Pseudomonas lacticola strain wg7-43, microbial inoculum and use thereof

Abstract

The application belongs to the technical field of microorganisms, discloses a strain of Pseudomonas lacticola WG7-43, a microbial agent and application of the strain and the microbial agent. Pseudomonas lactis The Pseudomonas lacticola (Pseudomonas lacticola) WG7-43 provided in the application can directly promote crop growth by continuously playing the role of dissolving phosphorus and the like after being planted in the rhizosphere, and can effectively block the absorption of cadmium by rice and improve the resistance of crops to cadmium stress by secreting extracellular polysaccharides and efficiently adsorbing heavy metals and the like. The microbial agent has the advantages of small dosage, low cost and environmental friendliness, is suitable for “production and repair simultaneously” of medium and light cadmium-polluted agricultural land, and has a wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of microbial technology, specifically relating to a strain of Pseudomonas lactis WG7-43, its inoculant, and its application. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Cadmium in soil often exists as a water-soluble and highly mobile divalent ion (Cd). 2+ Cadmium exists in its cadmium-contaminated form and can enter the human body through the food chain, causing serious damage to multiple organs, including the brain, kidneys, bones, and reproductive system. Rice has a strong ability to accumulate cadmium, and the cadmium content in its grains can easily exceed food safety standards. Therefore, developing effective remediation technologies for cadmium-contaminated farmland to ensure the safety of agricultural products is of urgent practical significance.

[0004] In terms of remediation technologies, bioremediation (including phytoremediation and microbial remediation) is more advantageous than physicochemical methods due to its environmental friendliness and cost-effectiveness. Microbial remediation overcomes the drawbacks of phytoremediation, such as its long cycle and impact on agricultural production, enabling "remediation while production is underway," making it particularly suitable for lightly to moderately polluted farmland. The core mechanism of microbial remediation of heavy metals lies in reducing the bioavailability and mobility of heavy metals through cell adsorption, extracellular polymeric substance (EPS) fixation, valence state transformation, and induced precipitation, thereby reducing plant absorption and accumulation and ensuring the safety of agricultural products.

[0005] Pseudomonas spp. ( Pseudomonas ) is one of the most widely used bacterial genera in soil heavy metal remediation (such as cadmium, lead, copper, etc.). Some strains are also important plant growth-promoting rhizobacteria (PGPR), with functions such as nitrogen fixation, phosphorus solubilization, potassium solubilization, and antagonism of pathogenic microorganisms.

[0006] Numerous studies have confirmed that certain species within this genus exhibit high efficiency in fixing cadmium in soil. Related patents (such as CN201410101334.8 and CN202410907065.8) also disclose the application of *Pseudomonas* strains in improving the cadmium stress tolerance of crops (such as rice and tomatoes). However, the *Pseudomonas* genus comprises over 200 species, and existing research and published technologies largely focus on a few known species within this genus (such as *Pseudomonas aeruginosa*). P. aeruginosa Fluorescent Pseudomonas P. fluorescens Pseudomonas aeruginosa P. chlororaphisFurthermore, different strains of *Pseudomonas lactis* exhibit significantly different blocking effects against cadmium. Recent studies suggest that *Pseudomonas lactis* (etc.) Pseudomonas lactis Lactobacillus has potential in the biocontrol of crop diseases and in the use of its iron carriers to wash away heavy metals in soil, but no literature or patents have disclosed its potential. Pseudomonas lactis Reports indicate that *Pseudomonas aeruginosa* strains can simultaneously and efficiently promote crop growth and block cadmium absorption under cadmium stress. Therefore, identifying and validating *Pseudomonas aeruginosa* strains with cadmium-enhancing functions is of great significance for enriching the bioremediation microbial resources of cadmium-contaminated farmland and developing novel microbial products. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a strain of *Pseudomonas lactis* (… Pseudomonas lactis WG7-43, bacterial agent and its application: The strain provided by this invention has cadmium resistance, can decompose inorganic phosphorus, produce extracellular polysaccharides and adsorb cadmium ions; it can colonize the roots of rice, block the absorption of heavy metal cadmium by rice by more than 51% and achieve a yield increase of more than 17%.

[0008] To achieve the above objectives, the present invention provides the following technical solution.

[0009] In a first aspect, the present invention provides a strain of *Pseudomonas lactis* (… Pseudomonas lactis WG7-43 was deposited on December 26, 2022, at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 26287. The deposit address is No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing, Institute of Microbiology, Chinese Academy of Sciences.

[0010] Secondly, the present invention provides the *Pseudomonas lactis* described in the first aspect (… Pseudomonas lactis Application of WG7-43 in cadmium adsorption or cadmium fixation.

[0011] In some embodiments of the present invention, *Pseudomonas lactis* ( Pseudomonas lactis WG7-43 fermentation produces adsorbent extracellular polysaccharides. Surprisingly, under the same extraction conditions, based on the *Pseudomonas lactis* provided in this invention (…), Pseudomonas lactis The extracellular polysaccharides extracted from the fermentation broth of WG7-43 showed a significantly higher adsorption effect on cadmium than those from other strains, thus making them suitable for adsorption and fixation of cadmium.

[0012] Based on the experimental results in the embodiments of the present invention, the possible causes may include the following two aspects.

[0013] 1) Functional group type and density: The metal adsorption capacity of extracellular polysaccharides mainly depends on their chemical composition, such as the number and type of functional groups like carboxyl (-COOH), hydroxyl (-OH), and phosphate (-PO4). The *Pseudomonas lactis* provided in this invention... Pseudomonas lactis The extracellular polysaccharides produced by G7-43 may contain more or higher affinity functional groups, thereby significantly enhancing cadmium binding capacity.

[0014] 2) Polysaccharide structure: The molecular weight, chain conformation (e.g., linear or branched), and spatial arrangement of extracellular polysaccharides may affect their accessibility and the degree of exposure of adsorption sites. The *Pseudomonas lactis* (…) provided in this invention… Pseudomonas lactis The extracellular polysaccharide of G7-43 may have a structure that is more conducive to the coordination of cadmium ions.

[0015] Thirdly, the present invention provides the *Pseudomonas lactis* described in the first aspect (… Pseudomonas lactis Application of WG7-43 in improving crop resistance to cadmium stress.

[0016] Fourthly, the present invention provides the *Pseudomonas lactis* described in the first aspect (… Pseudomonas lactis Application of WG7-43 in blocking crop absorption of cadmium.

[0017] Fifthly, the present invention provides the *Pseudomonas lactis* described in the first aspect (… Pseudomonas lactis Application of WG7-43 in crop growth promotion.

[0018] In the third, fourth, and fifth aspects, the crop mentioned includes rice. Because rice has a strong ability to accumulate cadmium, this invention used rice as the test subject in pot experiments and cadmium-contaminated experimental fields. The results demonstrated that the *Pseudomonas lactis* (…) provided by this invention… Pseudomonas lactis WG7-43 has a strong cadmium adsorption effect, which can effectively reduce the cadmium content in rice grains and significantly increase rice yield.

[0019] Sixthly, the present invention provides the *Pseudomonas lactis* described in the first aspect (… Pseudomonas lactis Application of WG7-43 in cadmium-containing wastewater treatment or soil remediation.

[0020] In a seventh aspect, the present invention provides a microbial agent comprising the *Pseudomonas lactis* described in the first aspect (…). Pseudomonas lactis WG7-43.

[0021] The preparation method of the bacterial agent is as follows: *Pseudomonas lactis* (Lactobacillus) is picked up from the preservation slant using an inoculation needle. Pseudomonas lactisWG7-43 colonies were streaked onto NA (Nutrient Agar) plates and activated at 30±2℃; then, seed culture was inoculated into NB (Nutrient Broth) medium and cultured in shake flasks at 30±2℃ and 150-200 rpm for 10-30 h, preferably 12-16 h; further culture in shake flasks or fermenters yielded *Pseudomonas lactis*. Pseudomonas lactis The bacterial culture of WG7-43 was tested using the plate serial dilution method, and the CFU of the bacterial culture was found to be ≥2×10⁻⁶. 8 / mL, bacterial contamination rate ≤10%, dispensed and refrigerated for later use.

[0022] Eighthly, the present invention provides the application of the microbial agent described in the seventh aspect in promoting crop growth.

[0023] Optionally, in the application described in aspect eight, the method of applying the microbial agent is as follows:

[0024] (1) Seed dressing with microbial agent: Dilute the microbial agent described in the seventh aspect with water to a concentration equal to that of *Pseudomonas lactis* ( Pseudomonas lactis The CFU concentration of WG7-43 is at 10 6 -10 7 / mL for seed dressing;

[0025] (2) Application of microbial agent: When the crop is transferred to the field, it is applied with the water for planting. When the seedlings of direct-seeded crops emerge, it is applied during the first watering. The dosage is 5-10L per mu.

[0026] In one or more embodiments of the present invention, a strain of *Pseudomonas lactis* (…) is provided. Pseudomonas lactis WG7-43, microbial agents and their application have produced the following beneficial effects.

[0027] 1. The rice rhizosphere microorganism *Pseudomonas lactis* (…) provided by this invention Pseudomonas lactis WG7-43 can continuously promote crop growth by solubilizing phosphorus after rhizosphere colonization; and it can effectively block the absorption of cadmium by rice and improve the crop's resistance to cadmium stress by secreting extracellular polysaccharides and efficiently adsorbing heavy metals.

[0028] 2. The microbial agent provided by this invention requires a small amount, is low in cost, and is environmentally friendly. It is suitable for "simultaneous production and remediation" of farmland with moderate to mild cadmium pollution, and has broad application prospects. Attached Figure Description

[0029] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0030] Figure 1 The *Pseudomonas lactis* provided by this invention ( Pseudomonas lactis ) Colony morphology diagram of WG7-43.

[0031] Figure 2 The *Pseudomonas lactis* provided by this invention ( Pseudomonas lactis Phylogenetic tree diagram of WG7-43.

[0032] Figure 3 The *Pseudomonas lactis* provided by this invention ( Pseudomonas lactis Diagram of the phosphorus solubility zone on WG7-43 plate. Detailed Implementation

[0033] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0034] In embodiments of the present invention, *Pseudomonas lactis* (…) is provided. Pseudomonas lactis WG7-43, preservation information is as follows.

[0035] Preservation institution: China General Microbiological Culture Collection Center, China Microbial Culture Collection Committee.

[0036] Address: No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing, Institute of Microbiology, Chinese Academy of Sciences.

[0037] Date of deposit: December 26, 2022.

[0038] Accession number: CGMCC No.26287.

[0039] Classification: Pseudomonas lactis ( Pseudomonas lactis ).

[0040] The control strains used in this embodiment include: Bacillus subtilis obtained from previous laboratory screening (… Bacillus subtilis AM17, accession number CGMCC No. 27031, disclosed in prior patent CN202311127233.3, is referred to as AM17 in this invention; *Ailuropoda spp.* obtained from previous screening (… Ochrobactrum daejeonense MG35, accession number CGMCC No.19745, was disclosed in prior patent CN202010443089.4, and is referred to as MG35 in this invention.

[0041] The components of the culture media and solutions used in the embodiments of the present invention are as follows: NB (Nutrient Broth) liquid culture medium: 10g peptone, 3g beef extract, 5g sodium chloride, 1000mL distilled water, pH 6.5-7.5.

[0042] NA (Nutrient Agar) solid medium: Add 15g-20g of agar per 1000mL to the NB liquid medium.

[0043] 1 / 5 NB liquid medium: Dilute NB liquid medium 5 times with distilled water, pH 6.5-7.5.

[0044] pH 6.0 Acetic Acid-Sodium Acetate Buffer Solution: Add 11g of anhydrous sodium acetate (or 18.3g of sodium acetate trihydrate) to 90mL of distilled water, adjust the pH to 6.0 with acetic acid, and bring the volume to 100mL with distilled water.

[0045] Statistical analysis was performed using DPS (v 9.50) software. The significance of differences between groups was tested by one-way ANOVA. The Duncan's method was used for pairwise comparisons in the multiple comparison method, and the significance level was judged as P < 0.05.

[0046] The technical content of the present invention will now be further illustrated with reference to the embodiments.

[0047] Example 1

[0048] Pseudomonas lactis Screening and identification of WG7-43.

[0049] 1) Isolation of resistant strains: Weigh 10g of rice rhizosphere soil (soil from the top 1mm-2mm of mature rice roots in Xinyu City, Jiangxi Province), place it in an Erlenmeyer flask containing 100mL of sterile water and 3-5 glass strains, and mix on a shaker at 200r / min for 20min to obtain 10 -1 A diluted soil suspension. 10 -1 The soil suspension was serially diluted 10-fold to 10 ... -6 Dilution, respectively coated on Cd-containing areas 2+ NA plates with concentrations of 0 mg / L, 56.2 mg / L, 112.4 mg / L, 168.6 mg / L, 224.8 mg / L, 281.0 mg / L, and 337.2 mg / L (calculated as CdCl2·2.5H2O) were incubated for 5 days. Cd2+ Concentration of 281 mg / L, 10 -1 Eighty-three cadmium-resistant bacteria were obtained from Cd-containing plates at various dilutions. Single colonies were selected based on morphological differences. 2+ The NA plates at 281.0 mg / L were purified by three streak tests, yielding 51 single strains for subsequent screening.

[0050] 2) Screening of cadmium-adsorbing microorganisms: Single isolated cadmium-resistant microorganisms were inoculated into Cd-containing... 2+The culture was carried out in 24-well plates containing 5 mL of 1 / 5 NB liquid medium at 33 mg / L, with three replicates for each strain, at 30℃ ± 2℃ and 150 rpm for approximately 24 h. 1.0 mL of the cultured bacterial solution was transferred to an EP tube and centrifuged at 3000 rpm for 10 min. 0.3 mL of the supernatant was transferred to a 50 mL centrifuge tube containing 9.5 mL of distilled water, along with 0.1 mL of ionic strength adjuster (for the Bante931 instrument) and 0.1 mL of pH 6.0 acetate-sodium acetate buffer. 1 / 5 NB liquid medium served as a blank control (CK).

[0051] 3) Preheat the Bante931 Cd ion meter by turning it on and following the instructions in the equipment manual, using the Cd ion meter that comes with the instrument. 2+ Detected after calibration with 0.1 mg / L and 1.0 mg / L standard solutions. Cd in the bacterial culture. 2+ Cd can accumulate intracellularly, be fixed by adsorption onto EPS (extracellular EPS) on the cell wall, or be bound to EPS secreted extracellularly, transforming into exchangeable or bound Cd, such as organically bound Cd. The concentration of Cd in centrifuged supernatant can be determined by measuring this concentration. 2+ Calculation unit OD 600nm The adsorption capacity of the strain can be used to remove Cd mainly through adsorption. 2+ The ability to screen for positive strains:

[0052] ,

[0053] .

[0054] Where R is the adsorption rate (%), and C0 is the initial Cd of the culture medium. 2+ Concentration, mg / L, Ct is the Cd of the culture medium at the end of fermentation. 2+ Concentration, mg / L, A is the concentration per bacterial cell (Cd). 2+ Adsorption capacity, mg / L, M is OD 600nm Values. The controls were AM17 and MG35 (data are expressed as mean ± standard deviation (n=3)), and two strains with strong adsorption capacity during screening, WG7-16 and WG7-26, were also included (see Table 1).

[0055] By comparing the adsorption rate (R) and adsorption capacity per unit cell (A) of each strain, the strain with the strongest overall adsorption capacity was screened. The strain with the strongest adsorption capacity, WG7-43, was obtained, capable of adsorbing Cd. 2+ 22.1 mg / L.

[0056] Table 1. Results of adsorption capacity determination for each strain

[0057] CK AM17 MG35 WG7-16 WG7-26 WG7-43 Adsorption capacity A mg / L 0 13.1±0.3 2.5±0.2 15.2±0.4 15.7±0.2 22.1±0.4 Adsorption rate R % 0 40.0 7.6 46.1 47.6 66.7

[0058] 4) Strain Identification: The purified strains were sent to Qingke Biotechnology for 16S rDNA sequencing. The returned data was compared with existing sequences in the NCBI database. Strains with similar homology were selected, and a phylogenetic tree was constructed using MEGA 11 software (v12.0.11) using the neighbor-joining method. Evolutionary distance was calculated based on the p-distance model, and the confidence of branch nodes was assessed using 1000 bootstrap coefficients to construct the phylogenetic tree. Figure 2 As shown. The results showed that the strain WG7-43 selected above was similar to... Pseudomonas lactis The similarity of DSM 29167 (NR 156986.1) is 99.86%, and it clusters in a branch with high support (97%). Figure 1 The colony morphology of this strain after incubation on NA solid medium at 30°C for 2 days is shown to be: round, milky white, with smooth edges, and a moist, glossy surface. It was identified as... Pseudomonas lactis Named Pseudomonas lactis WG7-43.

[0059]

[0060] The aforementioned Pseudomonas lactis ( Pseudomonas lactis The WG7-43 strain was deposited on December 26, 2022, at the China General Microbiological Culture Collection Center (CGMCC), located at No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing, Institute of Microbiology, Chinese Academy of Sciences, with accession number CGMCC No. 26287.

[0061] Example 2

[0062] Pseudomonas lactis Preparation of WG7-43 liquid bacterial agent.

[0063] 1) Use an inoculation needle to take a small amount of the sample preserved on the NA slant. Pseudomonas lactis WG7-43 strain was transferred to NA plates and incubated at 30°C for 1 day.

[0064] 2) Select two well-grown colonies from the activated NA plate and inoculate them into a 250mL Erlenmeyer flask containing NB liquid medium, filling the flask to 50% capacity. Incubate on a shaker at 30℃ and 200r / min for 16h.

[0065] 3) Inoculate 5% of the culture into a 2L fermentation shake flask and incubate for 24 hours to obtain the bacterial culture. The fermentation shake flask should be 50% full, the temperature 30℃, and the rotation speed 200r / min; the fermentation tank should be 80% full, and the rotation speed and ventilation should be adjusted to dissolved oxygen ≥1%. During the stable fermentation period, add an appropriate amount of soybean oil defoamer to control foam.

[0066] 4) Quality control: The CFU of the bacterial culture was determined using the plate dilution method to be ≥2×10⁻⁶. 8 / mL, bacterial contamination rate ≤10%, after aliquoting, store at 4℃ for later use.

[0067] Example 3

[0068] Extraction of extracellular polysaccharides and detection of cadmium adsorption capacity.

[0069] 1) Detection of Extracellular Polysaccharide (EPS) Production Capacity: Bacterial culture was prepared according to Example 2, and the extracellular polysaccharide was detected using the phenol-sulfuric acid method. Under the action of concentrated sulfuric acid, the extracellular polysaccharide is first hydrolyzed into monosaccharides, then dehydrated to form a uronic acid derivative, which reacts with phenol to form an orange-yellow solution with a characteristic absorption peak at 490 nm. Quantification was performed by comparison with a standard series. First, a standard curve was plotted: 0 mL, 0.2 mL, 0.4 mL, 0.6 mL, 0.8 mL, and 1.0 mL of 100 mg / L glucose standard solution were pipetted into 20 mL stoppered test tubes (with water added to 1.0 mL each), and 0.5 mL of 5% phenol solution was added. 2.5 mL of sulfuric acid solution was quickly added (vertically, avoiding contact with the sides), and the mixture was allowed to stand for 10 min. The mixture was then vortexed to mix, and incubated in a 30°C water bath for 20 min. The absorbance was measured at 490 nm using a spectrophotometer. A standard curve was plotted with glucose concentration on the x-axis and absorbance on the y-axis. For testing, 5 mL of bacterial culture was added to a 100 mL centrifuge tube, and 20 mL of anhydrous ethanol was slowly added. The mixture was vortexed and thoroughly mixed. The mixture was extracted using an ultrasonic extractor at 120 W for 30 min on ice. The extract was centrifuged at 4000 rpm for 10 min, and the supernatant was discarded. The extract was washed with 80% ethanol and centrifuged at 4000 rpm for 10 min. The insoluble residue was transferred to a round-bottom flask containing 100 mL of water and sonicated at 120 W for 30 min. This process was repeated twice (filtering after the first sonication, followed by sonication and filtration of the precipitate). After cooling to room temperature, the supernatant was transferred to a 200 mL volumetric flask, and the residue was washed three times with water. The washings were transferred to a volumetric flask and diluted to volume with water. 0.5 mL of the sample was taken for testing, and 0.5 mL of 5% phenol solution and 2.5 mL of sulfuric acid solution were added sequentially. The mixture was allowed to stand for 10 min. The mixture was then vortexed and thoroughly mixed. After incubating in a 30°C water bath for 20 min, the absorbance of the sample solution was measured at 490 nm. The extracellular polysaccharide content was calculated based on the standard curve. The results of comparison with existing strains AM17 and MG35, as well as the screened strains WG7-16 and WG7-26 are shown in Table 2 (data are expressed as mean ± standard deviation (n=4) and significance).

[0070] The results show that Pseudomonas lactis WG7-43 can produce 2.75 g / L of extracellular polysaccharide after fermentation in NB liquid medium, which is much higher than that of other strains.

[0071] Table 2 Results of extracellular polysaccharide production capacity of each strain

[0072] CK AM17 MG35 WG7-16 WG7-26 WG7-43 extracellular polysaccharide g / L 0 1.86±0.07c 1.11±0.06d 1.56±0.14d 2.17±0.06b 2.75±0.08a

[0073] 2) Cd adsorption capacity test of extracellular polysaccharides: Bacterial culture was prepared according to Example 2, extracellular polysaccharides were extracted, and the Cd adsorption capacity of the extracellular polysaccharides was determined. 2+Adsorption capacity. The fermentation broth was centrifuged at 3000-3500 rpm for 10 min, the bacterial cells were discarded, and the supernatant was retained. The supernatant and anhydrous ethanol were mixed at a 1:3 ratio, stirred, and allowed to stand for 0.5 h. The mixture was then centrifuged at ≥3500 rpm, and the flocculent precipitate was collected. The precipitate was washed with the original volume of distilled water, centrifuged at ≥3500 rpm, and the flocculent precipitate was collected. This step was repeated twice. The precipitate was dried in a 60℃ oven for at least 6 h, then pulverized and used for later use. 1.0 g of the extracted extracellular polysaccharide powder was weighed and placed in a container containing Cd. 2+ In a 1000 mL Erlenmeyer flask containing 112.4 mg of cadmium, after reacting for 6 hours, three volumes of pre-cooled anhydrous ethanol were added to the reaction system for alcohol precipitation. The mixture was then centrifuged at 10000 rpm for 10 minutes, and the supernatant was collected, appropriately diluted, and the concentration of unadsorbed cadmium was determined by ICP-OES. WG7-26, AM17, and MG35 were used as controls, and distilled water was used as a blank control (CK). Four replicates were performed, and the results are shown in Table 3 (data are expressed as mean ± standard deviation (n=4) and significance level).

[0074] The results show that Pseudomonas lactis WG7-43 extracellular polysaccharide adsorption of Cd 2+ The concentration reached 79.05 mg / g, which was significantly higher than that of the control strain.

[0075] Table 3. Cd adsorption by extracellular polysaccharides produced by each strain 2+ result

[0076] deal with CK AM17 MG35 WG7-26 WG7-43 <![CDATA[Cd 2+ mg / g]]> 0 31.6±0.33c 17.17±0.68d 35.40±0.31b 79.05±0.76a

[0077] It is evident that the strain provided by this invention has superior Cd adsorption capabilities compared to existing strains. 2+ Its effects can be used for the treatment of cadmium-containing wastewater or the remediation of cadmium-containing soil.

[0078] Example 4

[0079] Pseudomonas lactis Qualitative test of phosphorus solubility of WG7-43.

[0080] Will Pseudomonas lactis After activation, strain WG7-43 was plated onto Pikovskaya's agar medium containing tricalcium phosphate (Ca3(PO4)2) (0.5 g yeast extract, 10.0 g glucose, 5.0 g tricalcium phosphate, 0.5 g ammonium sulfate, 0.2 g potassium chloride, 0.1 g magnesium sulfate, 0.0001 g manganese sulfate, 0.0001 g ferrous sulfate, 15.0 g agar, 1000 mL distilled water) and incubated at 30°C for 3 days. The visible transparent areas around the bacterial colonies indicated available phosphate. WG7-26, AM17, and MG35 were used as controls. Results are as follows: Figure 3As shown, the results indicate that WG7-43 produced a phosphate-solubilizing zone, which was more pronounced than that of the positive bacterium MG35, demonstrating that it has a certain ability to dissolve inorganic phosphorus.

[0081] Example 5

[0082] Application trials on rice.

[0083] 1) Hydroponic Experiment: Rice variety Zhongzao 39 was soaked in 5% sodium hypochlorite for 10 minutes, rinsed with distilled water, and treated with 75% alcohol for 30 seconds to promote germination until the seeds showed white sprouts and reached 2 / 3 of their length. The inoculum was prepared according to Example 3, with a CFU of 7.2 × 10⁻⁶. 8 / mL, diluted 100 times with water to make CFU at 10 6 -10 7 Seeds were mixed with 1 mL of solution. Hoagland broth (Coolaber, dry powder + concentrate) was used for hydroponics. The hydroponic cups had an upper diameter of 90 mm, a lower diameter of 57 mm, and a height of 175 mm. The planting baskets had an inner diameter of 80 mm, an outer diameter of 110 mm, and a height of 70 mm, with 15 rice seeds placed evenly in each basket. Cadmium chloride (CdCl2·2.5H2O) was used, with the concentration expressed as Cd, and divided into Cd... 2+ Two experimental groups were established: 0 mg / L and 6 mg / L. NB liquid medium was used as a blank control, with MG-35 and AM17 as comparisons. Each treatment was repeated six times. Seeds treated with nutrient solution were placed in hydroponic containers in planting baskets. The climate chamber temperature was maintained at 26℃, and the light intensity at approximately 10000 lux. The light / dark cycle was 15h / 9h. Plant height and root length were measured after 15 days of cultivation. A portable chlorophyll meter was used to measure the chlorophyll content in the mid-leaf portion. After washing, the plants were blanched at 105℃ and dried at 65℃-70℃ to constant weight. Ten plants were selected from each hydroponic container to measure the overall dry weight, and the Cd content was determined using ICP-OES. The results are shown in Table 4. Compared to the blank control, WG7-43 showed higher Cd content. 2+ Hydroponic cultivation at 6 mg / L reduced total cadmium in plants by 60.7%, and also reduced Cd... 2+ Hydroponic concentrations of 0 mg / L and 6 mg / L significantly promoted plant growth and provided significant relief from heavy metal stress.

[0084] Table 4. Results of the effects of different bacterial strains on plant growth in the hydroponic experiment.

[0085]

[0086] 2) Rice pot experiment: The rice variety was Zhongzao 39. The inoculum agent prepared according to Example 3 had a CFU of 7 × 10⁻⁶. 8 / mL, diluted 50 times with water to make CFU at 10 6 -10 7The soil was mixed with water at a concentration of 4.5 kg / mL. Soil samples were collected from Qujiang District, Shaoguan City, Guangdong Province, and the crop grown was double-cropping rice. The soil composition was: total nitrogen 0.20±0.01%, total potassium 1.50±0.04%, total phosphorus 0.32±0.01%, available nitrogen 119±5 mg / kg, available phosphorus 24±3 mg / kg, available potassium 175±5 mg / kg, pH 5.41±0.01, organic matter 22.3 g / kg, and total cadmium 0.75±0.03 mg / kg. Distilled water was added as a blank treatment. Strains WG7-26 and AM17 were used as controls. Each treatment was replicated 6 times, for a total of 24 pots. Each pot was 20 cm in diameter and 20 cm in height, containing 4.5 kg of soil. Five rice seedlings were transplanted per clump per hill. For potted rice, apply nitrogen fertilizer at 60 mg N / kg soil, divided into three applications: basal, tillering, and panicle, with a ratio of basal:tillering:panicle ratio of 4:3:3; phosphorus fertilizer at 25 mg P2O5 / kg soil, applied as a single basal fertilizer; and potassium fertilizer at 50 mg K2O / kg soil, applied twice, basal and panicle, each accounting for 50%. During each growth and development stage, pay attention to fertilizer and water management and pest and disease control. Cultivate in a greenhouse with a 16h / 8h day / night cycle, 25℃ / 16℃, and a relative humidity of 60%. When transferring rice from seedling trays to pots, add a microbial agent (approximately 1 billion CFU / mL) with the transplanting water at a rate of 10L / acre. For a control group, add the corresponding amount of distilled water. Samples were taken at maturity. After removing panicles, the aboveground dry matter weight and the number of effective panicles in the entire pot of rice were measured. The grains were threshed manually, dried at 80℃ to constant weight, and the yield of the entire pot was measured. After yield measurement, the grains were crushed and the cadmium content was determined by ICP-OES (for rice samples with Cd concentrations below 0.1 mg / kg, atomic absorption spectrophotometry-graphite furnace method was used). The results are shown in Table 5, indicating that WG7-43 reduced total cadmium in the grains by 67.1%. The yield increased by 21.2% compared to the control.

[0087] Table 5. Results of the effects of different bacterial strains on plant growth in rice pot experiments.

[0088] deal with Plant height (cm) Dry weight of above-ground stems and leaves g / pot Effective spikelets / pot Yield (g / pot) Cadmium in grains (mg / kg) CK 80±1.5a 17.34±0.53c 12.5±1.3b 28.25±3.27b 0.498±0.057a AM17 80.9±2.5a 17.90±0.72c 12.3±1.7b 28.75±2.48b 0.512±0.061a WG7-26 78.2±2.3a 20.67±0.67b 13.5±1.3b 30.25±2.68b 0.347±0.038b WG7-43 79.8±1.6a 24.92±1.1a 16.5±1.3a 34.50±2.69a 0.164±0.030c

[0089] 3) Application in rice trials in Zhuzhou, Hunan: The inoculant CFU prepared according to Example 3 was 10 × 10⁻⁶. 8 / mL, diluted 80 times with water to make CFU at 10 6 -10 7Seed dressing was performed using a conventional rice variety. A rice-growing plot of 9 mu (approximately 0.66 acres) was selected in Bujiang Town, Youxian County, Zhuzhou City, southeastern Hunan Province, with soil pH 5.65 and total cadmium 1.75 mg / kg. AM17 was used as the control, and uninoculated NB liquid medium was used as the blank control. A total of three treatments were administered, with three replicates. When the rice was transferred from seedling trays to the experimental field, the inoculant (approximately 1.5 billion CFU / mL) was added with the transplanting water at a rate of 10 L / mu. The corresponding amount of NB liquid medium was added to the blank control. Other agronomic conditions were the same. The yield results are shown in Table 6. Pseudomonas lactis Seed dressing with WG7-43 combined with fertigation can significantly reduce total cadmium accumulation in grains by 51.6% and increase yield by 19.1%.

[0090] Table 6. Results of the effects of various bacterial strains on yield in rice experiments in Zhuzhou, Hunan Province.

[0091] deal with <![CDATA[Yield kg / 667m 2 > Increased production by % compared to CK Total cadmium content in grains (mg / kg) Total cadmium decreased by % compared to CK CK 545.6±66.5b - 0.24±0.03a - AM17 581.3±47.4b 6.6 0.20±0.03b 9.6 WG7-43 671.8±73.5a 23.1 0.11±0.02c 54.2

[0092] 4) Application in rice trials in Shaoguan, Guangdong: The inoculant prepared according to Example 3 had a CFU of 12 × 10⁻⁶. 8 / mL, diluted 100 times with water to make CFU at 10 6 -10 7 Seed dressing was performed using a medium of approximately 10 × 10⁶ CFU / mL. The rice variety was Meizhanxiang 2. The experimental field, covering 9 mu (approximately 0.67 hectares), was selected from a rice planting plot in Zhangshi Town, Qujiang District, Shaoguan City, Guangdong Province, with a total cadmium concentration of 1.375 mg / kg. MG-35 was used as a control, and uninoculated NB liquid medium served as a blank control. A total of three treatments were administered, with three replicates. When the rice was transferred from seedling trays to the experimental field, a bacterial agent (approximately 10 × 10⁶ CFU / mL) was added with the transplanting water. 8 / mL), the dosage was 10L / acre, and the corresponding amount of NB liquid medium was added to the blank. Other agronomic conditions were the same. The yield results are shown in Table 7. Pseudomonas lactis Seed dressing with WG7-43 combined with fertigation can significantly reduce total cadmium accumulation in grains by 51.6% and increase yield by 17.4%.

[0093] Table 7. Results of the effects of various bacterial strains on rice yield in rice trials in Shaoguan, Guangdong.

[0094] deal with <![CDATA[Yield kg / 667m 2 > Increased production by % compared to CK Total cadmium content in grains (mg / kg) Total cadmium decreased by % compared to CK CK 577.5±37.8b - 0.31±0a - MG-35 581.5±66.3b 0.7 0.31±0.02a 0 WG7-43 678.1±57.4a 17.4 0.15±0.02b 51.6

[0095] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A strain of *Pseudomonas lactis* ( Pseudomonas lactis WG7-43, characterized in that, It was deposited on December 26, 2022, at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 26287.

2. The *Pseudomonas lactis* as described in claim 1 ( Pseudomonas lactis Application of WG7-43 in cadmium adsorption or cadmium fixation.

3. The *Pseudomonas lactis* as described in claim 1 ( Pseudomonas lactis Application of WG7-43 in improving crop resistance to cadmium stress.

4. The *Pseudomonas lactis* as described in claim 1 ( Pseudomonas lactis Application of WG7-43 in blocking crop absorption of cadmium.

5. The *Pseudomonas lactis* as described in claim 1 ( Pseudomonas lactis Application of WG7-43 in promoting rice growth.

6. The *Pseudomonas lactis* as described in claim 1 ( Pseudomonas lactis Application of WG7-43 in cadmium-containing wastewater treatment or cadmium-containing soil remediation.

7. A microbial agent, characterized in that, Contains the *Pseudomonas lactis* as described in claim 1 ( Pseudomonas lactis WG7-43.

8. The application of the microbial agent according to claim 7 in promoting rice growth.

9. The application of the microbial agent according to claim 8 in promoting rice growth, characterized in that, The method of applying the microbial agent is as follows: (1) Inoculum treatment: Dilute the inoculum with water to a concentration equal to that of *Pseudomonas lactis* (…). Pseudomonas lactis The CFU concentration of WG7-43 is at 10 6 -10 7 / mL for seed dressing; (2) Application of microbial agent: When rice is transferred to the field, it is applied with the water for rice transplanting. When direct-seeded rice seedlings emerge, it is applied during the first watering after emergence. The dosage is 5-10L per mu.

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