CN112760264A

CN112760264A - Enterobacter cloacae strain and application thereof

Info

Publication number: CN112760264A
Application number: CN202110136246.1A
Authority: CN
Inventors: 丁兆军; 张春雷; 张蒙悦; 郭中信; 耿进华
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2021-02-01
Filing date: 2021-02-01
Publication date: 2021-05-07
Anticipated expiration: 2041-02-01
Also published as: CN112760264B

Abstract

The invention belongs to the technical field of microorganisms, and particularly relates to an enterobacter cloacae strain and application thereof. An enterobacter cloacae strain, which is preserved in the China general microbiological culture Collection center in 12 months and 23 days of 2020, with the preservation number being: CGMCC NO. 21529. The enterobacter cloacae strain provided by the invention can promote the synthesis of auxin by a plant root system and promote the development of a plant lateral root. The promotion of the development of the plant root system is specifically shown in the promotion of the generation and the elongation of the lateral root of the plant; the promotion of plant growth and development is embodied in the promotion of fresh weight and yield increase of plants. The enterobacter cloacae strain provided by the invention can also prepare auxin in a fermentation mode.

Description

Enterobacter cloacae strain and application thereof

Technical Field

The invention belongs to the technical field of microorganisms, and particularly relates to an enterobacter cloacae strain and application thereof.

Background

With the increase of the world population, the requirements of people on the yield and the quality of food and economic crops are higher and higher. The food problem is an important problem which is always present and needs to be solved. The land area of 960 ten thousand square kilometers in China is the third place in the world, and the land is large and has abundant resources. However, due to the mountains, deserts and grasslands in the country, the usable cultivated land area is about 140 ten thousand square kilometers, which occupies about 16% of the territorial area. Because the farmland in some areas of China has factors of desertification, returning to the farmland and urbanization, the farmland area is actually reduced year by year. In addition, the Chinese has about 14 hundred million population, the per capita cultivated land area is about 1.4 mu, and the rank is 126 in the world. China needs to use about 8% of the world cultivated land area to live 18% of the world population, how to utilize the limited cultivated land area, improve the quality and the yield of grain and economic crops, develop novel intelligent agriculture, realize the aim of green sustainable development, and also is an important problem facing the agriculture of China.

At present, the yield increasing mode of grain and economic crops is mainly to increase mineral elements such as nitrogen, phosphorus, potassium and the like in soil by applying chemical fertilizers and other methods. However, the application of a large amount of chemical fertilizers for a long time easily causes soil pollution, and for example, the application of a large amount of physiological acid fertilizers such as potassium chloride easily affects the physicochemical properties of the soil, changes the pH value of the soil, causes the soil to become acid, and increases the pH value of the soil⁺And Al³⁺The content is increased, thereby affecting the normal growth of plants; excessive application of chemical fertilizer also easily causes Cl^-、NO3^-And the accumulation of heavy metal ions in the soil affects the quality of crops, which does not meet the pursuit of people for green organic food; in addition, unreasonable application of chemical fertilizers can reduce organic matter content of farmland cultivated layers, destroy granular structures, reduce water and fertilizer storage capacity, affect effective utilization of the fertilizers, easily harden soil, reduce oxygen content, and further affect development of plant roots. Long-term application of chemical fertilizer not only causes soil ecosystemContamination and damage to the system affects crop quality and can also severely affect the water ecosystem. Research and investigation show that the fertilizer used by the plants only accounts for 30-40% of the applied amount, the rest is fixed in the soil, and a large part of the fertilizer enters the water body through leakage and leaching, so that eutrophication of the water body is caused, plankton such as algae and the like are propagated in a large quantity, the dissolved oxygen in the water body is reduced, the water quality is deteriorated, and fish and other organisms are killed in a large quantity. The phenomena of 'water bloom' and 'red tide' are closely related to the application of a large amount of chemical fertilizers besides industrial wastewater and domestic sewage. Therefore, the combination of agricultural development and environmental protection can improve the quality of crops while increasing the yield of the crops, and the development of green agriculture is an important concept of agricultural development in China.

A large number of microorganisms are enriched around the root system of the plant, namely rhizosphere microorganisms, and the rhizosphere microorganisms interact with the plant root system, thereby playing an important role in regulating and controlling the development of the plant root system and the growth of the plant. Beneficial rhizosphere microorganisms can enhance the disease resistance of plants, enhance the stress tolerance of the plants, promote the development of plant roots, enhance the absorption of the plants on nutrient elements and enhance the applicability of the plants to the external environment. Moreover, unlike chemical fertilizers and pesticides, rhizosphere microorganisms are widely present in nature and have less side effects on the ecological environment. Therefore, the research on the molecular mechanism of rhizosphere microorganisms for promoting the growth and development of plants and the development of environment-friendly microbial fertilizers have important significance for guiding agricultural production and developing green intelligent agriculture.

Disclosure of Invention

The invention aims to find rhizosphere microorganisms capable of promoting plant growth and develop an excellent microbial fertilizer.

In order to achieve the purpose, the invention provides the technical scheme that: an enterobacter cloacae strain, which is preserved in the China general microbiological culture Collection center in 12 months and 23 days of 2020, with the preservation number being: CGMCC number 21529.

As a preferred mode of the invention, the 16S rDNA sequence of the Enterobacter mucosae strain is shown in SEQ ID No. 1.

The invention also provides application of the Enterobacter cloacae strain, and the strain is used for preparing a microbial agent for promoting the development of plant root systems or a growth promoter for promoting the growth and development of plants.

The invention further provides a microbial agent for promoting the development of plant roots, and the microbial agent comprises the Enterobacter cloacae strain.

The present invention further provides a plant growth promoter comprising the Enterobacter cloacae strain.

The invention further provides a method for producing the auxin, which adopts the enterobacter cloacae strain to ferment and produce the auxin.

The enterobacter cloacae strain provided by the invention can promote the synthesis of auxin by a plant root system and promote the development of a plant lateral root. The promotion of the development of the plant root system is specifically shown in the promotion of the generation and the elongation of the lateral root of the plant; the promotion of plant growth and development is embodied in the promotion of fresh weight and yield increase of plants.

Drawings

FIG. 1 is a diagram showing the experimental results of the lateral root development phenotype of Arabidopsis seedlings inoculated with Enterobacter cloacae strain 49 provided in the examples of the present invention;

FIG. 2 is a graph showing the results of experiments in which Enterobacter cloacae strain 49 according to the present invention is capable of synthesizing auxin by relying on tryptophan to activate auxin signaling pathway in plants;

wherein, A: phenotype of the plant after inoculation of strain 49 on medium with and without tryptophan;

b: transgenic Arabidopsis thaliana treated simultaneously with tryptophan and strain 49DR5:GUSThe expression level of (a);

FIG. 3 is a graph showing the results of experiments in which Enterobacter cloacae strain 49 provided in the examples of the present invention synthesizes auxin and secretes to the outside of cells by two ways, i.e., tryptophan-dependent and tryptophan-independent;

FIG. 4 is a graph showing the results of an experiment in which Enterobacter cloacae strain 49 provided in an example of the present invention promotes the growth of Arabidopsis thaliana in sterile soil;

FIG. 5 is a schematic representation of an Enterobacter cloacae strain 49 that can be recruited by the plant root system provided in an example of the invention;

FIG. 6 is a graph of the experimental results of Enterobacter cloacae strain 49 of promoting increased peanut production in a field provided in an example of the invention; wherein, A: treating peanut seedlings by using fermentation liquor of the strain 49, and obtaining appearance conditions of fruits and seeds;

b: treating peanut seedlings by using fermentation liquor of the strain 49, and obtaining the number of fruits and seeds;

c: peanut seedlings were treated with the fermentation broth of strain 49, the weight of harvested fruit and seeds.

Detailed Description

In order to facilitate an understanding of the invention, the invention is described in more detail below with reference to the accompanying drawings and specific examples. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Example 1 origin and isolation, identification of strains

The inventor of the application separates and obtains the strain 49 from the rhizosphere soil microbial pool of the east-nutrition salt land, and identifies the strain 49 as enterobacter cloacae by observing the morphological characteristics of the strain 49 and combining the 16S rDNA sequence and homology analysis thereof (R) ((R))Enterobactercloacae) (ii) a Meanwhile, the functions of the plant growth promoter in promoting the development of plant root systems and promoting the growth and development of plants are researched.

(1) Morphological Observation of Strain 49

Streaking 49 on LB solid medium, culturing at 30 ℃ for 12-24 hours, observing colony morphology and staining the strain 49 in logarithmic growth phase by gram staining, and then observing morphological characteristics of the Enterobacter cloacae strain 49 by a light microscope.

The single bacterial colony of the bacterial strain 49 is observed to be round, the center of the bacterial colony is convex, white and yellowish, opaque, moist and neat in edge. In addition, microscopic observation revealed that the cells of strain 49 were short rod-shaped, gram-negative, and spore-free.

(2) 16S rDNA sequence homology analysis of Strain 49

Extracting the genome DNA of the strain 49 by using a bacterial genome DNA extraction kit, and performing 16S rDNA amplification by using the extracted genome DNA as a template and a bacterial 16S rDNA universal primer.

27F：5’- AGAGTTTGATCCTGGCTCAG-3’， SEQ ID No.2；

1492R：5’- GGTTACCTTGTTACGACTT-3’，SEQ ID No.3。

The high Fidelity DNA Polymerase used was Phanta Max Super-Fidelity DNA Polymerase from vayme. The PCR system was 50. mu.L: ddH₂O is 20 mu L; 25 μ L of 2X Phanta Max buffer; 1. mu.L of dNTP Mix (10 mM); 27F (10 mM) 1. mu.L; 1492R (10 mM) 1 μ L; phanta Max Super-Fidelity DNA Polymerase: 1. mu.L; 49 genomic DNA 1. mu.L. The PCR conditions were: pre-denaturation at 95 ℃ for 2 min, denaturation at 95 ℃ for 15 sec, annealing at 57 ℃ for 15 sec, extension at 72 ℃ for 1 min, denaturation to extension for 35 cycles, and complete extension at 72 ℃ for 5 min.

The target fragment obtained by PCR amplification was sent to the Protecidae sequencing company for sequencing analysis, and it was found that the double peak of C, T at position 407 of the obtained fragment was represented by Y, the double peak of A, G at position 429 of the obtained fragment was represented by R, the double peaks of A, T at positions 966 and 977 of the obtained fragment were represented by W, and the double peaks of G, C at positions 967 and 976 of the obtained fragment were represented by S, and it was assumed that there were multiple copies of 16S rDNA in the strain and the sequence was slightly different, and the specific sequence was shown in SEQ ID No. 1. The 16S rDNA gene sequence of the strain 49 of the present invention was compared with the 16S rDNA gene sequence of the relevant strain by referring to the International related GenBank at the National Center for Biotechnology Information (NCBI) and found to be identical to that of Enterobacter cloacaeEnterobactercloacaeWith 98% similarity. Identification of the inventive Strain 49 as Enterobacter cloacae by combining colony morphology with its 16S rDNA Gene sequence: (Enterobactercloacae) The 16S rDNA sequence is shown in SEQ ID No. 1.

The strain is preserved in China general microbiological culture Collection center (CGMCC) at 12 months and 23 days in 2020. The preservation number is CGMCC number 21529. The address of the depository: xilu No.1 Hospital No. 3, Beijing, Chaoyang, North.

Example 2 Experimental study of Enterobacter cloacae Strain 49 on promoting the development of Arabidopsis lateral roots

Arabidopsis seeds were sterilized, plated for 5 days, and transferred to a two-plate petri dish, inoculated with Enterobacter cloacae strain 49, and cultured vertically. Half of the Arabidopsis seedlings in the two-plate dish were control and half were treated with the inoculum strain 49, and the plant phenotype was observed after 5 days of culture. As a result, it was found that after treatment with strain 49, Arabidopsis seedlings exhibited a phenotype in which the main roots were slightly shortened but the lateral roots were significantly increased, as compared to the control, as shown in FIG. 1, indicating that strain 49 was able to promote the development of Arabidopsis lateral roots.

The method for sterilizing and plating arabidopsis seeds comprises the following steps: taking a certain amount of arabidopsis thaliana seeds in a 1.5 mL EP tube, adding a 1% sodium hypochlorite solution, reversing, uniformly mixing, resuspending for 15 minutes, discarding the sodium hypochlorite waste liquid, and resuspending and rinsing for 3 times by using sterile water. Uniformly scattering the seeds to 1/2MS solid (containing 1% of sucrose and 0.8% of agar powder) culture medium, treating at 4 ℃ for 24-48 hours, taking out the plate, vertically placing the plate, culturing to 22 ℃ long-day (16-hour light/8-hour dark) illumination incubator, and culturing for 3-8 days.

The specific culture and inoculation method of the strain 49 comprises the following steps: streaking the strain 49 on an LB solid culture medium, culturing for 12-24 hours at 30 ℃, selecting and blowing the thalli in sterile water for resuspension, fully resuspending the thalli in the sterile water, measuring the OD value of the bacteria liquid, and diluting the bacteria liquid by the sterile water until the OD value is 0.01-0.1. Transferring the Arabidopsis seedlings vertically cultured on 1/2 solid medium to a biplate containing 1/2MS solid medium (without sucrose), inoculating diluted bacteria solution to the root of the Arabidopsis seedlings in half of the biplate, and inoculating no bacteria in the other half as a control (control). Wherein, 1 mu L of the root of each arabidopsis thaliana is inoculated with bacteria, the total culture is carried out for 4 to 6 days, and the phenotype of the plant is observed.

Example 3 Experimental study of Strain 49 synthesizing auxin dependent on Tryptophan activation of auxin signalling pathway

Transgenic seedlings capable of reflecting auxin signal level and grown for 5 days at 1/2MS (containing 1% sucrose and 0.8% agar powder)DR5:GUSTransferring to a new 1/2MS biplate solid culture medium (containing 0.8% agar powder) containing and not containing 50 μ M tryptophan, inoculating the strain 49 to the plant root system, continuously culturing for 5 days (the specific plant culture and inoculation method is the same as that in example 2), observing the phenotype of the plant root system, and finding that the lateral root density of arabidopsis thaliana is obviously increased after inoculating the strain 49 compared with that of a control; in particular, after inoculation of strain 49 on a medium containing tryptophan, the plants exhibited a phenotype similar to that of high auxin treatment, i.e., the main roots were significantly shortened and the lateral root density was significantly increased, as shown in a in fig. 2. It was also found using GUS staining that transgenic Arabidopsis thaliana treated with tryptophan and strain 49 simultaneouslyDR5:GUSThe expression level of (a) was significantly increased, as shown by B in fig. 2, suggesting that its auxin signal was activated. Since tryptophan is a precursor for auxin synthesis, it is presumed that strain 49 is capable of synthesizing auxin using tryptophan and activating the auxin signaling pathway in plants.

Example 4, experimental study of the synthesis of auxin by both tryptophan-dependent and tryptophan-independent means and secretion outside of the cells by strain 49.

To further confirm that the strain 49 was able to synthesize auxin, the strain 49 was shake-cultured in 1/2MS liquid medium (containing 0.1% sucrose) containing no tryptophan and different concentrations of tryptophan, and transgenic Arabidopsis seedlings grown for 5 days were treated with the culture solution containing cells and the supernatant (containing no cells) after centrifugation of the culture solutionDR5:GUSAnd performing GUS staining, and observing that the treated product is treated by tryptophan with high concentrationDR5:GUSAll can induce in accordance with the treatment with high concentration of auxinDR5: GUSThe culture broth obtained by shaking culture broth containing no tryptophan and tryptophan at different concentration gradients, and the resulting culture broth and supernatant thereof were inducedDR5:GUSAs shown in fig. 3, it was revealed that the strain 49 can synthesize auxin by both tryptophan-dependent and tryptophan-independent means and secrete it into the fermentation broth.

The specific method for treating arabidopsis by fermenting the strain 49 to produce auxin is as follows: streaking a strain 49 on an LB solid culture medium, culturing at 30 ℃ for 12-24 hours, selecting a single colony to 500 mu L of LB liquid culture medium, shaking for 8-16 hours, inoculating 10-100 mu L of shaken bacterial liquid to 5-10 mL of 1/2MS liquid culture medium (containing 0.1% of sucrose) containing tryptophan (0, 0.01, 0.1, 1, 10 mM) with different concentrations for shaking for 6-10 hours to a stable growth period to obtain bacterial liquid of the strain 49, centrifuging a part of the bacterial liquid for 10 minutes by 7000g, taking supernatant 0.5-1.5 mL to 2 mL of sterile EP tube, boiling for 10 minutes to inactivate residual bacteria to obtain a fermentation liquid of the strain 49, cooling the fermentation liquid, and growing a transgenic arabidopsis thaliana seedling on a sterile 1/2MS plate for 5-8 daysDR5:GUSTransferring to a bacterial liquid of a strain 49 and fermentation supernatant liquid, and treating for 12-18 hours, and then carrying out GUS staining on arabidopsis seedlings.

Example 5 experimental study of the recruitment of strain 49 by the plant root system and the promotion of plant growth.

Strain 49 was isolated from the plant rhizosphere and to further confirm that plants could recruit strain 49, the inventors of the present application designed a methodology to verify whether a bacterium could be specifically recruited by a plant. The specific method comprises the following steps:

(1) scribing 49 on a solid LB culture medium, placing in an incubator at 30 ℃, and culturing overnight until colonies grow out;

(2) resuspending, scraping the bacterial colony into sterile water, lightly blowing, resuspending, and adjusting the OD value to 1 to prepare bacterial weight suspension;

(3) and (3) seedling transplanting and inoculating, namely transferring the arabidopsis thaliana seedlings growing for 5 days on a sterile culture medium into a culture bottle containing sterile nutrient soil (121 ℃, and sterilizing for 15 minutes), inoculating 1mL of bacterial weight suspension, placing in a long-day culture room (22 ℃, 16h of light/8 h of dark) for culturing for 20-30 days, and observing the plant phenotype.

As a result, it was found that Arabidopsis thaliana grown after inoculating the strain 49 in the sterile culture flask was significantly better than the control, and the strain 49 was able to promote the growth and fresh weight increase of Arabidopsis thaliana in the sterile culture flask, as shown in FIG. 4. As a result of statistical examination of the bacterial load in the rhizosphere soil and non-rhizosphere soil in the culture flask after inoculation of the strain 49, it was found that the content of the strain 49 in the rhizosphere soil was about 10 times higher than that in the surrounding non-rhizosphere soil, as shown in fig. 5, indicating that the strain 49 could be recruited by the plant root system.

The statistical method of the bacterial content in the rhizosphere soil and the non-rhizosphere soil is as follows: 1, weighing soil, weighing 1g of non-rhizosphere soil (soil) in a culture bottle on an aseptic operation platform, pulling out the aseptic arabidopsis seedlings with roots slightly, shaking off redundant soil on the roots, collecting the root systems of the whole seedlings and attached soil into an aseptic tube, and weighing 1g of the soil, namely rhizosphere soil (Rhizophere). Dissolving and diluting, respectively adding 10 mL of sterile water into tubes of non-rhizosphere soil and rhizosphere soil, shaking and uniformly mixing, adding 1mL of sterile water into 9 mL of sterile water, shaking, uniformly mixing and diluting by 10 times, adding 1mL of diluent into 9 mL of sterile water, shaking, uniformly mixing and diluting by 100 times, and repeating the steps until the diluent is diluted to 10 times⁵-10⁷And taking 1mL of diluent again to smear on an LB solid medium, and culturing overnight at 30 ℃ until visible monoclonals grow out. The number of colonies n on the monoclonal plate was counted, multiplied by 10^（M+1）Wherein M is an index of dilution times, namely the total number N of bacteria in soil, and N = N10^（M+1）And dividing by the weight of the soil (W = 1 g) to obtain the content of bacteria C in each gram of soil, wherein C = N/W.

Example 6: experimental study on promotion of peanut yield by strain 49

In order to further determine whether the strain 49 can promote the increase of the plant yield and can be applied to agricultural production, the inventor of the present application utilized the fermentation broth of the strain 49 to treat peanut seedlings in a field and observed the conditions of harvested fruits and seeds of each peanut, as shown in a in fig. 6, and counted the number and weight of the fruits and seeds, as shown in B and C in fig. 6, respectively. As a result, the strain 49 can obviously improve the yield of peanuts.

The specific method for treating peanuts by inoculating the strain 49 comprises the following steps:

(1) streaking and shaking the strains, streaking the strains 49 to LB solid culture medium, culturing overnight at 30 ℃ until a single clone grows out, selecting the single clone to LB liquid culture medium (without NaCl), and shaking at 30 ℃ for 8-12 hours until the OD value is 1.5-2.0;

(2) the roots of peanut seedlings are directly irrigated with 10 mL of bacterial liquid for 3 weeks, each peanut seedling is irrigated once every two weeks, and the irrigation is conducted for 3 times.

Sequence listing

<110> Shandong university

<120> Enterobacter cloacae strain and use thereof

<141> 2021-01-29

<160> 3

<170> SIPOSequenceListing 1.0

<210> 1

<211> 1432

<212> DNA

<213> Enterobacter cloacae

<400> 1

gcgaaggcag ctaacatgca gtcgacggta gcacagagag cttgctctcg ggtgacgagt 60

ggcggacggg tgagtaatgt ctgggaaact gcctgatgga gggggataac tactggaaac 120

ggtagctaat accgcataac gtcgcaagac caaagagggg gaccttcggg cctcttgcca 180

tcagatgtgc ccagatggga ttagctagta ggtggggtaa cggctcacct aggcgacgat 240

ccctagctgg tctgagagga tgaccagcca cactggaact gagacacggt ccagactcct 300

acgggaggca gcagtgggga atattgcaca atgggcgcaa gcctgatgca gccatgccgc 360

gtgtatgaag aaggccttcg ggttgtaaag tactttcagc ggggaggaag gtgttgyggt 420

taataaccrc agcaattgac gttacccgca gaagaagcac cggctaactc cgtgccagca 480

gccgcggtaa tacggagggt gcaagcgtta atcggaatta ctgggcgtaa agcgcacgca 540

ggcggtctgt caagtcggat gtgaaatccc cgggctcaac ctgggaactg cattcgaaac 600

tggcaggcta gagtcttgta gaggggggta gaattccagg tgtagcggtg aaatgcgtag 660

agatctggag gaataccggt ggcgaaggcg gccccctgga caaagactga cgctcaggtg 720

cgaaagcgtg gggagcaaac aggattagat accctggtag tccacgccgt aaacgatgtc 780

gacttggagg ttgtgccctt gaggcgtggc ttccggagct aacgcgttaa gtcgaccgcc 840

tggggagtac ggccgcaagg ttaaaactca aatgaattga cgggggcccg cacaagcggt 900

ggagcatgtg gtttaattcg atgcaacgcg aagaacctta cctactcttg acatccagag 960

aacttwscag agatgswttg gtgccttcgg gaactctgag acaggtgctg catggctgtc 1020

gtcagctcgt gttgtgaaat gttgggttaa gtcccgcaac gagcgcaacc cttatccttt 1080

gttgccagcg gtccggccgg gaactcaaag gagactgcca gtgataaact ggaggaaggt 1140

ggggatgacg tcaagtcatc atggccctta cgagtagggc tacacacgtg ctacaatggc 1200

gcatacaaag agaagcgaac tcgcgagagc aagcggacct cataaagtgc gtcgtagtcc 1260

ggattggagt ctgcaactcg actccatgaa gtcggaatcg ctagtaatcg tagatcagaa 1320

tgctacggtg aatacgttcc cgggccttgt acacaccgcc cgtcacacca tgggagtggg 1380

ttgcaaaaga agtaggtagc taacctcgga gggcgctacc cagcttgaag cc 1432

<210> 2

<211> 20

<212> DNA

<213> Artificial Sequence

<400> 2

agagtttgat cctggctcag 20

<210> 3

<211> 19

<212> DNA

<213> Artificial Sequence

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ggttaccttg ttacgactt 19

Claims

1. An Enterobacter cloacae strain, characterized by: the strain is preserved in China general microbiological culture Collection center (CGMCC) at 12 months and 23 days in 2020, and the preservation number is as follows: CGMCC NO. 21529.

2. The Enterobacter cloacae strain of claim 1, wherein: the 16S rDNA sequence of the strain is shown in SEQ ID No. 1.

3. Use of an enterobacter cloacae strain according to claim 1 or 2, characterized in that: the strain is used for preparing a microbial agent for promoting the development of plant root systems or a growth promoter for promoting the growth and development of plants.

4. A microbial agent for promoting the development of plant roots is characterized in that: the microbial inoculum comprises an enterobacter cloacae strain according to claim 1 or 2.

5. A plant growth promoter characterized by: the plant growth promoter comprises the Enterobacter cloacae strain of claim 1 or 2.

6. A method for producing a plant auxin, which is characterized by comprising the following steps: the use of an Enterobacter cloacae strain according to claim 1 or 2 for the fermentative production of auxin.