Biological fertilizer for promoting plant growth and enriching selenium and preparation method thereof

Abstract

The application provides a biological fertilizer for promoting plant growth and selenium enrichment and a preparation method thereof, and belongs to the technical field of biological fertilizers.The biological fertilizer is based on dry sterilized mixed organic matter and a direct-throwing group-forming pantoea agens, and the mass fractions of N, P2O5 and K2O in the mixed organic matter are 4-8%, 1.6-3.3% and 1.6-3.3% respectively, and the biological fertilizer is characterized in that: the biological fertilizer for promoting plant growth and selenium enrichment is prepared by fermenting the mixed organic matter, superphosphoric acid calcium, sodium selenite and the direct-throwing group-forming pantoea agent after mixing, wherein the group-forming pantoea AKFX-001 is preserved in the China General Microbiological Culture Collection Center, and the preservation number is CGMCC No. 36122.The strain has the effects of resisting high-concentration selenium, converting inorganic selenium into organic selenium and promoting plant growth, and the single strain can realize the functions that can only be realized by mixed strains in the prior art, and has a good market prospect.

Description

Technical Field

[0001] This invention belongs to the field of bio-fertilizer technology, specifically relating to a bio-fertilizer that promotes plant growth and selenium enrichment, and its preparation method. Background Technology

[0002] Bio-fertilizer, also known as microbial fertilizer, refers to a preparation containing specific living microorganisms that provide nutrients to crops or promote nutrient absorption through their life activities, thereby increasing yield, improving quality, and enhancing stress resistance. Currently, different strains have different effects. Generally, bio-fertilizers are produced through natural fermentation or mixed fermentation with multiple microorganisms. Different microorganisms play different roles. For example, nitrogen-fixing bacteria and rhizobia can convert free nitrogen (N2) in the air, which plants cannot directly utilize, into nitrogen-containing compounds such as ammonia (NH3) that plants can absorb. This is equivalent to establishing a "mini nitrogen fertilizer factory" at the plant's roots. The soil contains a large amount of ineffective phosphorus and potassium that cannot be directly absorbed by plants. Phosphate-solubilizing Bacillus megaterium can decompose this into effective phosphorus and potassium that plants can absorb. Rhizosphere growth-promoting bacteria can produce plant hormones such as auxin, cytokinin, and gibberellin during metabolism, directly stimulating root development and promoting plant growth. However, as is well known, there is competition and inhibition between microorganisms. Generally, dominant strains inhibit the growth of weaker microorganisms. Therefore, the effectiveness of mixed-strain fermentation is affected by field management levels and the underlying soil microbial environment, resulting in unstable efficacy. Biofertilizers prepared using the mixed microbial method generally do not have an all-around effect.

[0003] Pantothecinia clumps ( Pantoea agglomerans Pantotheca acuminata is a Gram-negative rod-shaped bacterium with cell size of 0.5-1.0 × 1-3 micrometers. It possesses peritrichous flagella and produces yellow pigments. Most strains are facultative anaerobic chemoheterotrophs. Currently, some reported Pantotheca acuminata species cause damage to plants primarily through pathogenicity, especially in specific crops. For example, studies have shown that some Pantotheca acuminata species are pathogenic to rice, affecting grain filling and development, leading to symptoms such as delayed heading, (partial) panicles, white panicles, grain discoloration, and high chaff rate. It also inhibits the elongation of rice germ and radicle, easily causing seedling death. However, no damage from Pantotheca acuminata has been found in tea plants.

[0004] Since Pantotheca clumps is a Gram-negative rod-shaped bacterium with a thin cell wall, although it has been reported that Pantotheca clumps can synthesize nano-selenium, according to the inventors' previous experiments, the highest selenium concentration that Pantotheca clumps can grow at is 2 mM. Its selenium concentration tolerance is low, so the selenium conversion rate is also much lower than that of other microorganisms. It can only convert a small amount of selenium into organic selenium or nano-selenium at a low concentration.

[0005] Microbial transformation utilizes the metabolic functions of microorganisms such as yeast, lactic acid bacteria, and fungi to reduce inorganic selenium to nano-selenium or assimilate it to organic selenium. Due to its advantages such as mild reaction conditions, environmental friendliness, good biocompatibility of the products, and ease of process control, it has become a current research hotspot. For example, existing patents disclose the use of *Lactobacillus acidophilus* for the synthesis of nano-selenium or *Candida utilis* for the production of selenium-enriched yeast. However, existing microbial technologies still face a series of severe challenges: the primary bottleneck is that many strains have limited tolerance to selenium concentrations, and their growth is significantly inhibited under high selenium pressure, leading to a sharp decline in conversion efficiency. For example, the growth of some lactic acid bacteria is severely inhibited when the sodium selenite concentration exceeds 2 mM. Secondly, existing strains tend to have single functions, often only proficient in synthesizing nano-selenium or accumulating organic selenium, making it difficult to achieve the targeted and efficient synthesis of two products in the same fermentation system through simple condition control. More importantly, microbial strains with both high selenium conversion capabilities and multiple plant growth-promoting functions (such as secreting growth hormones, dissolving phosphorus and potassium, and fixing nitrogen) are extremely scarce, which greatly limits their integrated application prospects in functional agriculture. In addition, most of the nano-selenium synthesized by microorganisms is an intracellular product, and its extraction and crushing processes are complex. Moreover, nanoparticles are easily oxidized and aggregated after extraction, and maintaining their long-term dispersion stability remains a major challenge for achieving large-scale application. Summary of the Invention

[0006] The inventor isolated a cluster of pantothenic bacteria from selenium-rich tea leaves. Pantoea agglomerans This strain exhibits rapid growth in sodium selenite medium at concentrations of 2–100 mM and can partially convert sodium selenite into beneficial compounds, making it suitable for preparing microbial fertilizers. This strain was deposited at the China General Microbiological Culture Collection Center on September 30, 2025. Pantoea agglomerans The accession number is: CGMCC No.36122, Latin name: Pantoea agglomerans AKFX-001, Address: Institute of Microbiology, Chinese Academy of Sciences, No. 3, No. 1 Beichen West Road, Chaoyang District, Beijing, 100101, China. Tel: 010-64807596.

[0007] Based on this, the present invention provides a direct-inoculation pantothenic acid inoculum, wherein the direct-inoculation pantothenic acid inoculum is prepared by activating and culturing pantothenic acid AKFX-001 and then inoculating it into TSA liquid medium containing 0.5~5mM sodium selenite. When the bacterial cell count is 2.0×10⁻⁶, the inoculum is cultured. 9 ~5.0×10 9 When the concentration of cfu / mL is between 0.45 μm, filter the product using a 0.45 μm pore size membrane and collect the clump-forming Pantotheca AKFX-001 cells. Then, mix the clump-forming Pantotheca AKFX-001 cells with a saline solution of trehalose, maltodextrin, glycine, and sorbitol and freeze-dry to obtain a direct-inoculation Pantotheca AKFX-001 inoculum.

[0008] Among them, the clump-forming pantothenia is pantothenia clump-forming. AKFX-001 It is deposited in the China General Microbiological Culture Collection Center, with accession number CGMCC No. 36122.

[0009] In this composition, by mass-volume ratio, the AKFX-001 bacterial cells account for 0.5-5%, trehalose accounts for 2-5%, maltodextrin accounts for 1-3%, glycine accounts for 0.2-1.5%, and sorbitol accounts for 0.2-0.3%.

[0010] Based on the dried and sterilized mixed organic matter and the above-mentioned direct-inoculation agglomerative microbial agent, the present invention also provides a bio-fertilizer that promotes plant growth and selenium enrichment. The mass fractions of N, P2O5 and K2O in the mixed organic matter are between 4-8%, 1.6-3.3% and 1.6-3.3%, respectively. The bio-fertilizer that promotes plant growth and selenium enrichment is prepared by fermenting the mixed organic matter with superphosphate, sodium selenite and direct-inoculation agglomerative microbial agent.

[0011] The mixed organic matter includes sheep manure, rapeseed cake, and plant straw.

[0012] The mixed organic matter is dried and sterilized at 70-80°C for 10-48 hours.

[0013] The mixture comprises, by mass percentage, 45% to 65% mixed organic matter, 0.5% to 1% superphosphate, 0.1% to 0.3% sodium selenite, 1% to 5% direct-inoculation flocculation agent, and the remainder is water.

[0014] The fermentation is carried out at a temperature between 28 and 32°C, a humidity between 60 and 80%, and a fermentation time of 3 to 10 days.

[0015] Meanwhile, this invention also provides a method for preparing a bio-fertilizer that promotes plant growth and is enriched with selenium, comprising the following steps:

[0016] ① Dry sheep manure, rapeseed cake and plant straw, controlling the moisture content of sheep manure and rapeseed cake to be less than 8% and the moisture content of plant straw to be less than 5%, to obtain insect-killed, sterilized and dried organic matter, and then crush it.

[0017] ② Mix sheep manure, rapeseed cake, and plant straw in proportions of N, P2O5, and K2O in the mixed organic matter, respectively, at a mass fraction of 4-8%, 1.6-3.3%, and 1.6-3.3%, to obtain mixed organic matter;

[0018] ③ Add sterile water, superphosphate, sodium selenite and direct-inoculation clump-forming pantothecin inoculant to the mixed organic matter to obtain mixed fermentation material;

[0019] ④ Ferment the mixed fermentation materials at 28~32℃ and 60~80% humidity for 3~10 days to obtain a bio-fertilizer that promotes plant growth and is rich in selenium.

[0020] In this mixture, by mass ratio, the direct-inoculation agglomerate inoculant accounts for 1-5%, superphosphate accounts for 0.5-1%, sodium selenite accounts for 0.1-0.3%, mixed organic matter accounts for 45%-65%, and the remainder is water.

[0021] The drying process involves drying at 70-80°C for 10-48 hours.

[0022] The direct-application, clustered pantothenic inoculant or the plant growth-promoting and selenium-enriching bio-fertilizer, when applied to the soil, is used to increase the plant's growth rate and selenium content. Beneficial effects

[0023] First, this invention provides a *Pantotheca agglutinosa* strain, which is deposited at the China General Microbiological Culture Collection Center (CGMCC) under accession number CGMCC No. 36122. This strain exhibits high selenium tolerance and transformation capabilities, enabling it to convert highly toxic inorganic selenium (such as Se(IV)) into less toxic organic selenium (such as selenomethionine and selenocysteine) and zero-valent nano-selenium (Se) in a culture medium containing sodium selenite. 0 ).

[0024] Secondly, the *Pantotheca agglomerata* obtained in this invention exhibits characteristics of selenophilic microorganisms. Due to its strong selenium tolerance, it can bioconvert inorganic selenium in a high-concentration selenium environment for the microbial synthesis of nano-selenium, thus significantly improving the synthesis efficiency of nano-selenium. By optimizing fermentation conditions (such as selenium concentration, temperature, pH, and time), the organic selenium conversion rate can reach up to 92.5%, and the nano-selenium synthesis efficiency reaches 88.3%. The prepared nano-selenium particles are uniformly distributed with an average particle size of 200-500 nm.

[0025] Furthermore, after culturing at 30°C for 48 h in a medium containing L-tryptophan, the IAA production of strain AKFX-001 was determined to be 45.2 ± 2.1 mg / L using the Salkowski colorimetric method. Its indoleacetic acid production was stronger than that of traditional pantothenic bacteria. After 7 days of cultivation on PVK solid plates, a distinct phosphate-solubilizing zone appeared around the colonies, with a phosphate solubility index of 2.5, indicating good phosphate solubility. After 48 h of cultivation on CAS detection plates, an orange-yellow halo appeared around the colonies, indicating the ability to produce siderophores.

[0026] Finally, the *Pantothecinus* species preserved in this invention exhibits strong environmental adaptability, combined with its ability to produce indoleacetic acid, solubilize phosphorus, and produce iron carriers. A single strain can ferment organic matter to produce substances that promote tea tree growth and selenium enrichment; the single strain implies a fixed metabolic pathway and products. Under the same process conditions, each fermentation produces a product with highly consistent composition and strength, avoiding batch-to-batch quality fluctuations caused by activity fluctuations in mixed microbial communities. This makes it highly suitable for large-scale industrial production, demonstrating excellent stability in industrial production. Therefore, inoculation and fermentation on sterilized organic matter can ensure the quality and safety of the organic fertilizer. Attached Figure Description

[0027] Figure 1 The colony morphology of strain AKFX-001 on LB plate (after 48 h of incubation).

[0028] Figure 2 This is a comparison diagram showing the growth of *Panthera clumps* preserved in this invention and other *Panthera clumps* under different concentrations of sodium selenite stress.

[0029] Figure 3 A comparative graph showing the effect of applying the fungal agent AKFX-001 from Example 3 on cucumber growth (top: treatment group; bottom: control group). Detailed Implementation

[0030] The present invention will be described in detail below with reference to examples. All methods and techniques, unless otherwise specified, are conventional. Example

[0031] This embodiment provides a cluster of pantothecin ( Pantoea agglomerans The Latin name of this strain is: Pantoea agglomerans AKFX-001, This strain was deposited on September 30, 2025 at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 36122. The address is: Institute of Microbiology, Chinese Academy of Sciences, No. 3, No. 1 Beichen West Road, Chaoyang District, Beijing, 100101, China. The telephone number is 010-64807596.

[0032] The strain preserved in this invention was collected from surface soil samples of a selenium-rich tea garden in Naore Village, Ziyang County, Ankang City, Shaanxi Province. Specifically, 1 g of soil sample was added to 100 mL of LB liquid medium (containing 0.5 mM sodium selenite) and cultured at 30°C and 180 rpm for 48 h with shaking. The culture solution was serially diluted and spread onto LB solid plates (containing 1 mM sodium selenite), and incubated upside down at 30°C for 48 h. Single colonies were picked and purified repeatedly. Finally, the purified strain was inoculated onto LB plates containing different concentrations of sodium selenite (0, 5, 10, 20, 50, 100 mM) and cultured at 30°C for 48 h. The selected clustered pantothenic acid bacteria could still grow on plates containing 100 mM sodium selenite, indicating that it has extremely strong selenium tolerance. The clustered pantothenic acid bacteria were then enhanced to obtain the clustered pantothenic acid bacteria AKFX-001.

[0033] After testing, the clump-forming pantothecin preserved in this invention has the functions of efficiently converting organic selenium, producing indoleacetic acid, fixing nitrogen (converting nitrogen in the air into nitrogen fertilizer that crops can absorb), solubilizing phosphorus, and releasing potassium (activating phosphorus and potassium elements fixed in the soil) during the metabolic process. It covers the functions of microbial fertilizers, so it is suitable for preparing bio-fertilizers fermented by a single strain.

[0034] The method for strain identification was as follows: Gram staining (negative, short rod-shaped), physiological and biochemical tests were performed on strain AKFX-001, and genomic DNA was extracted. The 16S rRNA gene was amplified using universal primers 27F / 1492R and sequenced. The sequence was compared with the NCBI database using BLAST, showing the highest homology (99.8%) with Pantoea agglomeransstrain XYZ. This strain was identified as Pantoea agglomeransstrain XYZ. Pantoea agglomerans It was named AKFX-001.

[0035] Partial 16S rRNA gene sequence (1403 bp) of strain AKFX-001:

[0036] Example

[0037] This embodiment provides a method for determining the ability of Pantotheca acuminata AKFX-001 colonies to convert selenium and promote plant growth. The specific determination method is as follows.

[0038] ① Nano-selenium production capacity: The activated strain was inoculated at a 5% inoculum in TSA medium supplemented with 3 mM sodium selenite at pH 7.0 and cultured at 30℃ and 150 rpm for 96 h with shaking. The culture medium was observed to gradually change from colorless to orange-red, indicating the formation of zero-valent nano-selenium. The AKFX-001 clump-forming strain has a strong nano-selenium conversion capacity.

[0039] ② Indoleacetic acid (IAA) production capacity: After incubation at 30°C for 48 h in a medium containing L-tryptophan, the IAA production of strain AKFX-001 was determined using the Salkowski colorimetric method to be 45.2 ± 2.1 mg / L. The IAA production capacity was stronger than that of traditional pantothenic bacteria.

[0040] ③ Phosphorus solubility: After culturing on PVK solid plates for 7 days, a clear phosphorus solubility zone appeared around the colonies, and the phosphorus solubility index was 2.5.

[0041] ④ Siderogenic capacity: After culturing on CAS test plates for 48 h, the appearance of an orange-yellow halo around the colony indicates that it has the ability to produce siderogenic substances. Example

[0042] Based on the characteristics of the clump-forming pantothecin AKFX-001 determined in Examples 1 and 2, a direct-inoculation pantothecin inoculant is provided, the preparation method of which includes the following steps:

[0043] Prepare TSA solid culture medium and TSA liquid culture medium containing 1 mM sodium selenite.

[0044] The formula for TSA solid culture medium is: 15 g / L tryptone, 5 g / L soybean peptone, 5 g / L sodium chloride, and 15 g / L agar.

[0045] The formula for TSA liquid culture medium containing 1mM sodium selenite is: 15g / L tryptone, 5g / L soybean peptone, 5g / L sodium chloride, and 0.173 g / L sodium selenite.

[0046] Clumps of *Pantotheca cum Microsporum* AKFX-001 were picked using an inoculation loop and streaked onto TSA solid medium to isolate single colonies. After incubation for 12-24 hours, once single colonies had grown on the plates, they were picked and incubated for 12-20 hours in TSA liquid medium containing 1 mM sodium selenite to obtain a bacterial suspension. The bacterial cell count in the suspension was determined using OD600 to be between 2.0 × 10⁻⁶. 9 ~5.0×10 9When the cfu / mL ratio is between 0.45 μm, a polycarbonate filter membrane with a pore size of 0.45 μm is used. Under the negative pressure of a 0.01 MPa vacuum pump in a sterile environment, the bacterial suspension is passed through the filter membrane, while the bacterial cells are trapped on the membrane surface, resulting in clustered pantothenic acid AKFX-001 cells.

[0047] Trehalose, maltodextrin, glycine, and sorbitol were added to 0.90% physiological saline to prepare a physiological saline solution containing 3% trehalose, 2% maltodextrin, 1% glycine, and 0.5% sorbitol by mass-volume ratio. After complete dissolution, the solution was sterilized. 1% of Pantothenia glutinosa AKFX-001 cells were added in a sterile environment, and the solution was freeze-dried at -70℃ for 24 h to obtain a direct-inoculation Pantothenia glutinosa inoculum agent.

[0048] A direct-inoculation, clustered pan-based inoculant was mixed with soil from normal cucumber cultivation at a concentration of 3%, superphosphate at 1%, and sodium selenite at 0.2%. This mixture was used to grow cucumbers, with air humidity maintained between 60% and 80%, and soil humidity between 80% and 90%. The plants were treated with 12 hours of artificial light followed by 12 hours of darkness, with a light temperature of 25°C and a darkness temperature of 18°C. After the cucumbers matured and bore fruit, the selenium content in the cucumber fruits was determined according to GB 5009.93-2017, "National Food Safety Standard - Determination of Selenium in Food," using the same soil and a control group containing 0.2% sodium selenite.

[0049] The results of the cucumber cultivation process are shown below Figure 3 As shown, according to Figure 3 It is evident that the inoculant treatment group (top image) grew better than the control group (bottom image), showing a significant increase in cucumber growth. After the cucumbers fruited, the selenium content of cucumbers grown in soil treated with the direct-inoculation AKFX-001 inoculant mixture was between 0.02 and 0.05 mg / kg, while the selenium content of cucumbers in the control group was below 0.01 mg / kg. This demonstrates that the direct-inoculation AKFX-001 inoculant mixture not only effectively increases the selenium content of cucumber fruits but also promotes cucumber growth, with the average weight of the cucumber fruits being 16.92% higher than that of the control group.

[0050] Of course, the above is just one formulation of direct-inoculation Pantotheca agglomerates. According to experimental results, using TSA liquid medium containing 0.5-5mM sodium selenite to cultivate Pantotheca agglomerates AKFX-001, and freeze-drying with physiological saline solution containing 0.5-5% Pantotheca agglomerates AKFX-001 cells, 2-5% trehalose, 1-3% maltodextrin, 0.2-1.5% glycine, and 0.2-0.3% sorbitol according to the mass-volume ratio, can ensure the activity of Pantotheca agglomerates AKFX-001. This allows it to quickly reach the logarithmic growth phase in the soil, thus enabling Pantotheca agglomerates AKFX-001 to quickly become the dominant strain in the soil and exert its role in promoting plant growth and selenium enrichment. Example

[0051] This embodiment utilizes a direct-inoculation, clustered pantothenic acid agent for the single fermentation of traditional organic fertilizer to obtain a bio-fertilizer that promotes plant growth and is enriched with selenium. The preparation method is as follows.

[0052] Sheep manure, rapeseed cake, and plant straw are dried in a drying oven at 70-80℃ for 10-48 hours. Depending on the amount of material, the moisture content of sheep manure and rapeseed cake is controlled to be below 8%, and the moisture content of plant straw is controlled to be below 5%, so as to obtain insect-killed, sterilized, and dried organic matter. The organic matter is then crushed.

[0053] By mass percentage, sheep manure accounts for 50%, rapeseed cake for 20%, and plant straw for 30%. These three substances are mixed to obtain mixed organic matter. Ensure that the mass fractions (on a dried basis) of N, P2O5, and K2O in the mixed organic matter are between 4-8%, 1.6-3.3%, and 1.6-3.3%, respectively.

[0054] Subsequently, sterile water, superphosphate, sodium selenite, and the direct-inoculation agglomerative pantothenic acid prepared in Example 3 were added to the mixed organic matter. According to the mass ratio, the direct-inoculation agglomerative pantothenic acid accounted for 1-5%, superphosphate accounted for 0.5-1%, sodium selenite accounted for 0.1-0.3%, the mixed organic matter accounted for 45%-65%, and the remainder was water, thus obtaining the mixed fermentation material.

[0055] The mixed fermentation materials are piled into a heap 1-1.5 meters high and 1.5-2 meters wide, and covered with straw mats to ensure the temperature is between 28-32℃ and the humidity is between 60-80%. If the temperature exceeds 32℃, the heap needs to be turned over; if it is below 28℃, it needs to be kept warm. Fermentation takes 3-10 days to obtain bio-fertilizer that promotes plant growth and is rich in selenium.

[0056] Because the sheep manure, rapeseed cake, and plant straw have undergone insecticidal and sterilization treatments, and the Pantotheca AKFX-001 bacteria have a rapid activation rate and a single fermentation strain, the organic fertilizer prepared by the method of this invention has stable quality and has not yet been contaminated by other bacteria or produced any off-odors.

[0057] A fertilization experiment was conducted in a tea garden in Pingli County, Ankang City, Shaanxi Province. Ziyang selenium-rich tea trees with uniform soil and growth were selected. The tea trees were planted in a group, with a spacing of 25-30 cm between trees and 120-150 cm between rows. Random 10m x 10m square areas were marked out, with a 1-meter deep trench dug in the center of each area. The experiment consisted of three groups: a blank control group, a naturally fermented organic matter group, and a group undergoing pantothenic fermentation.

[0058] The blank control group was given unfermented and sterilized organic matter, and the same sterile water was added as the group fermented with Pantotheca agglomerata. At the same time, 0.5-1% superphosphate and 0.1-0.3% sodium selenite were added. The organic matter application rate was 150 kg / mu, and the fertilization time was October 15, 2024.

[0059] The naturally fermented organic matter group uses naturally fermented organic matter prepared as follows: rapeseed cake and plant straw are crushed and added to sheep manure, with sheep manure accounting for 50%, rapeseed cake for 20%, and plant straw for 30%. Water is added to adjust the moisture content of the mixed organic matter to between 45% and 65%, and 0.5% to 1% superphosphate and 0.1% to 0.3% sodium selenite are added. The mixture is then piled and fermented at 28 to 32℃ for 3 to 10 days to obtain naturally fermented organic fertilizer. The application rate of organic fertilizer is 150 kg / mu, and the fertilization time is October 15, 2024.

[0060] The organic fertilizer prepared by the Pantothenic aerosol fermentation group in this example was applied at a rate of 150 kg / mu on October 15, 2024.

[0061] The total selenium content (GB5009.93-2017), tea polyphenol content (GB / T 8313-2018), and free amino acid content (GB / T 8314-2013) of tea were measured for three consecutive months on March 15, April 15, and May 15, 2025. The results are shown in Tables 1, 2, and 3.

[0062]

[0063]

[0064]

[0065] As can be seen from Tables 1, 2, and 3, the tea leaves in the clump fermented with Pantothenic Acid group grew significantly faster than those in the naturally fermented organic matter group and the blank control group. This indicates that the mixed organic fertilizer fermented with Pantothenic Acid in the blank control group can significantly increase the content of free amino acids and tea polyphenols in tea leaves, as well as significantly increase the selenium content in tea leaves, thus meeting the standards for selenium-rich tea.

Claims

1. A direct-inoculation method for forming clusters of pantothecin ( Pantoea agglomerans The bacterial agent is characterized by: The direct-inoculation pantothenic acid inoculum is prepared by activating and culturing pantothenic acid AKFX-001, then inoculating it into TSA liquid medium containing 0.5-5 mM sodium selenite. When the bacterial count reaches 2.0 × 10⁻⁶... 9 ~5.0×10 9 When the concentration of cfu / mL is between 0.45 μm, filter the product using a 0.45 μm pore size membrane and collect the clump-forming Pantotheca AKFX-001 cells. Then, mix the clump-forming Pantotheca AKFX-001 cells with a saline solution of trehalose, maltodextrin, glycine, and sorbitol and freeze-dry to obtain a direct-inoculation Pantotheca AKFX-001 inoculum. The aforementioned Pantotheca clumps is Pantotheca clumps AKFX-001, which is deposited at the China General Microbiological Culture Collection Center with accession number CGMCC No. 36122.

2. The direct-inoculation, clustering pantothenic acid agent according to claim 1, characterized in that: According to the mass-volume ratio, the AKFX-001 bacterial cells in the agglomerate contain 0.5-5%, trehalose contains 2-5%, maltodextrin contains 1-3%, glycine contains 0.2-1.5%, and sorbitol contains 0.2-0.3%.

3. A bio-fertilizer that promotes plant growth and selenium enrichment, the bio-fertilizer being based on dried and sterilized mixed organic matter and the direct-inoculation clump-forming pantothecin agent as described in claim 1, wherein the mass fractions of N, P2O5, and K2O in the mixed organic matter are between 4-8%, 1.6-3.3%, and 1.6-3.3%, respectively, characterized in that: The bio-fertilizer that promotes plant growth and is enriched with selenium is prepared by fermenting a mixture of organic matter, superphosphate, sodium selenite, and direct-inoculation pantothenic acid inoculant.

4. The bio-fertilizer for promoting plant growth and selenium enrichment according to claim 3, characterized in that: The mixed organic matter includes sheep manure, rapeseed cake, and plant straw.

5. The bio-fertilizer for promoting plant growth and selenium enrichment according to claim 3, characterized in that: The aforementioned mixed organic matter is dried and sterilized at 70-80℃ for 10-48 hours.

6. The bio-fertilizer for promoting plant growth and enriching selenium according to claim 3, characterized in that: By mass percentage, the mixture consists of 45% to 65% organic matter, 0.5% to 1% superphosphate, 0.1% to 0.3% sodium selenite, 1% to 5% direct-inoculation flocculation agent, and the remainder is water.

7. The bio-fertilizer for promoting plant growth and selenium enrichment according to claim 3, characterized in that: The fermentation is carried out at a temperature between 28 and 32°C, a humidity between 60 and 80%, and a fermentation time of 3 to 10 days.

8. A method for preparing a bio-fertilizer that promotes plant growth and is enriched with selenium as described in claim 3, characterized in that: The method for preparing the plant growth-promoting and selenium-enriched bio-fertilizer includes the following steps: ① Dry sheep manure, rapeseed cake and plant straw, controlling the moisture content of sheep manure and rapeseed cake to be less than 8% and the moisture content of plant straw to be less than 5%, to obtain insect-killed, sterilized and dried organic matter, and then crush it. ② Mix sheep manure, rapeseed cake, and plant straw in proportions of N, P2O5, and K2O in the mixed organic matter, respectively, at a mass fraction of 4-8%, 1.6-3.3%, and 1.6-3.3%, to obtain mixed organic matter; ③ Add sterile water, superphosphate, sodium selenite and direct-inoculation clump-forming pantothecin inoculant to the mixed organic matter to obtain mixed fermentation material; ④ Ferment the mixed fermentation materials at 28~32℃ and 60~80% humidity for 3~10 days to obtain bio-fertilizer that promotes plant growth and is rich in selenium.

9. The method for preparing the bio-fertilizer that promotes plant growth and is enriched with selenium according to claim 8, characterized in that: According to the mass ratio, the direct-inoculation agglomerate inoculant accounts for 1-5%, superphosphate accounts for 0.5-1%, sodium selenite accounts for 0.1-0.3%, mixed organic matter accounts for 45%-65%, and the remainder is water.

10. The use of the P. polymyxa bacterial agent of claim 1 or the bio-fertilizer for promoting plant growth and selenium enrichment of claim 3, characterized in that: The direct-application, clustered pantothenic inoculant or the plant growth-promoting and selenium-enriching bio-fertilizer, when applied to the soil, is used to increase the plant's growth rate and selenium content.

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