A strain of Streptomyces XL-34, its microecological preparation and preparation method thereof

Abstract

A strain of Streptomyces XL-34, a microecological preparation thereof and a preparation method thereof, wherein the Streptomyces is deposited in the China Center for Type Culture Collection, the strain deposit number is CCTCC NO: M 20231087, the classification name is: novel Streptomyces XL-34, the Latin name is: Streptomyces sp. XL‑34. The microecological preparation is made by fermentation of Streptomyces XL‑34. The present invention also includes a method for preparing the microecological preparation. The microecological preparation suitable for aquaculture prepared by the strain through a corresponding method acts on freshwater fish in the form of a feed additive, has a broad spectrum of activity in inhibiting fish pathogens, and its protection rate reaches 41.67%, among which the effect on freshwater fish against infection by Aeromonas veronii is particularly significant. At the same time, it can also stably colonize in freshwater fish and effectively improve the immunity of freshwater fish, and has a certain effect on promoting fish growth.

Description

Technical Field

[0001] The present invention relates to the field of microecological preparations, and in particular to a strain of Streptomyces XL-34, a microecological preparation thereof and a preparation method thereof. Background Art

[0002] The rapid development of aquaculture has brought people high profits and a diversified diet, but it has also brought huge challenges. The sustainable development of aquaculture, especially the sustainable development of the environment, has attracted much attention. The sustainable development goal of aquaculture is to develop aquaculture in a healthy way without destroying the aquatic ecosystem and exceeding the self-renewal limit of the water body, and to continuously supply safe and beneficial aquatic nutrients to humans. In order to ensure the healthy growth of aquatic animals, a large number of chemical drugs such as antibacterial agents, anthelmintics and antibiotics are used in the breeding process. These drugs will not only accumulate in the downstream estuaries through the aquatic circulation system, but also accumulate in the bodies of aquatic animals, posing a potential threat to human health and causing the emergence of drug-resistant super pathogens.

[0003] The aquaculture method of fish has evolved from the traditional extensive aquaculture method with high trophic level richness to the current intensive or semi-intensive aquaculture method with relatively simple trophic levels. Although the scale has been expanded, this development has reduced the self-renewal ability of the aquatic environment of fish, suppressed the immunity of fish, and increased the susceptibility of fish to bacterial diseases. With the in-depth study of bacterial pathogens of fish, people have taken a variety of measures to cope with the challenges of these pathogens, including the use of chemical drugs, Chinese herbal medicines, vaccines, antagonistic microecological preparations and other prevention and control measures. Sunish et al. fed shrimp with the actinomycete Nocardiopsis alba MCCB 110 as a biological immunomodulator. The results showed that the total protein content, AKP and ACP enzyme activities in the shrimp serum of the experimental group were significantly higher than those of the control group. The strain was evaluated for its enhancing effect on the immune defense ability of shrimp, which can protect shrimp from Vibrio disease (Sunish KS, Biji M, Rosamma P, et al. Marine actinomycetes Nocardiopsis alba MCCB 110 has immunomodulatory property in the tiger shrimp Penaeus monodon [J]. Fish & shellfish immunology, 2020, 2020 v. 102: 125-132.). Li et al. discovered a broad-spectrum antibacterial Streptomyces amritsarensis N1-32, which was fed to grass carp (Ctenopharyngodon idellus) by mixing bacteria with feed. The results showed that it could significantly increase the expression of immune-related genes in the liver, spleen, kidney and head kidney tissues of C. idellus. The challenge test showed that the survival rate of grass carp in the S. amritsarensis N1-32 feeding group was significantly higher than that in the control group (Li Y, Hu S, Gong L, et al. Isolating a new Streptomyces amritsarensis N1-32 against fish pathogens and determining its effects on disease resistance of grass carp [J]. Fish & shellfish immunology, 2020, 98: 632-640.). However, there are very few aquatic microecological preparations made using Streptomyces. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a strain of Streptomyces XL-34. The microecological preparation prepared by the Streptomyces has a good antagonistic effect on a variety of common pathogens of fish and can resist the infection of a variety of bacterial diseases of fish.

[0005] The technical problem to be further solved by the present invention is to provide a Streptomyces microecological preparation suitable for preventing and treating fish diseases in aquaculture and a preparation method thereof.

[0006] The technical solution adopted by the present invention to solve its technical problems is as follows: a strain of Streptomyces XL-34, which was deposited in the China Center for Type Culture Collection on June 25, 2023, with a strain collection number of CCTCC NO: M 20231087; it is classified and named: Streptomyces XL-34, and its Latin name is Streptomyces sp. XL-34.

[0007] The gyrB sequence of Streptomyces XL-34 of the present invention is shown in the sequence listing SEQ ID No. 1.

[0008] The Streptomyces XL-34 of the present invention was screened from 115 soil samples in Henan Province and other regions.

[0009] The present invention further solves the technical problem by adopting the following technical solution: a Streptomyces microecological preparation suitable for aquaculture, which is fermented by Streptomyces XL-34 with a strain collection number of CCTCC NO: M 20231087. The antibacterial active substances in the fermentation liquid of the strain have good medium and high temperature, acid and alkali, ultraviolet irradiation and protease stability, and are relatively stable in actual production applications; it has a good inhibitory effect on freshwater fish pathogens, can promote fish growth, and improve the immunity of fish.

[0010] Furthermore, the microecological preparation is a liquid preparation or a solid preparation.

[0011] Furthermore, the aquaculture animals are freshwater fish.

[0012] Furthermore, the freshwater fish is crucian carp, grass carp or carp.

[0013] The present invention further solves the technical problem by adopting the following technical solution: A method for preparing a microecological preparation suitable for aquaculture, comprising the following steps:

[0014] (1) Inoculation and activation: transferring the preserved slant strain of Streptomyces XL-34 to an activated slant culture medium for activation to obtain an activated seed solution; the activated slant culture medium is Am3 liquid culture medium (Am3 culture medium is non-synthetic broth antibiotic culture medium 3);

[0015] The activation culture conditions are as follows: temperature 28-30°C, liquid volume 10-30% of the container volume, and shaking speed 180-200 rpm;

[0016] (2) First expansion culture: The seed liquid activated in step (1) is inoculated into a fermentation tank at an inoculation rate of 1 to 2% for first expansion culture;

[0017] The fermentation medium formula is: soluble starch 14-16g / L, bacteriological peptone 8-12g / L, soybean powder 4-6g / L, glycerol 14-16g / L, CaCO3 1.5-2.5g / L, acid hydrolyzed casein 2-4g / L, pH 7.0-7.4;

[0018] The preferred formula of the fermentation medium is: soluble starch 15g / L, bacteriological peptone 10g / L, soybean powder 5g / L, glycerol 15g / L, CaCO3 2g / L, acid hydrolyzed casein 3g / L, pH 7.0-7.4;

[0019] The culture conditions are as follows: the entire culture process is monitored online, the dissolved oxygen concentration is 35-55%, the temperature is 28-30°C, the culture time is 72-96h, and the defoaming agent is added online in real time;

[0020] (3) Second expansion culture: inoculate the seed solution of the first expansion culture in step (2) into a fermentation tank containing a fermentation medium at an inoculum amount of 10-15% for fermentation culture, wherein the fermentation medium formula is the same as the fermentation medium formula in step (2); the culture conditions are: dissolved oxygen concentration of 35-55%, temperature of 28-30° C., culture for 96-168 hours, and real-time online addition of a defoaming agent;

[0021] Furthermore, in step (3), the fermentation tank is preferably filled with a fermentation medium equivalent to 65%-70% of the volume of the fermentation tank, and more preferably a 500L-1000L fermentation tank.

[0022] (4) Concentration and collection: After the culture is completed, the fermentation product is collected in a tank and concentrated to obtain a microecological liquid bacterial agent, or spray-dried to obtain a microecological solid preparation.

[0023] The identification and research methods of Streptomyces XL-34 of the present invention are as follows.

[0024] (A) Observation of cell morphological characteristics of strain Streptomyces XL-34;

[0025] (ii) identification using the gyrB gene;

[0026] (III) Physical and chemical properties detection of antibacterial active substances of Streptomyces XL-34;

[0027] (IV) Detection of colonization of Streptomyces XL-34 in crucian carp;

[0028] (V) Effects of Streptomyces XL-34 as a feed additive on the growth and disease resistance of crucian carp.

[0029] The invention has the following beneficial effects: (1) the strain is identified as Streptomyces (strain collection number: CCTCC NO: M 20231087; classified and named as Streptomyces XL-34, Latin name: Streptomyces sp. XL-34) through gyrB gene sequence determination, and has good antibacterial effect on various freshwater fish pathogens such as Aeromonas hydrophila, Aeromonas veronii, Edwardsiella tarda, etc.; (2) Streptomyces XL-34 can survive and colonize in fish bodies and is harmless to fish, which lays a foundation for the strain to play a stable disease prevention and growth promotion role in fish farming; (3) Streptomyces XL-34 is added to feed as a feed additive to feed fish, which can promote the growth rate and feed efficiency of fish, improve the immunity of fish, and enhance the resistance of fish to pathogens; (4) The method for preparing Streptomyces XL-34 into a microecological preparation is relatively simple and has a low production cost. At the same time, it can also effectively reduce the risks of drug residues and pathogenic bacteria resistance caused by the abuse of antibiotics, and has good application prospects.

[0030] SEQ ID №1:

[0031]

[0032]

[0033] Description of Microbiological Deposit

[0034] The Streptomyces XL-34 of the present invention was deposited in the China Center for Type Culture Collection (CCTCC for short, address: Wuhan University, Wuhan, China) on June 25, 2023, and the strain collection number is CCTCC NO: M 20231087; the classification name is: Streptomyces XL-34; Latin name: Streptomyces sp.XL-34. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a diagram showing the antibacterial effect of Streptomyces XL-34 of the present invention on fish pathogens;

[0036] Figure 2 Observation diagrams of morphological characteristics of Streptomyces XL-34 of the present invention; a: observation diagram of plate colony morphology of strain XL-34; b: observation diagram of strain XL-34 under phase contrast microscope; c: observation diagram of Gram staining of strain XL-34; d, e: observation diagrams of strain XL-34 under scanning electron microscope;

[0037] Figure 3The phylogenetic tree diagram is constructed by the gyrB sequence of Streptomyces XL-34 of the present invention;

[0038] Figure 4 It is a RAST species identification circle diagram of the whole genome of Streptomyces XL-34 of the present invention;

[0039] Figure 5 It is a RAST strain identification point map of the whole genome of Streptomyces XL-34 of the present invention;

[0040] Figure 6 This is a diagram of the physical and chemical properties of the antibacterial active substance of Streptomyces XL-34 of the present invention (*, P < 0.05; **, P < 0.01; ***, P < 0.001);

[0041] Figure 7 This is a diagram of the colonization and protection of Streptomyces XL-34 labeled strain in crucian carp observed by the small animal living imaging system of the present invention;

[0042] Figure 8 This is a graph showing the effect of the microecological preparation prepared by Streptomyces XL-34 on the activity of immune-related enzymes in the serum of crucian carp (*, P < 0.05; **, P < 0.01; ***, P < 0.001);

[0043] Fig. 9 This is a diagram showing the antagonistic effect of the microecological preparation prepared by Streptomyces XL-34 on Aeromonas veronii in crucian carp observed by the small animal living imaging system of the present invention. DETAILED DESCRIPTION

[0044] The present invention will be further described below in conjunction with the embodiments and drawings.

[0045] Unless otherwise specified, the chemical reagents used in the embodiments of the present invention were obtained through conventional commercial channels.

[0046] (I) Screening of Streptomyces XL-34 and determination of antibacterial spectrum

[0047] 115 soil samples from Henan Province and other regions were fully mixed in sterile water, spread on Goll plates after gradient dilution, and cultured at 30℃ for 4 days. The growth status of the strains was observed and single clones of actinomycetes were picked and inoculated on new culture medium to purify the picked strains. The fish pathogens Aeromonas veronii AvX005, Aeromonas hydrophila, Aeromonas caviae, Aeromonas salmonicida, Aeromonas allosaccharophila, Edwardsiella tarda, Citrobacter freundii, Shewanella xiamenensis, Aeromonas sobria, Plesiomonas shigella shigelloide) was used as the indicator bacteria, and the antibacterial activity of the fermentation supernatant against the above pathogens was detected using the Oxford cup method (the results are shown in Figure 1 ) and found a strain with good antibacterial effect on 10 fish pathogens, named XL-34.

[0048] (II) Cell morphological characteristics of Streptomyces XL-34

[0049] When strain XL-34 was streaked on Gao's solid medium No. 1, it was observed that the colonies of strain XL-34 were small, dry, and had irregular serrated edges. The colonies were in the shape of concentric circles with white edges and pink in the middle. Phase contrast microscopy showed that strain XL-34 had well-developed mycelium with many branches. Gram staining showed that strain XL-34 was a Gram-positive bacterium. Cold-field scanning electron microscopy showed that strain XL-34 had many branches and well-developed mycelium, and its spore hyphae were tightly spiraled. Based on the above morphological characteristics, strain XL-34 was preliminarily identified as an actinomycete (see Figure 2 ).

[0050] (III) Identification of the gyrB gene of Streptomyces XL-34

[0051] The strain XL-34 was inoculated into liquid Gould's medium and cultured at 30°C and 120 rpm for 4 days. The bacteria were collected and the genomic DNA of the strain XL-34 was extracted using the Ezup column bacterial genomic DNA extraction kit (Shanghai Sangon Biotechnology Co., Ltd.) and the gyrB gene amplification primers were used.

[0052] gyrB F: 5′-GAAGTCATCATGACCGTTCTGCAYGCNGGNGGNAARTTYGA-3′;

[0053] gyrB R: 5′-AGCAGGGTACGGATGTGCGAGCCRTCNACRTCNGCRTCNGTCAT-3′.

[0054] The gyrB gene sequence was amplified with the above primers, and the expected length of the sequence was about 1500 bp.

[0055] PCR reaction system (20 μL): sterile double distilled water, 14 μL; 10× Buffer, 2 μL; dNTP, 1.6 μL; Bf-R (10 μM), 0.6 μL; Bf-F (10 μM), 0.6 μL; genomic template, 1 μL; PrimerSTAR DNA Polymerase (Takara), 0.2 μL;

[0056] PCR reaction program: pre-denaturation at 95°C for 5 min; 30 cycles: 95°C, 45 sec; 55°C, 45 sec; 72°C, 1.5 min; 72°C, 10 min.

[0057] The gyrB gene PCR product was detected by 1.0% agarose gel electrophoresis, and the successfully amplified product was sent to Shanghai Shenggong Biotechnology Co., Ltd. for sequencing.

[0058] The gyrB gene sequence of strain XL-34 was sequenced and showed to be 1280 bp in length. The amplified sequencing results were analyzed by BLAST comparison on NCBI, and the phylogenetic tree of the strain was constructed by the neighbor-joining method in MEGA X software (see Figure 3 ).

[0059] (IV) RAST identification of Streptomyces XL-34 whole genome

[0060] After the whole genome of strain XL-34 was sequenced, the whole genome sequence of strain XL-34 and its closest relative strain were compared online using the RAST database, and dot plots and circle plots were drawn (see Figure 4 , Figure 5 ), the similarity between strain XL-34 and them is only about 90%. Combining the morphological characteristics and molecular biological identification of strain XL-34, the strain can be further identified as a new species of Streptomyces and named Streptomyces sp. XL-34 (XL-34).

[0061] (V) Analysis of the physicochemical properties of antibacterial active substances of Streptomyces XL-3

[0062] (1) Thermal stability

[0063] The strain XL-34 was inoculated into liquid Am3-1 medium and cultured at 30°C and 120 rpm for 7 days. The fermentation broth was treated at 30°C, 50°C, 70°C, and 90°C for 1 hour. Aeromonas vernii was used as the pathogen indicator bacteria, and the plate well method was used to detect the antibacterial activity of the fermentation supernatant after treatment at different temperatures (see Figure 6 ).

[0064] (2) Acid and alkali tolerance

[0065] The strain XL-34 was inoculated into liquid Am3-1 medium and cultured at 30°C and 120 rpm for 7 days. The fermentation broth was treated at pH 1, 3, 5, 7, 9, 11, and 13 for 1 hour and then restored to the original pH. Aeromonas vernii was used as the pathogen indicator bacteria, and the plate well method was used to detect the antibacterial activity of the fermentation supernatant after different pH treatments (see Figure 6 ).

[0066] (3) UV light tolerance

[0067] The strain XL-34 was inoculated into liquid Am3-1 medium and cultured at 30°C and 120 rpm for 7 days. The fermentation broth was irradiated under ultraviolet light for 10 to 60 minutes. Aeromonas vernix was used as the pathogen indicator bacteria. The plate well method was used to detect the antibacterial activity of the fermentation supernatant after different ultraviolet irradiation times (see Figure 6 ).

[0068] (4) Protease resistance

[0069] The strain XL-34 was inoculated into liquid Am3-1 medium and cultured at 30°C and 120 rpm for 7 days. Proteinase K, trypsin and pepsin were used for treatment at 37°C for 1 hour. Aeromonas vernii was used as the pathogen indicator bacteria. The plate well method was used to detect the antibacterial activity of the fermentation supernatant after treatment with different proteases (see Figure 6 ).

[0070] It can be seen that the antibacterial active substances in the fermentation broth of this strain have good medium-high temperature, acid-base, ultraviolet irradiation and protease stability.

[0071] (VI) Preparation of Streptomyces XL-34 microecological preparation

[0072] (1) Inoculation and activation: transferring the preserved slant strain of Streptomyces XL-34 to an activated slant culture medium for activation to obtain an activated seed solution; the activated slant culture medium is Am3-1 liquid culture medium, and the activation culture conditions are: temperature 28-30° C., liquid volume 10-30% of the container volume, and shaking speed 180-200 rpm;

[0073] (2) First expansion culture: The seed liquid activated in step (1) is inoculated into a fermentation tank at an inoculum amount of 1-2% for the first expansion culture; the fermentation medium formula is: soluble starch 15g / L, bacteriological peptone 10g / L, soybean powder 5g / L, glycerol 15g / L, CaCO3 2g / L, acid hydrolyzed casein 3g / L, pH 7.0-7.4; the culture conditions are: the entire culture process is monitored online, the dissolved oxygen concentration is 35-55%, the temperature is 28-30°C, the culture is 72-96h, and the defoaming agent is added online in real time;

[0074] (3) Second expansion culture: inoculate the seed solution expanded in step (2) at an inoculum rate of 10-15% into a 500L fermentation tank filled with 65%-70% fermentation medium, the fermentation medium formula is the same as the fermentation medium formula described in step (2); the culture conditions are: dissolved oxygen concentration of 35-55%, temperature of 28-30° C., culture for 96-168 hours, and add defoaming agent online in real time;

[0075] (4) Concentration and collection: After tanking, the fermentation products are collected and concentrated to obtain a microecological liquid bacterial agent, or spray-dried to obtain a microecological solid preparation.

[0076] (VII) Application of Streptomyces XL-34 in fish farming

[0077] Example 1: Colonization and protective ability of Streptomyces XL-34 in crucian carp

[0078] The crucian carps of uniform body size were randomly divided into two groups, 30 in each group, and the two groups of crucian carps were acclimated for 7 days. The experiment was carried out when the state of each group of crucian carps was stable. The control group was fed with ordinary feed, and the experimental group was fed with a concentration of 1×10 8 CFU / mL of strain XL-34 EGFP The feeding amount was 2% of the crucian carp's body weight. After 15 days of continuous feeding, three crucian carps from the experimental group were randomly selected every 1 day to observe the strain XL-34 using a small animal imaging system. EGFP Colonization in crucian carp.

[0079] The results showed that feeding strain XL-34 EGFP On the second day, the fluorescence signal could be observed in the small animal imaging system, and the fluorescence signal continued to increase over time. The fluorescence signal first appeared in the gills and the front half of the abdomen of the crucian carp, and then continued to deepen and extend to the back half of the abdomen (see Figure 7 This result shows that strain XL-34 can stably colonize in crucian carp, laying the foundation for the subsequent study of the effect of strain XL-34 on the growth and immune defense ability of crucian carp.

[0080] Example 2: Effects of Streptomyces XL-34 on growth and disease resistance of crucian carp

[0081] The crucian carps with uniform body shape were randomly divided into 6 frames, including 3 frames for the experimental group and 3 frames for the control group, with 10 crucian carps in each frame. The experiment was carried out after the crucian carps were domesticated for 7 days and their state was stable. The control group was fed with ordinary feed, and the experimental group was fed with a concentration of 1×10 8 The strain XL-34 with a CFU / mL was fed at a rate of 2% of the crucian carp's body weight for 30 consecutive days, with feed given twice a day at 8:00 and 20:00, and the indoor temperature was controlled at 25±2℃.

[0082] (1) Effects of Streptomyces XL-34 on the growth performance of crucian carp

[0083] The weight of crucian carp before grouping was taken as the initial weight (W0), and the weight of crucian carp fed for 30 days was taken as the final weight (W t ), feeding time (t), feed intake (g), initial number of crucian carp in the experiment (n0), and final number of crucian carp in the experiment (n1) were used to calculate the weight growth rate (WGR), specific growth rate (SGR), feed efficiency (FE), and survival rate (SR): WGR = ((W t -W0) / W0)×100%, SGR=((lnW t -lnW0) / t)×100%FE=((W t -W0) / g)×100%, SR=(n1 / n0)×100% (see Table 1).

[0084] Table 1 Crucian carp growth performance parameters

[0085]

[0086] Note: Ⅰ: control group; II: experimental group 1×10 8 CFU / g (*, P<0.05; **, P<0.01; ***, P<0.001)

[0087] It can be seen that the Streptomyces XL-34 of the present invention has a promoting effect on the growth of crucian carp.

[0088] (2) Effects of Streptomyces XL-34 on nonspecific immune parameters in crucian carp serum

[0089] The strain Streptomyces XL-34 was added to the feed and fed to crucian carp for 30 days. The activities of alkaline phosphatase (AKP) and acid phosphatase (ACP) in the serum of the XL-34-fed group were significantly higher than those of the control group (P < 0.001). Phosphatase is an important regulatory enzyme, among which AKP can increase the amount of inorganic phosphate involved in ATP synthesis, improve the body's metabolic capacity and thus improve the immunity of crucian carp, thereby promoting the healthy growth of crucian carp. There was no significant difference in the enzyme activities of glutathione (GSH) and catalase (CAT) in the XL-34-fed group and the control group. The activities of total superoxide dismutase (T-SOD) and lysozyme (LZM) in the serum of the XL-34-fed group were higher than those of the control group, with a significant difference (P < 0.01). Among them, the increase in T-SOD activity helps the body to scavenge superoxide anion free radicals and protect the body's cells from damage (see Figure 8 ).

[0090] (3) Experiment on the protective effect of Streptomyces XL-34 on crucian carp

[0091] In order to study the protective effect of strain XL-34 on crucian carp infected with Aeromonas veroni, 100 μL of Aeromonas veroni was injected intraperitoneally into crucian carp fed continuously for 30 days. The living status and survival rate of crucian carp in the control group and the strain XL-34 feeding group after infection were observed for 7 days. The survival rate of crucian carp in the strain XL-34 feeding group was 41.67%, which was significantly higher than that of the control group (see Table 2).

[0092] Table 2 Experimental study on the protective effect of strain XL-34 on crucian carp

[0093]

[0094]

[0095] (VIII) Antagonistic effect of the microecological preparation prepared by Streptomyces XL-34 on Aeromonas veroni in crucian carp

[0096] Carassius auratus with uniform body size were randomly divided into 2 groups, 30 in each group. Carassius auratus were acclimated for 7 days and starved for 24 hours. The carassius auratus in the control group and the experimental group were intraperitoneally injected with 200 μL of 1×10 8 CFU / mL of AvX005 mCherry The strain AvX005 was observed every 1 day using a small animal imaging system. mCherry The colonization and distribution of the carp were observed for 7 consecutive days. After the 7th day, the carp in the experimental group were fed with a concentration of 1×10 8 The distribution and brightness changes of red fluorescence in crucian carp were observed using a small animal imaging system every 1 day for 7 consecutive days.

[0097] The results showed that the fluorescence intensity of Aeromonas verticillata in crucian carp increased over time. On the first day, the fluorescence signal first appeared in the gills and tail, and on the third day, it spread throughout the body, and the signal continued to increase. 8 The small animal imaging system found that the fluorescence signal of the crucian carp fed with strain XL-34 was significantly weakened compared with the control group, indicating that strain XL-34 can alleviate the infection of Aeromonas veronis in crucian carp (refer to Fig. 9 ).

Claims

1. A strain of Streptomyces XL-34, characterized in that: It is deposited in China Center for Type Culture Collection, with the strain number CCTCC NO: M 20231087; the classification name is: Streptomyces XL-34, the Latin name Streptomyces sp. XL-34.

2. A microecological preparation suitable for aquaculture, characterized in that: The product is prepared by fermenting the Streptomyces XL-34 strain with the strain collection number of CCTCC NO: M 20231087 as claimed in claim 1.

3. The microecological preparation suitable for aquaculture according to claim 2, characterized in that: The microecological preparation is a liquid preparation or a solid preparation.

4. The microecological preparation suitable for aquaculture according to claim 2 or 3, characterized in that: The aquaculture animals are freshwater fish.

5. The microecological preparation suitable for aquaculture according to claim 4, characterized in that: The freshwater fish is crucian carp, grass carp or carp.

6. A method for preparing a microecological preparation suitable for aquaculture as claimed in claim 2 or 3, characterized in that: The following steps are involved: (1) Inoculation and activation: transfer the stored slant strain of Streptomyces XL-34 to the activated slant culture medium for activation to obtain activated seed liquid; (2) First expansion culture: The seed liquid activated in step (1) is inoculated into a fermentation tank at an inoculation rate of 1-2% for the first expansion culture; (3) Second expansion culture: Inoculate the seed solution from the first expansion culture in step (2) into a fermentation tank containing fermentation medium at an inoculum rate of 10-15%. (4) Concentration and collection: After tanking, the fermentation products are collected and concentrated to obtain a microecological liquid bacterial agent, or spray-dried to obtain a microecological solid preparation.

7. The method for preparing a microecological preparation suitable for aquaculture according to claim 6, characterized in that: In step (1), the activated slant culture medium is Am3 liquid culture medium, and the activation culture conditions are: temperature 28-30°C, liquid volume 10-30% of the container volume, and shaking speed 180-200 rpm.

8. The method for preparing a microecological preparation suitable for aquaculture according to claim 6 or 7, characterized in that: In step (2), the fermentation medium formula is: soluble starch 14-16 g / L, bacteriological peptone 8-12 g / L, soybean powder 4-6 g / L, glycerol 14-16 g / L, CaCO3 1.5-2.5 g / L, acid hydrolyzed casein 2-4 g / L, pH 7.0-7.4; And / or the culture conditions are: the entire culture process is monitored online, the dissolved oxygen concentration is 35-55%, the temperature is 28-30°C, the culture is 72-96 hours, and the defoaming agent is added online in real time.

9. The method for preparing a microecological preparation suitable for aquaculture according to claim 8, characterized in that: In step (3), the formula of the fermentation medium is the same as the formula of the fermentation medium described in step (2); And / or the culture conditions are: dissolved oxygen concentration of 35-55%, temperature of 28-30°C, culture for 96-168 hours, and real-time online addition of defoaming agent.

10. The method for preparing a microecological preparation suitable for aquaculture according to claim 6 or 7, characterized in that: In step (3), the fermentation tank is filled with fermentation medium equivalent to 65-70% of the volume of the fermentation tank.

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