Method for synthesizing gamma-polyglutamic acid through rapid fermentation

Abstract

The invention discloses a method for synthesizing gamma-polyglutamic acid through rapid fermentation, and belongs to the technical field of microbial fermentation. The method comprises the following steps: (1) seed culture: inoculating bacillus subtilis into a seed culture medium, and carrying out gradual amplification culture through a first-stage seed tank and a second-stage seed tank to obtain liquid seeds; (2) preparing a fermentation initial culture medium; and (3) fermentation culture: inoculating the liquid seeds into an initial fermentation culture medium, adding plant hormones, alpha-ketoglutaric acid and a carbon source in the culture process by supplementing materials, and culturing to obtain the gamma-polyglutamic acid. The method is low in sterilization temperature and high in strain growth speed, polyglutamic acid can be rapidly synthesized, fermentation time is shortened, yield is increased, production cost is reduced, and the problems that in the prior art, in order to avoid infectious microbe pollution, high-temperature and high-pressure sterilization needs to be conducted on a fermentation culture medium, material loss is serious, and production cost is low are solved. The strain growth is slow, and the polyglutamic acid fermentation synthesis time is long.

Description

Technical Field

[0001] The invention relates to a method for rapidly fermenting and synthesizing gamma-polyglutamic acid, belonging to the technical field of microbial fermentation. Background Art

[0002] At present, γ-polyglutamic acid is mainly produced by microbial fermentation. In order to avoid contamination by bacteria during the fermentation process, the fermentation medium needs to be sterilized at high temperature and high pressure. In order to achieve the effect of thorough sterilization, the sterilization conditions usually used are heating at 121℃ for 20min or 115℃ for 30min. High temperature and high pressure sterilization not only has high requirements for fermentation equipment, but also destroys the nutrients in the culture medium, resulting in waste of raw materials. If the sterilization temperature is too low or the sterilization time is insufficient, only some microorganisms in the culture medium can be killed, and the effect of thorough sterilization cannot be achieved. As the fermentation time increases, the spores in the culture medium will recover and germinate, and then multiply in large numbers, causing fermentation failure. The key to solving the above problems lies in the rapid transition of the strain from the retardation period to the logarithmic growth period, and the rapid synthesis of secondary metabolites to form a competitive advantage, which will ensure the smooth progress of strain cultivation and fermentation. In the fermentation process of γ-polyglutamic acid, the first 20h is the critical period for fermentation production. After 20h, the γ-polyglutamic acid fermentation strain multiplies in large numbers. With the synthesis of γ-polyglutamic acid, the viscosity of the fermentation liquid increases, and it is difficult for other bacteria to survive.

[0003] Plant hormones are bioactive substances synthesized in plants. Although the concentration is very low, they have a significant effect on the physiological processes and growth and development of plants. Currently, there are five types of plant hormones discovered, including cytokinins, auxins, gibberellins, ethylene and folic acid. Studies have shown that plant hormones have a certain effect on the growth and metabolism of fungi. Hu Xianlong (2008) studied the effect of plant hormones on the growth of Aspergillus niger; the use of plant hormones can promote Streptomyces to increase the production of secondary metabolites. Wei Baodong et al. (2014) studied the effect of plant hormones on the fermentation of Natamycin by Streptomyces natalis. However, the effect of plant hormones on the growth and metabolism of Bacillus subtilis has not been reported. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for rapidly fermenting and synthesizing γ-polyglutamic acid, which has a low sterilization temperature and a fast bacterial growth rate, and can rapidly synthesize γ-polyglutamic acid while reducing production costs.

[0005] In order to solve the above technical problems, the technical solutions provided by the present invention are as follows: A method for rapidly fermenting and synthesizing γ-polyglutamic acid comprises the following steps: (1) Seed culture: Bacillus subtilis is inoculated into a seed culture medium, and after gradual expansion of culture in primary seed and secondary seed tanks, liquid seeds are obtained; (2) Prepare the initial fermentation medium, the composition and content of which are as follows: sodium glutamate 50-100 g / L, citric acid 2-5 g / L, MgSO4 0.1-0.5 g / L, K2HPO4 1-4 g / L, tyrosine 0.1-0.5 g / L, phenylalanine 0.1-0.5 g / L, aspartic acid 0.1-0.5 g / L, inorganic nitrogen source 1-10 g / L, and the rest is water, sterilized at 100°C for 20 min; (3) Fermentation culture: The liquid seeds are inoculated into the initial fermentation culture medium. During the culture process, plant hormones, α-ketoglutaric acid and carbon sources are added through feeding to obtain γ-polyglutamic acid.

[0006] Furthermore, in step (1), the Bacillus subtilis is Bacillus subtilis FRD518, which was deposited in the General Microbiological Center of China National Microbiological Culture Collection Committee on November 2, 2012, with a deposit number of CGMCC No.6772.

[0007] Furthermore, in step (1), the preparation method of the liquid seed is: 1 mL of frozen Bacillus subtilis seed liquid is inoculated into a 500 mL Erlenmeyer flask containing 100 mL of seed culture medium, and cultured in a shaking incubator at a temperature of 35-38°C and a rotation speed of 180-250 r / min until the seed OD is 600 When the concentration reaches 1.6-2.2, the first-level seed liquid is obtained; the first-level seed liquid is inoculated into a seed tank, the culture temperature is 35-38°C, and the culture is stirred and ventilated to obtain the second-level seed liquid, which is the liquid seed.

[0008] Furthermore, in step (1), the composition and content of the seed culture medium used for the primary seeds and secondary seeds are as follows: 10 g / L glucose, 5 g / L yeast powder, 2 g / L ammonium sulfate, 0.2 g / L MgSO4, and the remaining ingredients are water, the pH is adjusted to 7.2-7.5, and sterilized at 115°C for 30 min.

[0009] Furthermore, in step (2), the inorganic nitrogen source is one or more of ammonium sulfate, ammonium nitrate, ammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate or urea.

[0010] Furthermore, in step (3), the liquid seed inoculation amount is 3-5%, the culture method is a fermentation tank ventilation stirring culture, the culture conditions are temperature 35-38°C, ventilation volume 0.5-1.5vvm, stirring speed 100-400r / min, and culture time 40-64h.

[0011] Furthermore, in step (3), the plant hormone is a mixture of gibberellin, α-naphthylacetic acid, choline chloride and triacontanol in a mass ratio of 1:1:1:1, and is added by feeding at a feeding rate of 0.2-2.0 mg / (L·h).

[0012] Gibberellins can promote cell activation and proliferation. The use of exogenous gibberellins can induce the synthesis of nucleases and proteases, shorten the lag period, stimulate cell division, and thereby rapidly increase the growth rate of Bacillus subtilis.

[0013] α-Naphthylacetic acid belongs to the auxin hormone class that induces cell division and elongation, which can enhance the absorption of nutrients, increase the activity of multiple enzymes, strengthen bacterial respiration, and accelerate metabolism, thereby promoting the growth of Bacillus subtilis.

[0014] Choline chloride can help the recombination and transformation of amino acids in the body, improve the utilization rate of amino acids, and promote amino acid metabolism.

[0015] Triacontanol can improve the permeability of crop cells, facilitate the absorption, transformation and utilization of nitrogen, and also has the special physiological function of promoting energy metabolism.

[0016] Furthermore, in step (3), the plant hormone is added during the fermentation period of 0-8 hours.

[0017] Furthermore, in step (3), the α-ketoglutaric acid is added by dissolving the α-ketoglutaric acid in sterile water and adding the solution by feeding at a feeding rate of 0.1-1.0 mg / (L·h) and a feeding time of 0-8 h during fermentation.

[0018] α-ketoglutarate is a key node connecting carbon-nitrogen metabolism in cells and an important link in the tricarboxylic acid cycle. It needs to be produced through the transamination of glutamate and can also generate glutamate through transamination. Adding α-ketoglutarate to the fermentation production of γ-polyglutamate can regulate the synthesis of glutamate from glutamate.

[0019] Furthermore, in step (3), the carbon source is glucose, which is added by feeding, and the glucose concentration is controlled at 5-15 g / L during the fermentation process.

[0020] Furthermore, in step (3), during the fermentation process, the pH is controlled to be greater than 6.5. When the pH drops below 6.5, the pH is controlled to be greater than 6.5 by adding ammonia water. When the pH is greater than 6.5, no operation is required.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) The method of the present invention has a low sterilization temperature, a fast bacterial growth rate, and can quickly synthesize γ-polyglutamic acid, thereby shortening the fermentation time, increasing the yield, and reducing the production cost. It solves the problem in the prior art that the fermentation medium needs to be sterilized at high temperature and high pressure to avoid contamination by foreign bacteria, resulting in serious material loss, slow bacterial growth, and long fermentation time for γ-polyglutamic acid synthesis.

[0022] (2) The present invention adds plant hormones gibberellins, α-naphthylacetic acid, choline chloride, triacontanol and α-ketoglutaric acid to enable the bacteria to quickly transition from the retardation phase to the logarithmic growth phase and quickly synthesize secondary metabolites, thereby forming a competitive advantage and ensuring the smooth progress of bacterial culture and fermentation without causing fermentation failure.

[0023] (3) The present invention reduces the sterilization temperature of the fermentation medium from the commonly used 121°C heating for 20 min to 100°C heating for 20 min, thereby reducing the amount of steam used and saving costs. At the same time, the lower sterilization temperature does not destroy the nutrients in the medium, retains most of the nutrients in the medium, and does not cause waste of raw materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The effect of feeding plant hormones, α-ketoglutarate and not feeding plant hormones, α-ketoglutarate on the yield of γ-polyglutamic acid fermentation; Figure 2 The effect of different sterilization conditions on the fermentation yield of γ-polyglutamic acid. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0026] Bacillus subtilis FRD518 used in the following examples was deposited in the General Microbiological Center of China National Microbiological Culture Collection Administration on November 2, 2012, with a deposit number of CGMCC No. 6772. The strain has been disclosed in the applicant's prior patent application CN201210555304.5.

[0027] Since the determination method of γ-polyglutamic acid is not uniform, the determination results are different for different determination methods. The determination method of γ-polyglutamic acid content in this embodiment adopts the method described in QB / T 5189-2017 Polyglutamic Acid.

[0028] Example 1 A method for rapidly fermenting and synthesizing γ-polyglutamic acid comprises the following steps: (1) Seed culture: Inoculate 1 mL of frozen Bacillus subtilis seed solution into a shake flask and culture at 36°C and 180 r / min on a shaker until the seed OD 600 When the concentration reaches 1.6, the first-level seed liquid is obtained; the first-level seed liquid is inoculated into a seed tank, the culture temperature is 36°C, and the aeration is stirred to obtain the second-level seed liquid, which is the liquid seed; The composition and content of the seed culture medium used for first-level and second-level seeds are as follows: glucose 10g / L, yeast powder 5g / L, ammonium sulfate 2g / L, MgSO4 0.2g / L, and the remaining ingredients are water, adjusted to pH 7.2, and sterilized at 115℃ for 30min; (2) Prepare the initial fermentation medium, the composition and content of which are as follows: sodium glutamate 60 g / L, citric acid 2 g / L, MgSO4 0.2 g / L, K2HPO4 2 g / L, tyrosine 0.2 g / L, phenylalanine 0.2 g / L, aspartic acid 0.2 g / L, ammonium sulfate 4 g / L, ammonium phosphate 4 g / L, and the rest is water, sterilized at 100°C for 20 min; (3) Fermentation culture: The liquid seeds were inoculated into the initial fermentation culture medium with an inoculation amount of 3%. The culture was carried out in a fermenter with ventilation and stirring. The culture conditions were a temperature of 37°C, a ventilation volume of 1.0 vvm, a stirring speed of 250 r / min, and a culture time of 64 h. During the culture process, the pH was controlled to be above 6.5 by adding ammonia water, and glucose was fed to control the glucose concentration to 5-15 g / L. At 0-8 h after the start of fermentation, gibberellin, α-naphthylacetic acid, choline chloride, and triacontanol were fed at a feeding rate of 1.1 mg / (L·h). At 0-8 h after fermentation, α-ketoglutaric acid was added by feeding at a feeding rate of 0.5 mg / (L·h) to obtain γ-polyglutamic acid.

[0029] Example 2 A method for rapidly fermenting and synthesizing γ-polyglutamic acid comprises the following steps: (1) Seed culture: Inoculate 1 mL of frozen Bacillus subtilis seed solution into a shake flask and culture in a shaker at 36°C and 180 r / min until the seed OD 600 When the concentration reaches 1.6, the first-level seed liquid is obtained; the first-level seed liquid is inoculated into a seed tank, the culture temperature is 36°C, and the aeration is stirred to obtain the second-level seed liquid, which is the liquid seed; The composition and content of the seed culture medium used for first-level and second-level seeds are as follows: glucose 10g / L, yeast powder 5g / L, ammonium sulfate 2g / L, MgSO4 0.2g / L, and the remaining ingredients are water, adjusted to pH 7.2, and sterilized at 115℃ for 30min; (2) Prepare the initial fermentation medium, the composition and content of which are as follows: sodium glutamate 80 g / L, citric acid 4 g / L, MgSO4 0.25 g / L, K2HPO4 3 g / L, tyrosine 0.3 g / L, phenylalanine 0.25 g / L, aspartic acid 0.5 g / L, diammonium hydrogen phosphate 4 g / L, urea 5 g / L, and the rest is water, sterilized at 100°C for 20 min; (3) Fermentation culture: The liquid seeds were inoculated into the initial fermentation culture medium with an inoculation amount of 5%. The fermentation tank was ventilated and stirred at 36°C. The culture conditions were a temperature of 35°C, a ventilation volume of 1.5 vvm, a stirring speed of 100 r / min, and a culture time of 64 h. During the culture process, the pH was controlled to be above 6.5 by adding ammonia water, and glucose was fed to control the glucose concentration to 5-15 g / L. At 0-8 h after the start of fermentation, gibberellin, α-naphthylacetic acid, choline chloride, and triacontanol were fed at a feeding rate of 0.2 mg / (L·h). α-ketoglutaric acid was added by feeding at a feeding rate of 0.8 mg / (L·h) to obtain γ-polyglutamic acid.

[0030] Example 3 A method for rapidly fermenting and synthesizing γ-polyglutamic acid comprises the following steps: (1) Seed culture: Inoculate 1 mL of frozen Bacillus subtilis seed solution into a shake flask and culture in a shaker at 36°C and 180 r / min until the seed OD 600 When the temperature reaches 2.2, the first-level seed liquid is obtained; the first-level seed liquid is inoculated into a seed tank, the culture temperature is 36°C, and the aeration is stirred to obtain the second-level seed liquid, which is the liquid seed; The composition and content of the seed culture medium used for first-level and second-level seeds are as follows: glucose 10g / L, yeast powder 5g / L, ammonium sulfate 2g / L, MgSO4 0.2g / L, and the remaining ingredients are water, adjusted to pH 7.2, and sterilized at 115℃ for 30min; (2) Prepare the initial fermentation medium, the composition and content of which are as follows: sodium glutamate 80 g / L, citric acid 4 g / L, MgSO4 0.25 g / L, K2HPO4 3 g / L, tyrosine 0.3 g / L, phenylalanine 0.25 g / L, aspartic acid 0.5 g / L, ammonium nitrate 4 g / L, diammonium phosphate 5 g / L, and the rest is water, sterilized at 100°C for 20 min; (3) Fermentation culture: The liquid seeds were inoculated into the initial fermentation culture medium with an inoculation amount of 4%. The culture was carried out in a fermenter with ventilation and stirring. The culture conditions were a temperature of 38°C, a ventilation volume of 0.5 vvm, a stirring speed of 400 r / min, and a culture time of 40 h. During the culture process, the pH was controlled to be above 6.5 by adding ammonia water, and glucose was fed to control the glucose concentration to 5-15 g / L. At 0-8 h after the start of fermentation, gibberellin, α-naphthylacetic acid, choline chloride, and triacontanol were fed at a feeding rate of 2.0 mg / (L·h). α-ketoglutaric acid was added by feeding at a feeding rate of 1.0 mg / (L·h) to obtain γ-polyglutamic acid.

[0031] Example 4 A method for rapidly fermenting and synthesizing γ-polyglutamic acid comprises the following steps: (1) Seed culture: Inoculate 1 mL of frozen Bacillus subtilis seed solution into a shake flask and culture in a shaker at 36°C and 180 r / min until the seed OD 600 When the temperature reaches 1.8, the first-level seed liquid is obtained; the first-level seed liquid is inoculated into a seed tank, the culture temperature is 36°C, and the aeration is stirred to obtain the second-level seed liquid, which is the liquid seed; The composition and content of the seed culture medium used for first-level and second-level seeds are as follows: glucose 10g / L, yeast powder 5g / L, ammonium sulfate 2g / L, MgSO4 0.2g / L, and the remaining ingredients are water, adjusted to pH 7.2, and sterilized at 115℃ for 30min; (2) Prepare the initial fermentation medium, the composition and content of which are as follows: sodium glutamate 80 g / L, citric acid 4 g / L, MgSO4 0.25 g / L, K2HPO4 3 g / L, tyrosine 0.3 g / L, phenylalanine 0.25 g / L, aspartic acid 0.5 g / L, diammonium hydrogen phosphate 4 g / L, urea 5 g / L, and the rest is water, sterilized at 100°C for 20 min; (3) Fermentation culture: The liquid seeds were inoculated into the initial fermentation culture medium with an inoculation amount of 5%. The fermentation tank was ventilated and stirred at 36°C. The culture conditions were as follows: temperature of 36°C, ventilation volume of 1.2 vvm, stirring speed of 200 r / min, and culture time of 50 h. During the culture process, the pH was controlled to be above 6.5 by adding ammonia water, and glucose was fed to control the glucose concentration to 5-15 g / L. At 0-8 h after the start of fermentation, gibberellin, α-naphthylacetic acid, choline chloride, and triacontanol were fed at a feeding rate of 1.5 mg / (L·h). α-ketoglutaric acid was added by feeding at a feeding rate of 0.1 mg / (L·h) to obtain γ-polyglutamic acid.

[0032] Experimental Example 1 In step (3), gibberellin, α-naphthylacetic acid, choline chloride, triacontanol, and α-ketoglutaric acid were not added, and the other steps were the same as those in Example 1. The sterilization conditions of the fermentation medium in step (2) were set to 100° C. for 20 min, 115° C. for 30 min, 121° C. for 20 min, 121° C. for 60 min, and 121° C. for 120 min, respectively, and were recorded as experimental groups 1-5. The effects of different sterilization conditions on the fermentation yield of γ-polyglutamic acid were studied. Three parallel experiments were performed for each group. The results are shown in Table 1.

[0033] Table 1. Effect of different sterilization conditions on fermentation yield In the prior art, the sterilization conditions of the fermentation medium are usually heated at 121°C for 20 minutes or 115°C for 30 minutes. As shown in Table 1, the sterilization conditions of experimental group 1 are 100°C for 20 minutes, and the fermentation culture will cause contamination of bacteria and fermentation failure; the sterilization conditions of experimental group 2 are 115°C for 30 minutes, and the average fermentation yield of γ-polyglutamic acid is 5.46%. The sterilization conditions of experimental group 3 are 121°C for 20 minutes, and the average fermentation yield is 4.86%. The sterilization temperature is increased from 115°C to 121°C, the sterilization time is reduced by 10 minutes, and the fermentation yield of γ-polyglutamic acid is reduced by 10.99%, indicating that high temperature sterilization has an effect on the fermentation yield. The sterilization temperature of experimental groups 3-5 was 121°C. When the sterilization time was increased from 20 min to 60 min, the γ-polyglutamic acid fermentation yield decreased by 8.45%. When the time was extended from 60 min to 120 min, the fermentation yield remained almost unchanged, indicating that when the sterilization time is within 60 min, the high-temperature sterilization time increases, the nutrients in the culture medium are seriously lost, affecting the fermentation yield.

[0034] Experimental Example 2 It can be seen from Experimental Example 1 that when gibberellin, α-naphthylacetic acid, choline chloride, triacontanol, and α-ketoglutaric acid are not added, step (2) is sterilized at 100°C for 20 minutes, which is easy to be contaminated with foreign bacteria, resulting in fermentation failure. Therefore, step (2) is sterilized at 115°C for 30 minutes, and step (3) is not added with gibberellin, α-naphthylacetic acid, choline chloride, triacontanol, and α-ketoglutaric acid. The other steps are the same as those in Example 1. The changes in the yield of γ-polyglutamic acid fermentation over time when plant hormones, α-ketoglutaric acid and plant hormones, α-ketoglutaric acid are added are respectively detected. The test results are shown in the attached figure. Figure 1 .

[0035] from Figure 1It can be seen that after adding plant hormones and α-ketoglutaric acid, the yield of γ-polyglutamic acid continued to increase from 4h to 44h of fermentation, and the yield tended to be stable after 44h, and the fermentation yield reached 7.72%. When plant hormones and α-ketoglutaric acid were not added, the yield increased slowly in the first 16h of fermentation, and the yield only tended to be stable at 68h of fermentation, and the fermentation yield was only 5.46%; it shows that when plant hormones and α-ketoglutaric acid were not added, the yield of γ-polyglutamic acid was low and the fermentation time was long. It can be seen that the method of the present invention can shorten the fermentation time and improve the fermentation yield.

[0036] Experimental Example 3 Step (2) sterilize the initial fermentation medium at 121°C for 20 min. The other steps are the same as those in Example 1. Detect the change in the yield of γ-polyglutamic acid fermentation. The detection results are shown in the attached figure. Figure 2 .

[0037] from Figure 2 It can be seen that after adding plant hormones and α-ketoglutaric acid, under different fermentation medium sterilization conditions, the growth trend of γ-polyglutamic acid production was the same from 0 to 24 hours of fermentation. As the fermentation time increased, the fermentation yield of γ-polyglutamic acid in the fermentation medium sterilized at 121°C for 20 minutes increased slowly, reaching a maximum of 5.24% at 52 hours. It is possible that sterilization at high temperature of 121°C for 20 minutes reduced the components of the fermentation medium, and the nutrients were exhausted in the later stage, resulting in a slow growth of γ-polyglutamic acid production.

Claims

1. A method for rapidly fermenting and synthesizing γ-polyglutamic acid, characterized in that: The following steps are involved: (1) Seed culture: Bacillus subtilis is inoculated into a seed culture medium, and after gradual expansion of culture in primary seed and secondary seed tanks, liquid seeds are obtained; (2) Prepare the initial fermentation medium, the composition and content of which are as follows: sodium glutamate 50-100 g / L, citric acid 2-5 g / L, MgSO4 0.1-0.5 g / L, K2HPO4 1-4 g / L, tyrosine 0.1-0.5 g / L, phenylalanine 0.1-0.5 g / L, aspartic acid 0.1-0.5 g / L, inorganic nitrogen source 1-10 g / L, and the rest is water, sterilized at 100°C for 20 min; (3) Fermentation culture: The liquid seeds are inoculated into the initial fermentation culture medium. During the culture process, plant hormones, α-ketoglutaric acid and carbon sources are added through feeding to obtain γ-polyglutamic acid.

2. The method for rapidly fermenting and synthesizing γ-polyglutamic acid according to claim 1, characterized in that: In step (1), the Bacillus subtilis is Bacillus subtilis FRD518, which was deposited in the General Microbiological Center of China National Microbiological Culture Collection Administration on November 2, 2012, with a deposit number of CGMCC No.6772.

3. The method for rapidly fermenting and synthesizing γ-polyglutamic acid according to claim 1, characterized in that: In step (1), the preparation method of the liquid seed is as follows: 1 mL of frozen Bacillus subtilis seed liquid is inoculated into a 500 mL Erlenmeyer flask containing 100 mL of seed culture medium, and cultured in a shaking incubator at a temperature of 35-38°C and a rotation speed of 180-250 r / min until the seed OD is 600 When the concentration reaches 1.6-2.2, the first-level seed liquid is obtained; the first-level seed liquid is inoculated into a seed tank, the culture temperature is 35-38°C, and the culture is stirred and ventilated to obtain the second-level seed liquid, which is the liquid seed.

4. The method for rapidly fermenting and synthesizing γ-polyglutamic acid according to any one of claims 1 to 3, characterized in that: In step (2), the inorganic nitrogen source is one or more of ammonium sulfate, ammonium nitrate, ammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate or urea.

5. The method for rapidly fermenting and synthesizing γ-polyglutamic acid according to claim 4, characterized in that: In step (3), the liquid seed inoculation amount is 3-5%, the culture method is a fermentation tank ventilation stirring culture, the culture conditions are temperature 35-38°C, ventilation volume 0.5-1.5vvm, stirring speed 100-400r / min, and culture time 40-64h.

6. The method for rapidly fermenting and synthesizing γ-polyglutamic acid according to claim 1, characterized in that: In step (3), the plant hormone is a mixture of gibberellin, α-naphthylacetic acid, choline chloride and triacontanol in a mass ratio of 1:1:1:1, and the addition method is feeding at a feeding rate of 0.2-2.0 mg / (L·h).

7. The method for rapidly fermenting and synthesizing γ-polyglutamic acid according to claim 6, characterized in that: In step (3), the plant hormone is added during the fermentation period of 0-8 hours.

8. The method for rapidly fermenting and synthesizing γ-polyglutamic acid according to claim 1, characterized in that: In step (3), the α-ketoglutaric acid is added by dissolving the α-ketoglutaric acid in sterile water and adding the solution by feeding at a feeding rate of 0.1-1.0 mg / (L·h) and a feeding time of 0-8h during fermentation.

9. The method for rapidly fermenting and synthesizing γ-polyglutamic acid according to claim 8, characterized in that: In step (3), the carbon source is glucose, which is added by feeding, and the glucose concentration is controlled at 5-15 g / L during the fermentation process.

10. The method for rapidly fermenting and synthesizing γ-polyglutamic acid according to claim 9, characterized in that: In step (3), during the fermentation culture, the pH is controlled to be greater than 6.5; when the pH drops below 6.5, the pH is controlled to be greater than 6.5 by adding ammonia water. When the pH is greater than 6.5, no operation is required.

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