Bacillus strain stf4 and application thereof

Abstract

A strain of Bacillus STF4 and its applications, relating to the field of microbiology, this invention relates to Bacillus ( Bacillus sp. STF4 is deposited at the China Center for Type Culture Collection (CCTCC), Wuhan University, Wuhan, China, on February 24, 2025, with accession number CCTCC NO: M2025290. It is used as a microbial agent to promote maize growth in saline-alkali soils and enhance maize's tolerance to salt and alkali stress. The Bacillus STF4 of this invention plays an important role in selecting microbial agents that enhance crop tolerance to salt and alkali stress and promote growth in saline-alkali soils. This not only provides important scientific basis for the development of microbial agents for saline-alkali soils but also opens up new avenues for solving the problem of crop yield reduction caused by soil salinization.

Description

Technical Field

[0001] This invention belongs to the field of microbiology, specifically relating to a strain of Bacillus STF4 and its applications. Background Technology

[0002] Bacillus, a type of microorganism widely found in the natural environment, belongs to the phylum Firmicutes, class Bacillus, and order Bacillus. These bacteria are known for their ability to produce spherical or elliptical spores and are classified as Gram-positive bacteria. They can be both aerobic and anaerobic, exhibiting facultative anaerobic characteristics. Bacillus spores possess a strong ability to adapt to their environment, surviving for extended periods in soil even under extremely harsh conditions. Many strains within the genus possess specialized functions, producing various enzymes such as proteases and amylases, thus demonstrating significant research and application value in agriculture.

[0003] my country has a vast territory, with a land area of ​​approximately 3.7 × 10⁻⁶. 7 China possesses hectares of usable saline-alkali land resources, with immense potential for management and utilization, and is considered one of the most important reserve soil resources in the country. However, salinization exacerbates soil compaction, leading to generally low nutrient and organic matter content, and consequently, a significant decline in land productivity and fertility. This condition is extremely detrimental to crop growth and development, often resulting in a substantial reduction in crop yield. To address this challenge, researchers have discovered that inoculating crops with Bacillus subtilis can significantly enhance their growth capacity in saline-alkali land. The presence of Bacillus subtilis can effectively reduce the osmotic stress of salt and alkali on crops, partially eliminating the negative impact of salinization on crop growth. Summary of the Invention

[0004] To address the problems existing in corn cultivation in saline-alkali land, this invention provides a strain of Bacillus STF4 and its applications.

[0005] The present invention provides a strain of Bacillus STF4, Bacillus ( Bacillus sp. STF4 is deposited at the China Center for Type Culture Collection (CCTCC), Wuhan University, Wuhan, China, with accession number CCTCC NO:M2025290 and deposit date of February 24, 2025.

[0006] The Bacillus subtilis provided by this invention ( Bacillus sp. The use of STF4 in the preparation of microbial agents that promote maize growth in saline-alkali soils and enhance maize's tolerance to salt and alkali stress.

[0007] Furthermore, the method of promoting corn growth in saline-alkali soil involves using the Bacillus (… Bacillus sp.STF4 is applied to sterilized or non-sterilized saline-alkali soils to promote corn growth.

[0008] Furthermore, the promotion of maize growth in saline-alkali soil is achieved by improving the activity of catalase, β-glucosidase, alkaline phosphatase, urease, and cellulase in the rhizosphere soil.

[0009] Contains Bacillus of the present invention ( Bacillus sp. STF4 is a microbial agent that promotes maize growth in saline-alkali soil and enhances maize's tolerance to salt and alkali stress.

[0010] The Bacillus subtilis provided by this invention ( Bacillus sp. STF4 can effectively promote the growth of maize in saline-alkali soil and enhance its tolerance to salt and alkali stress. Application of an inoculant prepared from this strain significantly improves various growth indicators and root indicators of maize seedlings in saline-alkali soil, while also improving rhizosphere soil enzyme activity. This invention relates to Bacillus (…). Bacillus sp. STF4 plays a crucial role in selecting microbial agents for saline-alkali soils that enhance crop tolerance to salt and alkali stress and promote growth. This research not only provides important scientific evidence for developing microbial agents specifically for saline-alkali soils but also opens up new avenues for addressing crop yield reduction caused by soil salinization. This research finding is of great significance for improving the utilization rate of saline-alkali land and ensuring food security. Attached Figure Description

[0011] Figure 1 The present invention is a Bacillus subtilis ( Bacillus sp. Morphological characteristics of STF4 strain.

[0012] Figure 2 The present invention is a Bacillus subtilis ( Bacillus sp. Phylogenetic tree diagram of the 16S rRNA sequence of STF4 strain.

[0013] Figure 3 The present invention is a Bacillus subtilis ( Bacillus sp. Figure 1 shows the experimental results of the phosphorus-solubilizing and potassium-solubilizing abilities of the STF4 strain.

[0014] Figure 4 The present invention is a Bacillus subtilis ( Bacillus sp. Figure showing the results of the salt tolerance test for STF4 strain.

[0015] Figure 5 The present invention is a Bacillus subtilis ( Bacillus sp. Growth curve of STF4 strain.

[0016] Figure 6 The present invention is a Bacillus subtilis ( Bacillus sp.(a) Plant height, (b) Fresh weight above ground, (c) Fresh weight below ground.

[0017] Figure 7 The present invention is a Bacillus subtilis ( Bacillus sp. (a) Bar graph showing the effect of STF4 strain on maize root indicators: (b) total root length, (c) root surface area, (d) average root diameter.

[0018] Figure 8 The present invention is a Bacillus subtilis ( Bacillus sp. (a) Root scans of maize plants promoted by STF4 strain, (b) Roots of maize plants under CK treatment, (c) Roots of maize plants under STF4 treatment, (d) Roots of maize plants under STF4-S treatment.

[0019] Figure 9 The present invention is a Bacillus subtilis ( Bacillus sp. Figure 1 shows the results of enzyme activity experiments in pot experiments of STF4 strain. (a) Catalase, (b) Urease, (c) β-glucosidase, (d) Cellulase, (e) Alkaline phosphatase.

[0020] Figure 10 The present invention is a Bacillus subtilis ( Bacillus sp. (a) Corn plants under CK treatment, (b) Corn plants under CK-S treatment, (c) Corn plants under STF4 treatment, (d) Corn plants under STF4-S treatment. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the spirit of the contents disclosed in the present invention will be described in detail below. After understanding the embodiments of the present invention, any person skilled in the art can make changes and modifications based on the technology taught in the present invention without departing from the spirit and scope of the present invention.

[0022] The illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention. Example 1

[0023] Bacillus ( Bacillus sp. Isolation and purification of STF4 strain Five g of sample was weighed from a moderately saline-alkali land sample in Songyuan City, Jilin Province, and added to 95 mL of 10 mM MgCl2 solution. The sample was then incubated on a shaker at 28°C and 180 r / min for 2 h, followed by standing for 30 min.

[0024] Collect the supernatant from the above culture medium and dilute it to 10 in a clean bench. −6 ; Take 10 −3 10 −4 10 −5 10 −6 For each gradient, 100 μL was spread onto a pre-prepared LB solid medium plate, and each gradient was replicated three times. The LB solid medium formula is: sodium chloride 10 g / L, peptone 10 g / L, yeast extract 5 g / L, agar 15 g / L, pH 7.0.

[0025] Invert the plate and place it in a 28℃ constant temperature incubator with light on for 1-3 days; When a large number of single colonies appear on the plate, single colonies with different morphology, color and other characteristics are picked in the laminar flow hood and streaked onto the corresponding solid plates for separation. The single colonies are then expanded to solid plates until purification is achieved.

[0026] When colonies are streaked to LB solid plates for 4-5 generations, if the color and morphology of the strains on the plate are relatively uniform, colony PCR can be performed. In a clean bench, add 1 mL of sterile pure water to a 2 mL centrifuge tube, pick up a single colony and put it into the centrifuge tube to mix the strain thoroughly. Add the Taq PCR reaction mixture, upstream primer, downstream primer, and bacterial culture to a sterile PCR tube. See Table 1 for the specific PCR system. Table 1 PCR system Components volume Final concentration Taq PCR reaction mixture 25μL 1x concentration DNA template 1μL Bacterial suspension prepared from fresh single colonies Upstream primer (10 μmol / L) 2μL 0.4μM Downstream primer (10 μmol / L) 2μL 0.4μM sterile double-distilled water Make up to 50 μL - Taq PCR reaction mixture, upstream primer, and downstream primer need to be thawed on ice beforehand; After adding all the ingredients, centrifuge the reaction tube for 30-60 seconds, then place the reaction tube into the PCR instrument for the reaction. The reaction time is approximately 2 hours. For detailed PCR reaction cycle procedures, please refer to Table 2; Table 2 PCR Cyclic Program step temperature time Loop count Pre-variation 94℃ 4 min 1 cycle transsexual 94℃ 30 s - annealing 45-68℃ 30 s 30-35 cycles extend 72℃ 1 min - Final extension 72℃ 10 min 1 cycle 4℃ 4℃ - - The gel preparation formula is agarose powder: 50×TAE solution: nucleic acid dye 1 g: 100 mL: 10 μL; Spot the PCR product onto the pre-prepared gel, 5 μL per well. Add 5 μL of marker as a control; After completion, place it in an electrophoresis apparatus with a current of 210A, a voltage of 210V, and an electrophoresis time of 10 minutes. After electrophoresis, the electrophoretic bands and their positions are observed using a gel imaging system and compared with the nucleic acid molecular weight standard marker. The bands can be further detected at approximately 1400 bp. Example 2

[0027] Bacillus ( Bacillus sp. Molecular biological identification and morphological characteristics of STF4 strain Bacillus ( Bacillus sp. The morphological characteristics of STF4 strain are as follows: Bacillus ( Bacillus sp. STF4 strain is yellowish-white in color with a slightly glossy surface. A single strain is nearly round in shape with relatively smooth edges and is opaque. Bacillus ( Bacillus sp. The 16S rRNA sequence of strain STF4 is as follows: GGGGCGGGCG GGTGCTATAC ATGCAAGTCG AGCGAATGGA TTGAGAGCTT GCTCTCAAGAAGTTAGCGGC GGACGGGTGA GTAACACGTG GGTAACCTGC CCATAAGACT GGGATAACTC CGGGAAACCGGGGCTAATAC CGGATAACAT TTTGAACTGC ATGGTTCGAA ATTGAAAGGC GGCTTCGGCT GTCACTTATGGATGGACCCG CGTCGCATTA GCTAGTTGGT GAGGTAACGG CTCACCAAGG CAACGATGCG TAGCCGACCTGAGAGGGTGA TCGGCCACAC TGGGACTGAG ACACGGCCCAG ACTCCTACGG GAGGCAGCAG TAGGGAATCTTCCGCAATGG ACGAAAGTCT GACGGAGCAA CGCCGCGTGA GTGATGAAGG CTTTCGGGTC GTAAAACTCTGTTGTTAGGG AAGAACAAGT GCTAGTTGAA TAAGCTGGCA CCTTGACGGT ACCTAACCAG AAAGCCACGGCTAACTACGT GCCAGCAGCC GCGGTAATAC GTAGGTGGCA AGCGTTATCC GGAATTATTG GGCGTAAAGCGCGCGCAGGT GGTTTCTTAA GTCTGATGTG AAAGCCCACG GCTCAACCGT GGAGGGTCAT TGGAAACTGGGAGACTTGAG TGCAGAAGAG GAAAGTGGAA TTCCATGTGT AGCGGTGAAA TGCGTAGAGA TATGGAGGAACACCAGTGGC GAAGGCGACT TTCTGGTCTG TAACTGACAC TGAGGCGCGA AAGCGTGGGG AGCAAACAGGATTAGATACC CTGGTAGTCC ACGCCGTAAA CGATGAGTGC TAAGTGTTAG AGGGTTTCCG CCCTTTAGTGCTGAAGTTAA CGCATTAAGC ACTCCGCCTG GGGAGTACGG CCGCAAGGCT GAAACTCAAA GGAATTGACGGGGGCCCGCA CAAGCGGTGGAGCATGTGGT TTAATTCGAA GCAACGCGAA GAACCTTACC AGGTCTTGACATCCTCTGAA AACCCTAGAG ATAGGGCTTC TCCTTCGGGA GCAGAGTGAC AGGTGGTGCA TGGTTGTCGTCAGCTCGTGT CGTGAGATGT TGGGTTAAGT CCCGCAACGA GCGCAACCCT TGATCTTAGT TGCCATCATTAAGTTGGGCA CTCTAAGGTG ACTGCCGGTG ACAAACCGGA GGAAGGTGGG GATGACGTCA AATCATCATGCCCCTTATGA CCTGGGCTAC ACACGTGCTA CAATGGACGG TACAAAGAGC TGCAAGACCG CGAGGTGGAGCTAATCTCAT AAAACCGTTC TCAGTTCGGA TTGTAGGCTG CAACTCGCCT ACATGAAGCT GGAATCGCTAGTAATCGCGG ATCAGCATGC CGCGGTGAAT ACGTTCCCGG GCCTTGTACA CACCGCCCGT CACACCACGAGAGTTTGTAA CACCCGAAGT CGGTGGGGTA ACCTTTTGGA GCCAGCCGCG TAAGGGTGAT AC Molecular identification of the strain was performed using its 16S rRNA sequence. If the sequencing results were normal, the BLAST function in the NCBI database could be used to search for similar sequences to identify strains with the same 16S rRNA sequence. Bacillus toyonensis strain BCT-7112 Bacillus thuringiensis strain IAM 12077 Bacillus thuringiensis strain ATCC 10792 showed the highest similarity (99.59%), followed by... Bacillus thuringiensis strain NBRC101235 (99.52%) Based on homology analysis, a phylogenetic tree of the strains was constructed using MEGA software; The 16S rRNA phylogenetic tree shows that strain STF4 is related to... Bacillus paramobilis strain BmL-BC017 is most closely related to Bacillus and belongs to the genus Bacillus, thus it has been confirmed as a Bacillus (Bacillus). Bacillus sp. ), and named it Bacillus sp. STF4. Example 3

[0028] Bacillus ( Bacillus sp. Phosphorus solubility, potassium solubility, salt tolerance tests and growth curve plotting of STF4 strain.

[0029] Bacillus (spores) stored in a -80°C freezer were removed. Bacillus sp. STF4 bacterial culture in glycerol tubes was used for bacterial activation. Insoluble inorganic phosphorus medium was selected to test the phosphorus solubilization ability of microorganisms, medium M1997 was selected to test the potassium solubilization ability of microorganisms, and LB liquid medium with NaCl mass fractions of 1%, 5%, 10% and 15% was prepared to test the salt tolerance of microorganisms.

[0030] The formulation of the phosphorus-solubilizing solid culture medium is as follows: glucose 10 g / L, ammonium sulfate 0.5 g / L, tricalcium phosphate 5.0 g / L, manganese sulfate 0.03 g / L, ferrous sulfate 0.03 g / L, magnesium sulfate 0.3 g / L, sodium chloride 0.3 g / L, potassium chloride 0.3 g / L, agar 15 g / L, and pH adjusted to 7.0-7.2.

[0031] The potassium-soluble solid culture medium formula is: magnesium sulfate 0.5 g / L, calcium carbonate 0.1 g / L, potassium aluminum silicate 2.0 g / L, glucose 5.0 g / L, ferric chloride 0.005 g / L, calcium phosphate 2.0 g / L, agar 15 g / L, and pH adjusted to 7.0.

[0032] Salt-tolerant culture media: LB liquid culture media with sodium chloride mass fractions of 1%, 5%, 10%, and 15% were prepared respectively.

[0033] 5 μL of bacterial culture sample was inoculated onto phosphorus-solubilizing and potassium-solubilizing solid medium, with 5 replicates. Inoculate 1 mL of bacterial culture sample onto salt-tolerant liquid medium, and set up 3 replicates; Phosphorus- and potassium-soluble solid culture media were cultured at 28℃ for 7 days in a constant temperature and light incubator. Observe the size of bacterial colonies and the diameter of the clear and turbid zones surrounding them. Measure the diameters of the clear and turbid zones using calipers on days 1, 3, 5, and 7. Calculate the phosphate-solubilizing and potassium-solubilizing abilities of the strain using the formula PSI = D / d, where PSI represents Bacillus (…). Bacillus sp. The relative phosphorus solubility and potassium solubility index of STF4 strain, where D is the diameter of the clear zone and d is the diameter of the turbid zone, the higher the PSI value, the stronger the phosphorus solubility of the strain, thus preliminarily determining its phosphorus solubility and potassium solubility. Salt-tolerant liquid culture medium was incubated in a shaker at 28°C for 48 h, and the bacterial concentration was measured at 24 h and 48 h. OD The value was used to preliminarily determine its salt tolerance. Bacillus ( Bacillus sp. The phosphorus-solubilizing and potassium-solubilizing abilities of strain STF4 are shown in Table 3, and are specifically as follows: Bacillus ( Bacillus sp. The STF4 strain showed stronger phosphorus-solubilizing and potassium-solubilizing abilities on day 7 than on day 1, and these abilities gradually increased over time, demonstrating that the strain could exert its phosphorus-solubilizing and potassium-solubilizing abilities in a relatively short period of time, and that these abilities could be exerted for a relatively long period of time.

[0034] Table 3 Bacillus ( Bacillus sp. Qualitative detection of phosphorus solubility and potassium solubility in STF4 strain (D / d value) ability 1d 3d 5d 7d Phosphate solubilization 1.11±0.03cd 1.12±0.03c 1.15±0.03d 1.23±0.06b Potassium dissolution 1.04±0.02b 1.06±0.03b 1.07±0.01b 1.11±0.03b Note: Different lowercase letters indicate that the same strain showed significant differences at different testing days (P<0.05).

[0035] Bacillus ( Bacillus sp. The salt tolerance of strain STF4 is shown in Table 4, and its specific characteristics are as follows: When the mass fraction of NaCl is 1%, Bacillus ( Bacillus sp. STF4 strain OD 600nm The values ​​were high at both 24 h and 48 h; when the NaCl mass fraction was 5%, Bacillus ( Bacillus sp. STF4 strain OD The values ​​remained high at 24h and 48h and continued to increase, indicating that the strain could tolerate this low-salt environment; when the NaCl mass fraction was 10% and 15%, OD The values ​​are low and show no significant increase, indicating that Bacillus (B) at this salt concentration... Bacillus sp. STF4 strains cannot develop tolerance.

[0036] Table 4 Bacillus ( Bacillus sp. Qualitative detection of salt tolerance in STF4 strain OD 600nm value time 1% NaCl 5% NaCl 10% NaCl 15% NaCl 24h 1.036±0.015 0.891±0.017 0.081±0.011 0.066±0.003 48h 1.091±0.005 1.082±0.003 0.086±0.017 0.061±0.003 Bacillus ( Bacillus sp. The STF4 bacterial suspension was placed in a shaking incubator and shaken at 28°C and 180 rpm. The concentration of the bacterial suspension was measured every 3 hours using a UV spectrophotometer. OD 600nm The absorbance at a certain point was measured and a growth curve was plotted to determine its growth capacity; Bacillus ( Bacillus sp. The growth curve of STF4 strain is as follows: Figure 5 As shown, the specific manifestation is as follows: During 0-3 hours, Bacillus ( Bacillus sp.STF4 strain is in a slow growth phase; within 3-18 hours, Bacillus ( Bacillus sp. STF4 strain is in the logarithmic growth phase, with viable cell count increasing geometrically and metabolism being vigorous; within 18-39 hours, Bacillus ( Bacillus sp. STF4 strain was in its stationary growth phase, with the viable count reaching its maximum and remaining stable; after 39 hours, the strain entered its decline phase. (Bacillus) Bacillus sp. STF4 strain has strong growth ability and reaches stable growth period relatively quickly. Example 4

[0037] Bacillus ( Bacillus sp. Pot experiment of STF4 strain in maize.

[0038] Bacillus ( Bacillus sp. STF4 was used for viable cell counting; Bacillus ( Bacillus sp. The STF4 bacterial solution was diluted to 10 in a clean bench. −9 ; Take 10 −6 10 −7 10 −8 10 −9 For each gradient, 100 μL was spread onto a pre-prepared LB solid medium plate, and each gradient was replicated three times. Invert the plate and incubate it under light in a 28℃ constant temperature incubator for 24 h. Count the first gradient of plates from which no single colonies have grown; the effective viable count should be at least 1 × 10⁻⁶. 10 CFU / mL can be used for subsequent pot experiments; Bacillus ( Bacillus sp. The effective viable count of STF4 is 7 × 10⁻⁶. 10 CFU / mL; Bacillus ( Bacillus sp. STF4 was formulated into a microbial inoculant for treating corn seedlings growing in saline-alkali soil. The bacterial agent is formulated with an effective viable count of 1×10⁻⁶. 10 When CFU / mL, the single dose is 15 mL / mL. 2 ; The experiment included four treatments: sterilized soil + STF4 inoculant (STF4-S), non-sterile soil + STF4 inoculant (STF4), sterilized soil + water (CK-S), and non-sterile soil + water (CK), with eight parallel samples in each group. The fungal agent was applied to the roots every 7 days for a total of three treatments. After observing for another 7 days, the experiment was completed in 28 days before harvesting. The corn seedlings treated for 28 days were carefully removed from the pots. The roots of the plants were gently shaken until large soil particles no longer fell off. The small amount of soil remaining attached to the roots was defined as rhizosphere soil. The rhizosphere soil was collected for subsequent experiments. The soil attached to the roots was cleaned off. The plants were placed flat on the table and the plant height was measured with a ruler. Use absorbent paper to dry the surface moisture of the plant, and weigh the dry weight of its above-ground and underground parts separately. The underground part of the root system was scanned and root system analysis was performed using WinRHIZO to analyze the total root length, root surface area and average root diameter.

[0039] Record and analyze the plant height, aboveground fresh weight, underground fresh weight, total root length, root surface area, and average root diameter of the samples in the four treatments. Table 5 shows the plant height, aboveground fresh weight, and belowground fresh weight of the samples in the four treatments. Specifically: The height of plants treated with sterilization increased by 25.43%; the height of plants treated without sterilization increased by 11.53%. The above-ground fresh weight increased by 71.76% with sterilization treatment; the above-ground fresh weight increased by 28.61% with non-sterilization treatment. Sterilization treatment increased the underground fresh weight by 65.25%; non-sterilization treatment increased the underground fresh weight by 74.07%. Table 5. Plant height, above-ground fresh weight, and below-ground fresh weight of the samples. deal with Plant height (cm) Fresh weight on the ground (g) Fresh weight underground (g) CK 41.60±2.30c 3.39±0.32b 1.35±0.21b CK-S 45.60±3.97b 2.62±0.56c 1.41±0.30b STF4 46.40±1.95b 4.36±0.23a 2.35±0.17a STF4-S 57.20±2.28a 4.50±0.38a 2.33±0.30a Table 6 shows the total root length, root surface area, and average root diameter of the samples in the four treatments. Specifically: The total root length increased by 12.84% after sterilization treatment; the total root length increased by 9.32% after non-sterilization treatment. Sterilization treatment increased root surface area by 7.91%; non-sterilization treatment increased root surface area by 1.26%. The average root diameter decreased by 10.37% after sterilization treatment; the average root diameter decreased by 9.47% after non-sterilization treatment. Table 6. Total root length, root surface area, and average root diameter of the sample. deal with Total root length (cm) <![CDATA[Root surface area (cm 2 )]]> Average root diameter (mm) CK 184.41±29.21b 53.69±6.32a 0.92±0.1a CK-S 221.34±82.62ab 57.52±14.5a 0.87±0.13a STF4 230.63±62.07ab 63.15±18.17a 0.87±0.04a STF4-S 295.01±64.72a 74.55±18.96a 0.88±0.15a The enzyme activities of catalase, β-glucosidase, alkaline phosphatase, urease, and cellulase in the rhizosphere soil of each sample were analyzed, and the specific manifestations were as follows; The activity of catalase in the rhizosphere soil decreased in both sterilized and unsterilized soil treatments. The number of microorganisms in the sterilized soil treatment decreased, and since microorganisms are the main source of many soil enzymes, this reduction may lead to decreased enzyme activity. The activity of urease in the rhizosphere soil increased in the sterilized soil treatment. Urease is an important enzyme involved in nitrogen transformation, and its increased activity may be related to enhanced nitrogen transformation capacity in the soil. The decreased urease activity in the rhizosphere soil of the unsterilized soil treatment may be due to changes in microbial community structure or competition. The activity of β-glucosidase in the rhizosphere soil decreased in the sterilized soil treatment and increased in the unsterilized soil treatment, promoting carbohydrate decomposition and utilization. The increased cellulase activity in the rhizosphere soil of both sterilized and unsterilized soil treatments indicates enhanced carbon cycling in the soil and interactions between microorganisms and plants. The decreased alkaline phosphatase activity in the rhizosphere soil of the sterilized soil treatment and increased in the unsterilized soil treatment promoted phosphorus transformation and utilization.

[0040] In summary, Bacillus ( ) was screened out Bacillus sp. The STF4 strain was studied, and its growth-promoting effect on maize was investigated. Specifically, the following beneficial effects were observed: The Bacillus subtilis described in this invention ( Bacillus sp. STF4 strain can increase the plant height, above-ground fresh weight and below-ground fresh weight of maize seedlings grown in saline-alkali soil under both sterilized and non-sterilized treatment, thereby promoting growth. The Bacillus subtilis described in this invention ( Bacillus sp. STF4 strain can increase the total root length and root surface area of ​​maize seedlings grown in saline-alkali soil under both sterilized and non-sterilized treatments, secrete auxin, develop maize root system, promote maize growth, and thus achieve the effect of promoting growth. The Bacillus subtilis described in this invention ( Bacillus sp. Microbial agents prepared from the STF4 strain can alter the activity of enzymes in the rhizosphere soil of plants. Overall, these changes in enzyme activity reflect the complex interactions between soil microorganisms, plants, and the environment. The different effects of sterilization and non-sterilization treatments on soil enzyme activity indicate that microorganisms play a crucial role in the soil ecosystem, influencing not only the transformation and cycling of nutrients in the soil but also the growth and health of plants.

[0041] This invention provides a method for isolating and screening a strain of Bacillus STF4 and its application in promoting crop growth. Direct application of the inoculant prepared from this strain can significantly improve various indicators of maize seedlings in saline-alkali soils. This invention plays an important role in selecting microbial inoculants that enhance crop tolerance to salt and alkali stress and promote growth in saline-alkali soils, and has a significant impact on the future use of microbial fertilizers to replace chemical fertilizers.

Claims

1. A strain of Bacillus STF4, characterized in that, Bacillus ( Bacillus sp. STF4 is deposited at the China Center for Type Culture Collection, Wuhan University, Wuhan, China, on February 24, 2025, with accession number CCTCCNO:M2025290.

2. The Bacillus subtilis according to claim 1 ( Bacillus sp. The use of STF4 in the preparation of microbial agents that promote maize growth in saline-alkali soils and enhance maize's tolerance to salt and alkali stress.

3. The use according to claim 2, characterized in that, The method of promoting corn growth in saline-alkali soil involves using the Bacillus (… Bacillus sp. STF4 is applied to sterilized or non-sterilized saline-alkali soils to promote corn growth.

4. The use according to claim 2 or 3, characterized in that, The promotion of maize growth in saline-alkali soil is achieved by improving the activity of catalase, β-glucosidase, alkaline phosphatase, urease, and cellulase in the rhizosphere soil.

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