Desert algae fungus composite preparation and preparation method thereof

Abstract

The present application relates to the field of environmental biotechnology and microbial culture, and particularly to a desert algae fungus composite preparation and a preparation method thereof; the preparation method comprises the following steps: preparing functional desert algae, preparing a microcapsule embedding matrix liquid, phase change microcapsule embedding, and gradient freeze drying; the preparation combines gel-producing bacteria and nitrogen-fixing bacteria to induce and culture single-cell desert algae; the core is to construct a functional algae fungus complex with surface-attached bacteria and extracellular polymers, and to use sodium alginate and high-hydrophilic mesoporous nano-silicon powder as a matrix for phase change microcapsule embedding and programmed temperature freeze drying; the present application overcomes the defects of easy rupture and death of simple inoculation, easy separation of physical mixing of free bacteria and algae, and ecological toxicity of chemical bonding agents, and solves the problem of low survival rate of algae cells in extreme environments by using stress induction and nuclear shell microcapsule physical protection, effectively improves the anti-erosion and stress resistance of beneficial living organisms, and realizes rapid construction and efficient sand fixation of desert crust.

Description

Technical Field

[0001] This invention relates to the fields of environmental biotechnology and microbial culture, specifically to a desert algae-bacterial compound preparation and its preparation method. Background Technology

[0002] Constructing biological soil crusts on the surface of shifting sand using single-celled desert algae is a promising method for sand fixation and ecological restoration. However, existing technologies have the following drawbacks: when single-celled algae are simply inoculated in the extremely arid, ultraviolet-rich, and nutrient-poor desert environment, the cells are prone to rupture and die due to oxidative stress and dehydration, and the crust formation cycle usually takes several years. Existing methods typically involve a simple physical spraying of algae and growth-promoting bacteria. However, under wind erosion and occasional heavy rain, free bacteria and algae easily separate in the pores of sand, failing to form an effective mutually beneficial symbiotic microenvironment and resulting in the failure of synergistic metabolism. Some technologies introduce chemical polymer binders such as polyacrylamide for initial sand fixation. However, such chemical cross-linking networks severely clog the capillary pores of sand, hindering gas exchange by single-celled algae. Furthermore, their degradation monomers have a potential toxic effect on the desert micro-ecology, which has a weak ability to resist disturbance, often leading to the inactivation of biological crusts. Summary of the Invention

[0003] The purpose of this invention is to provide a desert algae-bacterial composite preparation and its preparation method, aiming to solve the problems in existing technologies such as the easy oxidation, dehydration and death of single-celled desert algae under extreme environments, the easy spatial separation and synergistic failure caused by physical mixing and spraying of bacteria and algae, and the clogging of sand pores and ecotoxicity of chemical binders, thereby achieving rapid construction of desert crusts and efficient sand fixation; specifically, the technical solution of this invention is as follows: A desert algae-bacterial composite preparation comprises a microcapsule embedding matrix and induced functional desert algae embedded within the microcapsule embedding matrix; the microcapsule embedding matrix comprises sodium alginate, trehalose, skim milk powder, and highly hydrophilic mesoporous nano-silica powder; the functional desert algae is prepared by culturing single-celled desert algae under light and shaking in a stress-induced culture medium containing gum-producing bacteria and nitrogen-fixing bacteria, thereby transforming the desert algae cells into functional desert algae with strong stress resistance and extracellular polymers attached to their surface; the single-celled desert algae is selected from Scenedesmus obliquus or Microsheatha spp., the gum-producing bacteria are Bacillus polymyxa, and the nitrogen-fixing bacteria are Azotobacter chroococcus.

[0004] Preferably, the preparation method of the functional desert algae is as follows: The single-celled desert algae were inoculated into BG-11 medium, and the polymyxa bacillus and the azotobacter chrysophagus were inoculated into LB medium. They were cultured to the end of the logarithmic growth phase, and the bacterial cells and algal cells were collected by centrifugation. They were washed twice with sterile physiological saline to obtain the washed algal cells and bacterial cells. The washed algae, Bacillus polymyxa, and Azotobacter chrysophagus were inoculated into the stress-inducing medium at a cell ratio of 10:1:1 and cultured under light and shaking conditions for 48-72 hours. After centrifugation, the sediment was collected to obtain functional desert algae with bacterial cells and their secreted extracellular polymers attached to the surface. The stress-inducing medium is based on nitrogen-free BG-11 medium, with the addition of NaCl at a concentration of 0.15-0.25 mol / L and N-hexanoylhomoserine lactone at a concentration of 0.5-1.0 mg / L.

[0005] Preferably, in the microcapsule encapsulation matrix, the mass ratio of sodium alginate, trehalose, skim milk powder and highly hydrophilic mesoporous nano-silica powder is (1.5-2.0):2.0:5.0:(0.5-1.0); the highly hydrophilic mesoporous nano-silica powder has a pore size of 2-10 nm and a specific surface area greater than 500 m² / g.

[0006] Preferably, a method for preparing the above-mentioned desert algae-bacterial compound preparation includes the following steps: Step 1: Preparation of functional desert algae: Single-celled desert algae were inoculated into a stress-induced culture medium containing gum-producing bacteria and nitrogen-fixing bacteria and cultured under light and shaking. After centrifugation, the sediment was collected to obtain functional desert algae with bacterial cells and their secreted extracellular polymers attached to the surface. Step 2: Prepare the microcapsule encapsulation matrix solution: Add sodium alginate, trehalose, skim milk powder and highly hydrophilic mesoporous nano silica powder to deionized water, stir and mix evenly to obtain the microcapsule encapsulation matrix solution; Step 3, Phase Change Microencapsulation: The functional desert algae obtained in Step 1 are added to the microcapsule encapsulation matrix solution obtained in Step 2, and the mixture is resuspended and mixed to obtain a mixture. Using a high-voltage electrostatic droplet generator, the mixture is dripped at a constant rate into a cross-linking coagulation bath containing calcium ions and chitosan, and cross-linked and solidified for 30 minutes. The mixture is then filtered to obtain hydrogel microcapsules. The phase change refers to the process in which sodium alginate in the microcapsule encapsulation matrix solution undergoes a sol-gel phase transition with calcium ions and chitosan in the cross-linking coagulation bath containing calcium ions and chitosan, forming a three-dimensional network structure of hydrogel microcapsules. Step 4, Gradient freeze-drying: The hydrogel microcapsules obtained in Step 3 are pre-frozen at -80℃ for 4 hours, and then placed in a freeze dryer for programmed temperature rise dehydration freeze-drying until the water content drops to 3-5%, to obtain the desert algae-bacterial complex preparation; The gradient freeze-drying refers to the drying process of crossing the freezing point and room temperature in stages through multi-stage programmed temperature control at a specific low heating rate, so as to avoid the rapid sublimation of water generating ice crystal stress that would damage the structure of the microcapsules and algae-bacterial complex.

[0007] Preferably, in step one, the preparation method of the functional desert algae is as follows: The single-celled desert algae were inoculated into BG-11 medium, and the polymyxa bacillus and the azotobacter chrysophagus were inoculated into LB medium. They were cultured to the end of the logarithmic growth phase, and the bacterial cells and algal cells were collected by centrifugation. They were washed twice with sterile physiological saline to obtain the washed algal cells and bacterial cells. The washed algae, Bacillus polymyxa, and Azotobacter chrysophagus were inoculated into the stress-inducing medium at a cell ratio of 10:1:1 and cultured under light and shaking conditions for 48-72 hours. The sediment was collected by centrifugation to obtain functional desert algae. The stress-inducing medium is based on nitrogen-free BG-11 medium, with the addition of NaCl at a concentration of 0.15-0.25 mol / L and N-hexanoylhomoserine lactone at a concentration of 0.5-1.0 mg / L.

[0008] Preferably, in step two, the microcapsule embedding matrix solution contains, based on the total mass of the microcapsule embedding matrix solution as 100%, sodium alginate with a mass fraction of 1.5-2.0%, trehalose with a mass fraction of 2.0%, skim milk powder with a mass fraction of 5.0%, highly hydrophilic mesoporous nano-silica powder with a mass fraction of 0.5-1.0%, and the remainder is deionized water; the highly hydrophilic mesoporous nano-silica powder has a pore size of 2-10 nm and a specific surface area greater than 500 m² / g.

[0009] Preferably, in step three, the crosslinking coagulation bath is an aqueous acetic acid solution containing 0.1 mol / L CaCl2 and 0.5% chitosan by mass.

[0010] Preferably, in step four, the vacuum degree in the freeze dryer is less than 10 Pa.

[0011] The beneficial effects of this invention are as follows: Inside the composite formulation of the present invention, functional desert algae are tightly wrapped by the bacterial cells and their secreted extracellular polymers, and are combined with the microcapsule embedding matrix to form a stable cross-linked solidification network. After 30 days of simulated desert ultraviolet radiation and continuous drought stress, the survival rate of single-celled algae in the compound preparation of this invention reached 68.5%, while the survival rate of direct spraying of traditional pure algae solution was only 4.2%, showing a significant survival advantage compared with the control group of traditional pure algae solution. Laboratory wind tunnel tests show that after spraying this preparation, a continuous biological crust with a thickness of 3-5 mm can be formed on the surface of quicksand within 10-15 days under the condition of providing only a trace amount of moisture. This crust can resist wind erosion of 15 m / s, while traditional single-celled algae need 3-4 months to form a crust of the same strength under the same conditions. Detailed Implementation

[0012] The technical solutions in the embodiments of the present invention will be clearly and completely described below; the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. The Scenedesmus obliquus, Microsheatha spp., Bacillus polymyxa, and Azotobacter chrysophyllus used in the various embodiments of this invention can all be purchased through conventional commercial channels; the N-hexanoylhomoserine lactone, highly hydrophilic mesoporous nano-silica powder, and other chemical raw materials and reagents involved are all commercially available products; the specific surface area of ​​the highly hydrophilic mesoporous nano-silica powder described in this specification was determined by the BET method, and the pore size was determined by the BJH method; the average particle size of the functional desert algae flocs and hydrogel microcapsules was determined by a laser particle size analyzer. Example 1

[0013] This embodiment provides a stress-resistant desert algae-bacterial compound preparation, which specifically includes the following steps: S1 Preparation of Functional Desert Algae An algal strain of *Scenedesmus obliquus* was inoculated into BG-11 medium and cultured at 25℃, light intensity of 4000 lx, and light-dark ratio of 12 h:12 h until the end of the logarithmic growth phase. *Bacillus polymyxa* and *Azotobacter chrysophagus* were inoculated into LB medium and cultured at 30℃ and 180 rpm until the end of the logarithmic growth phase. The algal and bacterial solutions were centrifuged at 5000 rpm for 10 min, the supernatant was discarded, and the algae and bacteria were washed twice with sterile physiological saline to obtain the washed algal and bacterial cells. A stress-inducing medium was prepared based on nitrogen-free BG-11 medium, with NaCl added to a final concentration of 0.20 mol / L and N-hexanoylhomoserine lactone added to a final concentration of 0.8 mg / L. Washed algae, *Bacillus polymyxa*, and *Azotobacter chrysophagus* were inoculated into the stress-inducing medium at a cell ratio of 10:1:1, with the initial inoculation concentration of *Scenedesmus obliquus* controlled at 1.0 × 10⁶ cells / mL. 6 The initial inoculation concentration of Bacillus polymyxa was 1.0 × 10⁶ cells / mL. 5 The initial inoculum concentration of *Azotobacter chrysophagus* was 1.0 × 10⁶ cells / mL. 5 Cells / mL, cultured under light and shaking at 25℃, 150rpm, and 4000lx for 60h; After cultivation, the cells were centrifuged at 4000 rpm for 8 min, and the sediment was collected to obtain functional desert algae with bacterial cells and extracellular polymers attached to their surface. Microscopic observation showed that the average particle size of the obtained flocs was 90 μm. The extracellular polymers were mainly composed of polysaccharides and proteins secreted by Bacillus polymyxa and Azotobacter chrysophyll under stress induction, which were used to form a stress-resistant coating layer with adhesion and water retention functions on the surface of algal cells. Through the bacterial cells and extracellular polymers attached to their surface, this functional desert algae can significantly improve the stress resistance and survival rate of algal cells under subsequent drying and extreme drought conditions. S2 Preparation of Microcapsule Encapsulation Matrix Solution Weigh out 1.8% sodium alginate, 2.0% trehalose, 5.0% skim milk powder, and 0.8% highly hydrophilic mesoporous nano-silica powder by mass fraction, add them to deionized water, and stir at room temperature for 60 min to obtain a uniform microcapsule encapsulation matrix solution. The pore size of the mesoporous nano-silica powder used is 6 nm, and the specific surface area is 620 m² / g. This microcapsule encapsulation matrix solution provides a uniform matrix environment for subsequent encapsulation, effectively protecting algal cells from external mechanical and environmental stresses. At the same time, the mesoporous nano-silica powder enhances the water retention and water absorption capacity of the microcapsules. S3 phase change microencapsulation The functional desert algae obtained in step S1 were added to the embedding matrix solution obtained in step S2 at a mass-to-volume ratio of 1:8 (wet weight to embedding matrix solution). The mixture was stirred at low speed for 15 minutes to disperse it evenly, thus obtaining a mixed solution. Using a high-voltage electrostatic droplet generator, the mixed solution was uniformly dropped into a crosslinking coagulation bath containing 0.1 mol / L CaCl2 and 0.5% chitosan under the conditions of 8 kV voltage, 1.2 mm nozzle inner diameter, and 1.5 mL / min flow rate, and solidified for 30 minutes. After filtration, the microcapsules were quickly rinsed once with sterile water to obtain hydrogel microcapsules with an average particle size of 450 μm. These hydrogel microcapsules, as a spatially confining shell, can tightly encapsulate the bacterial-algae complex, which not only slows down the structural shrinkage during the drying process but also provides a stable microecological microenvironment for the synergistic metabolism of bacteria and algae after rehydration. S4 gradient freeze-drying The hydrogel microcapsules obtained in step S3 were pre-frozen at -80℃ for 4 hours, then transferred to a freeze dryer and subjected to programmed temperature rise dehydration freeze drying under a vacuum of 8 Pa. The specific program was as follows: the temperature was raised from -80℃ to -30℃ at a rate of 1℃ / min and held for 10 hours, then raised to 0℃ at a rate of 0.5℃ / min and held for 10 hours, and finally raised to 25℃ at a rate of 0.5℃ / min and held for 5 hours until the water content dropped to 4.0%, resulting in a powdered desert algae-bacterial composite preparation.

[0014] Example 2

[0015] The process steps in this embodiment are the same as those in Embodiment 1, the difference being that the parameters are a combination near the lower limit of the protection range: In S1, the NaCl concentration in the stress-inducing medium was 0.15 mol / L, the N-hexanoylhomoserine lactone concentration was 0.5 mg / L, and the initial inoculum concentration of *Scenedesmus obliquus* was 0.8 × 10⁻⁶ cells. 6 The initial inoculation concentration of Bacillus polymyxa was 0.8 × 10⁶ cells / mL. 5 The initial inoculum concentration of *Azotobacter chrysophagus* was 0.8 × 10⁶ cells / mL. 5 Cells / mL, cultured under light and shaking for 48h; the resulting functional desert algae can also improve the stress resistance and survival rate of algal cells under dry and arid conditions; In S2, the mass fraction of sodium alginate is 1.5%, the mass fraction of trehalose is 2.0%, the mass fraction of skim milk powder is 5.0%, and the mass fraction of highly hydrophilic mesoporous nano-silica powder is 0.5%. The pore size of the mesoporous nano-silica powder is 4 nm, and the specific surface area is 510 m² / g. The resulting microcapsule encapsulation matrix solution provides a uniform protective matrix environment for subsequent encapsulation, enhancing the water retention and water absorption capacity of the microcapsules. In step S3, the resulting hydrogel microcapsules can tightly encapsulate the bacterial-algae complex, slow down structural shrinkage during the drying process, and provide a stable micro-ecological environment for synergistic metabolism after rehydration. In S4, the specific program for temperature-controlled freeze drying is as follows: the temperature is increased from -80℃ to -30℃ at a rate of 1℃ / min and held for 8 hours, then increased to 0℃ at a rate of 0.5℃ / min and held for 8 hours, and finally increased to 25℃ at a rate of 0.5℃ / min and held for 4 hours, freeze-drying to a moisture content of 4.8%.

[0016] Example 3

[0017] The process steps in this embodiment are the same as those in Embodiment 1, the difference being that the parameters are a combination near the upper limit of the protection range: In S1, the NaCl concentration in the stress-inducing medium was 0.25 mol / L, the N-hexanoylhomoserine lactone concentration was 1.0 mg / L, and the initial inoculum concentration of *Scenedesmus obliquus* was 1.2 × 10⁻⁶ cells. 6 The initial inoculation concentration of *Bacillus polymyxa* was 1.2 × 10⁶ cells / mL. 5 The initial inoculum concentration of *Azotobacter chrysophagus* was 1.2 × 10⁶ cells / mL. 5 Cells / mL, cultured under light and shaking for 72 h; the resulting functional desert algae significantly enhanced the algal cells' resistance and survival rate under extreme conditions through the bacterial cells and extracellular polymers attached to their surface. In S2, the mass fraction of sodium alginate is 2.0%, the mass fraction of trehalose is 2.0%, the mass fraction of skim milk powder is 5.0%, and the mass fraction of highly hydrophilic mesoporous nano-silica powder is 1.0%. The pore size of the mesoporous nano-silica powder is 6-10 nm, and the specific surface area is 680 m² / g. The resulting microcapsule encapsulation matrix solution provides a stable matrix environment for subsequent encapsulation, effectively protecting algal cells from external stress and improving water retention and absorption performance. In step S3, the obtained hydrogel microcapsules serve as a spatially confining shell, tightly encapsulating the bacterial-algae complex, slowing down water loss, and providing an excellent microenvironment for synergistic metabolism after rehydration; In S4, the specific program for temperature-controlled freeze drying is as follows: the temperature is increased from -80℃ to -30℃ at a rate of 1℃ / min and held for 12 hours, then increased to 0℃ at a rate of 0.5℃ / min and held for 12 hours, and finally increased to 25℃ at a rate of 0.5℃ / min and held for 6 hours, freeze-drying to a moisture content of 3.2%.

[0018] Example 4

[0019] The process steps in this embodiment are the same as those in Embodiment 1, the difference being the type of desert algae and some intermediate parameters: In S1, *Microsheatha stenoptera* replaced *Scenedesmus obliquus*; the NaCl concentration in the stress-induced medium was 0.22 mol / L, the N-hexanoylhomoserine lactone concentration was 0.7 mg / L, and the culture was carried out under light and shaking for 60 h. In S2, the mass fraction of sodium alginate is 1.7%, the mass fraction of trehalose is 2.0%, the mass fraction of skim milk powder is 5.0%, the mass fraction of highly hydrophilic mesoporous nano-silica powder is 0.7%, the pore size of the mesoporous nano-silica powder is 3-7nm, and the specific surface area is 590m² / g. In S4, freeze-dry to a moisture content of 4.3%.

[0020] Comparative Example 1: The difference between this comparative example and Example 1 is that Bacillus polymyxa is omitted, while the remaining operation steps and process parameters are exactly the same as in Example 1. In step S1, only Scenedesmus obliquus and Azotobacter chrysotrichum are inoculated into the stress-inducing medium at a cell ratio of 10:1, and the subsequent embedding and freeze-drying steps remain unchanged.

[0021] Comparative Example 2: The difference between this comparative example and Example 1 is that: Azotobacter chrysozoans is omitted, while the remaining operation steps and process parameters are exactly the same as in Example 1; In step S1, only Scenedesmus obliquus and Bacillus polymyxa are inoculated into the stress-inducing medium at a cell ratio of 10:1, and the subsequent embedding and freeze-drying steps remain unchanged.

[0022] Comparative Example 3: The difference between this comparative example and Example 1 is that N-hexanoylhomoserine lactone is not added to the stress induction medium in step S1, while the remaining operation steps and process parameters are exactly the same as in Example 1.

[0023] Comparative Example 4: The difference between this comparative example and Example 1 is that in step S1, the nitrogen-free BG-11 medium is replaced with nitrogen-containing BG-11 medium, while the remaining operation steps and process parameters are exactly the same as in Example 1.

[0024] Comparative Example 5: The difference between this comparative example and Example 1 is that the highly hydrophilic mesoporous nano-silicon powder is omitted in step S2, while the remaining operation steps and process parameters are exactly the same as in Example 1.

[0025] Comparative Example 6: The difference between this comparative example and Example 1 is that the crosslinking coagulation bath in step S3 contains only 0.1 mol / L CaCl2 and does not contain chitosan. The remaining operation steps and process parameters are exactly the same as in Example 1.

[0026] Comparative Example 7: The difference between this comparative example and Example 1 is that steps S3 and S4 are omitted, and microencapsulation and freeze-drying are not performed; the functional desert algae flocculants obtained in step S1 are collected by centrifugation and used directly for subsequent performance testing, while the remaining operation steps and process parameters are exactly the same as in Example 1.

[0027] Performance Testing and Datasheets Each group of samples was mixed with sterilized quicksand at a mass ratio of 1:80, spread in petri dishes, and subjected to continuous stress for 30 days under UV-B irradiation intensity of 5 W / m² and sand moisture content of 0.5%. The survival rate of algal cells was determined by the fluorescein diacetate-propidium iodide live-dead staining method. During rehydration, 2 mm of water was sprayed evenly onto the sample surface, and the photosynthetic activity recovery rate was measured after standing for 24 hours. The crust thickness was measured as the average thickness of the profile after 15 days of cultivation, and the critical wind speed for wind erosion resistance was measured as the wind speed corresponding to a 5% mass loss of the sample in the wind tunnel.

[0028] Table 1. Performance test results of each group of desert algae and bacteria compound preparations.

[0029]

[0030] As can be seen from the comparison of the test results of Example 1 and Comparative Example 1 in the table, after omitting Bacillus polymyxa, the algal cell survival rate, the photosynthetic activity recovery rate after 24 hours of rehydration, the crust thickness and the critical wind speed for wind erosion resistance all showed a downward trend. Its mechanism of action is as follows: Bacillus polymyxa is an important source of complex extracellular polymers. When this bacterium is missing, the polysaccharide coating layer formed on the surface of algal cells is reduced, the intercellular connection strength inside the flocculant decreases, the rate of water loss during drying increases, and the local osmotic pressure fluctuations are aggravated during rehydration, resulting in increased cell membrane damage. The continuous network inside the microcapsules formed after encapsulation is insufficient, and the ability to bind sand particles after revival decreases. Therefore, the thickness of the crust and the wind erosion resistance are reduced simultaneously. As can be seen from the comparison of the test results of Example 1 and Comparative Example 2 in the table, after omitting Azotobacter chrysophagus, all the performances also showed a downward trend. Its mechanism of action is that Azotobacter chrysoprase can provide available nitrogen sources under nitrogen-deficient conditions and secrete stress-resistant metabolites such as trehalose and proline. Without this bacterium, the nitrogen supply in the co-culture system is insufficient, the protective substances accumulated by algal cells during the stress culture stage are reduced, and the metabolic recovery rate after rehydration is reduced. At the same time, the nutrient supply is insufficient in the early stage of crust formation, the ability of algae and bacteria to continue secreting extracellular polymers is weakened, resulting in a decrease in the crust thickening rate and mechanical stability. The comparison of the test results of Example 1 and Comparative Example 3 in the table shows that the absence of N-hexanoylhomoserine lactone leads to a decrease in various indicators; Its mechanism of action is that exogenous quorum sensing molecules can promote signal transduction in the algae-bacteria co-culture system, enhance extracellular polymer secretion and cell aggregation; when this molecule is missing, the degree of self-assembly between algae and bacteria is reduced, the proportion of tightly packed flocs in the sedimentation component decreases, the microecological structure before encapsulation is relatively loose, and the protective effect on cells during freeze-drying is weakened; after rehydration, the synchronicity of cell recovery is low, and the rate of crust formation and wind erosion resistance are both affected. As can be seen from the comparison of the test results of Example 1 and Comparative Example 4 in the table, the performance decreased after replacing the nitrogen-free BG-11 with the nitrogen-containing BG-11. Its mechanism of action is that nitrogen deficiency is an important factor in inducing a synergistic stress resistance response in algal-bacterial systems. When there is sufficient nitrogen in the culture medium, nitrogen fixation metabolism of Azotobacter chrysophyll is inhibited, the driving force of algal cells to secrete extracellular polymers and protective metabolites is weakened, and the compactness of flocs decreases. This change weakens the protective cell surface layer formed before encapsulation, thereby reducing the survival rate under drought and ultraviolet stress, and reducing the strength of the adhesion network during the crust formation process. The comparison of the test results of Example 1 and Comparative Example 5 in the table shows that omitting the highly hydrophilic mesoporous nano-silica powder will increase the decrease in photosynthetic activity recovery rate, crust thickness and critical wind speed for wind erosion resistance after 24 hours of rehydration, and also reduce the survival rate of algal cells. Its mechanism of action is that mesoporous nano-silica powder has a high specific surface area and capillary water absorption capacity, which can accelerate the water absorption and conduction process of microcapsules under low water conditions. When this component is missing, the rehydration rate of microcapsules under trace moisture conditions decreases, the recovery of local areas inside the capsule is asynchronous, and the recovery of cell metabolism is delayed, resulting in a decrease in the early growth rate of the crust. Due to the discontinuous distribution of extracellular polymers during the crust formation period, the wind erosion resistance decreases accordingly. The comparison of the test results of Example 1 and Comparative Example 6 in the table shows that the absence of chitosan in the crosslinking coagulation bath containing calcium ions and chitosan will lead to a decrease in various properties. Its mechanism of action is as follows: chitosan can form a surface polyelectrolyte complex membrane with sodium alginate, which improves the mechanical integrity of the microcapsule surface and slows down the structural shrinkage during the drying process; when chitosan is lacking, the microcapsules rely solely on Ca²⁺ cross-linking, resulting in insufficient outer layer density, which increases the probability of microcracks during freeze-drying and storage, exposing some cells to external stress environments, thus reducing survival rate and rehydration recovery rate; decreased capsule structural stability also affects the particle anchoring effect in the early stage of crust formation. As can be seen from the comparison of the test results of Example 1 and Comparative Example 7 in the table, all performance indicators decreased significantly after omitting the microcapsule encapsulation and freeze-drying steps. Its mechanism of action is as follows: Although the functional desert algal flocs have formed a certain degree of bacterial and algal aggregation structure, they lack the protective matrix composed of sodium alginate, trehalose, skim milk powder and mesoporous nano silica powder. The cells are directly exposed under dry stress and ultraviolet radiation, and the membrane structure and protein system are more severely damaged. Without the spatial constraint of the microcapsule shell, the flocs are easily dispersed between sand grains. After rehydration, the bacterial and algal synergistic recovery efficiency is low, resulting in the greatest reduction in crust thickness and wind erosion resistance. The test results from Examples 1 to 4 show that, within the scope of this invention, adjusting the salt concentration, quorum sensing molecule concentration, embedding matrix ratio, and algal species type can yield corresponding stress survival rates and stable crusting performance. In Example 2, when parameters were used near the lower limit, the algal flocculation and capsule skeleton strength decreased, so the performance was slightly lower than that of Example 1. In Example 3, when parameters were used near the upper limit, although the encapsulation strength and water retention capacity were improved, the higher salinity and higher matrix viscosity would increase the metabolic burden on some cells, so the overall performance was still slightly lower than that of Example 1. In Example 4, after using *Microsheatha spp.*, the high survival rate and crusting ability were maintained due to its strong extracellular secretion capacity, indicating that the present invention is applicable to different single-celled desert algae.

[0031] The above are merely specific embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any conventional modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. A desert algae and bacteria compound preparation, characterized in that: The aforementioned desert algae-bacteria composite preparation comprises a microcapsule embedding matrix and induced functional desert algae embedded within the microcapsule embedding matrix; the microcapsule embedding matrix comprises sodium alginate, trehalose, skim milk powder, and highly hydrophilic mesoporous nano-silica powder. The aforementioned functional desert algae is produced by culturing single-celled desert algae under light and shaking in a stress-induced medium containing gum-producing bacteria and nitrogen-fixing bacteria, thereby transforming the desert algae cells into functional desert algae with strong stress resistance and extracellular polymers attached to their surface; the single-celled desert algae are selected from Scenedesmus obliquus or Microsheatha spp., the gum-producing bacteria are Bacillus polymyxa, and the nitrogen-fixing bacteria are Azotobacter chrysophyll.

2. The desert algae and bacteria compound preparation according to claim 1, characterized in that, The preparation method of the aforementioned functional desert algae is as follows: The single-celled desert algae were inoculated into BG-11 medium, and the polymyxa bacillus and the azotobacter chrysophagus were inoculated into LB medium. They were cultured to the end of the logarithmic growth phase, and the bacterial cells and algal cells were collected by centrifugation. They were washed twice with sterile physiological saline to obtain the washed algal cells and bacterial cells. The washed algae, Bacillus polymyxa, and Azotobacter chrysophagus were inoculated into the stress-inducing medium at a cell ratio of 10:1:1 and cultured under light and shaking conditions for 48-72 hours. After centrifugation, the sediment was collected to obtain functional desert algae with bacterial cells and their secreted extracellular polymers attached to the surface. The stress-inducing medium is based on nitrogen-free BG-11 medium, with the addition of NaCl at a concentration of 0.15-0.25 mol / L and N-hexanoylhomoserine lactone at a concentration of 0.5-1.0 mg / L.

3. The desert algae and bacteria compound preparation according to claim 1, characterized in that, In the microcapsule encapsulation matrix, the mass ratio of sodium alginate, trehalose, skim milk powder and highly hydrophilic mesoporous nano-silica powder is (1.5-2.0):2.0:5.0:(0.5-1.0); the highly hydrophilic mesoporous nano-silica powder has a pore size of 2-10 nm and a specific surface area greater than 500 m² / g.

4. A method for preparing the desert algae and bacteria compound preparation according to claim 1, characterized in that, Includes the following steps: Step 1: Preparation of functional desert algae: Single-celled desert algae were inoculated into a stress-induced culture medium containing gum-producing bacteria and nitrogen-fixing bacteria and cultured under light and shaking. After centrifugation, the sediment was collected to obtain functional desert algae with bacterial cells and their secreted extracellular polymers attached to the surface. Step 2: Prepare the microcapsule encapsulation matrix solution: Add sodium alginate, trehalose, skim milk powder and highly hydrophilic mesoporous nano silica powder to deionized water, stir and mix evenly to obtain the microcapsule encapsulation matrix solution; Step 3, Phase Change Microencapsulation: The functional desert algae obtained in Step 1 are added to the microcapsule encapsulation matrix solution obtained in Step 2, and the mixture is resuspended and mixed to obtain a mixture. Using a high-voltage electrostatic droplet generator, the mixture is dripped at a constant rate into a cross-linking coagulation bath containing calcium ions and chitosan, and cross-linked and solidified for 30 minutes. The mixture is then filtered to obtain hydrogel microcapsules. The phase change refers to the process in which sodium alginate in the microcapsule encapsulation matrix solution undergoes a sol-gel phase transition with calcium ions and chitosan in the cross-linking coagulation bath containing calcium ions and chitosan, forming a three-dimensional network structure of hydrogel microcapsules. Step 4, Gradient freeze-drying: The hydrogel microcapsules obtained in Step 3 are pre-frozen at -80℃ for 4 hours, and then placed in a freeze dryer for programmed temperature rise dehydration freeze-drying until the water content drops to 3-5%, to obtain the desert algae-bacterial complex preparation; The gradient freeze-drying refers to the drying process of crossing the freezing point and room temperature in stages through multi-stage programmed temperature control at a specific low heating rate, so as to avoid the rapid sublimation of water generating ice crystal stress that would damage the structure of the microcapsules and algae-bacterial complex.

5. The preparation method of the desert algae and bacteria compound preparation according to claim 4, characterized in that, In step one, the specific method for preparing the functional desert algae is as follows: The single-celled desert algae were inoculated into BG-11 medium, and the polymyxa bacillus and the azotobacter chrysophagus were inoculated into LB medium. They were cultured to the end of the logarithmic growth phase, and the bacterial cells and algal cells were collected by centrifugation. They were washed twice with sterile physiological saline to obtain the washed algal cells and bacterial cells. The washed algae, Bacillus polymyxa, and Azotobacter chrysophagus were inoculated into the stress-inducing medium at a cell ratio of 10:1:1 and cultured under light and shaking conditions for 48-72 hours. The sediment was collected by centrifugation to obtain functional desert algae. The stress-inducing medium is based on nitrogen-free BG-11 medium, with the addition of NaCl at a concentration of 0.15-0.25 mol / L and N-hexanoylhomoserine lactone at a concentration of 0.5-1.0 mg / L.

6. The method for preparing the desert algae-bacterial compound preparation according to claim 4 or 5, characterized in that, In step two, the microcapsule embedding matrix solution contains, based on the total mass of the microcapsule embedding matrix solution as 100%, sodium alginate with a mass fraction of 1.5-2.0%, trehalose with a mass fraction of 2.0%, skim milk powder with a mass fraction of 5.0%, highly hydrophilic mesoporous nano-silica powder with a mass fraction of 0.5-1.0%, and the remainder is deionized water; the highly hydrophilic mesoporous nano-silica powder has a pore size of 2-10 nm and a specific surface area greater than 500 m² / g.

7. The preparation method of the desert algae-bacterial compound preparation according to claim 4 or 5, characterized in that, In step three, the cross-linking coagulation bath is an aqueous acetic acid solution containing 0.1 mol / L CaCl2 and 0.5% chitosan by mass.

8. The method for preparing the desert algae-bacterial compound preparation according to claim 4 or 5, characterized in that, In step four, the vacuum level in the freeze dryer is less than 10 Pa.

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