Methylomonas bacteria and uses thereof

Abstract

This invention discloses a methylbacterium XC1 strain screened from the rhizosphere soil of contaminated paddy fields. Methylbacterium XC1 can stably survive in cadmium-contaminated soil and effectively fix available cadmium in the soil, thereby reducing the content of available cadmium in the soil and achieving effective remediation of cadmium pollution in the soil.

Description

Technical Field

[0001] This invention belongs to the field of microbial technology, specifically relating to a type of methylbacterium and its applications. Background Technology

[0002] Cadmium (Cd) is a heavy metal pollutant with significant biotoxicity and cumulative effects. It can migrate and accumulate in the soil-plant-food chain, and long-term exposure can harm the human kidneys, bones, and immune system. Due to factors such as mining and smelting, industrial waste discharge, application of cadmium-containing fertilizers and pesticides, irrigation with sludge and reclaimed water, transportation, and atmospheric deposition, farmland and soil in some areas face varying degrees of cadmium pollution risk. The environmental behavior of cadmium in soil is influenced by pH, organic matter, clay minerals, and redox conditions. In particular, when the content of available cadmium increases, it is more easily absorbed by plants and enters agricultural products, thus posing potential risks to the quality and safety of agricultural products.

[0003] Existing cadmium-contaminated soil remediation technologies mainly include engineering ex-situ treatment (such as excavation, replacement, solidification / stabilization, and landfill), physicochemical remediation (such as soil washing, electrokinetic remediation, chemical precipitation / passivation and stabilization), and bioremediation (such as phytoremediation, microbial remediation, and combined remediation). Engineering and chemical methods often suffer from high costs, significant disturbance, potential damage to soil structure and fertility, risks of secondary pollution, or the need for subsequent treatment; phytoremediation has a long cycle and is limited by climate, crop type, and pollution level.

[0004] Microbial induced carbonate precipitation (MICP), as an emerging bioremediation method, immobilizes heavy metals by producing carbonate precipitates through microbial metabolic activity. It offers potential advantages such as environmental friendliness, in-situ implementation, and minimal disturbance to soil structure. However, the actual effectiveness of this technology is highly dependent on the performance of the microbial strains used. Currently, in MIP remediation research on cadmium-contaminated soils, commonly used exogenous functional microorganisms (such as Bacillus pasteurellii) generally face problems in real soil environments, including insufficient colonization capacity, poor adaptability to complex soil systems, and large fluctuations in remediation efficiency. Furthermore, the introduction of exogenous strains may disturb the indigenous microbial community, posing ecological risks.

[0005] Methylobacterium ( Methylorubrum Methylbacteria are widely distributed in soil and on / within plants, exhibiting strong environmental adaptability and the ability to coexist with plants. Existing research on Methylbacteria largely focuses on their plant growth-promoting properties; research and reports on their ability to stably survive in cadmium-contaminated soil and specifically passivate cadmium in the soil using the MIP principle are very limited. In particular, there is a lack of Methylbacteria strains that possess both significant cadmium passivation effects (such as effectively reducing cadmium bioavailability) and the ability to survive in cadmium-contaminated soil, as well as corresponding stabilizing agents and application technologies suitable for agricultural soils. Summary of the Invention

[0006] To overcome the problems of poor adaptability and potential ecological risks caused by the reliance on exogenous strains in existing MIP technologies, this invention provides a soil cadmium pollution remediation scheme based on indigenous methyl bacilli that can utilize the MIP principle. The purpose of this invention is to provide a methyl bacillus and its application, which can stably survive in cadmium-contaminated soil and effectively induce carbonate precipitation to reduce the content of available cadmium in the soil.

[0007] The objective of this invention is achieved by at least one of the following technical solutions: The first aspect of the present invention is to provide a methylbacterium XC1, wherein the preservation number of methylbacterium XC1 is GDMCC No. 67466; and the biological classification of methylbacterium XC1 is named as follows: Methylorubrum sp. . A second aspect of the present invention is to provide a biological agent comprising one or more of the following: live cells, dormant cells, inactivated cells, and / or metabolites of the aforementioned Methylobacterium XC1.

[0008] Furthermore, the biological agent contains live cells of the aforementioned Methylobacterium XC1.

[0009] Furthermore, the biological agent is a powder, granule, suspension, wettable powder, freeze-dried bacterial powder, or encapsulated microspheres.

[0010] Furthermore, the biological agent also includes a carrier and / or adjuvants.

[0011] Furthermore, the carrier is selected from one or more of peat, vermiculite, zeolite, kaolin, biochar, wood ash organic fertilizer, and humic acid-based carriers.

[0012] Furthermore, the additive is selected from one or more of the following: protectants, binders, dispersants, slow-release agents, and nutrients.

[0013] A third aspect of the present invention is to provide the application of the Methylobacterium XC1 described in the first aspect of the present invention or the biological agent described in the second aspect of the present invention in the treatment of cadmium pollution.

[0014] Furthermore, the application is to reduce the content of available cadmium in the soil and / or reduce the bioavailability of cadmium in the soil.

[0015] A fourth aspect of the present invention is to provide a method for remediating cadmium pollution in soil, specifically comprising the following steps: The biological agent described in the second aspect of the present invention is applied to the soil to be remediated and then incubated.

[0016] Furthermore, the application method includes spraying or rotary tillage.

[0017] Furthermore, the applied amount is 300-800 mL / kg, and the bacterial concentration is OD0.05. 600 =0.6-1.2.

[0018] Furthermore, the applied amount is 500 mL / kg, and the bacterial concentration is OD0.05. 600 =1.0.

[0019] Furthermore, the microorganisms are prepared using a bacterial suspension of Methylobacterium XC1 in the logarithmic growth phase.

[0020] Furthermore, the cadmium content of the soil to be remediated was 0.3 mg·kg⁻¹. -1 -8.0 mg·kg -1 .

[0021] Furthermore, the cadmium content of the soil to be remediated is 0.5 mg·kg⁻¹. -1 -1.5 mg·kg -1 .

[0022] Furthermore, the remediation temperature of the soil to be remediated is 24-36 ℃, and the soil pH is 7.0-8.9.

[0023] Furthermore, the remediation temperature of the soil to be remediated is 32 ℃.

[0024] Furthermore, the culture time is 5-20 days.

[0025] Furthermore, the biological agent is applied in combination with the improver, wherein the improver is selected from one or more of biochar, lime, phosphate, silicon fertilizer, humic acid or organic fertilizer.

[0026] Furthermore, the soil to be remediated is farmland soil, paddy field soil, mining area soil, or industrial site soil.

[0027] Furthermore, the soil to be remediated is paddy field soil, and the soil cadmium pollution remediation method is used to reduce the risk of cadmium accumulation in the edible parts of crops.

[0028] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) The Methylobacterium strain of the present invention is an indigenous strain that can survive stably in cadmium-contaminated soil, significantly reduce the content of available cadmium in the soil, thereby achieving effective remediation of cadmium pollution in soil, and is suitable for both in-situ and ex-situ remediation of soil.

[0029] (2) The present invention adopts a microbial remediation method, which reduces the dependence on strong acids and alkalis or large amounts of chemical passivating agents, minimizes the disturbance to soil structure and ecosystem, and reduces the risk of secondary pollution.

[0030] (3) The Methylobacterium strain of the present invention can be applied in situ through simple agronomic methods such as spraying, irrigation or mixing with soil, which is convenient for large-scale promotion, has low overall cost, and the strain has good adaptability to soil environment. It can be used for cadmium remediation of soils with different textures, different pH and different pollution levels, and is applicable to various scenarios such as farmland soil and general site soil. Attached Figure Description

[0031] Figure 1 Images of Methylobacterium XC1 colonies are shown, where a is a streak colony image of Methylobacterium XC1; b is the microstructure of Methylobacterium XC1; and c is the Gram staining result of Methylobacterium XC1.

[0032] Figure 2 This is a phylogenetic tree diagram of Methylobacterium XC1.

[0033] Figure 3 This is a growth curve of Methylobacterium XC1 at different temperatures in Example 2.

[0034] Figure 4 This is a line graph showing the change in urea concentration during the growth of Methylobacterium XC1 in Example 3.

[0035] Figure 5 This is a line graph showing the pH changes during the growth of Methylobacterium XC1 in Example 3.

[0036] Figure 6 For example, 0, 20, and 40 mg·L⁻¹ in Example 4 -1 Line graph showing the change in urease activity during the growth of Methylobacterium XC1 under cadmium concentration conditions.

[0037] Figure 7 The Cd values ​​of the fermentation broth of Methylobacterium XC1 and the corresponding sterile fermentation broth in Example 5 are... 2+ Removal rate bar chart.

[0038] Figure 8 The fermentation broth of Methylobacterium XC1 in Example 5 and Cd 2+ Image of the mixed precipitate products, where a is the fermentation broth of Methylobacterium and Cd. 2+ Scanning electron microscope (SEM) image of the mixed precipitate; d represents the fermentation broth of Methylobacterium and Cd. 2+ Particle size distribution of the mixed precipitate products.

[0039] Figure 9 The fermentation broth of Methylobacterium XC1 in Example 5 and Cd 2+ X-ray polycrystalline diffraction (XRD) pattern of the mixed precipitate products.

[0040] Figure 10The fermentation broth of the Methylobacterium XC1 strain in Example 5 and Cd 2+ Fourier transform infrared image of the mixed precipitate products.

[0041] Figure 11 The graph shows the effect of adding the fermentation broth of Bacillus methylbacterium XC1 strain to Example 6 on the content of available cadmium in the soil. Detailed Implementation

[0042] The specific implementation of the present invention will be further described below with reference to the accompanying drawings and examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that any processes not specifically described in detail below are those that can be implemented or understood by those skilled in the art by referring to the prior art. Reagents or instruments whose manufacturers are not specified are considered to be conventional products that can be purchased commercially.

[0043] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0044] In this invention, the terms "methylbacterium XC1" and "XC1" both refer to the strain with accession number GDMCC No. 67466. This strain was deposited on December 11, 2025, at the Guangdong Provincial Center for Microbial Culture Collection, located at 5th Floor, Building 59, No. 100 Xianlie Middle Road, Guangzhou. The biological classification of this strain is named as follows: Methylorubrum sp. .

[0045] In this invention, the urea-containing nutrient broth culture medium (NBU medium) is prepared as follows: 10 g / L peptone -1 NaCl 5 g·L -1 3 g·L of beef extract -1 urea 5 g·L -1 After adjusting the pH to 7.0 and autoclaving at 121℃ for 20 min, the prepared urea solution was added through a 0.22 μm sterile filter membrane.

[0046] In this invention, the glucose peptone liquid culture medium is prepared as follows: 5 g·L -1 Peptone, 20 g·L -1 Glucose, 2 g·L -1 Yeast extract, 1 g·L -1 KH2PO4, 0.24 g·L -1 Sterilize with Mg2SO4, pH=6.8, at 121℃ for 15 min, and add an additional 15 g·L⁻¹ to the solid culture medium. -1 Agar.

[0047] In this invention, the test soil was paddy field soil. The paddy soil collected in the field was naturally air-dried, passed through a 10-mesh sieve, and stored for later use. The soil's physicochemical properties are as follows: pH value 6.21, available phosphorus (P), available nitrogen (N), available potassium (K), and organic matter content 38.42 mg / kg. -1 113.31 mg·kg -1 106.23 mg·kg -1 29.4 g·kg -1 The total cadmium content in the soil was measured to be 0.02 ± 0.002 mg·kg⁻¹. -1 Take an appropriate amount of test soil and sterilize it by moist heat at 121℃ for 2 h. Then, add the test soil evenly with an exogenous CdCl2·2.5H2O solution to prepare cadmium-containing soil. After stabilizing at room temperature for one month, measure the cadmium content of the soil.

[0048] Example 1: Screening and Identification of Strains The rhizosphere soil of rice paddies contaminated with cadmium was selected, with a cadmium background value of 0.83 mg·kg⁻¹. -1 Multiple random samples were mixed, placed in sterilized kraft paper bags, and then stored in sealed bags at 4°C for later use.

[0049] Collect 1g of soil sample into a sterile 250mL Erlenmeyer flask and add 100mL of sterile water. Incubate at 30℃ and 150rpm. -1 Shake thoroughly for 20 min under the specified conditions to prepare rhizosphere soil bacterial suspension, and prepare 10 batches of each batch sequentially. -1 ~10 -4 Soil bacterial suspensions of different dilutions were stored at 4°C for later use. Take 10... -4 The diluted solution was inoculated at a 2% inoculum into sterilized Cd. 2+ The content is 20 mg·L -1 The culture was carried out in glucose peptone liquid medium until the bacterial culture OD 600 When the concentration is greater than 1, take an appropriate amount of bacterial solution and inoculate it into the sterilized Cd solution. 2+ The content is 40 mg·L -1 In glucose peptone liquid medium, repeat the above steps to add Cd 2+ Concentration increased to 100 mg·L -1 In Cd 2+ The content is 100 mg·L -1 100 μL of bacterial suspension was added to glucose peptone solid medium and spread onto the medium, then incubated upside down in a constant temperature incubator. After incubation, single colonies with good growth and obvious morphological differences were selected for continuous streak purification culture to obtain the initial screening strain XC1. Figure 1As shown, strain XC1 presents as flat, neatly edged, red spherical colonies on glucose peptone medium. Scanning electron microscopy reveals that it is a bacillus with a cell length of approximately 1 μm. Strain XC1 is Gram-negative.

[0050] The 16S rDNA sequencing of the initial screening strain XC1 was performed by Cambricon Biotechnology (Hangzhou) Co., Ltd. DNA extraction, PCR amplification, and sequencing were conducted using universal primers 16F27 and 16R1492. After obtaining the sequencing results, the sequences were spliced ​​and cut using DNAMAN software to obtain the assembled 16S rDNA gene sequence. The 16S rDNA sequence was then compared with the GenBank nucleotide database using the BLAST function in the NCBI database. A phylogenetic tree of the strain was constructed using MEGA 10.0 software and the Neighbor-Joining method. The phylogenetic tree of the initial screening strain XC1 is shown below. Figure 2 As shown, the initial screening strain XC1 belongs to the genus *Methylobacterium* (…). Methylorubrum ).

[0051] Example 2: Optimal growth temperature of the strain The bacterial suspension was inoculated into 200 mL of sterilized NBU medium at a 1% inoculum, and incubated at 24℃, 28℃, 32℃, 36℃, and 40℃, respectively, at 150 r·min. -1 The samples were cultured under constant temperature and shaking for 84 h. Samples were taken every 12 h, and the OD600 value was measured after each sample. Each group was repeated 3 times as a parallel control.

[0052] Growth curves of Methylobacterium XC1 at different temperatures are shown below. Figure 3 As shown, Methylobacterium XC1 grows most rapidly at 32℃, enters the logarithmic phase most quickly, and reaches the stationary phase OD at the highest temperature. 600 The value is the largest, and its logarithmic phase is delayed at a temperature of 40℃, and OD reaches its steady-state phase at that time. 600 The value is the smallest, at only 0.930.

[0053] Example 3: Determination of urea concentration and pH during strain growth Urease-producing microorganisms can promote the decomposition of urea into CO3 by producing urease. 2- CO3 2- Urease-producing microorganisms can combine with heavy metal ions to form carbonate products. These carbonates are relatively stable in the environment and not easily activated, thus reducing the bioavailability of heavy metal ions. During carbonate mineralization, urease-producing microorganisms can decompose urea into CO3. 2- and NH 4+ This increases the pH value in the culture medium.

[0054] The bacterial suspension was inoculated at a 1% inoculum into 200 mL of sterile NBU medium and cultured at 32 °C and 150 r·min. -1 The culture was kept at a constant temperature and shaken for 72 h. During the culture, the urea content and pH value in the culture medium were measured. The urea content was determined by the p-dimethylaminobenzaldehyde (PDAB) colorimetric method. Sterile NBU medium without inoculated strains was used as a blank control (CK). Each group was repeated 3 times as a parallel control.

[0055] Reference for the colorimetric method of p-dimethylaminobenzaldehyde (PDAB) (Miao Xiaojie, Jiang Enchen, Wang Jia, et al. Determination of trace amounts of urea in aqueous solution by colorimetric spectrophotometry of p-dimethylaminobenzaldehyde [J]. Journal of Northeast Agricultural University, 2011, 42(08): 87-92).

[0056] The results are as follows Figure 4 and Figure 5 As shown, the changes in urea content and pH value in the culture medium of Methylbacterium XC1 during its growth showed similar trends. The rate of urea consumption was higher during the logarithmic growth phase than during the lag and stationary phases. After 72 hours of culture, the hydrolysis rate of urea by Methylbacterium XC1 was approximately 68%. The pH value in the culture medium gradually increased with the growth of the strain. The highest pH value of the Methylbacterium XC1 culture medium was 8.89 during the entire culture process, reaching its peak after 72 hours, and then remained stable thereafter.

[0057] Example 4: Determination of urease activity during bacterial growth under cadmium stress The bacterial suspension was inoculated onto Cd at an inoculum concentration of 1%. 2+ Concentrations of 20 and 40 mg·L -1 The culture was carried out in 200 mL of sterile NBU medium at a temperature of 32 °C and a speed of 150 r·min. -1 The culture was carried out under constant temperature and shaking for 72 h. During the culture, the urease activity was measured. Sterile NBU medium without inoculated strains was used as a blank control (CK). Each group was repeated 3 times as a parallel control.

[0058] Urease activity was determined using Nessler's reagent method.

[0059] Preparation of ammonium sulfate standard working solution: Accurately weigh 0.9910 g of ammonium sulfate dried to constant weight, dissolve it in distilled water, and then dilute to a volumetric flask with distilled water. This solution contains approximately 15 μmol of NH4+ per mL. + Accurately transfer 5 mL of the stock solution into a 50 mL volumetric flask, and add distilled water to the mark. This solution contains approximately 1.5 μmol of NH4+ per mL. + .

[0060] Establishment of the standard curve: Accurately pipette 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0 mL of ammonium sulfate standard solution (corresponding to NH4+) + Concentrations of 0.0, 0.30, 0.60, 0.90, 1.20, and 1.50 μmol were placed in seven 25 mL stoppered colorimetric tubes, water was added to a final volume of 9 mL, 1 mL of Nessler's reagent was added to each tube, and distilled water was added to the mark. The absorbance was measured at 415 nm, and a standard curve was plotted. The bacterial suspension or spore suspension was inoculated into NBU medium and cultured for 72 h. The bacterial solution was then subjected to a hydroperfusion reaction at 4000 r·min⁻¹. -1 After centrifugation for 20 min, 0.1 mL of the supernatant was transferred to a 25 mL stoppered colorimetric tube, and 0.9 mL of 3% urea solution was added. The reaction was carried out at 35 °C for 7 min, and then 1 mL of 10% trichloroacetic acid solution was immediately added to terminate the reaction. After the sample was removed and cooled slightly, 1 mL of Nessler's reagent was added, and the mixture was distilled to the mark. After color development for 20 min, the absorbance was measured at 415 nm along with the standard curve. The NH4+ content in the sample was calculated based on the standard curve. + Concentration, at which 1 μmol of free NH4 is released per minute. + Urease activity is expressed as U, and urease activity = M / (0.1 × 7) × 250 (where M represents the NH4+ corresponding to the sample in the standard curve). + (amount of substance).

[0061] like Figure 6 As shown, *Methylobacterium* XC1 grows slowly after inoculation. During the lag phase, its urease activity is relatively low. However, once it enters the logarithmic phase, the strain grows rapidly with a high metabolic level, and its urease activity increases rapidly. During the growth process, the highest urease activity of *Methylobacterium* reaches 90.8 U·mL. -1， After reaching the stationary phase, the urease activity of all strains showed a decreasing trend. The logarithmic growth phase of *Methylobacterium* XC1 occurred between 14 and 34 hours, during which the strain's urease activity increased most rapidly. Cadmium reduces the urease activity of strains in the culture medium; when Cd in the culture medium... 2+ Concentration of 0-40 mg·L -1 At that time, with Cd 2+ With increasing concentration, the urease activity of Methylobacterium XC1 decreases.

[0062] Example 5: Cadmium removal rate of the strain's fermentation broth The bacterial suspension was inoculated into NBU medium at a 1% inoculum and cultured for 72 h to obtain the fermentation broth. The fermentation broth was then centrifuged at 8000 rpm for 10 min to obtain the bacterial cell-free fermentation broth. 4 ml of Cd was added to a sterilized 50 mL centrifuge tube. 2+ Concentration of 100 mg·L -1After adding CdCl2·2.5H2O solution, 16 mL of Methylobacterium fermentation broth or the corresponding strain of sterile bacteria was added. After standing for 2 h, the supernatant was filtered through a 0.22 μm filter membrane and the Cd content was determined. 2+ Content, calculate Cd 2+ The removal rate was determined, and the precipitate products were characterized and analyzed. Each group was repeated three times in parallel control.

[0063] Cd 2+ Removal rate, such as Figure 7 As shown, to the Cd-containing 2+ Adding the fermentation broth of methylbacterium XC1 to the solution can remove Cd. 2+ It transforms into a precipitate, thereby reducing the Cd concentration in the solution. 2+ Content, 2h Methylobacterium XC1 sterile fermentation broth Cd 2+ The removal rate was 51.15%. The fermentation broth with added Methylobacterium showed a positive effect on Cd. 2+ The removal rate was relatively higher than that of Methylobacterium XC1 bacterial culture fermentation broth, and the Cd removal rate of the 2-hour Methylobacterium fermentation broth was higher. 2+ The removal rate was 72.70%.

[0064] like Figure 8 a and Figure 8 As shown in Figure d, the fermentation broth of Methylobacterium XC1 and Cd 2+ The mixed precipitate products were ellipsoidal in shape with an uneven particle size distribution, ranging from 200 nm to 1 μm. Larger aggregates formed from ellipsoidal polymerization were also observed, possibly due to substances in the fermentation broth adhering to the smaller ellipsoidal particles and forming these larger aggregates. Random EDS spot scanning of the samples revealed the presence of C, O, and Cd elements in the precipitate, suggesting that the fermentation broth contains Cd. 2+ The reaction produced CdCO3 precipitate.

[0065] like Figure 9 As shown, the fermentation broth of Methylobacterium XC1 and Cd 2+ Sharp diffraction peaks were observed in the mixed precipitate, indicating strong crystalline properties. Analysis of some diffraction peaks in the product was compared with PDF#97-003-3662 in the PDF library; some peaks corresponded to the characteristic peak positions of the precipitate, confirming that the fermentation broth of *Methylobacterium* XC1 was similar to that of Cd. 2+ The precipitate formed by the reaction is mainly composed of CdCO3.

[0066] like Figure 10 As shown, in the range of 3200-3600 cm -1 The broad peaks observed are attributed to the stretching vibrations of the hydroxyl groups (-OH) and (-NH2). (1650 cm⁻¹) - ¹and 1540 cm -¹These are the stretching vibration peaks of C=O and NH in the amide I and amide II bands, respectively. (Fermentation broth of *Methylobacterium* XC1 strain and Cd...) 2+ Mixed precipitates at 1420-1480 cm⁻¹ -1 There are CO asymmetric stretching vibration peaks, which are close to the characteristic peaks of cadmium carbonate, at 1100 and 1000 cm⁻¹. -1 The absorption peak between the two peaks is due to the CO stretching vibration and is the strongest of all other peaks.

[0067] Example 6: Verification Experiment of Strain Removal of Cadmium from Soil 10 g of the test soil (initial available cadmium content was 1.23 mg·kg⁻¹) was evenly placed in a petri dish. -1 Add 5 mL of OD evenly. 600 The fermentation broth of Methylobacterium XC1 with a concentration of 1 was used as the experimental group, and the group with 5 mL of sterile water was used as the control. The samples were continuously cultured in a constant temperature incubator at 30℃. Soil samples were taken out and air-dried on the 5th, 10th and 20th days of culture, and the content of available cadmium in the soil was measured. Each group was repeated 3 times in parallel control.

[0068] Determination of available cadmium content in soil: Reference method for cadmium speciation extraction in soil: Determination of ion-exchangeable (including water-soluble) cadmium content (Ma Ling, Liu Wenchang, Cha Lixin, et al. Study on speciation of cadmium in soil samples [J]. Anhui Geology, 2010, 20(04):273-276).

[0069] like Figure 11 As shown, adding the fermentation broth of *Methylobacterium XC1* to cadmium-containing soil can reduce the content of available cadmium in the soil, and the content of available cadmium in the soil shows a decreasing trend with the increase of fermentation time after adding *Methylobacterium XC1*. The initial available cadmium content in the soil was 1.23 mg·kg⁻¹. -1 The available cadmium content in the soil after 20 days of fermentation broth supplemented with *Methylobacterium XC1* strain was 0.66 mg·kg⁻¹. -1 .

[0070] The above embodiments are merely preferred embodiments of the present invention and are only used to explain the present invention, not to limit the present invention. Any changes, substitutions, modifications, etc., made by those skilled in the art without departing from the spirit and essence of the present invention should be within the protection scope of the present invention.

Claims

1. A type of methylbacterium XC1, characterized in that, The preservation number of the *Methylobacterium* XC1 is: GDMCC No. 67466; the biological classification of the *Methylobacterium* XC1 is named... Methylorubrum sp. .

2. A biological agent, characterized in that, The biological agent comprises one or more of the live, dormant, inactivated cells and / or metabolites of Methylbacillus XC1 as described in claim 1.

3. The biological agent according to claim 2, characterized in that, The biological agent contains live cells of the aforementioned Methylobacterium XC1.

4. The biological agent according to claim 2, characterized in that, The biological agent is a powder, granule, suspension, wettable powder, freeze-dried bacterial powder, or encapsulated microspheres.

5. The biological agent according to claim 2, characterized in that, The biological agent also includes a carrier and / or adjuvants.

6. The biological agent according to claim 5, characterized in that, The carrier is selected from one or more of peat, vermiculite, zeolite, kaolin, biochar, wood ash organic fertilizer, and humic acid-based carriers.

7. The biological agent according to claim 5, characterized in that, The additives are selected from one or more of the following: protectants, binders, dispersants, slow-release agents, and nutrients.

8. The application of the Methylobacterium XC1 of claim 1 or the biological agent of any one of claims 2-7 in the treatment of cadmium pollution.

9. A method for remediating cadmium pollution in soil, characterized in that, Specifically, the following steps are included: The biological agent according to any one of claims 2-7 is applied to the soil to be remediated and then incubated.

10. The method for remediating cadmium pollution in soil according to claim 9, characterized in that, The applied amount is 300-800 mL / kg, and the bacterial concentration is OD. 600 =0.6-1.2; The remediation temperature of the soil to be remediated is 24-36 ℃, and the soil pH is 7.0-8.9; The soil to be remediated is farmland soil, paddy field soil, mining area soil, or industrial site soil.

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