Tetracycline antibiotic degrading bacterium immobilized microbial agent as well as preparation method and application thereof

Abstract

The invention provides a tetracycline antibiotic degrading bacterium immobilized microbial agent as well as a preparation method and application thereof, and belongs to the technical field of biology. The invention provides modified straw biochar, which is obtained by performing pyrolysis on soybean straw powder at 680-720 DEG C under an anaerobic condition and modifying the obtained biochar by using a KOH solution with the concentration of more than 0.4 mol / L. Modified straw biochar is used as a carrier, and a citrobacter mussmui strain DH3 is loaded on the carrier to prepare the novel immobilized microbial agent. The immobilized microbial agent has high efficiency of synergistically removing tetracycline antibiotics based on two mechanisms of adsorption of the modified straw biochar and biodegradation of the Citrobacter mussmusei strain DH3, and on one hand, functional strains for biologically, safely and efficiently degrading pollutants are developed; on the other hand, a new research and development thought and a new product are provided for resource utilization of agricultural wastes.

Description

Technical Field

[0001] The invention belongs to the field of biotechnology, and particularly relates to an immobilized bacterial agent for degrading tetracycline antibiotics, a preparation method and an application thereof. Background Art

[0002] Tetracycline antibiotic wastewater is one of the most commonly used, high-volume, and difficult-to-treat antibiotics in aquaculture wastewater. It contains high levels of suspended solids and residual antibiotics, making it challenging to treat directly using biological methods. When antibiotics remain in the environment, they are affected by both biological and non-biological processes, converting their parent compounds from large molecules to small molecules, ultimately forming H2O and CO2. Due to the extremely complex influencing factors within the environment, there are multiple different degradation pathways, primarily categorized as abiotic and biotic degradation. While each antibiotic removal method has its advantages, they also come with varying degrees of disadvantages, including high investment, energy consumption, operational difficulties, and the potential for secondary pollution. Microbial degradation, a safe and efficient method for removing antibiotics, involves the production of enzymes and other substances through microbial metabolism in specific environments. This process directly or indirectly alters the parent antibiotic structure, thereby inactivating it.

[0003] In recent years, immobilization technology has been gradually applied in a wider range of fields due to its unique advantages. The core principle of this technology lies in the physical bonding between the surface of a water-insoluble carrier and the microorganism. This physical interaction not only includes the ubiquitous van der Waals force, but also includes the electrostatic attraction between ions and the special intermolecular force of hydrogen bonding, which together ensure the fixation of the microorganism on the carrier surface. A search revealed that there is currently a lack of immobilized bacterial agents that can effectively biodegrade multiple tetracycline antibiotics, including oxytetracycline, chlortetracycline, tetracycline, and doxycycline. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a tetracycline antibiotic-degrading bacteria immobilized bacterial agent, which uses a specific modified biochar as a carrier and immobilizes the Citrobacter murliniae strain DH3, which can achieve efficient biodegradation of multiple tetracycline antibiotics such as oxytetracycline, chlortetracycline, tetracycline, and doxycycline.

[0005] The invention provides a modified straw biochar, which is obtained by pyrolyzing soybean straw powder at 680-720° C. under anaerobic conditions, and modifying the obtained biochar with a KOH solution having a concentration greater than 0.4 mol / L.

[0006] Preferably, the pyrolysis temperature is 700°C.

[0007] Preferably, the concentration of the KOH solution is 0.5 to 3 mol / L.

[0008] Preferably, the biochar is prepared by pyrolyzing soybean straw powder at 700° C. and then modifying the obtained biochar with a 0.5 mol / L KOH solution.

[0009] The present invention provides a tetracycline antibiotic-degrading bacteria immobilized bacterial agent, which uses the modified straw biochar as a carrier, and the Citrobacter muehii strain DH3 is loaded on the carrier;

[0010] The deposit number of the Citrobacter muehii strain DH3 is CGMCC No.29865.

[0011] The present invention provides a method for preparing the tetracycline antibiotic-degrading bacteria immobilized bacterial agent, comprising the following steps:

[0012] The bacterial liquid of Citrobacter muehii strain DH3 and the modified straw biochar are cultured in a culture medium to obtain a tetracycline antibiotic-degrading bacteria immobilized bacterial agent.

[0013] Preferably, the volume-to-mass ratio of the bacterial solution of the Citrobacter muehii strain DH3 to the modified straw biochar is 1 mL: 0.5-2.5 g;

[0014] The OD of the bacterial solution of the Citrobacter rodentium strain DH3 600 is 1.

[0015] Preferably, the culture temperature is 28-32°C;

[0016] The culture time is 22 to 26 hours;

[0017] The culture is a shaking culture; the rotation speed of the shaking culture is 130-170 rpm.

[0018] The present invention provides use of the modified straw biochar, the immobilized tetracycline antibiotic-degrading bacteria agent, or the immobilized tetracycline antibiotic-degrading bacteria agent prepared by the preparation method in degrading tetracycline antibiotics.

[0019] Preferably, the tetracycline antibiotics include at least one of the following: oxytetracycline, chlortetracycline, tetracycline and doxycycline.

[0020] The present invention provides a modified straw biochar. The biochar is obtained by pyrolyzing soybean straw powder at 680-720°C under anaerobic conditions. Irregular voids were observed using a scanning electron microscope (SEM). The biochar was modified with a KOH solution at a concentration greater than 0.4 mol / L. The KOH etching effect altered the biochar's surface morphology, removing ash and tar particles and clearing clogged pores. The resulting pores exhibited a regular honeycomb pattern with a large pore size of approximately 3-6 μm, enhancing both specific surface area and physical adsorption. Experiments showed that, compared with the biochar described above, the modified straw biochars modified with 0.5, 1, 2, and 3 mol / L KOH all exhibited improved adsorption of doxycycline. The adsorption rate for 50 mg / L doxycycline increased from 43.76% to 50-54.37%, with the greatest improvement in adsorption observed with 0.5 mol / L KOH.

[0021] The present invention provides an immobilized tetracycline antibiotic-degrading agent, using modified straw biochar as a carrier, onto which is loaded the Citrobacter muehii strain DH3; the Citrobacter muehii strain DH3 is deposited under the CGMCC No. 29865. The Citrobacter muehii strain DH3 is immobilized on the surface and interstices of the carrier, maintaining its activity and enhancing the biodegradation of various tetracycline antibiotics, including oxytetracycline, chlortetracycline, tetracycline, and doxycycline. Furthermore, the modified straw biochar exhibits excellent physical adsorption properties, facilitating the enrichment of tetracycline antibiotics in samples and further improving the degradation efficiency of various tetracycline antibiotics. Experimental results show that the immobilized agent achieves biodegradation rates of 77.61% to 93.25% for oxytetracycline, chlortetracycline, tetracycline, and doxycycline. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The results of the effects of different pyrolysis temperatures on the adsorption properties of the prepared biochar in Example 1 are as follows;

[0023] Figure 2 This is the SEM image of the biochar BC700 prepared in Example 1;

[0024] Figure 3 This is the SEM image of the biochar BC700-0.5KOH prepared in Example 1;

[0025] Figure 4 The adsorption effect of doxycycline on BC700 modified with different KOH concentrations prepared in Example 2;

[0026] Figure 5 This is a SEM image of the immobilized tetracycline antibiotic-degrading bacteria agent prepared in Example 3;

[0027] Figure 6 This is a diagram showing the removal effect of doxycycline by the immobilized bacterial agent prepared with different biochar dosages in Example 3;

[0028] Figure 7 This is a diagram showing the removal effect of the immobilized bacterial agent on different concentrations of doxycycline in Example 4;

[0029] Figure 8 This is a graph showing the removal effect of different types of tetracycline antibiotics by the Citrobacter rodentium strain DH3 in Example 5;

[0030] Figure 9 This is a diagram showing the removal effect of the immobilized bacterial agent in Example 6 on different types of tetracycline antibiotics.

[0031] Biomaterial deposit information

[0032] Citrobacter murliniae strain DH3 was deposited on February 4, 2024, at the General Microbiology Center of China Culture Collection Administration, CGMCC, located at No. 3, Yard 1, Beichen West Road, Chaoyang District, Beijing, with the deposit number CGMCC No. 29865. DETAILED DESCRIPTION

[0033] The invention provides a modified straw biochar, which is obtained by pyrolyzing soybean straw powder at 680-720°C under anaerobic conditions, and modifying the obtained biochar with a KOH solution having a concentration greater than 0.4 mol / L to obtain the modified biochar.

[0034] In the present invention, the soybean straw powder preferably has a particle size of 40-50 mesh, and may be 45 mesh. The anaerobic conditions are preferably nitrogen conditions. The pyrolysis temperature is preferably 700°C. The pyrolysis is preferably carried out in a vacuum tube furnace. Experiments have shown that different pyrolysis temperatures affect the porosity of straw biochar. BC700 biochar has irregular pores and numerous debris on its surface, which may be derived from the thermal decomposition of cellulose and hemicellulose.

[0035] In the present invention, the concentration of the KOH solution is preferably 0.5 to 3 mol / L, and may be 1 to 2 mol / L, or 1.5 mol / L. The modification temperature is preferably 58 to 62°C, and may be 60°C. The modification time is preferably 55 to 65 minutes, and may be 60 minutes. After the modification, the modified product is preferably washed. The washing solution is preferably ultrapure water. The washing is preferably rinsed to a neutral pH. After the washing, water removal is also required. The water removal method is preferably a drying treatment at 75 to 85°C.

[0036] In the present invention, the modified straw biochar is preferably prepared by pyrolyzing soybean straw powder at 700°C, and the resulting biochar is modified using a 0.5 mol / L KOH solution. The modified straw biochar has rich porosity and good physical adsorption properties. Experiments have shown that when biochar is modified using KOH solutions of different concentrations, the results show that compared with unmodified biochar, the modified straw biochar BC700-0.5KOH modified with 0.5 mol / L KOH solution has a stronger antibiotic adsorption capacity, while the adsorption capacity of BC700-1KOH, BC700-2KOH, and BC700-3KOH is slightly reduced.

[0037] In the present invention, a tetracycline antibiotic-degrading bacteria immobilized bacterial agent is provided, which uses the modified straw biochar as a carrier, and is loaded with the Citrobacter muehii strain DH3 on the carrier; the preservation number of the Citrobacter muehii strain DH3 is CGMCC No.29865.

[0038] In the present invention, the Citrobacter muehii strain DH3 has a high biodegradation activity against oxytetracycline, chlortetracycline, tetracycline and doxycycline. Experiments show that the biodegradation rate of strain DH3 to oxytetracycline, chlortetracycline, tetracycline and doxycycline is 49.02% to 54.67% in 72h. The Citrobacter muehii strain DH3 is loaded on the surface and gaps of the modified straw biochar. The modified straw biochar provides a habitat for the Citrobacter muehii strain DH3, so that the Citrobacter muehii strain DH3 maintains a high activity and a suitable growth environment, thereby improving the biodegradation of tetracycline antibiotics by the Citrobacter muehii strain DH3. At the same time, the modified straw biochar itself has a strong adsorption property, which is conducive to enriching the tetracycline antibiotics in the sample to be degraded by adsorption, accelerating the mass transfer efficiency of tetracycline antibiotics between biochar and immobilized strain DH3, thereby further improving the biodegradation of tetracycline antibiotics.

[0039] The present invention provides a preparation method of the tetracycline antibiotics degrading bacteria immobilized bacterial agent, comprising the following steps: culturing a bacterial liquid of Citrobacter muehii strain DH3 and the modified straw biochar in a culture medium to obtain the tetracycline antibiotics degrading bacteria immobilized bacterial agent.

[0040] In the present invention, the volume mass ratio of the bacterial solution of the Citrobacter muehii strain DH3 to the modified straw biochar is preferably 1 mL: 0.5-2.5 g, can be 1 mL: 1-2 g, or can be 1 mL: 1.5 g. The OD of the bacterial solution of the Citrobacter muehii strain DH3 is 600The culture medium is preferably LB medium. The culture temperature is preferably 28 to 32°C, and may be 30°C. The culture time is preferably 22 to 26 hours, and may be 24 hours. The culture is performed by shaking at a rotation speed of 130 to 170 rpm.

[0041] The present invention provides use of the modified straw biochar, the immobilized tetracycline antibiotic-degrading bacteria agent, or the immobilized tetracycline antibiotic-degrading bacteria agent prepared by the preparation method in degrading tetracycline antibiotics.

[0042] In the present invention, the tetracycline antibiotic preferably includes at least one of the following: oxytetracycline, chlortetracycline, tetracycline, and doxycycline. The concentration of the tetracycline antibiotic is 20-200 mg / L, 50-150 mg / L, or even 100 mg / L. Experiments have shown that compared with Citrobacter muehii strain DH3 and modified straw biochar, the immobilized bacterial agent significantly improves the biodegradation of oxytetracycline, chlortetracycline, tetracycline, and doxycycline, with degradation rates ranging from 77.61% to 93.25%.

[0043] The immobilized bacterial agent provided by the present invention is based on the adsorption of modified straw biochar and the biodegradation of Citrobacter muehii strain DH3, which synergistically removes tetracycline antibiotics with high efficiency. On the one hand, it promotes the development of functional strains that can biosafely and efficiently degrade pollutants, and on the other hand, it provides new research and development ideas and products for the resource utilization of agricultural waste.

[0044] The following is a detailed description of a tetracycline antibiotic-degrading bacteria immobilized bacterial agent provided by the present invention, as well as its preparation method and application, in conjunction with the examples. However, these examples should not be construed as limiting the scope of protection of the present invention.

[0045] Example 1

[0046] Preparation method of modified biochar

[0047] 1. Sources of biochar raw materials

[0048] Soybean straw was collected from farmland in a town in Xingyang City, Zhengzhou City.

[0049] 2. Biochar Preparation Method

[0050] Soybean straw was crushed and the resulting soybean straw powder was passed through a 40-mesh sieve. The fine powder was collected and placed in a vacuum tube furnace. Nitrogen was introduced into the furnace at a flow rate of 100 ml / min. The temperature was raised to 500°C at a rate of 10°C / min and pyrolyzed for 2 hours. The product was then cooled, ground, and passed through a 100-mesh sieve for later use. Biochars were prepared using the same method at pyrolysis temperatures of 600°C and 700°C. The biochars produced at 500°C, 600°C, and 700°C were designated BC500, BC600, and BC700, respectively.

[0051] To evaluate the effects of different pyrolysis temperatures on the performance of prepared biochar, doxycycline adsorption was tested on three biochars: BC500, BC600, and BC700. Doxycycline assay method: Doxycycline concentration in samples was determined using an Agilent 1260 HPLC. The sample injection volume was set to 20 mL. The mobile phase consisted of 0.1% trifluoroacetic acid in water, acetonitrile, and methanol in a volume ratio of 61:26:13, and the flow rate was set to 1 mL / min. A ZORBAX SB-C18 column (5 μm, 4.6 × 250 mm, Agilent) was used. The column oven temperature was set to 40°C, and the UV detector wavelength was 355 nm. The doxycycline removal rate was calculated according to Equation 1.

[0052] Doxycycline removal rate = (doxycycline initial concentration - doxycycline residual concentration) / doxycycline initial concentration × 100% Formula I;

[0053] See the results Figure 1 The results showed that different pyrolysis temperatures resulted in significant differences in the adsorption effects of soybean straw biochar on doxycycline. Pyrolysis at 700°C could effectively improve the adsorption efficiency of soybean straw biochar on doxycycline.

[0054] SEM observation of prepared biochar BC700. Figure 2 The results showed that the pores of biochar BC700 were irregular and there were many debris on the surface, which may come from the thermal decomposition of cellulose and hemicellulose.

[0055] 3. Biochar modification methods

[0056] The prepared biochar BC700 was mixed with KOH solutions with concentrations of 0.5 mol / L, 1 mol / L, 2 mol / L, and 3 mol / L in a ratio of 1:10 (g:ml), stirred at 60°C for 1 h, rinsed with ultrapure water until neutral, and dried at 80°C for use. The biochars treated with different potassium hydroxide concentrations were recorded as BC700-0.5KOH, BC700-1KOH, BC700-2KOH, and BC700-3KOH, respectively.

[0057] SEM observation of the modified biochar morphology. Figure 3 The pores of the modified BC700-0.5KOH biochar exhibit a regular honeycomb pattern with large pore sizes of approximately 3 to 6 μm. The changes in the surface morphology of the modified biochar are likely due to the etching effect of KOH. During the KOH treatment, ash and tar particles in the biochar are removed, clearing clogged pores and increasing the pore size and pore volume, which facilitates the diffusion of substances into the pores.

[0058] Example 2

[0059] Optimization of modified biochar

[0060] Prepare a culture medium containing 6 g / L peptone (also containing 1.5 g / L K₂HPO₄, 1.0 g / L NaCl, 0.5 g / L KH₂PO₄, and 0.2 g / L MgSO₄·7H₂O, with a pH of 7.0) and dispense it into 50 ml conical flasks. Add 0.2 g of each of the biochars prepared in Example 1, BC700, BC700-0.5KOH, BC700-1KOH, BC700-2KOH, and BC700-3KOH, to separate conical flasks. Sterilize the culture medium and biochar at 121°C for 25 min. Add filter-sterilized doxycycline stock solution to the sterilized culture medium to an initial doxycycline concentration of 50 mg / L. Pour the doxycycline-containing culture medium into the conical flasks containing the sterilized biochar to a biochar concentration of 4 g / L. The culture medium was placed in a shaker at 25° C. and 150 rpm for 48 h, and then a sample was taken to determine the residual concentration of doxycycline using the same method as described in Example 1.

[0061] See the results Figure 4 Compared with biochar BC700, biochar modified with 0.5 mol / L, 1 mol / L, 2 mol / L, and 3 mol / L KOH all showed improved adsorption of doxycycline. Among them, BC700-0.5KOH modified with 0.5 mol / L KOH showed the greatest improvement in doxycycline adsorption, with the adsorption rate of 50 mg / L doxycycline in 6 g / L peptone medium increasing from 43.76% to 54.37%. Therefore, BC700-0.5KOH was selected as the immobilized carrier biochar for subsequent experiments.

[0062] Example 3

[0063] Removal effect of immobilized bacterial agents prepared with different biochar dosages on doxycycline

[0064] 0.5 mL (OD 600=1) An activated Citrobacter rodentium strain DH3 was inoculated into a 150 mL Erlenmeyer flask containing 50 mL of sterilized LB medium. Then, 0.05 g, 0.1 g, 0.15 g, 0.2 g, and 0.25 g of sterilized BC700-0.5KOH (i.e., dosages of 1 g / L, 2 g / L, 3 g / L, 4 g / L, and 5 g / L) were added to the Erlenmeyer flask containing the LB medium. The Erlenmeyer flask was sealed with a breathable membrane and incubated in a shaking incubator at 30°C and 150 rpm for 24 hours to allow bacterial growth and attachment to the BC700-0.5KOH particles. After 24 hours, the culture medium was transferred to a centrifuge tube and centrifuged at 6000 rpm for 10 minutes, after which the supernatant was discarded. An equal volume of 0.85% NaCl solution was added to wash the immobilized bacterial culture, which was then centrifuged again and the supernatant discarded. This washing procedure was repeated four times to obtain the immobilized bacterial culture, which was then stored at 4°C for future use. SEM observation of immobilized bacteria, Figure 5 It shows that the DH3 strain in the immobilized bacterial agent is attached to the surface of BC700-0.5KOH biochar.

[0065] The removal rates of doxycycline by the different immobilized bacterial agents prepared above were measured according to the method of Example 2.

[0066] See the results Figure 6 When the reaction reached equilibrium, the removal effects of the immobilized bacterial agents prepared at different dosages on doxycycline showed little difference, and the removal rates of doxycycline in 72 hours were 83.02% to 90.07%.

[0067] Example 4

[0068] Removal effect of immobilized bacteria on doxycycline at different concentrations

[0069] Prepare a culture medium with a peptone concentration of 6 g / L and a pH of 7. Dispense the medium into 50 ml Erlenmeyer flasks and sterilize at 121°C for 25 min. Add filter-sterilized doxycycline stock solution to the sterilized medium, achieving initial doxycycline concentrations of 20 mg / L, 50 mg / L, 100 mg / L, 150 mg / L, and 200 mg / L, respectively. Add the prepared immobilized bacterial agent to one set of Erlenmeyer flasks as the immobilized bacterial agent degradation group, while strain DH3 alone serves as the control group. The flasks are shaken at 25°C and 150 rpm. Sampling is performed at 0 and 72 h. Each experiment is repeated three times.

[0070] The results are as follows Figure 7The results showed that the immobilized bacterial inoculum had high removal rates of 85.21% to 94.49% for doxycycline at concentrations ranging from 20 to 200 mg / L. However, strain DH3 only achieved degradation rates of 53.19% to 81.90% at concentrations of 20, 50, 100, 150, and 200 mg / L after 72 hours of treatment. Compared to the doxycycline degradation by the strain cultured alone, the initial inhibitory phase of high-concentration doxycycline on the strain disappeared, demonstrating that the immobilized bacterial inoculum is more adaptable to high-concentration doxycycline.

[0071] Example 5

[0072] Removal effect of DH3 on various tetracycline antibiotics

[0073] Prepare a culture medium with a peptone concentration of 6 g / L and a pH of 7. Dispense the culture medium into 50 ml conical flasks and sterilize at 121°C for 25 min. Add filter-sterilized oxytetracycline, chlortetracycline, tetracycline, and doxycycline stock solutions to the sterilized culture medium to an initial antibiotic concentration of 50 mg / L. Add the activated strain DH3 (bacterial liquid ratio of 1%) to each conical flask and place the conical flask in a shaker at 25°C and 150 rpm for reaction. Sampling times are 0 and 72 h. Repeat 3 times for each group of experiments.

[0074] The results are as follows Figure 8 The results showed that DH3 could grow and remove tetracycline antibiotics at a concentration of 50 mg / L. At 72 h, the removal rates of oxytetracycline, chlortetracycline, tetracycline and doxycycline were 51.60%, 49.02%, 50.28% and 54.67% respectively.

[0075] Example 6

[0076] Removal effect of immobilized bacterial agents on various tetracycline antibiotics

[0077] Prepare a culture medium with a peptone concentration of 6 g / L and a pH of 7. Dispense the medium into 50 ml Erlenmeyer flasks and sterilize at 121°C for 25 min. Add filter-sterilized stock solutions of oxytetracycline, chlortetracycline, tetracycline, and doxycycline to the sterilized medium to an initial antibiotic concentration of 50 mg / L. Add the prepared immobilized bacterial agent to one set of Erlenmeyer flasks to form the immobilized bacterial agent degradation group. Place the flasks in a shaker at 25°C and 150 rpm. Samples are collected at 0 and 72 h. Each experiment is repeated three times.

[0078] The results are as follows Figure 9The results showed that the immobilized bacteria degraded antibiotics at a tetracycline antibiotic concentration of 50 mg / L. At 72 h, the biodegradation rates of oxytetracycline, chlortetracycline, tetracycline and doxycycline were 84.86%, 77.61%, 82.97% and 93.25% respectively.

[0079] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A modified straw biochar, characterized in that: The biochar is obtained by pyrolyzing soybean straw powder at 680-720° C. under anaerobic conditions and then modifying the obtained biochar with a KOH solution having a concentration greater than 0.4 mol / L.

2. The modified straw biochar according to claim 1, characterized in that: The pyrolysis temperature is 700°C.

3. The modified straw biochar according to claim 1, characterized in that: The concentration of the KOH solution ranges from 0.5 to 3 mol / L.

4. The modified straw biochar according to any one of claims 1 to 3, characterized in that: The biochar is prepared by pyrolyzing soybean straw powder at 700°C and then modifying it with a 0.5 mol / L KOH solution.

5. A tetracycline antibiotic-degrading bacteria immobilized bacterial agent, characterized in that: The modified straw biochar according to any one of claims 1 to 4 is used as a carrier, and the Citrobactermurliniae strain DH3 is loaded on the carrier; The deposit number of the Citrobacter muehii strain DH3 is CGMCC No.29865.

6. A method for preparing the immobilized tetracycline antibiotic-degrading bacteria agent according to claim 5, characterized in that: The following steps are involved: The bacterial liquid of Citrobacter muehii strain DH3 and the modified straw biochar according to any one of claims 1 to 4 are cultured in a culture medium to obtain an immobilized bacterial agent of tetracycline antibiotic-degrading bacteria.

7. The preparation method according to claim 6, characterized in that: The volume mass ratio of the bacterial solution of the Citrobacter rodentium strain DH3 to the modified straw biochar is 1 mL: 0.5-2.5 g; The OD of the bacterial solution of the Citrobacter rodentium strain DH3 600 is 1.

8. The preparation method according to claim 6, characterized in that: The culture temperature is 28-32°C; The culture time is 22 to 26 hours; The culture is a shaking culture; the rotation speed of the shaking culture is 130-170 rpm.

9. Use of the modified straw biochar according to any one of claims 1 to 4, the immobilized tetracycline antibiotic-degrading bacteria agent according to claim 5, or the immobilized tetracycline antibiotic-degrading bacteria agent prepared by the preparation method according to any one of claims 6 to 8 in degrading tetracycline antibiotics.

10. The use according to claim 9, characterized in that: The tetracycline antibiotics include at least one of the following: oxytetracycline, chlortetracycline, tetracycline and doxycycline.

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