Bioproduction of Glycolic Acid from Glycolonitrile with a New Bacterial Isolate of Alcaligenes sp. ECU0401

Protein Engineering of Substrate Specificity toward Nitrilases: Strategies and Challenges

Nitrilase is extensively applied across diverse sectors owing to its unique catalytic properties. Nevertheless, in industrial production, nitrilases often face issues such as low catalytic efficiency, limited substrate range, suboptimal selectivity, and side reaction products, which have garnered heightened attention. With the widespread recognition that the structure of enzymes has a direct impact on their catalytic properties, an increasing number of researchers are beginning to optimize the functional characteristics of nitrilases by modifying their structures, in order to meet specific industrial or biotechnology application needs. Particularly in the artificial intelligence era, the innovative application of computer-aided design in enzyme engineering offers remarkable opportunities to tailor nitrilases for the widespread production of high-value products. In this discussion, we will briefly examine the structural mechanism of nitrilase. An overview of the protein engineering strategies of substrate preference, regioselectivity and stereoselectivity are explored combined with some representative examples recently in terms of the substrate specificity of enzyme. The future research trends in this field are also prospected.

Biologically active metabolites of Alcaligenes faecalis: diversity, statistical optimization, and future perspectives

Alcaligenes faecalis is a Gram-negative, rod-shaped bacterium that is common in the environment and has been reported to have various bioactive metabolites of industrial potential applications, including antifungal, antibacterial, antimycobacterial, antiparasitic, anticancer, antioxidant activities. In this review, we highlighted and discussed the respective metabolites, pointing out their chemical diversities, purification, current challenges, and future directions. A. faecalis has an industrial role in biodegradation, biosurfactants, and different enzyme production. In this review, the up-to-date various Response Surface Methodology methods (RSM) that can be employed for statistical optimization of the bioactive secondary metabolites have been discussed and highlighted, pointing out the optimal use of each method, current challenges, and future directions.

The challenges and prospects of Escherichia coli as an organic acid production host under acid stress

OBJECTIVE

Organic acids have a wide range of applications and have attracted the attention of many industries, and their large-scale applications have led fermentation production to low-cost development. Among them, the microbial fermentation method, especially using Escherichia coli as the production host, has the advantages of fast growth and low energy consumption, and has gradually shown better advantages and prospects in organic acid fermentation production.

IMPORTANCE

However, when the opportunity comes, the acidified environment caused by the acid products accumulated during the fermentation process also challenges E. coli. The acid sensitivity of E. coli is a core problem that needs to be solved urgently. The addition of neutralizers in traditional operations led to the emergence of osmotic stress inadvertently, the addition of strong acid substances to recover products in the salt state not only increases production costs, but the discharged sewage is also harmful to the environment.

ELABORATION

This article summarizes the current status of the application of E. coli in the production of organic acids, and based on the impact of acid stress on the physiological state of cells and the impact of industrial production profits, put forward some new conjectures that can make up for the deficiencies in existing research and application.

IMPLICATION

At this point, the diversified transformation of E. coli has become a chassis microbe that is more suitable for industrial fermentation, enhancing industrial application value.

KEY POINTS

• E. coli is a potential host for high value-added organic acids production. • Classify the damage mechanism and coping strategies of E. coli when stimulated by acid molecules. • Multi-dimensional expansion tools are needed to create acid-resistant E. coli chassis.

Multiple strategies for metabolic engineering of Escherichia coli for efficient production of glycolate

Glycolate is a bulk chemical with wide applications in the textile, food processing, and pharmaceutical industries. Glycolate can be produced from glucose via the glycolysis and glyoxylate shunt pathways, followed by reduction to glycolate. However, two problems limit the productivity and yield of glycolate when using glucose as the sole carbon source. The first is a cofactor imbalance in the production of glycolate from glucose via the glycolysis pathway, since NADPH is required for glycolate production, while glycolysis generates NADH. To rectify this imbalance, the NADP⁺ -dependent glyceraldehyde 3-phosphate dehydrogenase GapC from Clostridium acetobutylicum was introduced to generate NADPH instead of NADH in the oxidation of glyceraldehyde 3-phosphate during glycolysis. The soluble transhydrogenase SthA was further eliminated to conserve NADPH by blocking its conversion into NADH. The second problem is an unfavorable carbon flux distribution between the tricarboxylic acid cycle and the glyoxylate shunt. To solve this problem, isocitrate dehydrogenase (ICDH) was eliminated to increase the carbon flux of glyoxylate and thereby improve the glycolate titer. After engineering through the integration of gapC, combined with the inactivation of ICDH, SthA, and by-product pathways, as well as the upregulation of the two key enzymes isocitrate lyase (encoding by aceA), and glyoxylate reductase (encoding by ycdW), the glycolate titer increased to 5.3 g/L with a yield of 1.89 mol/mol glucose. Moreover, an optimized fed-batch fermentation reached a titer of 41 g/L with a yield of 1.87 mol/mol glucose after 60 h.

Microbial engineering for the production of C2-C6 organic acids

Covering: up to the end of 2020Organic acids, as building block compounds, have been widely used in food, pharmaceutical, plastic, and chemical industries. Until now, chemical synthesis is still the primary method for industrial-scale organic acid production. However, this process encounters some inevitable challenges, such as depletable petroleum resources, harsh reaction conditions and complex downstream processes. To solve these problems, microbial cell factories provide a promising approach for achieving the sustainable production of organic acids. However, some key metabolites in central carbon metabolism are strictly regulated by the network of cellular metabolism, resulting in the low productivity of organic acids. Thus, multiple metabolic engineering strategies have been developed to reprogram microbial cell factories to produce organic acids, including monocarboxylic acids, hydroxy carboxylic acids, amino carboxylic acids, dicarboxylic acids and monomeric units for polymers. These strategies mainly center on improving the catalytic efficiency of the enzymes to increase the conversion rate, balancing the multi-gene biosynthetic pathways to reduce the byproduct formation, strengthening the metabolic flux to promote the product biosynthesis, optimizing the metabolic network to adapt the environmental conditions and enhancing substrate utilization to broaden the substrate spectrum. Here, we describe the recent advances in producing C₂-C₆ organic acids by metabolic engineering strategies. In addition, we provide new insights as to when, what and how these strategies should be taken. Future challenges are also discussed in further advancing microbial engineering and establishing efficient biorefineries.

Chemoenzymatic conversion of Sorghum durra stalk into furoic acid by a sequential microwave-assisted solid acid conversion and immobilized whole-cells biocatalysis

In this study, chemoenzymatic conversion of Sorghum durra stalk (SDS) into furoic acid was developed by a sequential microwave-assisted solid acid conversion and immobilized whole-cells biocatalysis method. Dry dewaxed SDS (75 g/L) was catalyzed into furfural at 57.8% yield with heterogeneous Sn-argil (2.0 wt% dosage) in n-ethyl butyrate-H₂O (1:1, v:v) biphasic system using a microwave (600 W) for 10 min at 180 °C. In this biphasic media (pH 6.5), SDS-derived furfural (125.0 mM) was biologically oxidized to furoic acid by immobilized Brevibacterium lutescens cells harboring furfural-oxidizing activity at 30 °C, and furfural was wholly transformed to furoic acid within 24 h. Finally, the recovery and reuse of the Sn-argil catalyst and immobilized biocatalysts were conducted for synthesizing furoic acid from SDS in the biphasic system. This chemoenzymatic route can be attractive for furoic acid production.

Ethylene glycol and glycolic acid production by wild-type Escherichia coli

Ethylene glycol and glycolic acid are bulk chemicals with a broad range of applications. The ethylene glycol and glycolic acid biosynthesis pathways have been produced by microorganisms and used as a biological route for their production. Unlike the methods that use xylose or glucose as carbon sources, xylonic acid was used as a carbon source to produce ethylene glycol and glycolic acid in this study. Amounts of 4.2 g/L of ethylene glycol and 0.7 g/L of glycolic acid were produced by a wild-type Escherichia coli W3110 within 10 H of cultivation with a substrate conversion ratio of 0.5 mol/mol. Furthermore, E. coli strains that produce solely ethylene glycol or glycolic acid were constructed. 10.3 g/L of glycolic acid was produced by E. coli ΔyqhD+aldA, and the achieved conversion ratio was 0.56 mol/mol. Similarly, the E. coli ΔaldA+yqhD produced 8.0 g/L of ethylene glycol with a conversion ratio of 0.71 mol/mol. Ethylene glycol and glycolic acid production by E. coli on xylonic acid as a carbon source provides new information on the biosynthesis pathway of these products and opens a novel way of biomass utilization.

An Effective Hybrid Strategy for Conversion of Biomass into Furfurylamine by Tandem Pretreatment and Biotransamination

In this work, an effective hybrid strategy was developed for tandem conversion of biomass to furfurylamine with tin-based solid acid Sn-Maifanitum stone and recombinant Escherichia coli whole cells harboring ω-transaminase. 90.3 mM furfural was obtained from corncob (75 g/L) at 170 °C for 0.5 h over Sn-Maifanitum stone catalyst (3.5 wt%) in the aqueous media (pH 1.0), which could be further bioconverted into furfurylamine at 74.0% yield (based on biomass-derived furfural) within 20.5 h. Finally, an efficient recycling and reuse of Sn-Maifanitum stone catalyst and immobilized Escherichia coli AT2018 whole-cell biocatalyst was developed for the synthesis of furfurylamine from biomass in the one-pot reaction system.

Construction of a carbon-conserving pathway for glycolate production by synergetic utilization of acetate and glucose in Escherichia coli

Glycolate is a bulk chemical which has been widely used in textile, food processing, and pharmaceutical industries. Glycolate can be produced from sugars by microbial fermentation. However, when using glucose as the sole carbon source, the theoretical maximum carbon molar yield of glycolate is 0.67 mol/mol due to the loss of carbon as CO₂. In this study, a synergetic system for simultaneous utilization of acetate and glucose was designed to increase the carbon yield. The main function of glucose is to provide NADPH while acetate to provide the main carbon backbone for glycolate production. Theoretically, 1 glucose and 5 acetate can produce 6 glycolate, and the carbon molar yield can be increased to 0.75 mol/mol. The whole synthetic pathway was divided into two modules, one for converting acetate to glycolate and another to utilize glucose to provide NADPH. After engineering module I through activation of acs, gltA, aceA and ycdW, glycolate titer increased from 0.07 to 2.16 g/L while glycolate yields increased from 0.04 to 0.35 mol/mol-acetate and from 0.03 to 1.04 mol/mol-glucose. Module II was then engineered to increase NADPH supply. Through deletion of pfkA, pfkB, ptsI and sthA genes as well as upregulating zwf, pgl and tktA, glycolate titer increased from 2.16 to 4.86 g/L while glycolate yields increased from 0.35 to 0.82 mol/mol-acetate and from 1.04 to 6.03 mol/mol-glucose. The activities of AceA and YcdW were further increased to pull the carbon flux to glycolate, which increased glycolate yield from 0.82 to 0.92 mol/mol-acetate. Fed-batch fermentation of the final strain NZ-Gly303 produced 73.3 g/L glycolate with a productivity of 1.04 g/(L·h). The acetate to glycolate yield was 0.85 mol/mol (1.08 g/g), while glucose to glycolate yield was 6.1 mol/mol (2.58 g/g). The total carbon molar yield was 0.60 mol/mol, which reached 80% of the theoretical value.

A New Synthetic Pathway for the Bioproduction of Glycolic Acid From Lignocellulosic Sugars Aimed at Maximal Carbon Conservation

Glycolic acid is a two-carbon α-hydroxy acid with many applications in industrial sectors including packaging, fine chemistry, cosmetics, and pharmaceutics. Currently, glycolic acid is chemically manufactured from fossil resources. This chemical mode of production is raising some concerns regarding its use in health for personal care. Microbial production of GA stands as a remarkable challenge to meet these concerns, while responding to the increasing demand to produce bio-sourced products from renewable carbon resources. We here report on the design and expression of a novel non-natural pathway of glycolic acid in E. coli. The originality of this new pathway, termed "glycoptimus" relies on two pillars. On the one hand, it requires the overexpression of three naturally occurring E. coli genes, namely kdsD encoding a D-arabinose-5-P isomerase, fsaA encoding a class 1 aldolase that cleaves D-arabinose-5-P into glyceraldehyde-3-P and glycolaldehyde, and aldA coding for an aldehyde dehydrogenase that oxidizes glycoladehyde in glycolate. These three genes constitute the "glycoptimus module." On the other hand, the expression of these genes together with a reshaping of the central carbon metabolism should enable a production of glycolic acid from pentose and hexose at a molar ratio of 2.5 and 3, respectively, which corresponds to 50% increase as compared to the existing pathways. We demonstrated the 'in vivo' potentiality of this pathway using an E. coli strain, which constitutively expressed the glycoptimus module and whose carbon flow in glycolysis was blocked at the level of glyceraldehyde-3-P dehydrogenase reaction step. This engineered strain was cultivated on a permissive medium containing malate and D-glucose. Upon exhaustion of malate, addition of either D-glucose, D-xylose or L-arabinose led to the production of glycolic acid reaching about 30% of the maximum molar yield. Further improvements at the level of enzymes, strains and bioprocess engineering are awaited to increase yield and titer, rendering the microbial production of glycolic acid affordable for a cost-effective industrial process.

Chemoenzymatic Synthesis of Furfuryl Alcohol from Biomass in Tandem Reaction System

In this study, chemoenzymatic synthesis of furfuryl alcohol from biomass (e.g., corncob, bamboo shoot shell, and rice straw) was attempted by the tandem catalysis with Lewis acid (SnCl₄ or solid acid SO₄^2-/SnO₂-bentonite) and biocatalyst in one-pot manner. Compared with SnCl₄, solid acid SO₄^2-/SnO₂-bentonite had higher catalytic activity for converting biomass into furfural, which could be biologically converted into furfuryl alcohol with Escherichia coli CCZU-H15 whole-cell harboring reductase activity. Sequential catalysis of biomass into furfural with SO₄^2-/SnO₂-bentonite (3.0 wt%) at 170 °C for 0.5 h and bioreduction of furfural with whole cells at 30 °C for 4.5 h were used for the effective synthesis of furfuryl alcohol in one-pot media. Corncob, bamboo shoot shell, and rice straw (3.0 g, dry weight) could be converted into 65.7, 50.3, and 58.5 mM furfuryl alcohol with the yields of 0.26, 0.25, and 0.23 g furfuryl alcohol/(g xylan in biomass) in 40 mL reaction media. Finally, an efficient process of recycling and reusing of SO₄^2-/SnO₂-bentonite catalyst and immobilized whole-cell biocatalyst was developed for the chemoenzymatic synthesis of furfuryl alcohol from biomass in the one-pot reaction system.

Inhibitory Effect of Volatiles Emitted From Alcaligenes faecalis N1-4 on Aspergillus flavus and Aflatoxins in Storage

Controlling aflatoxigenic Aspergillus flavus and aflatoxins (AFs) in grains and food during storage is a great challenge to humans worldwide. Alcaligenes faecalis N1-4 isolated from tea rhizosphere soil can produce abundant antifungal volatiles, and greatly inhibited the growth of A. flavus in un-contacted face-to-face dual culture testing. Gas chromatography tandem mass spectrometry revealed that dimethyl disulfide (DMDS) and methyl isovalerate (MI) were two abundant compounds in the volatile profiles of N1-4. DMDS was found to have the highest relative abundance (69.90%, to the total peak area) in N1-4, which prevented the conidia germination and mycelial growth of A. flavus at 50 and 100 μL/L, respectively. The effective concentration for MI against A. flavus is 200 μL/L. Additionally, Real-time quantitative PCR analysis proved that the expression of 12 important genes in aflatoxin biosynthesis pathway was reduced by these volatiles, and eight genes were down regulated by 4.39 to 32.25-folds compared to control treatment with significant differences. And the A. flavus infection and AFs contamination in groundnut, maize, rice and soybean of high water activity were completely inhibited by volatiles from N1-4 in storage. Scanning electron microscope further proved that A. flavus conidia inoculated on peanuts surface were severely damaged by volatiles from N1-4. Furthermore, strain N1-4 showed broad and antifungal activity to other six important plant pathogens including Fusarium graminearum, F. equiseti, Alternaria alternata, Botrytis cinerea, Aspergillus niger, and Colletotrichum graminicola. Thus, A. faecalis N1-4 and volatile DMDS and MI may have potential to be used as biocontrol agents to control A. flavus and AFs during storage.

Marine Microorganisms for Biocatalysis: Selective Hydrolysis of Nitriles with a Salt-Resistant Strain of Meyerozyma guilliermondii

A screening among marine yeasts was carried out for nitrile hydrolyzing activity. Meyerozyma guilliermondii LM2 (UBOCC-A-214008) was able to efficiently grow on benzonitrile and cyclohexanecarbonitrile (CECN) as sole nitrogen sources. A two-step one-pot method for obtaining cells of M. guilliermondii LM2 (UBOCC-A-214008) endowed with high nitrilase activity was established; the resulting whole cells converted different nitriles with high molar conversions and showed interesting enantioselectivity toward racemic substrates. Nitrilase from M. guilliermondii LM2 (UBOCC-A-214008) displayed high activity on aromatic substrates, but also arylaliphatic and aliphatic substrates were accepted. Salt-resistant M. guilliermondii LM2 (UBOCC-A-214008) was used in media with different salinity, being highly active up to 1.5 M NaCl concentration. Finally, hydrolysis of nitriles was efficiently performed using a bioprocess (yeast growth and biotransformation with resting cells) entirely carried out in seawater.

One-step continuous/semi-continuous whole-cell catalysis production of glycolic acid by a combining bioprocess with in-situ cell recycling and electrodialysis

Bioprocess for successive bio-production of glycolic acid (GA) from ethylene glycol (EG) using Gluconobacter oxydans is hindered by strong end-product inhibitory effect. Based on the model of compressed oxygen supplied-sealed stirred tank reactor (COS-SSTR), we developed a new system by attaching an ultrafiltration instrument and electrodialysis cell to in-situ separate GA, including conductivity meter to control automatic EG feeding. The combined bioprocess was therefore set up as compressed oxygen supplied cell catalysis-ultrafiltration-electrodialysis (COS-CUE). In comparison with the conventional resin and electrodialysis separation process, this device simplified the whole bioprocess. We realized the potential of combined bioprocess for producing GA without EG through continuous/semi-continuous 'one-step' process. Finally, 288.4 g GA was obtained at the yield of 96.5% and average productivity of 4.0 g/L/h in 72 h, with an increment of 148.8% and 20.9% in production compared with batch and cell-recycling fermentation.

Biotechnological production of glycolic acid and ethylene glycol: current state and perspectives

Glycolic acid (GA) and ethylene glycol (EG) are versatile two-carbon organic chemicals used in multiple daily applications. GA and EG are currently produced by chemical synthesis, but their biotechnological production from renewable resources has received a substantial interest. Several different metabolic pathways by using genetically modified microorganisms, such as Escherichia coli, Corynebacterium glutamicum and yeast have been established for their production. As a result, the yield of GA and EG produced from sugars has been significantly improved. Here, we describe the recent advancement in metabolic engineering efforts focusing on metabolic pathways and engineering strategies used for GA and EG production.

Selective Synthesis of Furfuryl Alcohol from Biomass-Derived Furfural Using Immobilized Yeast Cells

Furfuryl alcohol (FA) is an important building block in polymer, food, and pharmaceutical industries. In this work, we reported the biocatalytic reduction of furfural, one of the top value-added bio-based platform chemicals, to FA by immobilized Meyerozyma guilliermondii SC1103 cells. The biocatalytic process was optimized, and the tolerance of this yeast strain toward toxic furfural was evaluated. It was found that furfural of 200 mM could be reduced smoothly to the desired product FA with the conversion of 98% and the selectivity of >98%, while the FA yield was only approximately 81%. The gap between the substrate conversion and the product yield might partially be attributed to the substantial adsorption of the immobilization material (calcium alginate) toward the desired product, but microbial metabolism of furans (as carbon sources) made a negligible contribution to it. In addition, FA of approximately 156 mM was produced within 7 h in a scale-up reaction, along with the formation of trace 2-furoic acid (1 mM) as the byproduct. The FA productivity was up to 2.9 g/L/h, the highest value ever reported in the biocatalytic synthesis of FA. The crude FA was simply separated from the reaction mixture by organic solvent extraction, with the recovery of 90% and the purity of 88%. FA as high as 266 mM was produced by using a fed-batch strategy within 15.5 h.

Integrated process for scalable bioproduction of glycolic acid from cell catalysis of ethylene glycol

Glycolic acid (GA) is presently booming as a versatile raw material in the fields of high-grade cosmetics, polymer degradable materials, and drug production. The biocatalysis of ethylene glycol (EG) to GA is promising, with environmentally friendly benefits, while the effective and straight bioproduction of GA qualified for polymer synthesis purity is a challenge. In this study, we combine whole cell catalysis step and acidification-purification step. A compressed oxygen supply in the sealed aerated stirred tank reaction (COS-SSTR) and a weak basic anion-exchange resins were integrated to develop an efficient process of GA bioproduction from EG. Finally, 110.5 g/L of GA was obtained at the yield of 94.4% and the volume productivity of 2.3 g/L/h in 48 h that presently is the greatest level for GA bioproduction. After 335 resins treatment of 5.0 L catalyzed broth containing 497.2 g EG, we obtained 575.4 g GA at the recovery rate of 98.9%.

Improving techno-economics of bioproduct glycolic acid by successive recycled-cell catalysis of ethylene glycol with Gluconobacter oxydans

Bioconversion of ethylene glycol (EG) to glycolic acid (GA) by the whole-cell of Gluconobacter oxydans in an aired stirred tank reactor (ASTR) with continuous substrate feeding yielded over 220 g/L of GA. However, the bioreactor productivity declined to an unfavorable level of 0.63 g/L/h due to negative feed-back by GA which inhibited the reaction. To overcome this problem, based on results obtained from techno-economic comparative analysis, we set up a successive recycled-cell catalytic bioprocessing ASTR, and carried out five consecutive cycles stably during 240 h. At the end of this process, total 490.7 g GA was accumulated with over 90% yield, and an average bioreactor productivity of 2.04 g/L/h. The twin strategies of end-product titer control and cell-recycling successfully demonstrated the large scale applicability of EG bioconversion to GA.

Metabolic engineering of a xylose pathway for biotechnological production of glycolate in Escherichia coli

BACKGROUND

Glycolate is a valuable chemical with extensive applications in many different fields. The traditional methods to synthesize glycolate are quite expensive and toxic. So, the biotechnological production of glycolate from sustainable feedstocks is of interest for its potential economic and environmental advantages. D-Xylose is the second most abundant sugar in nature and accounts for 18-30% of sugar in lignocellulose. New routes for the conversion of xylose to glycolate were explored.

RESULTS

Overexpression of aceA and ghrA and deletion of aceB in Escherichia coli were examined for glycolate production from xylose, but the conversion was initially ineffective. Then, a new route for glycolate production was established in E. coli by introducing NAD⁺-dependent xylose dehydrogenase (xdh) and xylonolactonase (xylC) from Caulobacter crescentus. The constructed engineered strain Q2562 produced 28.82 ± 0.56 g/L glycolate from xylose with 0.60 ± 0.01 g/L/h productivity and 0.38 ± 0.07 g/g xylose yield. However, 27.18 ± 2.13 g/L acetate was accumulated after fermentation. Deletions of iclR and ackA were used to overcome the acetate excretion. An ackA knockout resulted in about 66% decrease in acetate formation. The final engineered strain Q2742 produced 43.60 ± 1.22 g/L glycolate, with 0.91 ± 0.02 g/L/h productivity and 0.46 ± 0.03 g/g xylose yield.

CONCLUSIONS

A new route for glycolate production from xylose was established, and an engineered strain Q2742 was constructed from this new explored pathway. The engineering strain showed the highest reported productivity of glycolate to date. This research opened up a new prospect for bio-refinery of xylose and an alternative choice for industrial production of glycolate.

Balancing the carbon flux distributions between the TCA cycle and glyoxylate shunt to produce glycolate at high yield and titer in Escherichia coli

The glyoxylate shunt is a branch of the tricarboxylic acid (TCA) cycle which directly determines the synthesis of glycolate, and the balance between the glyoxylate shunt and TCA cycle is very important for the growth of Escherichia coli. In order to accumulate glycolate at high yield and titer, strategies for over-expressing glycolate pathway enzymes including isocitrate lyase (AceA), isocitrate dehydrogenase kinase/phosphatase (AceK) and glyoxylate reductase (YcdW) were analyzed. The genes encoding these three enzymes were transcribed under the control of promoter pTrc on pTrc99A, to form pJNU-3, which was harbored by strain Mgly1, resulting in strain Mgly13. Strain Mgly13 produced glycolate with 0.385 g/g-glucose yield (45.2% of the theoretical yield). Citrate synthase (GltA) converted excess acetyl-CoA and oxaloacetate to citrate and was over-expressed by pJNU-4 (pCDFDuet-1 backbone). Thus, the resulting strain Mgly134 produced glycolate with a 0.504 g/g-glucose yield (59.3% of the theoretical yield). We then eliminated the pathways involved in the degradation of glycolate, resulting in strain Mgly434, which produced glycolate with 92.9% of the theoretical yield. Following optimization of fermentation, the maximum glycolate titer from strain Mgly434 was 65.5 g/L.

Production and Characterization of a Nitrilase from Pseudomonas aeruginosa RZ44 and its Potential for Nitrile Biotransformation

BACKGROUND

The conversion of nitriles into amides or carboxylic acids by nitrilase has taken its application into consideration, as the scope of its applications has recently been extended.

OBJECTIVES

In this study, P. aeruginosa RZ44 was isolated from sewage in the Kerman which has Nitrile-degradation activity. In order to improve the nitrilase production, several optimization were done on environmental condition. Nitrilase activity was characterized against different pHs, temperatures, ions, and substrates.

MATERIALS AND METHODS

Enzyme activity was evaluated by determining the production of ammonia following to the modification of the phenol/hypochlorite method. Different factors that affect production of the enzyme by P. aeruginosa RZ44 were optimized and evaluated in the culture mediums.

RESULTS

The results showed that degradation of the acetonitrile by P. aeruginosa RZ44 increased the pH of the growth medium from the initial pH 7.0 to 9.37. Optimizing the medium for P. aeruginosa RZ44, it was found that glucose and starch (5 g.L-1) have strongly supported nitrilase production, compared to the control. As well, urea (5 g.L-1) and yeast extract (15 g.L-1) have favored an increased biomass and nitrilase production, as the nitrogen sources. These results show that nitrilase production increases in the pH range 5.0 to 7.0 and then start decreasing. Addition of the Mg2+, Fe2+ and Na+ has supported the biomass and nitrilase production. Co2+, Mn2+ and Cu2+ were confirmed to inhibit cell growth and enzyme production. Enzyme characterization results show that, P. aeruginosa RZ44 nitrilase exhibits comparatively high activity and stability at pH 7.0 and 40°C. Nitrilase was completely inhibited by CoCl2 and CaCl2, whereas, the inhibition in the presence of MnSO4 and CuSO4 was about 60%. Time course analysis of the nitrile conversion by the resting P. aeruginosa RZ44 cells showed that nitrile substrates (i.e. acetonitrile) was hydrolyzed within 8 h.

CONCLUSIONS

these results indicate that P. aeruginosa RZ44 has the potential to be applied in the biotransformation of nitrile compounds.

Nitrile-converting enzymes: an eco-friendly tool for industrial biocatalysis

Nitriles are organic compounds bearing a − C ≡ N group; they are frequently known to occur naturally in both fauna and flora and are also synthesized chemically. They have wide applicability in the fields of medicine, industry, and environmental monitoring. However, the majority of nitrile compounds are considered to be lethal, mutagenic, and carcinogenic in nature and are known to cause potential health problems such as nausea, bronchial irritation, respiratory distress, convulsions, coma, and skeletal deformities in humans. Nitrile-converting enzymes, which are extracted from microorganisms, are commonly termed nitrilases and have drawn the attention of researchers all over the world to combat the toxicity of nitrile compounds. The present review focuses on the utility of nitrile-converting enzymes, sources, classification, structure, properties, and applications, as well as the future perspective on nitrilases.

Enhanced bioconversion of ethylene glycol to glycolic acid by a newly isolated Burkholderia sp. EG13

Burkholderia sp. EG13 with high ethylene glycol-oxidizing activity was isolated from soil, which could be used for the synthesis of glycolic acid from the oxidation of ethylene glycol. Using the resting cells of Burkholderia sp. EG13 as biocatalysts, the optimum reaction temperature and pH were 30 °C and 6.0, respectively. After 24 h of biotransformation, the yield of glycolic acid from 200 mM ethylene glycol was 98.8 %. Furthermore, an integrated bioprocess for the production of glycolic acid which involved in situ product removal (ISPR) was investigated. Using fed-batch method with ISPR, a total of 793 mM glycolic acid has been accumulated in the reaction mixture after the 4th feed.

Effect of physicochemical parameters on nitrile-hydrolyzing potentials of newly isolated nitrilase of Fusarium oxysporum f. sp. lycopercisi ED-3

In recent years, nitrilases from fungus have received increasing attention, and most of the studies are performed on nitrilases of bacterial origin. Frequently used methods are based on analytical methods such as high-performance liquid chromatography, liquid chromatography-mass spectrometry, and gas chromatography; therefore, an efficient, user friendly, and rapid method has been developed to screen nitrilase enzyme based on the principle of color change of a pH indicator. Phenol red amended with the minimal medium appears light yellow at neutral pH, which changes into pink with the formation of ammonia, indicating nitrilase activity in the reaction medium. A highly potent strain ED-3 identified as Fusarium oxysporum f. sp. lycopercisi (specific activity 17.5 µmol/Min/mg dcw) was isolated using this method. The nitrilase activity of F. oxysporum f. sp. lycopercisi ED-3 strain showed wide substrate specificity toward aliphatic nitriles, aromatic nitriles, and orthosubstituted heterocyclic nitriles. 4-Aminobenzonitrile was found to be a superior substrate among all the nitriles used in this study. This nitrilase was active within pH 5-10 and temperature ranging from 25 to 60 °C with optimal at pH 7.0 and temperature at 50 °C. The nitrilase activity was enhanced to several folds through optimization of culture and biotransformation conditions from 1,121 to 1,941 µmol/Min.

Biosynthesis of ethyl (S)-4-chloro-3-hydroxybutanoate by NADH-dependent reductase from E. coli CCZU-Y10 discovered by genome data mining using mannitol as cosubstrate

The reductase (PgCR) from recombinant Escherichia coli CCZU-Y10 displayed high reductase activity and excellent stereoselectivity for the reduction of ethyl 4-chloro-3-oxobutanoate (COBE) into ethyl (S)-4-chloro-3-hydroxybutanoate ((S)-CHBE). To efficiently synthesize (S)-CHBE (>99 % enantiomeric excess (ee)), the highly stereoselective bioreduction of COBE into (S)-CHBE with the whole cells of E. coli CCZU-Y10 was successfully demonstrated in a dibutyl phthalate-water biphasic system. The appropriate ratio of the organic phase to water phase was 1:1 (v/v). The optimum reaction temperature, reaction pH, cosubstrate, NAD(+), and cell dosage of the biotransformation of 100 mM COBE in this biphasic system were 30 °C, 7.0, mannitol (2.5 mmol/mmol COBE), 0.1 μmol/(mmol COBE), and 0.1 g (wet weight)/mL, respectively. Moreover, COBE at a high concentration of (1,000 mM) could be asymmetrically reduced to (S)-CHBE in a high yield (99.0 %) and high enantiometric excess value (>99 % ee). Significantly, E. coli CCZU-Y10 shows high potential in the industrial production of (S)-CHBE (>99 % ee).

Isolation and Characterization of a Nitrile-Hydrolysing Bacterium Isoptericola variabilis RGT01

A nitrile-hydrolysing bacterium, identified as Isoptericola variabilis RGT01, was isolated from industrial effluent through enrichment culture technique using acrylonitrile as the carbon source. Whole cells of this microorganism exhibited a broad range of nitrile-hydrolysing activity as they hydrolysed five aliphatic nitriles (acetonitrile, acrylonitrile, propionitrile, butyronitrile and valeronitrile), two aromatic nitriles (benzonitrile and m-Tolunitrile) and two arylacetonitriles (4-Methoxyphenyl acetonitrile and phenoxyacetonitrile). The nitrile-hydrolysing activity was inducible in nature and acetonitrile proved to be the most efficient inducer. Minimal salt medium supplemented with 50 mM acetonitrile, an incubation temperature of 30 °C with 2 % v/v inoculum, at 200 rpm and incubation of 48 h were found to be the optimal conditions for maximum production (2.64 ± 0.12 U/mg) of nitrile-hydrolysing activity. This activity was stable at 30 °C as it retained around 86 % activity after 4 h at this temperature, but was thermolabile with a half-life of 120 min and 45 min at 40 °C and 50 °C respectively.

Biotransformation of methylphenylacetonitriles by Brazilian marine fungal strain Aspergillus sydowii CBMAI 934: eco-friendly reactions

This study reports the biotransformation of methylphenylacetonitriles by Brazilian marine filamentous fungus Aspergillus sydowii CBMAI 934 under eco-friendly reaction conditions. The phenylacetonitrile 1, 2-methylphenylacetonitrile 2, 3-methylphenylacetonitrile 3, and 4-methylphenylacetonitrile 4 were quantitatively biotransformed into 2-hydroxyphenylacetic 1a, 2-methylphenylacetic acid 2a, 3-methylphenylacetic acid 3a, and 4-methylphenylacetic acid 4a by enzymatic processes using whole cell as biocatalyst. The marine fungus A. sydowii CBMAI 934 is thus a promising biocatalyst for the preparation of important carboxylic acids under mild conditions (pH 7.5 and 32 °C) from nitrile compounds.

Purification and characterization of arylacetonitrile-specific nitrilase of Alcaligenes sp. MTCC 10675

Arylacetonitrile-hydrolyzing nitrilase (E.C. 3.5.5.5) of Alcaligenes sp. MTCC 10675 has been purified by up to 46-fold to homogeneity and 32% yield using ammonium sulfate fractionation, Sephacryl S-300 gel permeation, and anion exchange chromatography. The molecular weight of the native enzyme was estimated to be 520 ± 60 kDa. The subunit has a molecular weight of 60 ± 14 kDa in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The optimum pH and temperature of the purified enzyme were 6.5 and 50 °C, respectively. The purified arylacetonitrilase has a half-life of 3 H 20 Min at its optimum temperature. The value for Vmax, Km , kcat , and ki of enzyme for mandelonitrile as a substrate was 50 ± 05 µmol/Min/mg, 13 ± 02 mM, 26 ± 03 Sec(-) , and 32.4 ± 03 mM, respectively. Alcaligenes sp. MTCC 10675 arylacetonitrilase amino acid sequence has variations from other reported arylacetonitrilase, namely, A11G, N21H, D149N, S170T, P171R, S179A, Q180N, and S191A, and it has a high thermal stability and catalytic rate as compared with the already purified arylacetonitrilase.