Straw decomposition bacteria for passivating cadmium and arsenic and application thereof

Abstract

The application discloses a cadmium-arsenic passivation straw decomposition fungus and application thereof. The cadmium-arsenic passivation straw decomposition fungus is Fusarium oxysporum CA302, and the preservation number of the fungus in China Typical Culture Collection Center is CCTCC NO: M2023446. The strain CA302 and the bacterial liquid thereof can not only accelerate the decomposition efficiency of rice straw, but also can tolerate and remove cadmium and / or arsenic. The strain can also passivate cadmium and arsenic in soil, and provides guarantee for safe utilization of rice straw in cadmium-arsenic contaminated soil.

Description

Technical Field

[0001] This invention belongs to the fields of environmental microbiology technology and pollution control technology, and relates to a straw decomposing bacterium that passivates cadmium and arsenic and its application. Specifically, it relates to a Fusarium oxysporum CA302 that has the function of decomposing rice straw and can simultaneously passivate cadmium and arsenic. Background Technology

[0002] Heavy metals cadmium (Cd) and metalloid arsenic (As) are typical pollutants in soils of southern my country. Cd and As have significantly different physicochemical properties and exhibit opposite characteristics in soil migration, fixation, and absorption and translocation by plants. Therefore, the remediation and treatment of soils with combined pollution should not focus on a single pollutant, ignoring the comprehensive and complex nature of the pollution. Thus, conducting research on Cd-As combined pollution is essential.

[0003] Crop straw is a common biomass resource, containing carbonaceous compounds such as cellulose, hemicellulose, and lignin, as well as nitrogen, phosphorus, potassium, and other trace elements essential for plant growth. It is the crop residue remaining after grain harvest. my country is a major agricultural producer, generating hundreds of millions of tons of crop straw annually. Returning straw to the field, as an environmentally friendly form of resource reuse, has been widely promoted in recent years. Returning straw to the field can improve land use efficiency, increase soil microbial activity, and enhance soil fertility. However, the main components of crop straw have a dense structure, large molecular weight, and strong resistance to decomposition, making them difficult to decompose naturally and resulting in a long decomposition time. This may affect the emergence of subsequent crops and inhibit early crop growth. Therefore, it is necessary to specifically disrupt the structure of straw to achieve rapid decomposition. When straw grown in farmland contaminated with heavy metals is returned to the field, the heavy metals fixed in the straw will be released as the straw decomposes. Returning straw to the field can also alter the bioavailability of Cd and As in the soil, and have a toxic effect on soil microorganisms. Research progress has been made in the microbial rapid composting and microbial passivation technologies for straw. Numerous studies have been reported on the screening of microorganisms that can accelerate decomposition, such as straw-degrading bacteria, cellulose-degrading bacteria, and lignin-degrading bacteria. Among them, *Bacillus*, *Streptomyces*, *Trichoderma*, *Penicillium*, and *Aspergillus* are the main microbial groups that degrade lignocellulose. Chen Lulu (2019) found that inoculation with *Aspergillus fumigatus* significantly reduced lignin in straw by 52.22%; Huang Yali (2020) screened *Trichoderma longifolia*, which achieved a straw degradation rate of 56.73%. Microorganisms can transform cadmium and arsenic into relatively stable solid phases through precipitation and biotransformation. Li (2019) screened a cadmium-tolerant copper-loving bacterium (*Cupriavidus* sp.) that reduced available Cd in soil by 6.5%. Zhou Wuxian (2018) inoculated arsenic-oxidizing bacteria DWY-1 into arsenic-contaminated soil, which reduced the content of extractable arsenic in soil and pore water by 80% and 73%, respectively.

[0004] Currently, most microbial inoculants suffer from limitations due to their singular microbial function, and their activity is also affected by heavy metals, thus reducing their effectiveness. Overcoming the technical bottleneck of large-scale, rapid composting and returning of rice straw to the field while simultaneously passivating cadmium and arsenic is a pressing issue for the safe utilization of rice straw in southern my country. Therefore, it is necessary to develop strains capable of rapidly composting rice straw and tolerating and passivating heavy metals, thereby reducing the absorption and translocation of heavy metals by crops and ensuring food security. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a straw decomposing bacteria with the ability to rapidly decompose rice straw and tolerate and passivate heavy metals, which can be used for rapid decomposition of straw returned to the field in cadmium and arsenic contaminated soil and simultaneously passivate cadmium and arsenic, and its application.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution.

[0007] A straw-decomposing bacterium that passivates cadmium and arsenic, wherein the straw-decomposing bacterium that passivates cadmium and arsenic is Fusarium oxysporum CA302, whose accession number at the China Center for Type Culture Collection (CCTCC) is M2023446, the address of the depository is China Center for Type Culture Collection (CCTCC), No. 299 Bayi Road, Wuchang District, Wuhan City, Hubei Province, China (within the campus of Wuhan University), and the deposit date is March 31, 2023.

[0008] The colony characteristics of *Fusarium oxysporum* CA302 of this invention are as follows: The colonies are round, with flocculent protrusions, relatively regular edges, and a dense texture. In the early stages of cultivation, the mycelium is white with short, fluffy hyphae; later, the colonies become flocculent, and the center of the colony darkens to a light purple. In liquid culture medium, the colonies are initially white to light pink, and later turn pink to purple.

[0009] As a general technical concept, the present invention also provides an application of the above-mentioned passivated cadmium and arsenic straw-decomposing bacteria in the decomposition of rice straw.

[0010] As a general technical concept, the present invention also provides the application of the above-mentioned cadmium and arsenic passivating straw decomposing bacteria in tolerant Cd and / or As.

[0011] As a general technical concept, the present invention also provides the application of the above-mentioned straw decomposing bacteria that passivate cadmium and arsenic in the removal of Cd and / or As.

[0012] As a general technical concept, the present invention also provides a bacterial solution containing the above-mentioned straw-decomposing bacteria that passivate cadmium and arsenic.

[0013] Preferably, the preparation process of the bacterial solution is as follows: 1.5% to 2% of the cadmium- and arsenic-passivating straw-decomposing bacteria are inoculated into PDA liquid culture medium, and cultured with shaking at 28℃ to 35℃ and 150 rpm to 180 rpm for 3 to 5 days. Then, the bacteria are collected by centrifugation and washed with sterile water to obtain the bacterial solution; wherein, the concentration of potato flour in the PDA liquid culture medium is 6 g / L to 12 g / L, and the concentration of glucose is 20 g / L.

[0014] As a general technical concept, the present invention also provides an application of the above-mentioned bacterial solution in the decomposition of rice straw.

[0015] As a general technical concept, the present invention also provides the application of the above-mentioned bacterial solution in tolerance to Cd and / or As.

[0016] As a general technical concept, the present invention also provides the application of the above-mentioned bacterial solution in removing Cd and / or As from a solution.

[0017] As a general technical concept, the present invention also provides the application of the above-mentioned bacterial solution in passivated soil containing Cd and / or As.

[0018] Compared with the prior art, the advantages of the present invention are as follows:

[0019] The straw-decomposing bacterium for passivating cadmium and arsenic in this invention is *Fusarium oxysporum* CA302. This strain not only has good rice straw decomposition function but also exhibits good tolerance and removal efficiency for Cd and As. The decomposition rate of rice straw using the strain of this invention reached 57.92%, which is 59.41% higher than the decomposition rate of rice straw without the strain. The strain of this invention has a tolerance to Cd up to 100 mg / L and a tolerance to arsenic up to 200 mg / L, meaning it can grow well at Cd and As concentrations of 100 and 200 mg / L, respectively. This strain can passivate Cd and As in liquid culture medium; at an initial Cd and As concentration of 10 mg / L, the removal rates are 57.67% and 96.64%, respectively.

[0020] Preservation of biological materials

[0021] A straw-decomposing bacterium that passivates cadmium and arsenic, wherein the straw-decomposing bacterium that passivates cadmium and arsenic is Fusarium oxysporum CA302, whose accession number at the China Center for Type Culture Collection (CCTCC) is M2023446, the address of the depository is China Center for Type Culture Collection (CCTCC), No. 299 Bayi Road, Wuchang District, Wuhan City, Hubei Province, China (within the campus of Wuhan University), and the deposit date is March 31, 2023. Attached Figure Description

[0022] Figure 1 This is a colony diagram of Fusarium oxysporum CA302 screened in Example 1 of the present invention.

[0023] Figure 2 This is the phylogenetic tree of Fusarium oxysporum CA302 screened in Example 1 of the present invention.

[0024] Figure 3 This is a comparison chart of the weight loss rates of rice straw decomposed by Fusarium oxysporum CA302, commercially available straw composting agent, and control group CK in Example 2 of this invention.

[0025] Figure 4 This is a comparison chart of pH changes during the decomposition of rice straw by Fusarium oxysporum CA302, commercially available straw composting agent, and control group CK in Example 2 of this invention.

[0026] Figure 5 This is a biomass curve of Fusarium oxysporum CA302 under different Cd and As concentration levels in Example 3 of the present invention.

[0027] Figure 6 This is a comparative graph showing the effects of Fusarium oxysporum CA302, commercially available straw composting agent, rice straw, and the control group on the available Cd content in soil in Example 5 of this invention.

[0028] Figure 7 This is a comparative graph showing the effects of Fusarium oxysporum CA302, commercially available straw composting agent, rice straw, and the control group on the available As content in the soil in Example 5 of this invention. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention. The materials and instruments used in the following embodiments are all commercially available. The commercially available straw composting agent was purchased from Zhengzhou Yijiayi Biotechnology Co., Ltd. The composting agent is mainly composed of specialized probiotics such as Bacillus subtilis, lactic acid bacteria, yeast, and deamination and denitrification bacteria, as well as bioactive enzyme preparations, and is mainly used for the rapid composting of agricultural waste such as straw.

[0030] The culture medium and soil suspension used in the following examples are as follows:

[0031] Medium 1 (Czapek's medium): 2 g / L NaNO3, 1 g / L K2HPO4, 0.5 g / L MgSO4·7H2O, 0.5 g / L KCl, 0.01 g / L FeSO4, 30 g / L sucrose. Solid medium is this liquid medium with the addition of 15-20 g / L agar.

[0032] Medium No. 2 (PDA medium): 6 g / L potato flour, 20 g / L glucose, 20 g / L agar.

[0033] Soil suspension: Add 5g of soil to 100mL of sterile water, shake at 30℃ and 150rpm for 30min, let stand for 2h, filter the supernatant, and dilute the filtrate 100 times with sterile water for later use.

[0034] Example 1

[0035] The present invention discloses a straw-decomposing bacterium that passivates cadmium and arsenic. The straw-decomposing bacterium that passivates cadmium and arsenic is Fusarium oxysporum CA302, with accession number CCTCC NO: M2023446 at the China Center for Type Culture Collection (CCTCC), located at No. 299 Bayi Road, Wuchang District, Wuhan City, Hubei Province, China (within the campus of Wuhan University). The accession date is March 31, 2023.

[0036] The strain in this embodiment was taken from a cadmium-arsenic contaminated farmland soil in Zhuzhou City, Hunan Province. The soil sample was taken from the 5-20cm topsoil layer, with a pH of 5.47. The Cd and As concentrations were 22.86 mg / kg and 44.51 mg / kg, respectively, exceeding the risk screening values ​​for agricultural land soil in the "Soil Environmental Quality Standard for Agricultural Land Soil Pollution Risk Control (Trial) (GB 15618-2018)" by 76.2 times and 1.48 times, respectively. The soil was cadmium-arsenic contaminated. The isolation and screening process of strain Fusarium oxysporum CA302 is as follows:

[0037] (1) Two 5.0g soil samples were added to 50mL of Czapek's liquid medium (No. 1) containing 10mg / L Cd and 50mL of Czapek's liquid medium (No. 1) containing 10mg / L As, respectively. Both media were sterilized and cultured at 30℃ and 150rpm with shaking for 5 days as one culture cycle. After one cycle, a new 50mg / L Cd and As concentration of No. 1 liquid medium was inoculated at a 2% (v / v) inoculation rate, and the culture was continued with shaking for another cycle. The samples were then transferred to No. 1 medium containing 100, 150, and 200mg / L Cd and As, respectively. After the culture was completed, 0.2mL of the last liquid was taken, diluted 10 times, and spread on No. 1 solid medium plates. The plates were incubated upside down at 30℃ for 5 days. The colony growth was observed visually, and typical colonies with different morphologies were selected and purified on new plates until a pure strain with consistent colony characteristics was cultured.

[0038] (2) The three pure bacterial strains isolated in step (1) were inoculated into PDA medium No. 2 and cultured at 30℃ and 150 rpm with shaking. After 72 h of culture, the bacterial cells were centrifuged at 4000 rpm to remove the supernatant. The resulting precipitate was washed with 100 mL of sterile water, and 10 mL was transferred to 5 g of rice straw with a length of 2-3 cm. Soil suspension was added to bring the total volume to 80 mL. After 60 days of culture, the straw was washed with sterile water, dried to constant weight, and weighed. The weight loss rate (decomposition rate) of the straw = (weight of straw before decomposition - weight of straw after decomposition) / weight of straw before decomposition × 100%. The experiment was repeated three times, and the average value was taken. The strain used in the treatment with the highest weight loss rate (decomposition rate) of rice straw was the strain Fusarium oxysporum CA302 of this invention.

[0039] The colony characteristics of the strain Fusarium oxysporum CA302 of this invention are as follows: the colonies of strain CA302 are round, with flocculent protrusions, relatively regular edges, and a dense texture, such as... Figure 1 As shown. In the early stages of cultivation, the mycelium is white with short, fluffy strands. Later, the colonies become fluffy, and the center of the colony darkens to a light purple. In liquid culture medium, the mycelium is initially white to light pink, and later turns pink to purple.

[0040] The ITS region of this strain was amplified by PCR using primers ITS1 (5′-TCCGTAGGTGAACCTGCGG-3′, ITS4 (5′-TCCTCCGCTTATTGATATGC-3′)). The obtained sequences were then compared with data in the NCBI nucleic acid database using the NCBI BLAST program. A sequence highly similar to the strain's sequence was selected as a reference sequence. A phylogenetic tree was constructed using Mega 7.0, and the results are as follows. Figure 2 As shown. By Figure 2 It was found that strain CA302 shared 100% homology with Fusarium oxysporum strain LZ51, therefore it was identified as Fusarium oxysporum sp. and named Fusarium oxysporum CA302. The 16S rDNA sequence of this Fusarium oxysporum CA302 is shown in SEQ ID NO.1.

[0041] Example 2: Decomposition effect of strain Fusarium oxysporum CA302 on rice straw

[0042] The present invention relates to a straw-decomposing bacterium that passivates cadmium and arsenic and the application of its bacterial solution in the decomposition of rice straw.

[0043] The strain CA302 of this invention was inoculated into PDA medium and cultured at 30°C and 150 rpm with shaking. After 72 h of culture, the bacterial cells were centrifuged at 4000 rpm, the supernatant was removed, and the resulting precipitate was washed with 100 mL of sterile water. 10 mL of the precipitate was transferred and added to a series of systems containing 5 g of rice straw with a length of 2-3 cm. Soil suspension was added to bring the total volume of the system to 80 mL, and this system was labeled CA. A straw system without the strain but with added soil suspension was set up as a control (CK). At the same time, a commercially available straw composting agent was added to another group of rice straw at the same dry weight, labeled SD. Each treatment was repeated in triplicate. At 5, 10, 20, 30, 60, 90, and 180 days of culture, straw was collected for the corresponding number of days, the pH of the solution was measured, and the straw was washed with sterile water, dried to constant weight, and weighed. The weight loss rate (composting rate) of the straw = (mass of straw before composting - mass of straw after composting) / mass of straw before composting × 100%. The experiment was repeated three times, and the average value was taken.

[0044] See results Figure 3 and Figure 4 The application of the strain of this invention significantly increases the decomposition rate of rice straw and raises the pH. During the cultivation period, the decomposition rate (CA) of rice straw treated with the strain of this invention increased by 28.45%-79.65% compared to the control (CK). After 180 days of cultivation, the CA rice straw decomposition rate reached 57.92%, an increase of 59.41% compared to CK. Except for the 180th day of cultivation, the pH of the CA treatment increased by 0.50-0.94 pH units compared to CK. At 180 days of cultivation, the decomposition rate of commercially available straw composting agents on rice straw was 58.34%, only 0.42% higher than the composting effect of the CA agent. Therefore, the decomposition effect of the strain CA302 of this invention on rice straw can reach the level of commercially available straw composting products, and can effectively maintain a high decomposition rate of rice straw.

[0045] Example 3: Resistance of strain Fusarium oxysporum CA302 to cadmium and arsenic.

[0046] The present invention relates to a straw decomposing bacterium that passivates cadmium and arsenic and the application of its bacterial solution in tolerance to Cd and As.

[0047] In this embodiment, the cadmium system is a PDA liquid culture medium containing Cd, and the arsenic system is a PDA liquid culture medium containing As. The Cd and As concentrations were diluted using 1000 mg / L CdCl2 and Na3AsO4 stock solutions, respectively. The pH of the Cd and As stock solutions was adjusted to approximately 5.5 beforehand.

[0048] The strain CA302 of this invention was activated in PDA medium and then inoculated at a 2% inoculum into PDA liquid medium containing different concentrations of Cd and As. The culture was carried out at 30°C and 150 rpm for 5 days with shaking. The Cd and As concentrations were 0, 10, 50, 100, 200, 300, 400, and 500 mg / L. The growth of the strain was observed, and samples were taken every 6 or 12 hours. The cell weight was measured by centrifugation, and the tolerance to different Cd and As concentrations was determined. Growth curves of the strain of this invention were plotted for 6 days at Cd and As concentrations of 10 and 100 mg / L. Each treatment was performed in triplicate.

[0049] The biomass and growth curves of strain CA302 of this invention under different Cd and As concentrations are shown in Table 1 and 2. Figure 5 In pure culture medium, strain CA302 was in the logarithmic growth phase for 48-108 hours, with a cell dry weight (i.e., biomass dry weight) reaching 6.37 g at 72 hours and a maximum cell dry weight of 9.78 g. The addition of cadmium and arsenic affected the growth of strain CA302. With increasing Cd and As concentrations, the time for strain CA302 to enter the logarithmic growth phase was delayed, the inhibition of CA302 growth was enhanced, and the cell dry weight at maximum growth decreased. However, low concentrations of Cd and As had no significant effect on the growth of strain CA302. When the concentrations of Cd and As in the culture medium were both 10 mg / L, there was no significant effect on the timing of the logarithmic growth phase of CA302, and the cell dry weights at maximum growth were 8.26 g and 9.92 g, respectively. Compared to strain (CA) in pure culture medium, when the Cd concentration in the medium was 100 mg / L, the strain entered the logarithmic growth phase 24 hours later and the growth of strain CA302 was significantly inhibited, with a 60.94% reduction in biomass dry weight. When the Cd concentration in the medium was higher than 100 mg / L, the growth of the strain was severely inhibited, and the dry weight of CA302 cells decreased by more than 90%. Compared to strain (CA) in pure culture medium, when the As concentration in the medium was 100 mg / L, the strain entered the logarithmic growth phase 6 hours later, with a 34.87% reduction in biomass dry weight. When the As concentration in the medium was 200 mg / L, the biomass dry weight decreased by 52.56%. When the As concentration in the medium was higher than 200 mg / L, the growth of the strain was inhibited, and the dry weight of CA302 cells decreased by more than 70%. This indicates that strain CA302 of the present invention has a certain tolerance to Cd and As, with tolerance levels of 100 mg / L and 200 mg / L, respectively.

[0050] Table 1. Biomass results of the strain Fusarium oxysporum CA302 of this invention under different cadmium and arsenic concentrations.

[0051]

[0052]

[0053] Example 4: Removal of cadmium and arsenic by strain Fusarium oxysporum CA302

[0054] The present invention relates to a straw decomposing bacteria that passivates cadmium and arsenic and the application of its bacterial solution in the removal of Cd and As.

[0055] In this embodiment, the cadmium system was a PDA liquid medium containing Cd, and the arsenic system was a PDA liquid medium containing As. Cd and As concentrations were diluted using 1000 mg / L CdCl2 and Na3AsO4 stock solutions, respectively. The pH of the Cd and As stock solutions was adjusted to approximately 5.5 beforehand. The Cd and As concentrations were 1, 10, 50, and 100 mg / L. A control group without inoculation of strain CA302 was set up for each concentration, and each group had three replicates.

[0056] After activation of strain CA302 in PDA medium, it was inoculated at a rate of 2% into PDA liquid medium containing different concentrations of Cd and As, and cultured at 30°C and 150 rpm for 5 days with shaking. After culture, each system was centrifuged at 4000 rpm for 10 min, and the supernatant was collected and filtered through a 0.45 μm filter membrane. The Cd and As concentrations were determined using ICP-OES (PE8300, USA). The Cd and As concentrations measured in the control group were used as the initial concentrations to calculate the removal rate of Cd and As by strain CA302.

[0057] The removal rate of Cd / As (%) = (C1-C2) / C1, where C1 is the corresponding concentration of Cd / As in the control group (mg / L) and C2 is the corresponding concentration of Cd / As in the experimental group with added strains (mg / L).

[0058] The results are shown in Table 2. With increasing Cd / As concentration, the removal rates of both Cd and As by strain CA302 decreased. In the Cd system, the removal rate of Cd by the strain of this invention ranged from 39.38% to 98.12%; in the As system, the removal rate of As by the strain of this invention ranged from 25.31% to 100.00%. When the heavy metal concentration is below 50 mg / L, the removal rate of As by the strain of this invention is higher than that of Cd.

[0059] Table 2. Removal rates of different cadmium and arsenic concentrations by the strain Fusarium oxysporum CA302 of this invention.

[0060] Cd / As concentration (mg / L) Cd removal rate % As removal rate % 1 98.12 100.00 10 57.67 96.64 50 46.90 52.16 100 39.38 25.31

[0061] Example 5: Passivation effect of strain Fusarium oxysporum CA302 on cadmium and arsenic in soil.

[0062] The application of a bacterial solution containing strain Fusarium oxysporum CA302 of the present invention in passivated soil containing Cd and As.

[0063] The soil used in the experiment was collected from farmland contaminated with cadmium and arsenic. Its pH was 5.40, and the total Cd and As contents were 1.40 mg·kg⁻¹. -1 40.56 mg·kg -1 The soil incubation experiment consisted of four treatments, with three replicates for each treatment, as detailed in Table 3. The CA302 bacterial culture was prepared by culturing strain CA302 in PDA liquid medium for 72 hours, followed by centrifugation, and the bacterial cells were washed three times with sterile water. The dry weight of the CA302 bacterial culture applied to the soil was consistent with that of commercially available straw composting agent. Samples were taken on days 1, 10, 30, 60, and 90 of incubation to determine the available Cd and As content in the soil.

[0064] Table 3 Soil Culture Experiment Treatment Table

[0065] deal with Specific operations CK Control group, kept submerged in 2cm of water CA Add 10 mL of bacterial culture CA302 (0.05 g), the rest is the same as CK. RS+SD Add 1% rice straw (8g) + 0.05g commercially available straw composting agent, the rest is the same as CK. RS+CA Add 1% rice straw (8g) + 10mL of bacterial solution CA302 (0.05g), the rest is the same as CK.

[0066] The results showed that the strain Fusarium oxysporum CA302 of this invention can reduce the content of available Cd and As in the soil.

[0067] Combination Figure 6 It can be seen that adding the bacterial culture CA302 of this invention can reduce the content of available Cd in the soil. By the end of the culture, the content of available Cd in the CA-treated soil was reduced by 0.20 mg·kg compared with the control. -1 The concentration of Cd decreased by 33.26%. Under conditions of added rice straw, the treatment with commercially available straw composting agent and the bacterial solution of this invention also significantly reduced the available Cd content compared to the control (CK). Compared to the CK, the available Cd content in the RS+CA treatment was significantly reduced by 0.18 mg·kg⁻¹. -1 This represents a decrease of 30.35%.

[0068] Combination Figure 7It was found that adding the bacterial solution of this invention to the soil significantly reduced the content of available As. By the end of the culture, the content of available As in the CA-treated soil was 28.34% lower than that in the control (CK). The RS+SD and RS+CA treatments with added rice straw increased the content of available As in the soil, which may be related to changes in soil physicochemical properties and organic matter composition during straw decomposition. Compared with the RS+SD treatment, the CA treatment with added bacterial solution CA302 significantly reduced the content of available As in the soil, decreasing by 2.47%–36.53% compared to the RS+SD treatment. From day 10 to 90 of culture, the content of available As in the RS+CA treatment was significantly lower than that in the RS+SD treatment, indicating that the bacterial solution CA302 also has a passivating effect on As in the soil under straw addition conditions. By the end of the culture, the content of available As in the RS+CA treatment was 11.84% lower than that in the RS+SD treatment.

[0069] In summary, the *Fusarium oxysporum* CA302 of this invention can accelerate the decomposition of rice straw while passivating soil Cd and As, and simultaneously reducing the bioavailability of soil Cd and As. Under conditions where rice straw is added, the ability of the CA302 microorganisms to passivate soil As is stronger than that of commercially available straw composting agents.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall still fall within the protection scope of the technical solutions of the present invention.

Claims

1. A straw-decomposing bacterium that passivates cadmium and arsenic, characterized in that, The name of the straw-decomposing bacteria that passivates cadmium and arsenic is Fusarium oxysporum (Fusarium oxysporum). Fusarium oxysporum CA302, whose accession number at the China Center for Type Culture Collection is CCTCCNO: M2023446.

2. The application of the straw-decomposing bacteria that passivates cadmium and arsenic as described in claim 1 in the decomposition of rice straw.

3. The application of the straw decomposing bacteria that passivates cadmium and arsenic as described in claim 1 in the removal of Cd and / or As.

4. A bacterial solution, characterized in that, The bacterial solution contains straw-decomposing bacteria that passivate cadmium and arsenic as described in claim 1.

5. The bacterial solution according to claim 4, characterized in that, The preparation process of the bacterial solution is as follows: 1.5% to 2% of the straw-decomposing bacteria that passivate cadmium and arsenic is inoculated into PDA liquid culture medium and cultured with shaking at 28℃ to 35℃ and 150rpm to 180rpm for 3 to 5 days. Then, the bacteria are collected by centrifugation and washed with sterile water to obtain the bacterial solution. The concentration of potato flour in the PDA liquid culture medium is 6 g / L to 12 g / L, and the concentration of glucose is 20 g / L.

6. The application of the bacterial solution as described in claim 4 or 5 in the decomposition of rice straw.

7. The use of the bacterial solution as described in claim 4 or 5 in removing Cd and / or As from a solution.

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