Recombinant lactobacillus plantarum for secretory expression of chicken IGF-1 as well as construction method and application of recombinant lactobacillus plantarum

Abstract

The invention belongs to the fields of bioengineering and animal nutrition, and relates to recombinant lactobacillus plantarum for secretory expression of chicken IGF-1 (Insulin-like Growth Factor-1) as well as a construction method and application thereof. The recombinant lactobacillus plantarum takes lactobacillus plantarum as a host, the host contains a recombinant expression vector, and the recombinant expression vector contains an SlpA promoter, a lactobacillus plantarum extracellular protein Lp2007 signal peptide gene and a chicken IGF-1 gene; the sequence of the chicken IGF-1 gene is as shown in SEQ ID NO: 1, the sequence of the SlpA promoter is as shown in SEQ ID NO: 2, and the sequence of the lactobacillus plantarum extracellular protein Lp2007 signal peptide is as shown in SEQ ID NO: 3. The recombinant lactobacillus plantarum can secrete IGF-1 outside cells of the recombinant lactobacillus plantarum. When the recombinant lactobacillus plantarum for secreting and expressing the chicken IGF-1 is used for feeding chickens, the growth speed of the chickens can be remarkably increased, cost reduction and efficiency improvement of the poultry raising industry are realized, and the recombinant lactobacillus plantarum has important economic and social values.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of bioengineering and animal nutrition, and relates to a recombinant Lactobacillus plantarum capable of secreting chicken insulin-like growth factor 1 (IGF-1), a construction method thereof, and application thereof in promoting the growth of chickens. BACKGROUND

[0002] Chicken insulin-like growth factor 1 (IGF-1) is a polypeptide hormone belonging to the insulin family, mainly synthesized in the liver and plays an important biological role in the body. The molecular structure of IGF-1 is similar to that of insulin, consisting of 70 amino acid residues, with two polypeptide chains and multiple disulfide bonds, forming a stable three-dimensional structure. Chicken IGF-1 is mainly synthesized by the liver and is regulated by growth hormone (GH). Growth hormone stimulates hepatocytes to synthesize IGF-1, which enters the blood circulation and affects the whole body tissue. IGF-1 has multiple biological functions such as promoting animal growth and development, regulating metabolism, promoting cell proliferation and differentiation, and anti-apoptosis. IGF-1 plays a key role in the growth and development of chickens, promoting the growth of bone, muscle and fat metabolism. IGF-1 can improve the uptake of glucose by cells, promote protein synthesis and fat decomposition, thereby improving the metabolic state. IGF-1 promotes the proliferation and differentiation of muscle satellite cells, and has a significant impact on muscle growth and regeneration. IGF-1 can inhibit cell apoptosis and enhance cell survival, thereby supporting the healthy development of tissues. Optimizing the expression and activity of IGF-1 through genetic engineering, nutritional regulation or other technical means is expected to achieve more efficient breeding and meat quality improvement.

[0003] Recombinant IGF-1 expression is currently mainly achieved through gene cloning and recombination technologies, expressing chicken IGF-1 in *Escherichia coli*, yeast, *Lactococcus lactis*, eukaryotic cells, and transgenic plants. These studies provide a foundation for subsequent functional research and applications. Functional studies of IGF-1 primarily utilize viral vectors and transfection techniques to introduce the IGF-1 gene into chicken embryos or muscle cells, observing its role in muscle growth and development. Gene editing technologies such as CRISPR / Cas9 are also used to construct transgenic chicken models with IGF-1 overexpression or deletion to study its specific functions in growth, development, and metabolic regulation.Current research indicates that overexpression of the IGF-1 gene can significantly improve the growth performance and meat quality of chickens, enhance disease resistance, and has a certain regulatory effect on metabolic diseases [Wang, Y., et al. (2019). "Expression and Functional Analysis of Chicken IGF-1 in Transgenic Models." Transgenic Research, 28(3), 399-410; Zhao, R., et al. (2020). "Development of a Recombinant Chicken IGF-1 for Growth Promotion in Poultry." Poultry Science, 99(12), 6435-6444; Li, H., et al. (2021). "Gene Editing of IGF-1 in Chickens: Implications for Growth and Metabolism." Animal Biotechnology, 32(1), 55-64; Chen, Y., et al. (2022). "Advances in the Expression of Insulin-like Growth Factor 1 in Chicken Models." BMCGenomics, 23(1), 112; Sun, J., et al. (2023). "CRISPR / Cas9-Mediated Knockout of IGF-1 in Chickens and Its Impact on Growth Performance." Journal of Animal Science and Biotechnology, 14, 78; Liu S, Li Y, Deng B, XuZ. (2016)Recombinant Lactococcus lactis expressing porcine insulin-likegrowth factor I ameliorates DSS-induced colitis in mice. BMCBiotechnology.16:25.].Currently, IGF-1 expressed in *E. coli* typically exists as insoluble inclusion bodies, leading to cumbersome purification steps, high production costs, and the risk of *E. coli* endotoxin contamination. Current yeast and *Lactococcus lactis* expression systems require the addition of expensive inducers during the engineered bacterial culture process; some inducers are toxic to animals, and subsequent purification of the expressed IGF-1 is also necessary. Eukaryotic cell expression systems require expensive cell culture systems and subsequent isolation and purification. Developing a highly efficient IGF-1 expression system suitable for veterinary clinical use that does not require the addition of inducers is a practical need in the poultry industry.

[0004] Currently, the main methods for delivering chicken IGF-1 in clinical use include oral delivery, injection delivery, and delivery via genetically engineered vectors. However, each method has certain drawbacks. For example, oral delivery involves adding IGF-1 or its analogues to feed to improve growth performance and meat quality. During this process, IGF-1 molecules are interfered with and damaged by other components in the feed, and are also destroyed by gastric acid and some proteases as they pass through the stomach. Although some researchers have used microencapsulation or nanoparticle technology to delay IGF-1 release and improve its bioavailability and stability, this undoubtedly increases the cost of the product. Injection delivery involves direct intramuscular or subcutaneous injection of IGF-1, which can rapidly increase the concentration in the body and promote growth. However, with the large-scale development of poultry farming, intramuscular injection is impractical for delivering IGF-1.The use of genetic engineering technology to develop gene vectors to express IGF-1 for gene therapy or gene enhancement is currently limited to the treatment of human diseases, and has not yet been reported in the field of animal husbandry. [Parker, S., et al. (2018). "Oral Delivery of Insulin-like Growth Factor 1 Improves Growth Performance in Broilers." Poultry Science, 97(10), 3565-3572; Zhang, J., et al. (2020). "Effects of Different Delivery Methods of IGF-1 on Growth Performance in Chickens." Journal of Animal Science, 98(2), 1-8; Shen, W., et al. (2021). "Sustained Release of IGF-1 from Nanoparticles Enhances Muscle Growth in Poultry." Journal of Controlled Release, 330, 194-203; Li, X., et al. (2022). "Gene Delivery of IGF-1 in Chickens: A New Approach toEnhance Growth Performance." AnimalBiotechnology, 33(1), 1-10; Wang, Y., et al. (2023). "Comparative Study ofDifferent IGF-1 Delivery Systems onMuscle Development in Broilers." Frontiersin Veterinary Science, 10, 123456.]. Summary of the Invention

[0005] The purpose of this invention is to construct a recombinant *Lactobacillus plantarum* strain capable of efficiently expressing chicken IGF-1 without the need for an inducer, and to evaluate its application as an oral probiotic in promoting poultry growth. Addressing the shortcomings of traditional IGF-1 expression and delivery methods, this invention utilizes the recombinant *Lactobacillus plantarum* WCFS1, which colonizes well in the animal gut, as a vector. The codon-optimized chicken IGF-1 gene (SEQ ID NO. 1) is cloned into a vector containing the constitutive promoter SlpA (SEQ ID NO. 2) and the *Lactobacillus plantarum* autosecretory protein Lp0277 signal peptide (SEQ ID NO. 3), enabling the secretory expression of chicken IGF-1 in the gut without the need for an inducer. The prepared recombinant *Lactobacillus plantarum* can be administered orally as a probiotic, reducing costs and improving bioavailability, thus possessing significant economic and social value.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a recombinant *Lactobacillus plantarum* strain that secretes and expresses chicken IGF-1, wherein the recombinant *Lactobacillus plantarum* is a strain of *Lactobacillus plantarum* (… Lactobacillus plantarum The recombinant *Lactobacillus plantarum* is a host containing a recombinant expression vector. This vector contains the SlpA promoter, the *Lactobacillus plantarum* extracellular protein Lp2007 signal peptide gene, and the chicken IGF-1 gene. The sequence of the chicken IGF-1 gene is shown in SEQ ID NO:1, the sequence of the SlpA promoter is shown in SEQ ID NO:2, and the sequence of the *Lactobacillus plantarum* extracellular protein Lp2007 signal peptide is shown in SEQ ID NO:3. This recombinant *Lactobacillus plantarum* is capable of secreting IGF-1 extracellularly.

[0007] The extracellular protein Lp2007 signal peptide gene is located downstream of the SlpA promoter, and the chicken IGF-1 gene is located downstream of the extracellular protein Lp2007 signal peptide gene.

[0008] Furthermore, the recombinant Lactobacillus plantarum uses Lactobacillus plantarum WCFS1 as the host.

[0009] Secondly, the present invention provides a method for constructing the recombinant Lactobacillus plantarum, comprising: Step 1: The SlpA promoter, the Lp2007 signal peptide gene of Lactobacillus plantarum extracellular protein, and the chicken IGF-1 gene were cloned into an expression vector to obtain a recombinant expression vector; further, the expression vector is a Lactobacillus expression vector.

[0010] Step 2: Transform the recombinant expression vector into Lactobacillus plantarum to obtain the final product.

[0011] Thirdly, the present invention provides the application of the recombinant Lactobacillus plantarum or its culture in the preparation of oral microecological preparations for poultry.

[0012] Fourthly, the present invention provides an oral microecological preparation for poultry, which contains the recombinant Lactobacillus plantarum or its culture.

[0013] Fifthly, the present invention provides the application of the recombinant *Lactobacillus plantarum*, its culture, and / or the oral probiotic preparation for poultry in promoting poultry growth. In use, the recombinant *Lactobacillus plantarum*, its culture, and / or the oral probiotic preparation for poultry are added to the drinking water of poultry, wherein the number of recombinant *Lactobacillus plantarum* in the drinking water is not less than 10. 7 bacteria / ml

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention is the first to combine the promoter of Lactobacillus acidophilus S-layer protein SlpA and the Lp2007 signal peptide gene of Lactobacillus plantarum to successfully construct an expression vector that can achieve secretory expression of exogenous proteins in Lactobacillus plantarum without the addition of any inducing agent.

[0015] 2. In this invention, the chicken IGF-1 gene was codon optimized and inserted downstream of the SlpA promoter and the extracellular protein Lp2007 signal peptide in the expression vector to construct a recombinant expression vector. This vector was then transformed into Lactobacillus plantarum to prepare a recombinant Lactobacillus plantarum strain that secretes and expresses chicken IGF-1.

[0016] 3. The combination of the SlpA promoter and the Lp2007 signal peptide of Lactobacillus plantarum used in this invention has significant advantages in guiding the secretory expression level of chicken IGF-1 compared with the commonly reported combination sequences of P32 constitutive promoter (SEQ ID NO:4) and usp45 signal peptide (SEQ ID NO:5), and P32 constitutive promoter (SEQ ID NO:4) and Lp3050 signal peptide of Lactobacillus plantarum (SEQ ID NO:6).

[0017] 4. The recombinant Lactobacillus plantarum strain that secretes and expresses chicken IGF-1 can be added to the drinking water of chickens as a microecological preparation. This method of use is simple and does not cause any adverse stress reactions in the animals. Feeding chickens with the recombinant Lactobacillus plantarum strain that secretes and expresses chicken IGF-1 of this invention can significantly promote chicken growth, achieving cost reduction and efficiency improvement in poultry farming, and has significant economic and social value. Attached Figure Description

[0018] Figure 1: Schematic diagram of the construction process of recombinant Lactobacillus plantarum expression vector pSlpA-Lp2007-IGF-1.

[0019] Figure 2 Western blot detection of chicken IGF-1 expressed in recombinant Lactobacillus plantarum. Note: Lane 1 is cell lysate of recombinant Lactobacillus plantarum WCFS1 / SlpA-Lp2007-IGF-1; Lane 2 is control Lactobacillus plantarum WCFS1 without expression vector; Lane 3 is culture supernatant of recombinant Lactobacillus plantarum WCFS1 / SlpA-Lp2007-IGF-1.

[0020] Figure 3 Comparison of differences in chicken IGF-1 secretion expression levels guided by different promoter and signal peptide combinations. Note: Lane 1 is the culture supernatant of recombinant Lactobacillus plantarum WCFS1 / SlpA-Lp2007-IGF-1; Lane 2 is the culture supernatant of recombinant Lactobacillus plantarum WCFS1 / P32-usp45-IGF-1; Lane 3 is the culture supernatant of WCFS1 / P32-Lp3050-IGF-1; Lane 4 is the control of the culture supernatant of Lactobacillus plantarum WCFS1 without the expression vector.

[0021] Figure 4 Results: Recombinant Lactobacillus plantarum WCFS1 / SlpA-Lp2007-IGF-1 promotes weight gain in chickens. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the embodiments of this invention will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0023] Example 1 1. Construction of the recombinant expression vector pSlpA-Lp2007-IGF-1 like Figure 1 As shown, the construction of the recombinant expression vector pSlpA-Lp2007-IGF-1 includes: (1) Construction of secretory expression vector for Lactobacillus plantarum A synthetic fragment containing the promoter sequence of Lactobacillus acidophilus S-layer protein SlpA (hereinafter referred to as SlpA promoter, shown in SEQ ID NO:2) and the extracellular protein Lp2007 signal peptide sequence of Lactobacillus plantarum WCFS1 (commercially available product) (shown in SEQ ID NO:3), wherein the 5' and 3' of the fragment contain, respectivelyBsa I and Sal I restriction endonuclease site; then utilize Bsa I+ Sal The fragment synthesized by double enzyme digestion and the Lactobacillus expression vector pZJ were obtained. A diagram of the pZJ vector is shown below. Figure 1 The pZJ vector is a vector that stores the gene sequence of the signal peptide (as shown in SEQ IN NO:7) and anchoring region (as shown in SEQ IN NO:8) of the lipoprotein Lp1261 of Lactobacillus plantarum using [a specific method / technology]. Nde I and Sal I restriction endonuclease sites were cloned into the commercial lactic acid bacteria expression vector pSIP403. The digested fragments and pZJ vector were purified and ligated, and the ligation product was then transformed into E. coli DH5α competent cells. Positive clones were screened on LB agar plates containing 200 μg / ml erythromycin to obtain the recombinant expression vector pSlpA-Lp2007.

[0024] (2) Construction of expression vector containing chicken IGF-1 gene The chicken IGF-1 gene (SEQ ID NO:1) was artificially synthesized according to the preferred codons of *Lactobacillus plantarum*. The synthesized IGF-1 gene fragment contains at its 5' and 3' ends, respectively. Sal I and Hind III restriction endonuclease sites. Utilizing Sal I+ Hind III. The synthesized IGF-1 fragment and recombinant expression vector pSlpA-Lp2007 were digested with enzymes separately. The digested IGF-1 fragment and pSlpA-Lp2007 vector were purified and ligated. The ligation product was transformed into E. coli DH5α competent cells. Positive clones were screened on LB agar plates containing 200 μg / ml erythromycin to obtain the recombinant expression vector pSlpA-Lp2007-IGF-1.

[0025] 2. Construction of recombinant plant lactic acid bacteria expressing chicken IGF-1 The recombinant expression vector pSlpA-Lp2007-IGF-1 was electroporated into competent cells of Lactobacillus plantarum WCFS1. Positive clones were selected on MRS selection agar plates containing 5 μg / ml erythromycin to obtain recombinant Lactobacillus plantarum WCFS1 / SlpA-Lp2007-IGF-1 containing the chicken IGF-1 gene.

[0026] 3. Secretory expression of chicken IGF-1 Single clones of recombinant *Lactobacillus plantarum* WCFS1 / SlpA-Lp2007-IGF-1 were picked from MRS screening agar plates and inoculated into 10 mL of MRS liquid medium containing 5 μg / mL erythromycin. The culture was then incubated at 37°C for 12 hours. The culture was then diluted to 50 mL of fresh MRS medium preheated to 37°C and containing 5 μg / mL erythromycin. The dilution ratio was adjusted based on the bacterial density reaching the OD500 level. 600 The optimal value is 0.1. Then, incubate statically at 37°C until the OD... 600 The culture was harvested when the glutathione concentration reached 0.9. The culture was centrifuged at 4000g for 10 minutes at 4 ℃, and the supernatant and cell pellet were collected separately. The cell pellet was washed three times with PBS, then sonicated and lysed. The lysate was centrifuged at 10000g for 5 minutes, and the cell lysate supernatant was collected. The culture supernatant and cell lysate supernatant were electrophoresed on a 15% SDS-PAGE gel. The proteins in the gel were then electroblotted onto a nitrocellulose membrane. Western blot analysis was performed using an anti-chicken IGF-1 antibody as the primary antibody and horseradish peroxidase (HRP)-labeled rabbit anti-chicken IgG as the secondary antibody to detect the expression and expression pattern of chicken IGF-I.

[0027] like Figure 2 As shown, protein bands with the same size as the theoretical molecular weight (20 kDa) of IGF-1 were detected in both the cell lysate (lane 1) and the culture supernatant (lane 3) of recombinant Lactobacillus plantarum WCFS1 / SlpA-Lp2007-IGF-1, indicating that IGF-1 was successfully expressed and secreted in large quantities into the culture supernatant.

[0028] 4. Optimization of promoters and signal peptides To compare the SlpA promoter and Lp2007 signal peptide combination in this invention with existing promoter and signal peptide combinations in guiding chicken IGF-1 secretion expression, this invention synthesized 5' and 3' promoters containing... Bsa I and Sal The commonly used constitutive promoter P32 (SEQ ID NO:4) and usp45 signal peptide (SEQ ID NO:5) combination sequences of restriction endonuclease sites, and the combination sequences of constitutive promoter P32 (SEQ ID NO:4) and Lactobacillus plantarum Lp3050 signal peptide (SEQ ID NO:6) combination sequences, were then used... Bsa I+ SalI. The synthesized fragments and the Lactobacillus expression vector pZJ were digested with enzymes twice. The digested fragments and pZJ vector were purified and ligated. The ligation products were transformed into E. coli DH5α competent cells. Positive clones were screened on LB agar plates containing 200 μg / ml erythromycin to obtain the recombinant expression vectors pP32-usp45 and pP32-Lp3050, respectively.

[0029] The artificially synthesized 5' and 3' ends respectively contain Sal I and Hind Chicken IGF-1 gene (SEQ ID NO:1) with restriction endonuclease site III, using Sal I+ Hind III were cloned into expression vectors pP32-usp45 and pP32-Lp3050, respectively, to obtain recombinant expression vectors pP32-usp45-IGF-1 and pP32-Lp3050-IGF-1. These recombinant expression vectors were then electroporated into competent cells of *Lactobacillus plantarum* WCFS1. Positive clones were selected on MRS selection agar plates containing 5 μg / ml erythromycin to obtain recombinant *Lactobacillus plantarum* WCFS1 / P32-usp45-IGF-1 and WCFS1 / P32-Lp3050-IGF-1 containing the chicken IGF-1 gene.

[0030] Single clones of recombinant *Lactobacillus plantarum* WCFS1 / SlpA-Lp2007-IGF-1, WCFS1 / P32-usp45-IGF-1, and WCFS1 / P32-Lp3050-IGF-1 were picked from MRS screening agar plates and inoculated into 10 mL of MRS liquid medium containing 5 μg / mL erythromycin. The cultures were then incubated statically at 37°C for 12 hours. The cultures were then diluted into 50 mL of fresh MRS medium preheated to 37°C and containing 5 μg / mL erythromycin. The dilution ratio was adjusted to achieve an OD500 of 5 μg / mL. 600 The optimal value is 0.1. Then, incubate statically at 37°C until the OD... 600The culture was harvested when the concentration reached 0.9. The culture was centrifuged at 4000g for 10 minutes at 4 ℃, and the supernatant and cell pellet were collected separately. The cell pellet was washed three times with PBS, then sonicated and lysed. The lysate was centrifuged at 10000g for 5 minutes, and the cell lysate supernatant was collected. The culture supernatant and cell lysate supernatant were electrophoresed on a 15% SDS-PAGE gel. The proteins in the gel were then electroblotted onto a nitrocellulose membrane. Western blot analysis was performed using an anti-chicken IGF-1 antibody as the primary antibody and horseradish peroxidase (HRP)-labeled rabbit anti-chicken IgG as the secondary antibody to detect the differences in chicken IGF-I expression levels guided by different promoter and signal peptide combinations.

[0031] like Figure 3 As shown, the expression level of IGF- guided to the culture supernatant by the SlpA promoter and Lp2007 signal peptide combination used in this invention is significantly higher than the previously reported expression efficiency of the P32 promoter and usp45 signal peptide combination, and the P32 promoter and Lp3050 signal peptide combination.

[0032] 5. Application experiment of recombinant Lactobacillus plantarum in promoting growth 120 healthy one-day-old White Laihang chicks were selected as experimental subjects and divided into three groups of 40 chicks each. Group 1 was the blank control group, fed with regular feed; Group 2 was the blank Lactobacillus plantarum control group, fed with regular feed but with a culture of blank Lactobacillus plantarum without the expression vector added to the drinking water, increasing the Lactobacillus plantarum content in the drinking water to 10. 7 Group 3 was the recombinant Lactobacillus plantarum WCFS1 / SlpA-Lp2007-IGF-1 experimental group. In addition to their regular feed, a culture of recombinant Lactobacillus plantarum WCFS1 / SlpA-Lp2007-IGF-1 was added to their drinking water, increasing the Lactobacillus plantarum content in the drinking water to 10⁶ bacteria / mL. 7 100 bacteria / mL, fed once a week for 4 weeks. Clinical health status and weight were monitored weekly during the feeding period. Preparation methods for blank *Lactobacillus plantarum* culture without expression vector and recombinant *Lactobacillus plantarum* culture: Recombinant *Lactobacillus plantarum* WCFS1 / SlpA-Lp2007-IGF-1 was inoculated into MRS liquid medium containing 5 μg / mL erythromycin; blank *Lactobacillus plantarum* WCFS1 without expression vector was inoculated into MRS liquid medium without antibiotics. The cultures were incubated statically at 37°C for 12 hours.

[0033] like Figure 4As shown, compared with the control group, chickens fed with recombinant Lactobacillus plantarum showed a significant increase in average body weight at week 4. At the end of week 6, the average body weight of chickens in the recombinant Lactobacillus plantarum experimental group was 371.68 grams and 253.03 grams more than the blank control and blank Lactobacillus plantarum group, respectively. These results demonstrate that feeding chickens with the recombinant Lactobacillus plantarum WCFS1 / SlpA-Lp2007-IGF-1 that secretes and expresses chicken IGF-1 according to the present invention can significantly promote chicken growth.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A recombinant Lactobacillus plantarum that secretes chicken IGF-1, characterized in that, The recombinant *Lactobacillus plantarum* uses *Lactobacillus plantarum* as a host, and the host contains a recombinant expression vector. The recombinant expression vector contains the SlpA promoter, the *Lactobacillus plantarum* extracellular protein Lp2007 signal peptide gene, and the chicken IGF-1 gene. The sequence of the chicken IGF-1 gene is shown in SEQ ID NO:1, the sequence of the SlpA promoter is shown in SEQ ID NO:2, and the sequence of the *Lactobacillus plantarum* extracellular protein Lp2007 signal peptide is shown in SEQ ID NO:

3.

2. The recombinant Lactobacillus plantarum expressing chicken IGF-1 according to claim 1, characterized in that, The extracellular protein Lp2007 signal peptide gene is located downstream of the SlpA promoter, and the chicken IGF-1 gene is located downstream of the extracellular protein Lp2007 signal peptide gene.

3. The recombinant Lactobacillus plantarum expressing chicken IGF-1 according to claim 1, characterized in that, The recombinant Lactobacillus plantarum uses Lactobacillus plantarum WCFS1 as the host.

4. The method for constructing recombinant Lactobacillus plantarum according to any one of claims 1-3, characterized in that, include: Step 1: The SlpA promoter, the Lp2007 signal peptide gene of Lactobacillus plantarum extracellular protein, and the chicken IGF-1 gene were cloned into the expression vector to obtain the recombinant expression vector; Step 2: Transform the recombinant expression vector into Lactobacillus plantarum to obtain the final product.

5. The construction method according to claim 4, characterized in that, The expression vector mentioned in step 1 is a lactobacillus expression vector.

6. The use of the recombinant Lactobacillus plantarum or its culture as described in any one of claims 1-3 in the preparation of oral probiotics for poultry.

7. An oral probiotic preparation for poultry, characterized in that, The oral probiotic preparation for poultry contains the recombinant Lactobacillus plantarum or its culture as described in any one of claims 1-3.

8. The use of the recombinant Lactobacillus plantarum, its culture, and / or the poultry oral probiotic preparation of claim 7 in promoting poultry growth.

9. The application according to claim 8, characterized in that, When using, the recombinant Lactobacillus plantarum, its culture, and / or the poultry oral probiotic preparation are added to the drinking water of poultry, and the number of recombinant Lactobacillus plantarum in the drinking water is not less than 10. 7 bacteria / ml

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