Acinetobacter and use thereof in production of chiral 3-cyclohexene-1-carboxylic acid

Abstract

The invention discloses a strain of Acinetobacter and use thereof in the production of chiral 3-cyclohexene-1-carboxylic acid. Its taxonomic name is Acinetobacter sp., which is deposited on Jan. 21, 2019 at the China General Microbiological Culture Collection Center, under accession number CGMCC No. 17220. Using the Acinetobacter strain of the invention to produce chiral methyl 3-cyclohexene-1-carboxylate, the resulting methyl (S)-3-cyclohexene-1-carboxylate has an optical purity of 99% or more, and the catalyst has good stability, mild reaction condition and can withstand high concentrations of substrate and product. Using the resolution process of the invention, (S)-3-cyclohexene-1-carboxylic acid with high optical purity and high concentration can be simply and efficiently obtained, and the process is energy-saving and environmentally friendly, and the high-concentration of product is beneficial to downstream product recovery process. The invention provides an efficient method for production of (S)-3-cyclohexene-1-carboxylic acid, and has a good industrial application prospect.

Claims

1. A method for preparing (S)-3-cyclohexene-1-carboxylic acid, comprising: isolating a strain of Acinetobacter, wherein a taxonomic name thereof is Acinetobacter sp., deposited on Jan. 21, 2019 at the China General Microbiological Culture Collection Center, located at No. 1, Beichen West Road, Chaoyang District, Beijing, under accession number CGMCC No. 17220; producing an esterase by fermenting of the strain of Acinetobacter sp.; and using the esterase as a catalyst to catalyze a reaction for producing the (S)-3-cyclohexene-1-carboxylic acid from a methyl (R,S)-3-cyclohexene-1-carboxylate.

2. The method according to claim 1, wherein the catalysis specifically comprising catalyzing the enantioselective hydrolysis of the methyl (R,S)-3-cyclohexene-1-carboxylate in a buffer solution containing a cosolvent, and then collecting a methyl (S)-3- cyclohexene-1-carboxylate from the resulting mixture after hydrolysis, and performing hydrolysis of the said methyl (S)-3-cyclohexene-1-carboxylate by heating under an alkaline condition to obtain the (S)-3-cyclohexene-1-carboxylic acid.

3. The method according to claim 2, wherein the cosolvent is an organic solvent mutually soluble with water.

4. The method according to claim 2, wherein amount of the cosolvent added is 5-35% of the total volume of the solution.

5. The method according to claim 2, wherein the buffer solution is citrate buffer, phosphate buffer or glycine-NaOH buffer, and has a pH of 5.0-9.5.

6. The method according to claim 2, wherein the alkaline condition is a 0.5-1.5 M NaOH solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The present invention will be further described below in conjunction with specific examples, so that those skilled in the art can better understand and implement the present invention, but the examples described here are not intended to limit the present invention.

(2) The culture media used in the present invention are:

(3) Enrichment medium (g/L): methyl cyclohexene carboxylate 1.5, (NH.sub.4).sub.2SO.sub.4 2, KH.sub.2PO.sub.4, MgSO.sub.4 0.5, NaCl 1, DMSO 5% (v/v), pH 7.0, high temperature sterilization at 121° C. for 20 min. A small amount of soil sample was taken and suspended in a test tube containing the enrichment medium, and cultured at 30° C. and 180 rpm for 48 h. An appropriate amount of the culture solution was withdrawn and transferred to a test tube containing the second round of the enrichment medium, and further cultured under the same conditions for 48 h.

(4) Plate separation medium (g/L): tributyrin 10, Tween-80 10, peptone 16, yeast extract 10, NaCl 5, agar 15, KH.sub.2PO.sub.4 0.5, MgSO.sub.4 0.2, pH 7.0, high temperature sterilization at 121° C. for 20 min. The culture solution was gradient-diluted and spread on the plate medium, and a single colony with a transparent circle was a target colony.

(5) Fermentation medium (g/L): glycerol 15, peptone 5, yeast extract 5, NaCl 1, KH.sub.2PO.sub.4 0.5, pH 7.0, high temperature sterilization at 121° C. for 20 min. Sterilization was followed by cooling and inoculation with an inoculation volume of 5% (v/v). Fermentation was carried out at 30° C. and 180 rpm. The wet cell weight could reach 20 g/L after 12 h of culture. The specific activity (U) of the enzyme was defined as the amount of cells required to catalyze 1 μmol methyl (R,S)-3-cyclohexene-1-carboxylate per min. The measured enzyme production of JNU9335 could reach 180 U/L and the specific activity was 9 U/g wet cells.

(6) Reaction conditions for enantioselectively catalytic hydrolysis: cell concentration 20-200 g/L, substrate concentration 50-500 mM, reaction temperature 10-60° C., pH 5-9.5, reaction time 0.5-36 h.

(7) The enantiomeric excess (e.e.) and conversion rate of the substrate were analyzed by gas chromatography under the following analysis conditions: B-DM chiral column (30 m×0.25 mm×0.25 μm); nitrogen as carrier gas; injection port temperature 280° C.; air flow rate 300 mL/min, make-up gas flow rate 25 mL/min; split ratio 50:1; injection volume 1.0 μL. Column temperature program: 100° C. for 2 min, ramp at 2° C./min to 150° C. for 2 min. FID detector temperature: 280° C.

Example 1: Screening of Acinetobacter

(8) Screening was carried out from more than 300 soils in Jiangsu, Shaanxi, Shandong, Henan, Jiangxi and other regions, and the specific screening steps were as follows.

(9) Soil samples were collected from different environments, methyl cyclohexene carboxylate was used as the only carbon source for three rounds of enrichment culture, and esterase producing bacteria were screened. Through repeated screening, 7 strains with high enantioselective catalytic activity were isolated, and the 7 candidate strains were further analyzed and screened for the best performance.

(10) Performance of 7 candidate strains in enantioselective hydrolysis of methyl (R,S)-3-cyclohexene-1-carboxylate:

(11) 1.0 g of wet cells of each strain were suspended in 10 mL of phosphate buffer solution (100 mM, pH 7.0). The concentration of methyl (R,S)-3-cyclohexene-1-carboxylate was 50 mM and the addition amount of cosolvent DMSO was 5%. The reaction mixture was reacted on a constant temperature shaker at 30° C. and 180 rpm. Samples were taken at the time shown in Table 1. The product and the substrate were extracted with ethyl acetate, and dried with anhydrous Na.sub.2SO.sub.4, and then subjected to chiral gas chromatography to analyze the conversion rate and enantiomeric excess value of the substrate (e.e..sub.s). The catalytic performance of each strain is shown in Table 1.

(12) TABLE-US-00001 TABLE 1 Comparison of catalytic performance of candidate strains Microbial strain Reaction time (h) e.e.s (%) Conversion rate (%) JNU9335 12 99.5 46 JNU9308 12 96.9 41 JNU9324 12 98.0 41 JNU9210 12 91.9 39 JNU9124 12 95.5 36 JNU9105 12 99.1 28 JNU9008 12 99.9 25

(13) Table 1 shows that these 7 strains screened from the soil all have high enantioselective catalytic activity, among which JNU9335 has the fastest reaction speed and the highest conversion rate.

(14) Tolerance of 7 candidate strains to different concentrations of methyl (R,S)-3-cyclohexene-1-carboxylate:

(15) 1 g of wet cells of each strain were suspended in 10 mL of phosphate buffer solution (100 mM, pH 7.0). Methyl (R,S)-3-cyclohexene-1-carboxylate at different concentrations were added, and the reaction mixture was reacted on a constant temperature shaker at 30° C. and 180 rpm. Samples were taken after the reaction, the product and the substrate were extracted with ethyl acetate, dried over anhydrous Na.sub.2SO.sub.4, and then subjected to chiral gas chromatography to analyze the conversion rate of the substrate. The tolerance of each strain to different concentrations of the substrate is shown in Table 2.

(16) TABLE-US-00002 TABLE 2 Comparison of the tolerance of candidate strains to different concentrations of the substrate Methyl (R,S)-3-cyclohexene-1- carboxylate concentration (mM) Microbial strain 100 mM 200 mM 500 mM JNU9335 46 90 197 JNU9308 42 48 60 JNU9324 42 15 12 JNU9210 34 30 30 JNU9124 32 12 20 JNU9105 20 40 40 JNU9008 20 40 39

(17) Table 2 shows that as the substrate concentration increases, the activity of most strains is inhibited by the higher substrate concentration, and the increase in hydrolysate is very small. Only strain JNU9335 can still maintain a higher conversion rate and yield a higher concentration of the product at a higher substrate concentration (500 mM), indicating that the strain has excellent substrate and product tolerance. Thus, this strain was selected as the optimal strain for future work.

(18) Through the above screening, an esterase-producing bacterium JNU9335 that is stable in enzyme production with high activity and high selectivity was obtained. The strain was deposited on Jan. 21, 2019 at the China General Microbial Culture Collection and Management Center under the accession number CGMCC No. 17220.

Example 2: Morphological and Physiological Identification of Acinetobacter sp. JNU9335

(19) The strain JNU9335 has the following microbiological characteristics:

(20) 1. Shape and size

(21) Rod-shaped, uniformly stained, 0.5-0.9×1.5-3 μm, non-spore-forming, no flagella, Gram-staining negative.

(22) 2. Suitable growth environment

(23) The suitable growth temperature is 20-35° C., and it can survive in pH 5-9 environment.

(24) 3. Characteristics of plate culture colony

(25) A small colony can be formed after culture on a plate at 30° C. for 24 h, and a viscous, moist white colony with a smooth edge and a prominent middle is formed at 36 h. A transparent circle is formed on the tributyrin plate over time.

Example 3: Molecular Biological Identification of Acinetobacter sp. JNU9335

(26) The chromosomal DNA of strain JNU9335 was extracted, and the 16S ribosomal DNA (16S rDNA) was amplified enzymatically with primers (27F: 5′-AGAGTTTGATCCTGGCTCAG-3′; 1492R: 5′-TACCTTGTTACGACTT-3′). The PCR program of a thermal cycler was: denaturation at 95° C. for 5 min, at 95° C. for 40 s, 30 cycles of at 55° C. for 1 min and at 72° C. for 2 min, and the last step at 72° C. for 10 min. Analysis of 16S rDNA sequencing results identified it as Acinetobacter sp.

Example 4: Fermentation Culture of Acinetobacter sp. JNU9335

(27) Fermentation medium (g/L): glycerol 15, peptone 5, yeast extract 5, NaCl 1, KH.sub.2PO.sub.4 0.5, pH 7.0. High temperature sterilization at 121° C. for 20 min. Sterilization was followed by cooling and inoculation with an inoculation volume of 5% (v/v). Fermentation was carried out at 30° C. and 180 rpm for 12 h. The cells were collected at 8000 rpm for 10 min with the upper medium being discarded, washed once with normal saline, and dried in a vacuum freeze dryer (SCIENTZ-10N) for 24 h. The enzyme powder was collected for storage at −20° C. The activity (U) of the enzyme was defined as the amount of cells required to catalyze 1 μmol methyl (R,S)-3-cyclohexene-1-carboxylate per min. The specific activity of the enzyme powder was measured to be 96 U/g.

Example 5: Effect of Temperature on the Enzymatic Hydrolysis of Methyl Cyclohexene Carboxylate

(28) 70 mg methyl (R,S)-3-cyclohexene-1-carboxylate, 0.5 mL dimethyl sulfoxide, 25 mg lyophilized crude enzyme powder were added to 10 mL phosphate buffer (100 mM, pH 7.0), uniformly mixed, and reacted on a constant temperature shaker at 180 rpm for 6 h at 20, 30, 40 and 50° C., respectively. Samples were taken after the reaction, and the product and the substrate were extracted with ethyl acetate, dried over anhydrous Na.sub.2SO.sub.4, and then subjected to chiral gas chromatography to analyze the conversion rate and enantiomeric excess value of the substrate (e.e..sub.s). As shown in Table 3, when the temperature is 20-40° C., the esterase has a high conversion rate and stable e.e..sub.s, indicating that the esterase is relatively stable without great activity loss within this temperature range. When the temperature exceeds 50° C., the conversion capacity of the esterase is greatly reduced. This may be due to the changes in spatial configuration of the esterase caused by high temperature, which leads to the decrease in enzyme activity.

(29) TABLE-US-00003 TABLE 3 Effect of temperature on the enzymatic hydrolysis of methyl (R,S)- 3-cyclohexene-1-carboxylate catalyzed by acinetobacter esterase Temperature (° C.) e.e..sub.s (%) Conversion rate (%) 20 99.5 32 30 99.4 46 40 99.3 40 50 99.5 25

Example 6: Enzymatic Hydrolysis of Methyl (R,S)-3-Cyclohexene-1-Carboxylate at Different Concentrations by Acinetobacter Esterase

(30) Methyl (R,S)-3-cyclohexene-1-carboxylate at 100, 200 and 500 mM, respectively and 0.5 mL dimethyl sulfoxide were added to 10 mL phosphate buffer (100 mM, pH 7.0), and respective amounts of the enzyme were added respectively. The reaction mixture was put on a constant temperature shaker to react at 30° C. and 180 rpm. Samples were taken after the reaction, and the product and the substrate were extracted with ethyl acetate, dried over anhydrous Na.sub.2SO.sub.4, and then subjected to chiral gas chromatography to analyze the conversion rate and enantiomeric excess value of the substrate (e.e..sub.s). The results are shown in Table 4.

(31) TABLE-US-00004 TABLE 4 Enzymatic hydrolysis of methyl (R,S)3-cyclohexene-1-carboxylate at different concentrations by acinetobacter esterase Substrate Reaction Product concentration time concentration e.e..sub.s (mM) (h) (mM) (%) 100 3 48 99.5 200 6 94 99.4 500 12 215 99.1

(32) Table 4 shows that when the esterase catalyzes different concentrations of methyl (R,S)-3-cyclohexene-1-carboxylate, the product concentration increases as the substrate concentration increases and is up to 215 mM, and the product still has a high optical purity, indicating that higher concentrations of the substrates and the product do not have a significant impact on the activity of the Acinetobacter esterase, which can tolerate high concentrations of the substrates and the product. This is an example with the highest concentration of the product among the biocatalytic methods for the production of chiral cyclohexene carboxylic acid that have been reported so far, and it is also the only report on microbial enzymatic conversion. The method of the present invention has very broad practical industrial application prospects.

Example 7: Gram Scale Preparation of (S)-Cyclohexene-1-Carboxylic Acid

(33) 3.50 g methyl (R,S)-3-cyclohexene-1-carboxylate was uniformly mixed with 2.5 mL dimethyl sulfoxide and 47.5 mL phosphate buffer (200 mM, pH 7.0), and 1 g enzyme powder was added thereto. The reaction was carried out in a 250 mL round-bottomed flask at a constant temperature of 30° C., with mechanical stirring at 400 rpm. The conversion rate of the substrate and the enantiomeric excess of the product were monitored by means of chiral gas chromatography. After 12 h, the reaction was ended. After filtering to remove the enzyme, the pH was adjusted to 9, and ethyl acetate was added for extraction 3 times. The organic phases were combined and rotary evaporated until no liquid flowed out to obtain methyl (S)-3-cyclohexene-1-carboxylate. Then methyl (S)-3-cyclohexene-1-carboxylate was added to a 1 M NaOH aqueous solution, and heated to reflux at 50° C. with stirring for 6 h. A 1 M HCl aqueous solution was then added to adjust the pH to 5. An equal volume of ethyl acetate was added for extraction 3 times. The organic layers were combined, dried over anhydrous Na.sub.2SO.sub.4, filtered, and rotary evaporated to obtain (S)-3-cyclohexene-1-carboxylic acid. The resulting product was a liquid with a special odor. The total yield after separation was 40%, with an optical purity of 99% e.e.

(34) The examples described above are only preferred examples for fully explaining the present invention and the protection scope of the present invention is not limited thereto. Equivalent substitutions or changes made by those skilled in the art on the basis of the present invention are all within the protection scope of the present invention. The protection scope of the present invention is defined by the claims.