Cyanobacterium SCSIO17256 with high yield of exopolysaccharide and its application in coral reef erosion resistance

Abstract

The application discloses a cyanobacterium SCSIO17256 with high yield of exocellular polysaccharide and application of the cyanobacterium in anti-erosion of a coral island. The cyanobacterium is named as cyanobacterium Oculatella sp. SCSIO17256, and the preservation number is CCTCC NO: M2025524. The cyanobacterium Oculatella sp. SCSIO17256 provided by the application can effectively promote formation of a calcareous sand biological crust, has strong sand-fixing capacity, and has very strong shear resistance, and can be applied to prevention and treatment of water and soil loss of the coral island and construction of the calcareous sand biological soil crust of the coral island. Compared with physical sand-fixing, chemical sand-fixing and vegetation cultivation, the use of the microorganism as a new type of sand-fixing and cultivation crust has the advantages of strong adaptability, low cost, quick effect, etc.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of microorganisms, and particularly relates to a cyanobacterium Oculatella sp. SCSIO17256 with high yield of exopolysaccharide, and application of the cyanobacterium in anti-erosion of coral islands and construction of biological soil crust of coral islands. BACKGROUND

[0002] Tropical coral islands are mainly composed of coral calcareous sand. Due to the lack of real soil and freshwater resources, vegetation is difficult to colonize, and therefore these coral islands are regarded as "desert" in the ocean, which has the characteristics of high salt, strong alkali, high temperature, strong light, and serious water and soil loss. Healthy soil resources and underground ecological freshwater resources of coral islands are the source of life to support the coral island ecosystem and realize livability. Biological soil crust (BSC) in desert ecosystems, which is also in extreme environments, has brought great inspiration to change the "desert" state of coral islands. The complex biological soil crust formed by microorganisms, algae, mosses, lichens and other organisms and soil has the characteristics of drought tolerance, salt and alkali tolerance, carbon and nitrogen fixation capacity, strong reproduction ability, and can survive and reproduce in harsh environments, and can affect the surrounding microenvironment through physiological metabolism. Similar to desert systems, BSC is also an important part of the coral island ecosystem, accounting for about 6.25% of the land area of coral islands. The generation and development process of BSC is also the process of primary succession of vegetation, which makes the desert soil have the basic elements and conditions for plant growth after a series of physical, chemical and biological changes, and lays the foundation for the next succession process. BSC plays a role in soil processes, ecological hydrology, and geochemical cycles, and directly affects rainfall infiltration, soil erosion, nutrient cycling, seed germination, biodiversity, and plays an important role in the evolution of soil-water-vegetation systems. Light energy utilizing microorganisms are the most important functional components of BSC, and cyanobacteria with functions of photosynthetic carbon fixation, nitrogen fixation and polysaccharide production have been considered as the key groups for the formation and development of BSC. However, the research on BSC cyanobacteria in tropical coral islands is almost blank.

[0003] Cyanobacteria are a group of photosynthetic prokaryotes that contain chlorophyll and can carry out photosynthesis. They are the most important dominant group in biological soil crusts in arid and semiarid regions. Their growth can provide abundant nitrogen and carbon sources for the soil, especially the nitrogen fixed by some nitrogen-fixing cyanobacteria, which is an important source of nitrogen in desert soil. As an important source of nitrogen and carbon in desert ecosystems, cyanobacteria can increase the content of soil organic matter to some extent during photosynthesis and nitrogen fixation, and improve the microenvironment of the soil. At the same time, cyanobacteria can also form microbial populations with other microorganisms in the soil, increasing the number and activity of soil enzymes on the soil surface, thereby accelerating the development and maturation process of the soil. In arid desert regions, due to the characteristics of lack of organic matter and loose particle structure, this region is extremely susceptible to erosion. Cyanobacteria, especially the exopolysaccharide substances secreted by them, play an important role in preventing soil surface erosion. Related research results show that cyanobacteria increase the soil surface aggregation and soil particle stability, and this is largely determined by the biomass of cyanobacteria and the yield of polysaccharides. The exopolysaccharides produced by cyanobacteria improve the stability of the soil and other non-mycelial substances, and play a medium role between filamentous cyanobacteria and soil sand, serving as a basic framework and binding the upper and lower layers of soil. With the continuous increase of the number and biomass of cyanobacteria, the content of polysaccharides also increases, thereby continuously enhancing the aggregation effect of soil particles. In addition, polysaccharides can regulate the absorption and loss of cell water, provide a natural barrier for cyanobacterial cells to protect them from harm, and also reduce or delay the loss of water in the biological crust layer, thereby increasing the water holding capacity of the soil and laying a solid foundation for the improvement of the microenvironment. These functions are of great significance for the colonization of cyanobacterial groups in oligotrophic tropical coral islands.

[0004] Although cyanobacteria contain bacteriochlorophyll and can produce exopolysaccharides, there is no related research report on cyanobacteria reducing water and soil loss in coral islands and promoting the growth of biological crusts. SUMMARY

[0005] The purpose of the present application is to provide a cyanobacterium Oculatella sp. SCSIO17256 strain with high yield of exopolysaccharides isolated from biological soil crust samples in Chinese tropical coral islands, which provides a new microbial resource for reducing water and soil loss in coral islands and promoting the development of biological crusts in coral islands.

[0006] The cyanobacterium Oculatella sp. SCSIO17256 strain of the present application was preserved in the China Center for Type Culture Collection (CCTCC) on March 18, 2025, located at Wuhan University, Wuhan, China, with a postal code of 430072, and the preservation number is CCTCC NO: M2025524.

[0007] The present application determines the content of the exopolysaccharide of the strain SCSIO17256 according to the phenol-sulphuric acid method, and uses a glucose standard curve, and the results show that the exopolysaccharide yield of the strain SCSIO17256 is 595.23 mg / L. When the BG11 liquid culture solution of the cyanobacterium Oculatella sp. SCSIO17256 strain is uniformly sprayed on the sterile coral sand with a particle size less than 1.25 mm, and after 120 days of culture, it is found that the cyanobacterium Oculatella sp. SCSIO17256 can effectively promote the formation of soil aggregates and form a crust structure on the calcareous sand surface, and the shear strength is 5.25±0.61 KPa, which is significantly higher than that of the blank group 1.75±0.11 KPa, indicating that the cyanobacterium Oculatella sp. SCSIO17256 can effectively reduce the erosion of calcareous sand, and is helpful for the prevention and control of water and soil loss of coral islands.

[0008] A second object of the present application is to provide a biological agent comprising the cyanobacterium Oculatella sp. SCSIO17256. Preferably, the biological agent further comprises an auxiliary material for prolonging the activity time of the strain, or other biological agent acceptable auxiliary materials.

[0009] A third object of the present application is to provide the application of the cyanobacterium Oculatella sp. SCSIO17256 or the biological agent containing the strain in preventing water and soil loss. Preferably, the desertification prevention comprises reducing the water and soil loss of coral islands.

[0010] Preferably, the cyanobacterium Oculatella sp. SCSIO17256 promotes the formation of biological soil crust on the surface of calcareous sand, plays a role of sand stabilization and water retention, and thus reduces the water and soil loss.

[0011] Preferably, the bacterial liquid of the cyanobacterium Oculatella sp. SCSIO17256 is inoculated into an area where biological soil crust needs to be cultured. The bacterial liquid is obtained by culturing the cyanobacterium Oculatella sp. SCSIO17256 using the BG11 liquid culture medium, and the formula of the BG11 liquid culture medium is: NaNO3 (1.5 g / L), K2HPO4 (40 mg / L), MgSO4·7H2O (75 mg / L), CaCl2·2H2O (36 mg / L), Na2CO3 (20 mg / L), Citric Acid (6 mg / L), Ferric ammonium citrate (6 mg / L), EDTA (1 mg / L), and A5 trace elements 1 ml / L.

[0012] The fourth object of the present application is to provide a sand-fixing method, comprising the following steps: inoculating the bacterial liquid of cyanobacterium Oculatella sp. SCSIO17256 to the area where biological soil crust needs to be cultivated.

[0013] The fifth object of the present application is to provide the application of the above-mentioned sand-fixing method in the prevention and treatment of water and soil erosion of islands.

[0014] The exopolysaccharide content of the cyanobacterium Oculatella sp. SCSIO17256 provided by the present application is 595.23 mg / L, which has strong anti-erosion ability and can effectively promote the accumulation of nutrients and prevent and treat soil erosion of coral islands. It can be applied to reduce water and soil erosion of coral islands and construct biological crust of coral islands. The present application first discloses the qualitative and quantitative research on the ability of cyanobacterium Oculatella sp. SCSIO17256 to promote the growth of biological crust.

[0015] Oculatella sp. SCSIO17256 was preserved in China Center for Type Culture Collection (CCTCC) on March 18, 2025, the address is Wuhan University, Wuhan, China, the postcode is 430072, and the preservation number is CCTCC NO: M2025524. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 Effect pictures of the crust formed by cyanobacterium Oculatella sp. SCSIO17256 on the surface of calcareous sand at different periods. DETAILED DESCRIPTION

[0017] The following examples are further illustrations of the present application and are not intended to limit the present application.

[0018] Example 1: Isolation and identification of cyanobacterium Oculatella sp. SCSIO17256

[0019] 1. Sample collection

[0020] The biological crust sample was collected from a tropical coral island in China in December 2021. After sample collection, it was quickly packed into a sterile polyethylene sampling bag, dried in the shade, and stored at room temperature.

[0021] 2. Isolation medium

[0022] The cyanobacterial culture medium is BG-11 medium, with the following formula: NaNO3 (1.5 g / L), K2HPO4 (40 mg / L), MgSO4·7H2O (75 mg / L), CaCl2·2H2O (36 mg / L), Na2CO3 (20 mg / L), Citric Acid (6 mg / L), Ferric ammonium citrate (6 mg / L), EDTA (1 mg / L), and A5 trace elements 1 ml / L. The medium is sterilized before use.

[0023] 3. Isolation and screening of strains

[0024] The biocrust samples brought back to the laboratory were washed with sterile pure water to separate the algal plantlets from the sand. They were then inoculated into a sterile cyanobacteria culture medium at a 1:5 ratio and incubated under a light intensity of 200 μmol photons / m². -2 s -1 Enrichment culture was carried out at a temperature of 20±1℃ for 3-5 days. After the water sample showed a visible color, the pre-cultured culture was separated and purified by solid plate using the dilution plating method or streak plating method under aseptic conditions. The plate was placed on a light-illuminated culture rack under the above conditions for 7-15 days. The above separation steps were repeated multiple times until a completely sterile target cyanobacterial monoalgal colony SCSIO17256 was obtained.

[0025] A single colony of SCSIO17256 was picked from a solid plate and transferred to an Erlenmeyer flask containing 20 mL of sterile seawater medium. The flask was then placed on a light-controlled incubator and continuously incubated under light, with periodic shaking to obtain the cyanobacterium SCSIO17256 in the logarithmic growth phase. Genomic DNA was extracted from strain SCSIO17256 using the EasyPure Bacteria Genomic DNA Kit. The 16S rRNA gene fragment was then amplified using universal primers 27F / 1492R and sequenced, as shown in SEQ ID No. 1. Online alignment of the 16S rRNA gene sequence using the EZBioCloud website revealed that strain SCSIO17256 belongs to the genus *Oculatella* within the phylum Cyanobacteria; therefore, it was named *Oculatella* sp. SCSIO17256. The cyanobacterium Oculatellasp.SCSIO17256 was deposited on March 18, 2025, at the China Center for Type Culture Collection (CCTCC), Wuhan University, Wuhan, China, 430072, China, with accession number CCTCC NO: M2025524.

[0026]

[0027] Example 2: Determination of the content of exopolysaccharide of cyanobacterium Oculatella sp. SCSIO17256

[0028] Cyanobacterium SCSIO17256 was inoculated in BG11 liquid medium, and the medium components were as follows: NaNO3(1.5 g / L), K2HPO4(40 mg / L), MgSO4·7H2O(75 mg / L), CaCl2·2H2O(36 mg / L), Na2CO3(20 mg / L), Citric Acid(6 mg / L), Ferric ammonium citrate(6 mg / L), EDTA(1 mg / L), A5 trace elements 1 ml / L, sterilized and ready to use. The culture was carried out at 25°C and 180 r / min for 30 days. 2 ml of cyanobacterium culture solution(cultured for 15 days) was taken and centrifuged at 5000 rpm for 5 min to obtain the supernatant. 1 ml of the supernatant was taken, 0.5 ml of 6% phenol solution was added, and 2.5 ml of concentrated sulfuric acid was added. After shaking, it was placed in a 60°C water bath for 30 min. After cooling to room temperature, the absorbance value was measured at 490 nm wavelength, with reagent blank as reference, and D-glucose as reference. The content of exopolysaccharide was obtained by standard curve. The detection results showed that the yield of exopolysaccharide of cyanobacterium Oculatella sp. SCSIO17256 cultured in BG11 liquid medium for 30 days was 595.23 mg / L.

[0029] Example 3: Determination of the shear resistance of cyanobacterium Oculatella sp. SCSIO17256

[0030] The coral sand is passed through a 16 mesh (1.25 mm mesh) sieve to obtain coral sand with a particle size of less than 1.25 mm, which is sterilized in a culture dish at 121 DEG C for 25 minutes, dried in an oven at 60 DEG C, and stirred to be loose and uniform. The cyanobacterium Oculatella sp. SCSIO17256 is inoculated in BG11 liquid medium (same as in Example 2), and cultured at 25 DEG C and 180 r / min for 120 days. Then, the bacterial liquid is evenly sprayed on the coral sand in a sterile alcohol-soaked small sprayer, and a sterilized BG11 liquid medium is used as a blank control. After being cultured at room temperature for 120 days, the shear resistance of the biological crust formed on the surface is measured. The test results show that the cyanobacterium Oculatella sp. SCSIO17256 can effectively promote the formation of the biological crust, and the shear resistance is 5.25 ± 0.61 KPa, which is significantly higher than 1.75 ± 0.11 KPa of the blank group, which indicates that the cyanobacterium Oculatella sp. SCSIO17256 helps the formation of the biological crust and can effectively reduce the influence of soil erosion.

[0031] Therefore, the cyanobacterium Oculatella sp. SCSIO17256 provided by the present application can effectively promote the formation of the biological crust of the calcareous sand, Figure 1 ) has strong sand-fixing ability and strong shear resistance, and can be applied to the prevention and control of water and soil loss of coral islands and the construction of biological soil crust of calcareous sand of coral islands. Compared with physical sand fixation, chemical sand fixation and vegetation cultivation, the use of microorganisms as a new type of sand fixation and cultivation crust has the advantages of strong adaptability, low cost, quick effect, etc.

[0032] The above is only a preferred embodiment of the present application, and it should be pointed out that the above preferred embodiment should not be regarded as a limitation of the present application, and the protection scope of the present application should be limited by the scope defined in the claims. For ordinary skilled persons in the art, several improvements and refinements can be made without departing from the spirit and scope of the present application, and these improvements and refinements should also be regarded as the protection scope of the present application.

Claims

1. Cyanobacteria Oculatella sp. SCSIO17256, accession number: CCTCC NO: M2025524.

2. A biological agent, characterized in that, Contains the cyanobacteria of claim 1 Oculatella sp. SCSIO17256.

3. The cyanobacteria according to claim 1 Oculatella sp. Application of SCSIO17256 or biological agents containing this strain in preventing soil erosion.

4. The application according to claim 3, characterized in that, The aforementioned prevention of soil erosion includes reducing soil erosion on coral islands.

5. The application according to claim 3, characterized in that, It is cyanobacteria Oculatella sp SCSIO17256 promotes the formation of biocrusts on the surface of calcareous sand, which helps stabilize the sand and retain water, thereby reducing soil erosion.

6. The application according to claim 3, characterized in that, is Blue bacteria Oculatella sp. The bacterial culture of SCSIO17256 was inoculated into the area where biological soil crusts needed to be cultured.

7. The application according to claim 6, characterized in that, The bacterial culture solution is prepared by culturing cyanobacteria using BG11 liquid medium. Oculatella sp. The SCSIO17256 strain was obtained, and the formula of the BG11 liquid culture medium was as follows: NaNO3 1.5 g / L, K2HPO4 40 mg / L, MgSO4·7H2O 75 mg / L, CaCl2·2H2O 36 mg / L, Na2CO3 20 mg / L, citric acid 6 mg / L, ferric ammonium citrate 6 mg / L, EDTA 1 mg / L, and A5 trace elements 1 ml / L.

8. A method for sand fixation, characterized in that, The cyanobacterium described in claim 1 Oculatella sp. The bacterial culture of SCSIO17256 was inoculated into the area where biological soil crusts needed to be cultured.

9. The application of the sand-fixing method according to claim 8 in the prevention and control of soil erosion on islands and reefs.

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