomyces cerevisiae strains (CS182, GR1, MSE13 and MSE41) to ferment a raceme must with a pH of 2.9 at two concentrations (14° and 16° Babo degree) of total sugars. The inoculation of the strains was performed after a preadaptation at pH 2.5. The chemical parameters and kinetics of the fermentations were monitored. The experimental sparkling base wines were characterized by a very high total acidity with 16-17 g/L of tartaric acid and 9-10 g/L of malic acids. On the other hand, ethanol was detected at low values in the range 9-10% (v/v). The base wine obtained with GR1differed in their high acidity values, whereas trials inoculated with CS182 showed more intense odors and exotic fruit. Experimental wines produced in this study represent an innovative strategy for "blending wines" to produce sparkling wines in dry Mediterranean climate.

A Dose-Dependent Effect of Carnipure® Tartrate Supplementation on Endurance Capacity, Recovery, and Body Composition in an Exercise Rat Model.

The objective of this work is to investigate the effects of Carnipure® Tartrate (CT) supplementation with or without exercise on endurance capacity, recovery, and fatigue by assessing time to exhaustion as well as body weight and composition in rats. In addition, antioxidant capacity has been evaluated by measuring malondialdehyde (MDA) levels and antioxidant enzyme (superoxide dismutase, SOD; catalase, CAT; glutathioneperoxidase; GSHPx) activities. Fifty-six male Wistar rats were divided into eight groups including seven rats each. A control group did not receive CT nor exercise. Another control group received 200 mg/kg CT without exercise. The other six groups of rats went through an exercise regimen consisting of a 5-day training period with incremental exercise capacity, which was followed by 6 weeks of the run at 25 m/min for 45 min every day. CT was supplemented at 0, 25, 50, 100, 200, and 400 mg/kg per day during the 6 weeks. Rats submitted to exercise and supplemented with CT had a significant and dose-dependent increase in time to exhaustion and this effect seems to be independent of exercise (p < 0.05). Additionally, recovery and fatigue were improved, as shown by a significant and dose-dependent decrease in myoglobin and lactic acid plasma levels, which are two markers of muscle recovery. CT supplementation led to a dose-response decrease in body weight and visceral fat. These effects become significant at 200 and 400 mg/kg doses (p < 0.05). Additionally, the antioxidant capacity was improved, as shown by a significant and dose-dependent increase in SOD, CAT, and GSHPx. Serum MDA concentrations decreased in exercising rats with CT supplementation. CT supplementation led to a decrease in serum glucose, triglycerides, and total cholesterol concentrations with the lowest levels observed at 400 mg/kg dose (p < 0.05). These effects correlated with a significant dose-dependent increase in serum total L-carnitine, free L-carnitine, and acetyl-carnitine, which linked the observed efficacy to CT supplementation. These results demonstrate that CT supplementation during exercise provides benefits on exercise performance, recovery, and fatigue as well as improved the lipid profile and antioxidant capacity. The lowest dose leads to some of these effects seen in rats where 25 mg/kg corresponds to 250 mg/day as a human equivalent.

Isolation of a novel strain Aspergillus niger WH-2 for production of L(+)-tartaric acid under acidic condition.

OBJECTIVES: To isolate a novel cis-epoxysuccinate hydrolase (CESH)-producing fungus for production of L( +)-tartaric acid, before this, all strains were selected from bacteria. RESULTS: A CESH-producing fungus was first isolated from soil and identified as Aspergillus niger WH-2 based on its morphological properties and ITS sequence. The maximum activity of hyphaball and fermentation supernatants was 1278 ± 64 U/g and 5.6 ± 0.3 U/mL, respectively, in a 5 L fermenter based on the conditions optimized on the flask. Almost 70% of CESH was present in hyphaball, which maintained 40% residual activity at pH 4.0 and showed a good acid stability (pH 3.0-10.0), high conversion rate (> 98%), and enantioselectivity (EE > 99.6%). However, the reported CESHs from bacteria can't be catalyzed under acidic conditions. CONCLUSIONS: The Aspergillus niger WH-2 was the first reported CESH-producing fungus, which could biosynthesize L ( +)-tartaric acid under acidic conditions and provide an alternative catalyst and process.

Identification of major malate export systems in an engineered malate-producing Escherichia coli aided by substrate similarity search.

Optimization of export mechanisms for valuable extracellular products is important for the development of efficient microbial production processes. Identification of the relevant export mechanism is the prerequisite step for product export optimization. In this work, we identified transporters involved in malate export in an engineered L-malate-producing Escherichia coli strain using cheminformatics-guided genetics tests. Among all short-chain di- or tricarboxylates with known transporters in E. coli, citrate, tartrate, and succinate are most chemically similar to malate as estimated by their molecular signatures. Inactivation of three previously reported transporters for succinate, tartrate, and citrate, DcuA, TtdT, and CitT, respectively, dramatically decreased malate production and fermentative growth, suggesting that these transporters have substrate promiscuity for different short-chain organic acids and constitute the major malate export system in E. coli. Malate export deficiency led to an increase in cell sizes and accumulation of intracellular metabolites related to malate metabolism.

An aldo-keto reductase with 2-keto-l-gulonate reductase activity functions in l-tartaric acid biosynthesis from vitamin C in Vitis vinifera.

Tartaric acid has high economic value as an antioxidant and flavorant in food and wine industries. l-Tartaric acid biosynthesis in wine grape (Vitis vinifera) uses ascorbic acid (vitamin C) as precursor, representing an unusual metabolic fate for ascorbic acid degradation. Reduction of the ascorbate breakdown product 2-keto-l-gulonic acid to l-idonic acid constitutes a critical step in this l-tartaric acid biosynthetic pathway. However, the underlying enzymatic mechanisms remain obscure. Here, we identified a V. vinifera aldo-keto reductase, Vv2KGR, with 2-keto-l-gulonic acid reductase activity. Vv2KGR belongs to the d-isomer-specific 2-hydroxyacid dehydrogenase superfamily and displayed the highest similarity to the hydroxyl pyruvate reductase isoform 2 in Arabidopsis thaliana Enzymatic analyses revealed that Vv2KGR efficiently reduces 2-keto-l-gulonic acid to l-idonic acid and uses NADPH as preferred coenzyme. Moreover, Vv2KGR exhibited broad substrate specificity toward glyoxylate, pyruvate, and hydroxypyruvate, having the highest catalytic efficiency for glyoxylate. We further determined the X-ray crystal structure of Vv2KGR at 1.58 Å resolution. Comparison of the Vv2KGR structure with those of d-isomer-specific 2-hydroxyacid dehydrogenases from animals and microorganisms revealed several unique structural features of this plant hydroxyl pyruvate reductase. Substrate structural analysis indicated that Vv2KGR uses two modes (A and B) to bind different substrates. 2-Keto-l-gulonic acid displayed the lowest predicted free-energy binding to Vv2KGR among all docked substrates. Hence, we propose that Vv2KGR functions in l-tartaric acid biosynthesis. To the best of our knowledge, this is the first report of a d-isomer-specific 2-hydroxyacid dehydrogenase that reduces 2-keto-l-gulonic acid to l-idonic acid in plants.

Immobilization Mechanism of Nano-Hydroxyapatite on Lead in the Ryegrass Rhizosphere Soil Under Root Confinement.

The immobilization effect and mechanism of nano-hydroxyapatite(NHAP) on Pb in the ryegrass rhizosphere soil were studied by root-bag experiment. The speciation analysis results revealed that the residual Pb concentrations in the rhizosphere soil significantly increased after NHAP application. The acid-soluble and reducible Pb concentrations significantly decreased, indicating that NHAP had obviously immobilized Pb. Meanwhile, NHAP significantly promoted the secretion of tartaric acid from ryegrass roots, resulting the rhizosphere soil pH had been below that of the control group. This helped to relieve the stress of Pb on ryegrass, also promoted the dissolution of NHAP, resulting the formation of stable precipitation with more Pb ions. NHAP increased the rhizosphere soil pH by 0.03 to 0.17, which promoted the conversion of Pb to non-utilizable bioavailability. The total Pb mass balance indicated only a very small proportion Pb transferred to the shoots through ryegrass roots. The formation of pyromorphite by Pband NHAP in soil was accordingly to interpret the dominant mechanism for Pb immobilization.

Long noncoding RNAs and miRNAs regulating terpene and tartaric acid biosynthesis in rose-scented geranium.

This study aimed to explore the noncoding RNAs, which have emerged as key regulatory molecules in biological processes, in rose-scented geranium. We analyzed RNA-seq data revealing 26 784 long noncoding RNAs (lncRNAs) and 871 miRNAs in rose-scented geranium. A total of 466 lncRNAs were annotated using different plant lncRNA public databases. Furthermore, 372 lncRNAs and 99 miRNAs were detected that target terpene and tartarate biosynthetic pathways. An interactome, comprising of lncRNAs, miRNAs, and mRNAs, was constructed that represents a noncoding RNA regulatory network of the target mRNAs. Real-time quantitative PCR expression validation was done for selected lncRNAs involved in the regulation of terpene and tartaric acid pathways. This study provides the first insights into the regulatory functioning of noncoding RNAs in rose-scented geranium.

Development of a real-time PCR method for the genoserotyping of Salmonella Paratyphi B variant Java.

Discriminating between D-tartrate fermenting and non-fermenting strains of Salmonella enterica subsp. enterica serotype Paratyphi B is of major importance as these two variants have different pathogenic profiles. While D-tartrate non-fermenting S. Paratyphi B isolates are the causative agent of typhoid-like fever, D-tartrate fermenting isolates (also called variant Java) of the same serotype trigger the less dangerous gastroenteritis. The determination of S. Paratyphi B variants requires a time-consuming process and complex biochemical tests. Therefore, a quadruplex real-time PCR method, based on the allelic discrimination of molecular markers selected from the scientific literature and from whole genome sequencing data produced in-house, was developed in this study, to be applied to Salmonella isolates. This method was validated with the analysis of 178 S. Paratyphi B (D-tartrate fermenting and non-fermenting) and other serotypes reaching an accuracy, compared with the classical methods, of 98% for serotyping by slide agglutination and 100% for replacement of the biochemical test. The developed real-time PCR permits to save time and to obtain an accurate identification of a S. Paratyphi B serotype and its D-tartrate fermenting profile, which is needed in routine laboratories for fast and efficient diagnostics.

Enzyme promiscuity shapes adaptation to novel growth substrates.

Evidence suggests that novel enzyme functions evolved from low-level promiscuous activities in ancestral enzymes. Yet, the evolutionary dynamics and physiological mechanisms of how such side activities contribute to systems-level adaptations are not well characterized. Furthermore, it remains untested whether knowledge of an organism's promiscuous reaction set, or underground metabolism, can aid in forecasting the genetic basis of metabolic adaptations. Here, we employ a computational model of underground metabolism and laboratory evolution experiments to examine the role of enzyme promiscuity in the acquisition and optimization of growth on predicted non-native substrates in Escherichia coli K-12 MG1655. After as few as approximately 20 generations, evolved populations repeatedly acquired the capacity to grow on five predicted non-native substrates-D-lyxose, D-2-deoxyribose, D-arabinose, m-tartrate, and monomethyl succinate. Altered promiscuous activities were shown to be directly involved in establishing high-efficiency pathways. Structural mutations shifted enzyme substrate turnover rates toward the new substrate while retaining a preference for the primary substrate. Finally, genes underlying the phenotypic innovations were accurately predicted by genome-scale model simulations of metabolism with enzyme promiscuity.

Enantiomeric Tartaric Acid Production Using cis-Epoxysuccinate Hydrolase: History and Perspectives.

Tartaric acid is an important chiral chemical building block with broad industrial and scientific applications. The enantioselective synthesis of l(+)- and d(-)-tartaric acids has been successfully achieved using bacteria presenting cis-epoxysuccinate hydrolase (CESH) activity, while the catalytic mechanisms of CESHs were not elucidated clearly until very recently. As biocatalysts, CESHs are unique epoxide hydrolases because their substrate is a small, mirror-symmetric, highly hydrophilic molecule, and their products show very high enantiomeric purity with nearly 100% enantiomeric excess. In this paper, we review over forty years of the history, process and mechanism studies of CESHs as well as our perspective on the future research and applications of CESH in enantiomeric tartaric acid production.

Transcriptome mining and in silico structural and functional analysis of ascorbic acid and tartaric acid biosynthesis pathway enzymes in rose-scanted geranium.

Rose-scented geranium (Pelargonium sp.) is widely known as aromatic and medicinal herb, accumulating specialized metabolites of high economic importance, such as essential oils, ascorbic acid, and tartaric acid. Ascorbic acid and tartaric acid are multifunctional metabolites of human value to be used as vital antioxidants and flavor enhancing agents in food products. No information is available related to the structural and functional properties of the enzymes involved in ascorbic acid and tartaric acid biosynthesis in rose-scented geranium. In the present study, transcriptome mining was done to identify full-length genes, followed by their bioinformatic and molecular modeling investigations and understanding of in silico structural and functional properties of these enzymes. Evolutionary conserved domains were identified in the pathway enzymes. In silico physicochemical characterization of the catalytic enzymes revealed isoelectric point (pI), instability index, aliphatic index, and grand average hydropathy (GRAVY) values of the enzymes. Secondary structural prediction revealed abundant proportion of alpha helix and random coil confirmations in the pathway enzymes. Three-dimensional homology models were developed for these enzymes. The predicted structures showed significant structural similarity with their respective templates in root mean square deviation analysis. Ramachandran plot analysis of the modeled enzymes revealed that more than 84% of the amino acid residues were within the favored regions. Further, functionally important residues were identified corresponding to catalytic sites located in the enzymes. To, our best knowledge, this is the first report which provides a foundation on functional annotation and structural determination of ascorbic acid and tartaric acid pathway enzymes in rose-scanted geranium.

Ultrasound-assisted d-tartaric acid whole-cell bioconversion by recombinant Escherichia coli.

d-Tartaric acid has wide range of application in the pharmaceutical industry and scarcely exists in nature. In this study, cis-epoxysuccinate hydrolase (CESH)-containing Escherichia coli was used to perform whole-cell bioconversion of cis-epoxysuccinate (CES) to D-tartaric acid and the catalytic efficiency was investigated by ultrasound treatment. The bioconversion rate of CES sodium reached 70.36% after 60 min treated after ultrasound, which is 3-fold higher than that in the control. The specific rate could be further improved by 2-fold after 5 repeated batches compared with the first one, however, the specific rate gradually decreased with the increase of repeat batches (>5 batches). The CESH from Bordetella sp. BK-52 was a typical Michaelis-Menten enzyme with Vmax and Km values of 28.17 mM/h/g WCW (wet of cell weight) and 30.18 mM, respectively. The process for the d-tartaric acid bioconversion, which consisted of 102.31 g/L CES sodium, 8.78 mg/mL whole cell and ultrasound power of 79.36 W, is further optimized using response surface methodology. The specific rate finally reached 194.79 ±â€¯1.78 mM/h/g WCW under the optimal conditions. Furthermore, the permeability of inner and outer membrane was improved approximately 1.6 and 1.4-fold after ultrasound treatment, respectively, which may be a crucial factor for improvement of the bioconversion efficiency.