Salt-stress-resistant growth-promoting rhizobacteria pseudomonas arcustris GLSm-Q7 and application of salt-stress-resistant growth-promoting rhizobacteria pseudomonas arcustris

Abstract

The invention discloses a salt stress-resistant growth-promoting rhizosphere pseudomonas arcuata GLSm-Q7 and application thereof, and relates to the technical field of agricultural microorganisms, the strain number of the strain is GLSm-Q7, the strain is preserved in the China General Microbiological Culture Collection Center (CGMCC), and the preservation number is CGMCC No.35753. The invention further discloses a preparation method of the salt stress-resistant growth-promoting rhizosphere pseudomonas arcuata GLSm-Q7. The strain provided by the invention has the capabilities of fixing nitrogen, dissolving phosphorus, dissolving potassium, producing siderophores and the like, and can improve the soil environment and promote plant growth. The strain GLSm-Q7 is inoculated under salt stress, so that the salt tolerance of the plant can be improved, the root development of the plant is promoted, and the biomass of the plant is increased; and the damage of salt stress to plants can be resisted by generating plant hormones, inducing permeation substance accumulation and improving the activity of an antioxidant enzyme system. The strain resource developed by the invention and the application system thereof provide a new technical means for plant growth promotion and stress regulation and control, and provide theoretical support for saline-alkali soil improvement and sustainable agricultural development.

Description

Background Technology

[0001] This invention belongs to the field of agricultural microbial technology, specifically relating to the technology of *Pseudomonas aeruginosa* GLSm-Q7, a rhizosphere growth-promoting bacterium that is tolerant to salt stress. Technical Field

[0002] Soil salinization threatens global agricultural production, food security, and sustainable development. Globally, approximately 932 million hectares of soil are salinized, distributed across more than 100 countries on every continent except Antarctica. Countries affected by salinization are primarily located in arid and semi-arid climate zones, where low rainfall and high evaporation rates make them highly susceptible to soil salinization. It is reported that approximately 10 million hectares of irrigated land are abandoned annually due to salinization. China has approximately 36.7 million hectares of saline-alkali land, of which about 12.3 million hectares have agricultural development potential. Currently, 2.1 million hectares of saline-alkali land are cultivated but not effectively utilized, and another 10.2 million hectares are newly formed uncultivated land. Of these saline-alkali lands, approximately 6.67 million hectares have arable land potential, 2.33 million hectares are suitable for crop cultivation after improvement, and the remaining 4.34 million hectares are used for other agricultural purposes. Saline-alkali land is an important land resource in my country. Improving and enhancing the quality of saline-alkali land can effectively expand land use, alleviate food security pressures, help increase grain production, and ensure national food security.

[0003] Salt stress hinders key cellular processes that determine plant growth and productivity, such as cell division, elongation, and differentiation, thereby affecting plant growth factors, including root proliferation, leaf size, and stem elongation. Furthermore, reduced stomatal and mesophyll conductance due to salt stress limits carbon dioxide diffusion, photorespiration, lipid and cellular component biosynthesis, and hormone balance. Salinization lowers soil water potential, thus affecting mineral uptake by plant roots. Excessive sodium ion accumulation adversely affects plant metabolism, transpiration, photosynthesis, and, most importantly, ion balance and nutrient uptake. Salinization impedes plant physiological processes, and the cumulative effects on various physiological and biochemical characteristics (such as mineral ion homeostasis, water balance, osmotic regulation, antioxidant metabolism, nitrogen fixation, and photosynthetic capacity) lead to inhibited plant growth and development. High salt levels also alter Na+. + / K + Salt stress affects crop productivity and yield by influencing ratios, osmotic stress, impaired respiration, photosynthesis, nitrogen fixation, nitrification, denitrification, soil biodiversity, and microbial activity. Current methods for addressing salt stress include breeding salt-tolerant crop varieties, employing plant genetic engineering, using chemical methods, and applying organic matter to the soil to improve soil conditions in affected farmland. Among these strategies, utilizing plant-promoting rhizosphere bacteria has shown significant potential to mitigate the negative effects of salt stress on crops and increase their overall yield.

[0004] Plant growth-promoting rhizobacteria (PGPRs) are a class of plant-friendly soil microorganisms that directly or indirectly promote plant growth by secreting various regulatory compounds in the rhizosphere. Studies have shown that PGPRs can regulate all growth processes in plants, from root formation to flowering development. PGPRs can secrete specific compounds in the rhizosphere, dissolve essential minerals (such as potassium, phosphorus, zinc, and iron) necessary for plant development and nitrogen fixation, produce plant hormones, and synthesize antibiotic compounds, thereby improving the absorption of certain nutrients and directly promoting plant growth. PGPRs positively influence the nutritional parameters and physiological and biochemical characteristics of inoculated plants through multiple pathways, including promoting root development, thereby improving water and nutrient absorption; enhancing the production of osmotic regulators, which play a role in osmotic regulation and maintain cell turgor pressure to ensure plant survival; promoting the accumulation of antioxidant enzymes, thereby reducing the content of reactive oxygen species (ROS) in plants; and improving photosynthetic efficiency, pigment production, and plant hormone homeostasis. PGPR induces the expression of stress-related genes and the accumulation of proteins involved in metabolite synthesis, thereby helping plants cope with abiotic stress.

[0005] Inoculation with PGPR can effectively control the impact of salinization on plant growth and crop yield because root microbiota play a crucial role in enhancing plant tolerance to abiotic stresses and maintaining plant productivity. PGPR-containing biofertilizers can promote plant growth and increase yields by adding nutrients to the soil and improving soil fertility. They also help control plant diseases and parasites in a sustainable and environmentally friendly manner. Furthermore, the use of PGPR in crop breeding and genetic engineering can produce varieties more resistant to abiotic and biotic stresses such as drought, salinity, and plant diseases, enabling them to withstand changing environmental conditions and thus ensuring food security. PGPR provides a sustainable and environmentally friendly alternative to traditional agricultural practices and holds the promise of promoting more sustainable and resilient agricultural development. Therefore, researching and developing new, highly efficient microbial strains, inoculant preparation processes, key application technologies, and integrated application models is of great significance for the improvement of saline-alkali land. Summary of the Invention

[0006] This invention aims to provide a plant rhizosphere growth-promoting bacterium, *Pseudomonas aeruginosa* GLSm-Q7, with salt, acid, and alkali tolerance, and its applications. The purpose is to improve soil salinization caused by improper irrigation methods, excessive use of chemical fertilizers, and land development and destruction. Saline-alkali land is an important land resource in my country; its improvement and quality enhancement can not only effectively expand the area of ​​arable land but also significantly increase grain yield, alleviate the growing pressure on food security, ensure national food supply and sustainable agricultural development, and provide important support for the implementation of the food security strategy.

[0007] Based on the above objectives, the present invention employs the following technical means: According to a first aspect of the present invention, a plant rhizosphere growth-promoting bacterium, *Pseudomonas aeruginosa* GLSm-Q7, with salt, acid, and alkali tolerance is provided, wherein the plant rhizosphere growth-promoting bacterium *Pseudomonas aeruginosa* GLSm-Q7 is classified and named *Pseudomonas*. (Pseudomonas arcuscaelestis The gene was deposited on August 27, 2025, at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 35753. The deposit address is Institute of Microbiology, Chinese Academy of Sciences, No. 3, No. 1 Beichen West Road, Chaoyang District, Beijing.

[0008] According to a second aspect of the present invention, *Pseudomonas aeruginosa* GLSm-Q7 has been found to possess plant growth-promoting functions, including nitrogen fixation, phosphorus solubilization, potassium solubilization, siderophore production, and indole-3-acetic acid (IAA) production, thereby improving the absorption of certain nutrients by plants and directly promoting plant growth. *Pseudomonas aeruginosa* GLSm-Q7 was cultured in media with different salt concentrations and pH levels, and growth curves were plotted, demonstrating that this bacterium has strong salt, acid, and alkali tolerance.

[0009] According to a third aspect of the present invention, a plant growth-promoting agent comprising *Pseudomonas aeruginosa* GLSm-Q7 is provided.

[0010] According to a fourth aspect of the present invention, the method for preparing the plant rhizosphere growth-promoting bacterial agent is as follows: A single colony of strain GLSm-Q7 is picked and inoculated into a sterilized Erlenmeyer flask containing liquid LB medium, and cultured overnight at 28 °C and 180 rpm on a constant-temperature shaker to obtain the seed culture. 5 mL of the seed culture is then inoculated into 500 mL of LB liquid medium and cultured at 28 °C and 180 rpm on a constant-temperature shaker until the bacterial culture reaches its OD value. 600 When the value is 1-1.2, the bacterial culture is centrifuged at 6000 rpm for 10 min, the supernatant is removed, and the bacterial cells are resuspended in an equal volume of sterile water or NaCl solution to prepare bacterial cells.

[0011] According to a fifth aspect of the present invention, a plant growth promoter comprising *Pseudomonas aeruginosa* GLSm-Q7 is provided to promote the growth of sugar beet seedlings under salt stress.

[0012] The plant growth-promoting agent, *Pseudomonas aeruginosa* GLSm-Q7, has a positive impact on the nutritional parameters and physiological and biochemical characteristics of inoculated plants through multiple mechanisms of action.

[0013] The mechanism of action includes one or more of the following pathways; (1) Promotes root development and improves water and nutrient absorption; (2) Enhance plant leaf characteristics and improve photosynthetic efficiency; (3) It increases the fresh weight and stem diameter of plants, thereby increasing the biomass and yield of plants; (4) Enhance the production of osmotic regulators (soluble sugars, proline). Pro can improve seed germination rate, and its anabolism plays an important role in regulating osmotic pressure and biological nitrogen fixation. Soluble sugars are important osmotic regulators that help maintain osmotic balance and cell membrane stability, and improve plant adaptability.

[0014] (6) Enhancing the activity of antioxidant enzyme systems: Under salt stress, reactive oxygen species can participate in various physiological and biochemical processes of plants, such as relative water content, photosynthesis, stomatal conductance, and antioxidant enzyme activity, resulting in a significant reduction in plant biomass and yield. Superoxide dismutase converts superoxide anions into hydrogen peroxide, which is the first line of defense for ROS scavenging; catalase decomposes H2O2 into water and oxygen, reducing the toxicity of H2O2 to cells.

[0015] Peroxidases assist in the decomposition of H2O2 by oxidizing substrates, while also participating in cell wall reinforcement and signal transduction. Increased activity of these enzymes helps to alleviate the inhibitory effect of salt stress on cell division and expansion, and supports the normal growth of organs such as roots, stems, and leaves.

[0016] In summary, the beneficial effects of the present invention are, but not limited to, the following aspects: This invention identified a strain of *Pseudomonas aeruginosa* GLSm-Q7 with multiple functions, including nitrogen fixation, phosphorus solubilization, and IAA production. This strain can survive in high-salt and acid-base conditions. Under salt stress, it helps plants acquire more nutrients, effectively promoting plant growth and development. Furthermore, it can alleviate oxidative damage caused by salt stress by increasing the activity of plant antioxidant enzyme systems, maintaining redox balance in plant cells, enhancing photosynthesis and metabolic functions, and improving plant physiological state, thereby increasing the plant's tolerance to saline-alkali stress. The strain described in this invention provides new insights for research on saline-alkali land management and utilization technologies, and is of great significance for saline-alkali land improvement and the realization of green, friendly, and sustainable agricultural development. Attached Figure Description

[0017] Figure 1 - Figure 6 This invention relates to the detection of the growth-promoting effect of Pseudomonas aeruginosa GLSm-Q7, wherein... Figure 1 For nitrogen fixation, Figure 2 Organophosphorus, Figure 3 Inorganic phosphorus, Figure 4 To solubilize potassium, Figure 5 For iron carrier, Figure 6 For the IAA colorimetric reaction of strain GLSm-Q7, Figure 7This is a colorimetric reaction of IAA standard solution. The numbers in the graph represent different concentrations, and the unit is "mg / L". In the above graph, "CK" represents blank. Figure 1 (As shown in the abstract) Figure 8 This is the phylogenetic tree of *Pseudomonas aeruginosa* GLSm-Q7 as described in this invention.

[0018] Figure 9 The maximum salt tolerance concentration of Pseudomonas aeruginosa GLSm-Q7 was determined for this invention. The percentages in the figure represent the NaCl concentration in the culture medium.

[0019] Figure 10 This invention relates to the detection of acid and alkali tolerance of Pseudomonas aeruginosa GLSm-Q7. The numbers in the legend represent the pH value of the culture medium.

[0020] Figure 11 This invention illustrates the growth-promoting effect of *Pseudomonas aeruginosa* GLSm-Q7 at different NaCl concentrations on sugar beet seedlings. In the figure, "-GLSm-Q7" represents the uninoculated strain GLSm-Q7, and "+GLSm-Q7" represents the inoculated strain GLSm-Q7.

[0021] Figure 12 - Figure 17 This invention relates to the effects of *Pseudomonas aeruginosa* GLSm-Q7 on the biological parameters of sugar beet seedlings under different NaCl concentrations. Figure 12 Is it plant height, Figure 13 It is root long, Figure 14 It is a thick stem, Figure 15 It is fresh and heavy. Figure 16 Is it leaf length, Figure 17 The leaf width is represented by the error bars, which indicate the standard deviation. n= 3), lowercase letters indicate differences between different treatments reaching ( P <0.05) Significance level.

[0022] Figure 18 - Figure 25 This invention relates to the effects of *Pseudomonas aeruginosa* GLSm-Q7 on physiological parameters of sugar beet seedlings under different NaCl concentrations. Figure 18 For ABA content, Figure 19 For soluble sugar content, Figure 20 For MDA content, Figure 21 For Pro content, Figure 22 For total chlorophyll content, Figure 23 For CAT activity, Figure 24 For SOD activity, Figure 25 For POD activity, the error bars represent the standard deviation. n= 3), lowercase letters indicate differences between different treatments reaching ( P <0.05) Significance level. Detailed Implementation

[0023] The following embodiments are only used to better understand the technical solutions of the present invention and do not constitute a limitation of the present invention.

[0024] For those skilled in the art, various modifications or equivalent substitutions can be made to the embodiments without departing from the principles and spirit of the present invention, and all such modifications or equivalent substitutions fall within the protection scope of the present invention. Unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional techniques well known to those skilled in the art, and the raw materials, reagents, and equipment involved can all be purchased from conventional market channels.

[0025] Example 1: Isolation and screening of salt-tolerant Pseudomonas aeruginosa GLSm-Q7 (1) Soil samples were collected from the rhizosphere of sugar beets in saline-alkali land in Gulang County, Gansu Province. The soil sample should be taken from within 20 cm of the rootstock, and some plant roots should be attached to the soil. The collected soil, along with the roots, was stored in a sealed bag at 4 ℃ for later use. 15 g of the collected sugar beet rhizosphere soil was placed in a sterile 500 mL Erlenmeyer flask, mixed with 300 mL of sterile water, and placed in a constant temperature shaker at 28 ℃ and 180 r / min for 12 h for activation. After the incubation, the resulting soil suspension was allowed to stand for 2 min, and 1 mL of the supernatant was taken and processed stepwise (10⁻³, 10⁻³...). 4 10⁻ 5 Isolation was performed using the dilution method. 100 μL of each serially diluted solution was sequentially spread onto the surface of LB solid medium. After the surface liquid dried, the medium was sealed and incubated upside down at 28 °C until single colonies appeared. Single colonies with distinct morphological differences were selected and inoculated into LB liquid medium, and cultured until OD... 600 After reaching approximately 1.0, the culture was then streaked onto LB solid medium for isolation and purification, with each strain being purified three times. Single colonies of the purified strains were then inoculated into LB liquid medium and cultured until OD200 reached. 600 Approximately 1.0g, mixed with an equal volume of sterilized 50% glycerol, and stored at −80 °C for later use.

[0026] (2) After activating each strain on LB solid medium, single colonies growing on LB solid medium were selected and inoculated into sterilized LB liquid medium. Seed culture was prepared by activation at 28 ℃ and 180 r / min. LB solid medium with NaCl concentrations of 0%, 1%, 4%, 6%, 8%, and 10% was prepared. The activated seed culture was used to inoculate each strain onto LB solid medium of the above concentrations using the streak plating method. The strains were cultured at 28 ℃ for 3 days, and their growth was observed and recorded periodically. Strains growing on high-concentration LB solid medium were selected for subsequent experiments. Therefore, the salt-tolerant strain GLSm-Q7 was screened from the plant rhizosphere.

[0027] Example 2: Testing the growth-promoting properties of salt-tolerant strain GLSm-Q7 The selected salt-tolerant strain GLSm-Q7 was inoculated onto Ashby medium, inorganic phosphorus solubilizing medium, Monkina organic phosphorus medium, potassium solubilizing medium, and MKB medium, respectively. The nitrogen fixation, phosphorus solubilization, potassium solubilization, siderophore production, and IAA production characteristics of strain GLSm-Q7 were qualitatively determined. The specific detection method is as follows: (1) Nitrogen fixation ability: Ashby medium was divided into four regions using a cross-branching method. 5 μL of the activated strain GLSm-Q7 seed culture was inoculated into three of these regions using a pipette, with the remaining region serving as a blank. The inoculated nitrogen-fixing medium was placed in a 28 ℃ incubator for 3-4 days, and the growth of the strain was observed periodically. If the strain could grow normally on Ashby medium, it indicated that the strain had nitrogen-fixing ability. Figure 1 As shown, strain GLSm-Q7 can grow on Ashby medium, thus this strain has nitrogen-fixing properties.

[0028] (2) Phosphorus solubility: The inorganic phosphorus-solubilizing medium and the organic phosphorus-solubilizing medium were divided into four regions using a cross-branching method. 5 μL of the activated GLSm-Q7 seed culture solution was inoculated into three of these regions using a pipette, with the remaining region serving as a blank. The inoculated inorganic phosphorus-solubilizing medium and the organic phosphorus-solubilizing medium were then incubated at 28 ℃ for 3-4 days, and the growth of the strain was observed periodically. If a transparent white halo appears around the strain, it indicates that the strain possesses the ability to solubilize both organic and inorganic phosphorus. Figure 2 and Figure 3 As shown, a white transparent halo appeared around the inoculated strain GLSm-Q7 on the culture medium, indicating that strain GLSm-Q7 has the ability to dissolve both organic and inorganic phosphorus. The strength of the strain's phosphorus-dissolving ability was calculated based on the ratio of the halo diameter to the colony diameter; the larger the ratio, the stronger the phosphorus-dissolving ability.

[0029] (3) Potassium-solubilizing ability: The potassium-solubilizing medium was divided into four regions using a cross-branching method. 5 μL of the activated GLSm-Q7 seed culture was inoculated into three of these regions using a pipette, with the remaining region serving as a blank. The inoculated potassium-solubilizing medium was then placed in a 28 ℃ incubator for 3-4 days, and the growth of the strain was observed periodically. If the strain could grow normally on the potassium-solubilizing medium, it indicated that the strain possessed potassium-solubilizing ability. Figure 4 As shown, strain GLSm-Q7 can grow on potassium-solubilizing medium, thus this strain has potassium-solubilizing properties.

[0030] (4) Siderophore Production Capacity: MKB and CAS media were used to detect siderophore production, in two layers. The MKB medium was first divided into four regions using a cross-branching method. 5 μL of the activated GLSm-Q7 seed culture was inoculated into three of these regions using a pipette, with the remaining region serving as a blank. The inoculated MKB medium was then placed in a 28 ℃ incubator for 3-4 days, and the growth of the strain was observed periodically. When obvious colonies appeared in the medium, pre-sterilized 60 ℃ CAS medium was poured into the MKB medium. After the CAS medium solidified, it was left to stand for half an hour, and the presence of an orange-yellow transparent halo around the colonies was observed. The appearance of an orange-yellow transparent halo indicates that the strain has the ability to produce siderophores. Figure 5 As shown, strain GLSm-Q7 produced an orange-yellow transparent halo in MKB medium, indicating that this strain has the ability to produce siderophores.

[0031] (5) IAA (Inhibitory Acid) Production Ability: The strain GLSm-Q7 was inoculated into IAA detection medium (g / L: tryptone 20, K2HPO4 1.5, MgSO4 1.5, glycerol 15mL, L-tryptophan 0.1) and cultured at 28 ℃ and 180 r / min for 2-3 days. 500 μL of the bacterial suspension was transferred to a white ceramic colorimetric plate, and 500 μL of Salkowski colorimetric solution was added. 500 μL of uninoculated IAA medium and 500 μL of Salkowski colorimetric solution were added to the colorimetric plate as controls. The reaction was carried out at room temperature in the dark for 30 min. If the liquid in the colorimetric plate turned pink, it indicated that the bacterium had the ability to secrete IAA. The intensity of the IAA secretion was judged by the color intensity; the darker the color, the stronger the IAA secretion ability. Figure 6 As shown, strain GLSm-Q7 can turn liquid red, thus it has the ability to produce IAA.

[0032] Quantitative determination: After activation, 2 mL of bacterial culture was added to a 2 mL centrifuge tube of strain GLSm-Q7. The mixture was centrifuged at 8000 r / min for 5 min at room temperature. 1 mL of the supernatant was transferred to a colorimetric plate, and 1 mL of Salkowski colorimetric solution was added. The mixture was reacted in the dark at room temperature for 30 min, and the absorbance was measured at 530 nm. Figure 7 As shown, five aliquots of 1 mL blank colorimetric solution were taken, and equal volumes of 0, 15, 30, 45, 60, 75, and 100 μg / mL IAA standard solutions were added to each aliquot. After reacting for 30 min at room temperature in the dark, the absorbance was measured at 530 nm. A standard curve was plotted with the absorbance value on the ordinate and the IAA standard solution concentration on the abscissa. Each experiment was repeated three times. Substituting the absorbance value of strain GLSm-Q7 at 530 nm into the standard curve, the IAA yield of the strain was calculated to be 24.417 mg / L.

[0033] Example 3: Molecular identification and phylogenetic analysis of salt-tolerant bacterial strain GLSm-Q7 Sample pretreatment: Take 1 mL of overnight cultured strain GLSm-Q7 and add it to a 1.5 mL centrifuge tube. Centrifuge at 8000 rpm for 1 min at room temperature, discard the supernatant, and collect the bacterial cells. Add 180 µl of buffer digestion, then add 20 µl of Proteinase K solution, vortex to mix, and incubate at 56°C for 1 h until the cells are completely lysed. After sample pretreatment, extract bacterial DNA according to the Ezup column-based bacterial genomic DNA extraction kit instructions.

[0034] PCR amplification was performed using the extracted DNA solution as a template. Universal primers 27F (5′-AGAGTTTGATCCTGGCTCAG-3′) and 1492R (5′-GGTTACCTTGTTACGACTT-3′) were selected to amplify the 16S rRNA gene of the strain. The PCR reaction program was as follows: 94 °C pre-denaturation for 3 min, 94 °C denaturation for 40 s, 58 °C annealing for 30 s, 72 °C extension for 2 min, 30 cycles, and a final extension at 72 °C for 10 min, stored at 4 °C. The sequencing results were sent to Sangon Biotech Shanghai Co., Ltd. for sequencing. BLAST analysis was performed on the sequencing results using NCBI (www.ncbi.nlm.nih.gov). A phylogenetic tree was constructed using MEGA-64 software. Figure 8 As shown, strain GLSm-Q7 is related to *Pseudomonas aeruginosa* (…). Pseudomonas arcuscaelestis P66 is the most closely related strain, with a similarity of 99.66%. Therefore, strain GLSm-Q7 was identified as *Pseudomonas aeruginosa*.

[0035] Example 4: Detection of salt tolerance and acid-base tolerance of salt-tolerant strain GLSm-Q7 (1) Salt tolerance: Using LB liquid medium as a control, LB liquid medium with NaCl contents of 1%, 3%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, and 13% (all percentages are in g / 100 mL) was prepared for use. A bacterial suspension of strain GLSm-Q7 was inoculated into LB liquid medium at each of the above salt concentrations at a ratio of 1%, and the OD at that point was measured. 600 Each treatment was performed in triplicate, and the cells were incubated with shaking at 28 ℃ and 180 r / min. OD values ​​were measured at 0, 2, 5, 10, 20, 25, 30, 40, 50, 60, 70, and 80 h. 600 . with OD 600 Plot the bacterial growth curve with the vertical axis as the ordinate and the incubation time as the horizontal axis, and analyze the growth of the bacterial strain. Figure 9 As shown, strain GLSm-Q7 can grow and reproduce on LB liquid medium with 1%–12% NaCl. The fastest growth rate of this bacterium is observed at a concentration of 1%, and the OD of the bacterial culture is [not specified] at a concentration of 1%–11%. 600 All values ​​reached above 1.2, with the OD of the bacterial culture reaching 1.2 after 60 hours of growth when the NaCl concentration was 3%. 600 The maximum value was 1.703. The growth of this bacterium was significantly inhibited when the NaCl concentration was 10%–13%. It hardly grew during the first 0–40 h. After 40 h, the absorbance of the colonies in the culture medium began to rise. When the NaCl concentration was 13%, the bacterium stopped growing.

[0036] (2) Acid-base tolerance: Using LB liquid medium as a control, 100 mL of LB liquid medium with pH values ​​of 4, 5, 6, 7, 8, 9, 10, 11, and 12 were prepared for use. A bacterial suspension of strain GLSm-Q7 was inoculated into LB liquid medium at each of the above pH values ​​at a ratio of 1%, and the OD value was measured at each pH. 600 Each treatment was performed in triplicate, and the cells were incubated with shaking at 28 ℃ and 180 r / min. OD values ​​were measured at 0, 2, 5, 10, 20, 30, 40, 50, 60, 70, and 80 h. 600 . with OD 600 Plot the strain's growth curve with the vertical axis representing the ordinate and the incubation time representing the horizontal axis, and analyze the strain's growth under acidic and alkaline conditions. Figure 10 As shown, strain GLSm-Q7 can grow and reproduce on LB liquid medium with pH values ​​between 5 and 11. The fastest growth rate of this bacterium is observed at pH 7, and the OD of the bacterial culture is highest at pH values ​​between 5 and 11. 600All values ​​reached above 1.2, with the bacterial culture OD at pH 6 reaching a peak value of 1.2 after 50 hours of growth. 600 The maximum absorbance was 1.654. ​​The growth of this bacterium was significantly inhibited at pH 10–11. It hardly grew at 0–40 h. After 40 h, the absorbance of the colonies in the culture medium began to rise. The bacterium stopped growing at pH 4 and 12.

[0037] Example 5: Effects of salt-tolerant strain GLSm-Q7 on beet seedling biomass under different salt concentrations Three experimental groups and three control groups were set up. The experimental groups were inoculated with bacterial agents resuspended in distilled water, 200 mmol / L NaCl solution, and 400 mmol / L NaCl solution, respectively. The control groups were irrigated with distilled water, 200 mmol / L NaCl solution, and 400 mmol / L NaCl solution, respectively. Five replicates were set up. Inoculum preparation and plant culture conditions: A single colony of *Pseudomonas aeruginosa* GLSm-Q7 was inoculated into a 250 mL Erlenmeyer flask containing 100 mL of LB liquid medium and placed on a constant-temperature shaker for activation culture at 28 ℃ and 180 r / min. The culture was continued until the bacterial OD of the culture solution was reached. 600 Stop shaking at approximately 1.0, and use the bacterial suspension as seed culture for subsequent experiments. Inoculate 20 mL of each seed culture into separate 1000 mL wide-mouth bottles containing 800 mL of LB liquid medium, and incubate at 28 ℃ and 180 r / min until OD reaches 1.0. 600 At approximately 1.5 hours, all bacterial suspensions were centrifuged at 8000 rpm for 5 minutes. After removing the supernatant, the bacterial cells were resuspended in distilled water, 200 mmol / L NaCl, and 400 mmol / L NaCl solutions to prepare the bacterial inoculum for later use. Sugar beet seeds of similar size and with undamaged surfaces, designated "Gantang No. 7" (purchased from Wuwei Sannong Seed Industry Technology Co., Ltd.), were selected and planted in pots (10 cm long, 10 cm wide, and 12 cm high) containing a sterilized mixture of nutrient soil and vermiculite (nutrient soil: vermiculite = 3:1), with 9 seeds sown per pot. When the sugar beet seeds reached the stage of two leaves and one bud, thinning was performed to ensure uniform growth and even distribution. The above-mentioned bacterial inoculum was inoculated near the roots of the sugar beet seedlings. The control group received the corresponding solution. Inoculation was performed every three days. Physiological indicators were measured after 14 days of growth, and various biomass parameters of the sugar beet seedlings were measured after 30 days of growth. Culture conditions: soil culture temperature (25±2) ℃ / (23±2) ℃ (day / night), photoperiod 16 h / 8 h (day / night), light intensity 500−700 μmol / (m²). 2 (s), relative humidity 65%−75%.

[0038] like Figure 11The image shows the growth status of beet seedlings after 30 days. The beet seedlings exhibited different states with increasing salt concentration. Under 400 mmol / L NaCl stress, the seedling height decreased, leaves became smaller, thicker, and curled, leaf color gradually faded from green to yellow, and the overall plants showed signs of wilting. The biomass analysis of the control and treatment groups is as follows: Under normal conditions (0 mmol / L NaCl), compared with the uninoculated group, the beet seedlings inoculated with strain GLSm-Q7 had a significantly shorter plant height (…). Figure 12 ), root length ( Figure 13 They increased by 17.8% and 46.7% respectively. P <0.05), stem diameter ( Figure 14 Fresh weight Figure 15 ), leaf length ( Figure 16 ) and leaf width ( Figure 17 There were no significant differences in any of the above. Under 200 mmol / L NaCl treatment, compared with uninoculated seedlings, beet seedlings inoculated with strain GLSm-Q7 showed increases in plant height, root length, fresh weight, leaf length, and leaf width of 14.7%, 31.6%, 87.2%, 46.1%, and 77.7%, respectively. P <0.05), stem diameter showed no significant difference; under 400 mmol / L NaCl treatment, compared with uninoculated seedlings, the root length of beet seedlings inoculated with strain GLSm-Q7 increased by 43.3% ( P <0.05), there were no significant differences in plant height, root length, fresh weight, stem diameter, leaf length, and leaf width.

[0039] The above results indicate that inoculating with strain GLSm-Q7 can improve the salt tolerance of sugar beet seedlings, has a significant growth-promoting effect, and can maintain the survival of sugar beet seedlings under high-salt conditions.

[0040] Example 6: Effects of salt-tolerant strain GLSm-Q7 on physiological characteristics of sugar beet seedlings under different salt concentrations (1) Effects of inoculated strain GLSm-Q7 on the soluble matter content, total chlorophyll content and ABA content of sugar beet seedlings under salt stress To investigate the specific effects of inoculated strain GLSm-Q7 on sugar beet seedlings, this example measured the contents of malondialdehyde (MDA), abscisic acid (ABA), proline (Pro), soluble sugar, and total chlorophyll. The determination methods are as follows: MDA content can be measured by condensing with thiobarbituric acid (TBA) under acidic and high-temperature conditions to form a brownish-red trimethylolpropionate (3,5,5-trimethyloxazol-2,4-dione), with a maximum absorption wavelength of 532 nm. The MDA content in the sample can be estimated after colorimetric analysis.

[0041] ABA content was determined using an ELISA kit. This kit employs a competitive assay principle. Purified plant ABA was coated onto microplates to create a solid-phase carrier. The sample or standard, followed by biotin-labeled antibody, was added sequentially to the microplates coated with plant ABA. Streptomycin-HRP was then added after the reaction. After thorough washing, the sample was developed using the substrate TMB. TMB was converted to blue under the catalysis of peroxidase, and then to yellow under acidic conditions. The color intensity was negatively correlated with the amount of plant ABA in the sample. The absorbance was measured at 450 nm using a microplate reader to calculate the sample concentration.

[0042] The increase in proline content reflects stress resistance to some extent. Pro was extracted with sulfosalicylic acid (SA), and after heating, Pro reacted with acidic ninhydrin solution to produce a red color. The absorbance was measured at 520 nm.

[0043] Soluble sugars are an important component of plants, as well as the main raw materials and storage substances for metabolism. An increase in their content can help plants maintain cell water balance and reduce osmotic stress caused by salt stress. Their content is determined by the anthrone colorimetric method.

[0044] Chlorophyll a and chlorophyll b have maximum absorption at 645 nm and 663 nm, respectively. The contents of chlorophyll a, chlorophyll b, and total chlorophyll can be calculated using empirical formulas. Chlorophyll captures light energy and transfers it to the reaction centers in the photosystem, driving the electron transport chain to produce ATP and NADPH, providing energy for carbon assimilation. Higher chlorophyll content indicates stronger light energy absorption and conversion capabilities, which is beneficial for increasing the rate of photosynthesis and promoting plant growth.

[0045] After inoculation with strain GLSm-Q7, under 0 mmol / L NaCl conditions, the ABA content in beet seedlings was significantly lower than that in uninoculated seedlings. Figure 18 It decreased by 51.2%. P <0.05), soluble sugar content ( Figure 19 ) increased by 31.5% ( P <0.05), MDA( Figure 20 ), Pro Figure 21 ) and total chlorophyll content ( Figure 22There was no significant difference; under 200 mmol / L NaCl conditions, compared with uninoculated seedlings, the ABA and MDA contents in beet seedlings inoculated with strain GLSm-Q7 decreased by 52.4% and 29.5%, respectively. P <0.05), the content of soluble sugar and total chlorophyll increased by 95.4% and 62.6%, respectively. P <0.05), with no significant difference in Pro content; under 400 mmol / L NaCl conditions, compared with uninoculated, the ABA content in beet seedlings inoculated with strain GLSm-Q7 decreased by 25.9% ( P <0.05), the contents of soluble sugar, Pro, and total chlorophyll increased by 112.9%, 111.6%, and 57.5%, respectively. P <0.05), with no significant difference in MDA content. These results indicate that inoculation with strain GLSm-Q7 under salt stress can reduce MDA and ABA content in sugar beet seedlings, stabilize their cell membrane structure, alleviate membrane lipid peroxidation, reduce stomatal closure, improve CO2 supply, and increase photosynthetic efficiency. This helps plants resist the damage caused by salt stress and restore their growth status.

[0046] (2) Effects of inoculated strain GLSm-Q7 on the activity of antioxidant enzyme system in sugar beet seedlings under salt stress Weigh 0.1g of fresh leaves into a 2mL centrifuge tube, cool the centrifuge tube in liquid nitrogen, grind the plant tissue with a plant tissue grinder, and then place it on an ice bath for later use.

[0047] Superoxide dismutase (SOD) is an important oxygen free radical scavenger that catalyzes the disproportionation reaction of superoxide anions to generate H₂O₂ and O₂. SOD is not only a superoxide anion scavenger but also a major H₂O₂ generating enzyme, playing a crucial role in biological antioxidant systems. SOD activity was measured according to the kit (Solepro) instructions. Poly(hydrogen peroxide) (POD) is widely present in plant cells and can catalyze the oxidation of phenolic and amine compounds by hydrogen peroxide, exhibiting a dual function of eliminating the toxicity of hydrogen peroxide and phenolic and amine compounds. POD catalyzes the oxidation of specific substrates by H₂O₂ and exhibits specific light absorption at 470 nm. POD activity was measured according to the kit (Solepro) instructions. Excessive H₂O₂ can inhibit the activity of various enzymes and damage cellular components. Catalytic oxidase (CAT) promptly removes H₂O₂, which helps maintain cellular metabolic balance. CAT activity was measured according to the kit (Solepro) instructions.

[0048] After inoculation with strain GLSm-Q7, under 0 mmol / L NaCl conditions, the CAT activity in beet seedlings was significantly lower than that in uninoculated seedlings. Figure 23 It increased by 54.2% P <0.05), SOD( Figure 24 ) and POD activity ( Figure 25 There was no significant difference; under 200 mmol / L NaCl conditions, compared with uninoculated, the CAT activity in beet seedlings inoculated with strain GLSm-Q7 increased by 52.8%. P <0.05), with no significant difference in SOD and POD activities; under 400 mmol / L NaCl conditions, compared with uninoculated, the activities of POD and SOD in beet seedlings inoculated with strain GLSm-Q7 increased by 49.5% and 49.5%, respectively. P <0.05), with no significant difference in CAT activity. Studies have found that PGPR inoculation can stimulate the activity of antioxidant enzymes in plants, which are crucial in scavenging reactive oxygen species and protecting plant cells from oxidative damage. PGPR-induced antioxidant enzymes can improve plant salt tolerance by reducing hydrogen peroxide levels in roots under salt stress. In this example, it was found that the activities of antioxidant enzymes (SOD, POD, CAT) in beet seedlings inoculated with strain GLSm-Q7 under salt stress were higher than those in uninoculated beet seedlings. Therefore, inoculation with *Pseudomonas aeruginosa* GLSm-Q7 significantly enhances the antioxidant capacity of plants, giving them a stronger ability to scavenge reactive oxygen species under stress, thereby effectively reducing oxidative damage, improving the physiological state of plants, and mitigating the adverse effects of salt stress.

[0049] In summary, the *Pseudomonas aeruginosa* strain GLSm-Q7 of this invention possesses strong nitrogen fixation, phosphorus solubilization, potassium solubilization, siderophore production, and IAA production capabilities. It can promote plant growth and increase plant biomass under high salinity. Under salt stress, it can enhance the activity of antioxidant enzyme systems, helping plants scavenge reactive oxygen species caused by salt stress, repair oxidative damage caused by excessive MDA, and maintain the normal physiological state of plants under salt stress. The development and research of strain GLSm-Q7 has an effective role in improving the quality of saline-alkali land, and is of great significance for alleviating food security pressure, increasing grain yield, and ensuring national food security.

[0050] This strain has a clear origin and simple application method, making it suitable for saline-alkali land management and crop production, and has good potential for widespread application. The embodiments of this invention are only for illustrating the technical solutions of this invention and are not intended to limit the scope of protection of this invention; any equivalent substitutions or improvements made without departing from the spirit and substance of this invention should be within the scope of protection of this invention.

Claims

1. *Pseudomonas aeruginosa*, characterized by: The Pseudomonas aeruginosa (Pseudomonas arcuscaelestis The strain number is GLSm-Q7, and its registration number at the China General Microbiological Culture Collection Center is CGMCC No. 35753.

2. Using the *Pseudomonas aeruginosa* GLSm-Q7 as described in claim 1, a rhizosphere growth-promoting bacterial agent is prepared from it.

3. The rhizosphere growth-promoting bacterial agent according to claim 2, characterized in that, This bacterial agent is a suspension of the bacterial strain, and its OD... 600 It is around 1.

5.

4. The application of the rhizosphere growth-promoting bacterium *Pseudomonas aeruginosa* GLSm-Q7 as described in claim 2 in promoting sugar beet growth under salt stress.

5. According to claim 4, the rhizosphere growth-promoting bacterium *Pseudomonas aeruginosa* GLSm-Q7 promotes the growth and development of sugar beets under salt stress by increasing plant hormone levels and enhancing plant nutrient absorption.

6. According to claim 4, the rhizosphere growth-promoting bacterium *Pseudomonas aeruginosa* GLSm-Q7 promotes the growth of sugar beets under salt stress by regulating the content of soluble substances, wherein the soluble substances include proline and soluble sugars.

7. The application according to claim 4, wherein the rhizosphere growth-promoting bacterium *Pseudomonas aeruginosa* GLSm-Q7 promotes the growth of sugar beets under salt stress by enhancing the activity of antioxidant enzyme systems, wherein the antioxidant enzymes include superoxide dismutase, peroxidase, and catalase.

8. The application according to claim 4, characterized in that, The rhizosphere growth-promoting bacterium *Pseudomonas aeruginosa* GLSm-Q7 can promote the growth and development of sugar beets under stress of 200 mmol / L and 400 mmol / L NaCl concentrations.

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