Transesterification of primary and secondary alcohols using Pseudomonas aeruginosa lipase

Lipases of a newly isolated Pseduomonas aeruginosa MTCC 5113 were assessed for transesterification of benzyl alcohol and vinyl acetate to produce the flavoring agent benzyl acetate. Crude lipase preparations that minimized the cost of the biocatalyst, achieved benzyl alcohol conversion of 89% within 3h at 30 degrees C. In contrast, purified and expensive commercially available lipases of Candida antarctica and porcine pancreas achieved much lower conversions at 80% and 15%, respectively. A well-mixed ( approximately 800 rev.min(-1)) batch reactor having the aqueous phase finely dispersed in heptane was used in these studies. Benzyl alcohol conversion was maximal when the enzyme-containing aqueous phase constituted about 50% of the total reactor volume. Use of solvents such as hexane, benzene, toluene and dimethyl sulfoxide reduced conversion compared with the use of heptane.     

Yeast-mediated preparation of l-PAC in an organic solvent

The yeast-mediated acyloin condensation of benzaldehyde and pyruvic acid to form l-PAC occurs in a petroleum spirit solvent system at room temperature with moderate conversion (30%) and high enantioselectivity (86%ee) after 24 h. The addition of a small amount of ethanol (0.5% mL) to the reaction mixture inhibits the formation of the side product benzyl alcohol and increases the conversion to l-PAC. Conducting the reaction using 13C labeled pyruvate indicated that the pyruvate was incorporated into the l-PAC and that the excess pyruvate was converted into ethanol. Conducting the reaction at 5 degrees C results in similar conversion but higher enantioselectivity.     

Enzymatic synthesis of benzyl benzoate using different acyl donors: Comparison of solvent-free reaction techniques

In this study, benzyl benzoate was successfully synthesized via enzymatic acylation using three immobilized enzymes as biocatalysts. Different acyl donors (benzoic acid and benzoic anhydride), operation regimes (batch, fed-batch), mixing modes (conventional mechanical stirring and ultrasound), process parameters (temperature, substrate molar ratio of acyl donor to acyl acceptor), presence or absence of solvents, enzyme amount and type were evaluated. Benzoic acid is a solid that is difficult to solubilize and, thus, was not efficient as acyl donor for the synthesis of benzyl benzoate. On the other hand, benzoic anhydride was very effective for the acylation of benzyl benzoate, and the presence of an excess of benzyl alcohol was essential to ensure the solute-solvent intermolecular attractions and good substrate solubilization, allowing the ester synthesis to be performed in the absence of organic solvents. The ultrasound was effective in increasing increase the initial reaction rate and the final conversion (88 %). However, the Lipozyme TL-IM and RM-IM supports were damaged, and the reuse was unfeasible. The batch and fed-batch approaches in conventional stirring ensured high conversions of 92 and 90 %, respectively, for batch (anhydride: alcohol 1:6) and fed-batch (1:3) using the Lipozyme TL-IM as biocatalyst. The controlled addition of the anhydride (fed-batch) allowed the reduction of alcohol molar ratio but decreased the reaction rates, and the maximum conversions were reached only after 24 h, while the batch approach had 92 % of conversion after 6 h. The yield of benzyl benzoate was high at 6 wt.% of enzyme, low temperature (50 °C), and simple reactor operation (batch). Results show the feasibility of the synthesis of benzyl benzoate via acylation using a green process that may be an alternative route to the chemical synthesis.     

Enantioselective reduction of aryl ketones using immobilized cells of Candida viswanathii

Enantioselective reduction of 1-acetonapthone to S(−)-1-(1-naphthyl) ethanol, a key intermediate for the synthesis of HMG Co-A reductase inhibitor, was successfully carried out using immobilized cells of a newly isolated carbonyl reductase producing yeast strain Candida viswanathii MTCC 5158. Calcium alginate (1.5%, w/v) gave the best immobilization efficiency. Among different organic solvents and ionic liquids tried as reaction media, isopropanol gave the best enantioselectivity with moderate conversion. The immobilized cells (100 mg/ml in 50 mM Tris buffer pH 9) showed best results at a substrate concentration of 0.2 mg/ml at 30 °C. After twelve cycles of reaction, no significant decrease in bioreduction efficiency of the immobilized cells was observed as compared to the free cells.     

Toluene and ethylbenzene oxidation by purified naphthalene dioxygenase from Pseudomonas sp. strain NCIB 9816-4.

Purified naphthalene dioxygenase (NDO) from Pseudomonas sp. strain NCIB 9816-4 oxidized toluene to benzyl alcohol and benzaldehyde by reactions involving benzylic monooxygenation and dioxygen-dependent alcohol oxidation, respectively. Xylene and nitrotoluene isomers were also oxidized to substituted benzyl alcohol and benzaldehyde derivatives. NDO oxidized ethylbenzene sequentially through (S)-1-phenethyl alcohol (77% enantiomeric excess) and acetophenone to 2-hydroxyacetophenone. In addition, NDO also oxidized ethylbenzene through styrene to (R)-1-phenyl-1,2-ethanediol (74% enantiomeric excess) by reactions involving desaturation and dihydroxylation, respectively. Isotope experiments with 18O2, H2 18O, and D2O suggest that 1-phenethyl alcohol is oxidized to acetophenone by a minor reaction involving desaturation followed by tautomerization. The major reaction in the conversion of 1-phenethyl alcohol and benzyl alcohol to acetophenone and benzaldehyde, respectively, probably involves monohydroxylation to form a gem-diol intermediate which stereospecifically loses the incoming hydroxyl group to leave the carbonyl product. These results are compared with similar reactions catalyzed by cytochrome P-450.     

Green biosynthesis of floxuridine by immobilized microorganisms

This work describes an efficient, simple, and green bioprocess for obtaining 5-halogenated pyrimidine nucleosides from thymidine by transglycosylation using whole cells. Biosynthesis of 5-fluoro-2'-deoxyuridine (floxuridine) was achieved by free and immobilized Aeromonas salmonicida ATCC 27013 with an 80% and 65% conversion occurring in 1 h, respectively. The immobilized biocatalyst was stable for more than 4 months in storage conditions (4 °C) and could be reused at least 30 times without loss of its activity. This microorganism was able to biosynthesize 2.0 mg L(-1) min(-1) (60%) of 5-chloro-2'-deoxyuridine in 3 h. These halogenated pyrimidine 2'-deoxynucleosides are used as antitumoral agents.     

A predictive thermodynamic model for the bioreduction of acetophenone to phenethyl alcohol using resting cells of Saccharomyces cerevisiae.

Equilibrium conversions were observed in the range of 60.2-76.0% with different initial compositions of reaction media for the bioreduction of acetophenone using resting cells of Saccharomyces cerevisiae in aqueous solutions at 30 degrees C. The reduction of acetophenone in the cells under anaerobic conditions is considered to be coupled with the oxidation of ethanol to acetate in the cytoplasm. A biphasic thermodynamic model is proposed which includes a nonuniform distribution of reagents across the cell membrane, a transmembrane pH gradient, ideal and nonideal solution models, and a basic reaction stoichiometry (ACP + (1/2) EtOH + (1/2)H2O <--> PEA + (1/2)Ac- + (1/2)H+). The intracellular activity coefficients were based on the Lewis-Randall rule for acetophenone, phenethyl alcohol, and H2O and Henry's law for ethanol, acetate anion, and H+. The overall standard Gibbs free energy was estimated to be -0.11 kcal/mol at a pH 7, 25 degrees C, and 1 atm. The intracellular thermodynamic activity coefficients of acetophenone and phenethyl alcohol were predicted to be 471.2 and 866.4, respectively, using the measured initial distribution coefficients and calculated extracellular activity coefficients. The model reflected a zero Gibbs free energy change at calculated conversions within 4% of the measured equilibrium conversions. The analysis verified the effect of the concentration ratio of the substrate acetophenone to the co-substrate ethanol on the conversion efficiency and suggested that the intracellular pH and the pH gradient across the cell transmembrane significantly affect the predicted equilibrium conversion. The intracellular pH of resting, viable cells of Bakers' yeast at the bioconversion conditions was determined experimentally to be 5.77.     

Overcoming the thermodynamic limitation in asymmetric hydrogen transfer reactions catalyzed by whole cells

Whole lyophilized cells of an Escherichia coli overexpressing the alcohol dehydrogenase (ADH-'A') from Rhodococcus ruber DSM 44541 were used for the asymmetric reduction of ketones to secondary alcohols. The recycling of the required nicotinamide cofactor (NADH) was achieved in a coupled-substrate process. In the course of the reaction the ketone is reduced to the alcohol and the hydrogen donor 2-propanol is oxidized to acetone by one enzyme. This leads to a thermodynamic equilibrium between all four components determining the maximum achievable conversion. To overcome this limitation an in situ product removal technique (ISPR) for the application with whole cells was developed. In this method the most volatile compound is separated from the reaction vessel by an air flow resulting in a shift of the equilibrium towards the desired secondary alcohol. The so-called stripping process represents a simple and efficient method to overcome the thermodynamic limitation in biocatalytic reactions. Employing this method, the conversion of selected biotransformations was increased up to completeness.     

Transesterification of ethylparaben by free and entrapped cells of Pseudomonas cepacia

Ethylparaben was transesterified to methylparaben in the presence of methanol by Pseudomonas cepacia. When the bacterium was incubated in water-methanol solutions of ethylparaben in the range of 0.01 to 2% methanol, the higher the content of methanol, the higher the conversion ratios of ethylparaben. If over 5% methanol was used, the bacterium could not survive and the reaction did not proceed. Transesterifications also proceeded with 1-propanol or benzyl alcohol instead of methanol, though the conversion ratios were low. Conversion ratios were found to be higher throughout the conversion period by entrapping the cells to Ca alginate or polyurethanes than for free cells. The results are presumably due to the higher stability of cells in 10% alcohol in which free cells could not survive. PU-3 and PU-6 are urethane prepolymers consisting of polyetherdiol and phenylisocyanate segments. PU-3 has a high polypropyleneglycol content, while PU-6 is high in polyethyleneglycol (1).     

Decomposition of cholesterol by Achromobacter candicans]

The decomposition of cholesterol by the cell suspensions of Achromobacter candicans 42 and by the cell-free extracts of this bacterium was studied. The decomposition of cholesterol in the presence of the wet biomass during four hours of the incubation was 72.5 percent, and with the cells that were preliminarily lyophilized or treated by acetone 49.8 and 23.0 percent, respectively. The activity decreased from 70.0 to 50.0 percent if the biomass was kept at minus 3 degrees C during 70 days. The decomposition of cholesterol by the cell-free preparations (supernatant and protein after precipitation with ammonium sulphate to 0.7 saturation) constituted 40.0 percent of the cholesterol contained in a sample. One of the intermediate products of cholesterol decomposition was delta4-cholesten-3-one.     

Anaerobic degradation of toluene in denitrifying Pseudomonas sp.: indication for toluene methylhydroxylation and benzoyl-CoA as central aromatic intermediate

The anaerobic degradation of toluene has been studied with whole cells and by measuring enzyme activities. Cultures of Pseudomonas strain K 172 were grown in mineral medium up to a cell density of 0.5 g of dry cells per liter in fed-batch culture with toluene and nitrate as the sole carbon and energy sources. A molar growth yield of 57 g of cell dry matter formed per mol toluene totally consumed was determined. The mean generation time was 24 h. The redox balance between toluene consumed (oxidation and cell material synthesis) and nitrate consumed (reduction to nitrogen gas and assimilation as NH₃) was 77% of expectation if toluene was completely oxidized; this indicated that the major amount of toluene was mineralized to CO₂. It was tested whether the initial reaction in anaerobic toluene degradation was a carboxylation or a dehydrogenation (anaerobic hydroxylation); the hypothetical carboxylated or hydroxylated intermediates were tested with whole cells applying the method of simultanous adaptation: cells pregrown on toluene degraded benzyl alcohol, benzaldehyde, and benzoic acid without lag, 4-hydroxybenzoate and p-cresol with a 90 min lag phase and phenylacetate after a 200 min lag phase. The cells were not at all adapted to degrade 2-methylbenzoate, 4-methylbenzoate, o-cresol, and m-cresol, nor did these compounds support growth within a few days after inoculation with cells grown on toluene. In extracts of cells anaerobically grown on toluene, benzyl alcohol dehydrogenase, benzaldehyde dehydrogenase, and benzoyl-CoA synthetase (AMP forming) activities were present. The data (1) conclusively show anaerobic growth of a pure culture on tolucne; (2) suggest that toluene is anaerobically degraded via benzoyl-CoA; (3) imply that water functions as the source of the hydroxyl group in a toluene methylhydroxylase reaction.     

Bioconversion of benzonitrile to benzoic acid using free and agar entrapped cells of Nocardia globerula NHB-2

The free and agar immobilized cells of Nocardia globerula NHB-2 having nitrilase (EC 3.5.5.1) activity were used to catalyse the transformation of benzonitrile to benzoic acid. The whole cells of N. globerula NHB-2 were immobilized in agar which exhibited maximum conversion of benzonitrile to benzoic acid in 0.1 M potassium phosphate buffer pH 7.5 (free cells) 8.0 (immobilized cells), temperature 40 degrees C, cells 2 mg dcm ml(-1) reaction mixture and benzonitrile (4% v/v) in 4 h (free cells). The effect of temperature on the stability of nitrilase was studied and cells retained 100% activity at 30 degrees C and lost 50% activity at 40 degrees C. In a fed batch mode of reaction 108 and 84 gl(-1) benzoic acid was produced using free and agar entrapped cells (2 g dcm). The agar immobilized cells were recycled up to three times and 80, 62, 20 gl(-1) benzoic acid was again produced respectively in each of three cycles and a total 244 g benzoic acid was produced by recycling the same mass of immobilized biocatalyst.     

Nonconventional hydrolytic dehalogenation of 1-chlorobutane by dehydrated bacteria in a continuous solid-gas biofilter

Rhodococcus erythropolis NCIMB 13064 and Xanthobacter autotrophicus GJ10 are able to catalyze the conversion of halogenated hydrocarbons to their corresponding alcohols. These strains are attractive biocatalysts for gas phase remediation of polluted gaseous effluents because of their complementary specificity for short or medium and for mono-, di-, or trisubstituted halogenated hydrocarbons (C2-C8 for Rhodococcus erythropolis and C1-C4 for Xanthobacter autotrophicus).After dehydration, these bacteria can catalyze the hydrolytic dehalogenation of 1-chlorobutane in a nonconventional gas phase system under a controlled water thermodynamic activity (a(w)). This process makes it possible to avoid the problems of solubility and bacterial development due to the presence of water in the traditional biofilters.In the aqueous phase, the dehalogenase activity of Rhodococcus erythropolis is less sensitive to thermal denaturation and the apparent Michaelis-Menten constants at 30 degrees C were 0.4 mM and 2.40 micromol min(-1) g(-1) for Km and Vmax, respectively. For Xanthobacter autotrophicus they were 2.8 mM and 0.35 micromol min(-1) g(-1). In the gas phase, the behavior of dehydrated Xanthobacter autotrophicus cells is different from that observed with Rhododcoccus erythropolis cells. The stability of the dehalogenase activity is markedly lower. It is shown that the HCl produced during the reaction is responsible for this low stability. Contrary to Rhodococcus erythropolis cells, disruption of cell walls does not increase the stability of the dehalogenase activity.The activity and stability of lyophilized Xanthobacter autotrophicus GJ10 cells are dependant on various parameters. Optimal dehalogenase activity was determined for water thermodynamic activity (a(w)) of 0.85. A temperature of 30 degrees C offers the best compromise between activity and stability. The pH control before dehydration plays a role in the ionization state of the dehalogenase in the cells. The apparent Michaelis-Menten constants Km and Vmax for the dehydrated Xanthobacter autotrophicus cells were 0.07 (1-chlorobutane thermodynamic activity) and 0.08 micromol min(-1) g(-1) of cells, respectively. A maximal transformation capacity of 1.4 g of 1-chlorobutane per day was finally obtained using 1g of lyophilized Xanthobacter autotrophicus GJ10 cells.     

Bioconversion of D-galactose to D-tagatose: continuous packed bed reaction with an immobilized thermostable L-arabinose isomerase and efficient purification by selective microbial degradation

The continuous enzymatic conversion of D-galactose to D-tagatose with an immobilized thermostable L-arabinose isomerase in packed-bed reactor and a novel method for D-tagatose purification were studied. L-arabinose isomerase from Thermoanaerobacter mathranii (TMAI) was recombinantly overexpressed and immobilized in calcium alginate. The effects of pH and temperature on D-tagatose production reaction catalyzed by free and immobilized TMAI were investigated. The optimal condition for free enzyme was pH 8.0, 60°C, 5 mM MnCl(2). However, that for immobilized enzyme was pH 7.5, 75°C, 5 mM MnCl(2). In addition, the catalytic activity of immobilized enzyme at high temperature and low pH was significantly improved compared with free enzyme. The optimum reaction yield with immobilized TMAI increased by four percentage points to 43.9% compared with that of free TMAI. The highest productivity of 10 g/L h was achieved with the yield of 23.3%. Continuous production was performed at 70°C; after 168 h, the reaction yield was still above 30%. The resultant syrup was then incubated with Saccharomyces cerevisiae L1 cells. The selective degradation of D-galactose was achieved, obtaining D-tagatose with the purity above 95%. The established production and separation methods further potentiate the industrial production of D-tagatose via bioconversion and biopurification processes.     

Optimization of production and reaction conditions of polygalacturonase from Byssochlamys fulva

In the present study, the optimization of production and reaction conditions of polygalacturonase produced by a fungus Byssochlamys fulva MTCC 505 was achieved. The production of polygalacturonase with a considerable activity of 1.28 IU/ml was found when the culture was shaken at 30°C for 5 days in 100 ml of medium containing (w/v) 10 g/l pectin, 2 g/l NaNO?, 1 g/l KH?PO?, 0.5 g/l KCl, 0.5 g/l MgSO?. 7H?O, 0.001 g/l FeSO?. 7H?O, 0.001 g/l CaCl?. The best carbon and nitrogen source for this enzyme were pectin (1%) and Ca(NO?)? (0.1%), respectively. The enzyme gave maximum activity at incubation time of 72 h, temperature of 30°C and pH 4.5. During the optimization of reaction conditions, the enzyme showed maximum activity in sodium citrate buffer (50 mM) of pH 5.5 at 50°C reaction temperature for 15 minutes of incubation. The enzyme showed greater affinity for polygalacturonic acid as substrate (0.5%). Km and Vmax values were 0.15 mg/ml and 4.58 μmol/ml/min. The effect of various phenolics, thiols, protein inhibitors and metal ions on the enzyme activity was investigated. The enzyme was quite stable at 4°C and 30°C. At 40°C the half life of the enzyme was 6 h and at 60°C it was 2 h.     

Production of S‐lactoylglutathione by high activity whole cell biocatalysts prepared by permeabilization of recombinant Saccharomyces cerevisiae with alcohols

The permeabilization of yeast cells with methanol, ethanol, and isopropyl alcohol under various conditions was studied to develop the preparation method of high activity whole cell biocatalysts. Recombinant Saccharomyces cerevisiae, which intracellularly overexpresses glyoxalase I and catalyzes the conversion of methylglyoxal to S‐lactoylglutathione in the presence of glutathione, was used as the model system. The permeabilization treatments with alcohols significantly enhanced the activities of yeast cells. Especially, the initial S‐lactoylglutathione production rates of cells permeabilized with 40% ethanol and isopropyl alcohol solutions for 10 min at 4°C were high and were 364 and 582 times larger than those of untreated cells, respectively. These permeabilized yeast cells retained high activities during repeated batch reactions. Even in third batch reaction, they showed approximately 70–80% of the activity in the first batch. The plasma membrane of S. cerevisiae cells was damaged by the treatment with alcohol solutions in such a way that leakage of glyoxalase I from the cells is rather small and that both substrate and product show very high permeability. The initial S‐lactoylglutathione production rates of these permeabilized cells were 1.5–2.5 times larger than those of glyoxalase I in cell extracts prepared by ethyl acetate method from the same amount of cells. These results demonstrate that the recombinant S. cerevisiae cells permeabilized with alcohol solutions under the optimum condition are very effective whole cell biocatalysts. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 64: 54–60, 1999.     

Benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase II from Acinetobacter calcoaceticus. Purification and preliminary characterization.

A quick, reliable, purification procedure was developed for purifying both benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase II from a single batch of Acinetobacter calcoaceticus N.C.I.B. 8250. The procedure involved disruption of the bacteria in the French pressure cell and preparation of a high-speed supernatant, followed by chromatography on DEAE-Sephacel, affinity chromatography on Blue Sepharose CL-6B and Matrex Gel Red A, and finally gel filtration through a Superose 12 fast-protein-liquid-chromatography column. The enzymes co-purified as far as the Blue Sepharose CL-6B step were separated on the Matrex Gel Red A column. The final preparations of benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase II gave single bands on electrophoresis under non-denaturing conditions or on SDS/polyacrylamide-gel electrophoresis. The enzymes are tetramers, as judged by comparison of their subunit (benzyl alcohol dehydrogenase, 39,700; benzaldehyde dehydrogenase II, 55,000) and native (benzyl alcohol dehydrogenase, 155,000; benzaldehyde dehydrogenase II, 222,500) Mr values, estimated by SDS/polyacrylamide-gel electrophoresis and gel filtration respectively. The optimum pH values for the oxidation reactions were 9.2 for benzyl alcohol dehydrogenase and 9.5 for benzaldehyde dehydrogenase II. The pH optimum for the reduction reaction for benzyl alcohol dehydrogenase was 8.9. The equilibrium constant for oxidation of benzyl alcohol to benzaldehyde by benzyl alcohol dehydrogenase was determined to be 3.08 x 10(-11) M; the ready reversibility of the reaction catalysed by benzyl alcohol dehydrogenase necessitated the development of an assay procedure in which hydrazine was used to trap the benzaldehyde formed by the NAD+-dependent oxidation of benzyl alcohol. The oxidation reaction catalysed by benzaldehyde dehydrogenase II was essentially irreversible. The maximum velocities for the oxidation reactions catalysed by benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase II were 231 and 76 mumol/min per mg of protein respectively; the maximum velocity of the reduction reaction of benzyl alcohol dehydrogenase was 366 mumol/min per mg of protein. The pI values were 5.0 for benzyl alcohol dehydrogenase and 4.6 for benzaldehyde dehydrogenase II. Neither enzyme activity was affected when assayed in the presence of a range of salts. Absorption spectra of the two enzymes showed no evidence that they contain any cofactors such as cytochrome, flavin, or pyrroloquinoline quinone. The kinetic coefficients of the purified enzymes with benzyl alcohol, benzaldehyde, NAD+ and NADH are also presented.     

Enzymatic production of (R)-phenylacetylcarbinol by pyruvate decarboxylase from <Emphasis Type="Italic">Zymomonas mobilis</Emphasis>

Herein, we synthesized (R)-phenylacetylcarbinol (PAC), a pharmaceutical intermediate for ephedrine and pseudoephedrine, from benzaldehyde and pyruvate using a recombinant pyruvate decarboxylase (PDC) from Zymomonas mobilis. A whole cell reaction consisting of 30 mM benzaldehyde, 60 mM pyruvate, and a mutant PDC enzyme (PDC W329M; 1.6 mg DCW/mL) produced 12.4 mM (R)-PAC and less than 0.3 mM benzyl alchohol in 15 h at 20°C, outperforming the crude enzyme extract reaction (1.2 mM (R)-PAC) and minimizing formation of benzyl alchohol, the major by-product of S. cerevisiae whole cell reaction. These observations suggested that recombinant E. coli whole cell reactions are more efficient than crude enzyme extract or yeast-based reactions. We also demonstrated that the E. coli whole cell reaction performed effectively without expensive thiamin diphosphate cofactor. Finally, whole cell reaction (8 mg DCW/mL) was carried out with 200 mM benzaldehyde, 400 mM pyruvate in 10 mL of 500 mM phosphate buffer (pH 6.5), and 72 mM (R)-PAC was produced with 36% conversion for 15 h. © KSBB