Culture medium, microorganism screening method, and screening kit

Abstract

To provide a culture medium that makes it possible to suitably screen for plastic-degrading microorganisms.SOLUTION: The present invention discloses a culture medium that is used to screen for plastic-degrading microorganisms. The culture medium includes, as a carbon source, dissolved biodegradable plastic and undissolved biodegradable plastic lumps. The biodegradable plastic preferably has an ester bond; the biodegradable plastic is preferably polycaprolactone; and the plastic-degrading microorganisms are preferably filamentous fungi.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a technology for screening microorganisms, and more particularly to a culture medium for screening microorganisms having the ability to decompose plastics and a method for screening such microorganisms. [Background technology]

[0002] In recent years, marine pollution by plastics has become a problem. In other words, most plastics that leak into the environment end up in rivers and other bodies of water, eventually ending up in the ocean, causing enormous harm to the marine ecosystem. Furthermore, the impact of plastics on the ocean also damages industry, resulting in significant economic losses. Plastic breaks down into microplastic particles in the ocean, but even when general plastic breaks down into smaller particles, it does not naturally decompose and is thought to remain for hundreds of years or more. In this situation, the use of biodegradable plastics, which can be naturally decomposed, is becoming widespread in place of conventional plastics.

[0003] However, even if biodegradable plastics are used, it takes time for them to decompose naturally, and the plastics will remain in the ocean for a long period of time, making it difficult to solve the problem of marine pollution. Some types of microorganisms have the ability to decompose plastic. If plastic incorporating such plastic-degrading microorganisms can be developed in the future, it may be possible to rapidly decompose plastics using the power of microorganisms, thereby reducing marine pollution. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4915593 [Non-patent literature]

[0005] [Non-Patent Document 1] Fusarium Polycaprolactone Depolymerase Is Cutinase,CATHERINE A. MURPHY, JACAMERON, SAMUEL J.HUANG, ROBERT T. VINOPAL,APPLIED AND ENVIRONMENTAL MICROBIOLOGY,Feb. 1996,p.456-460 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when filamentous fungi are used as plastic-degrading microorganisms, there is a problem in that it is difficult to screen them. That is, a conventional screening method involves preparing an agar medium containing plastic dissolved in an appropriate organic solvent, culturing microorganisms, and then confirming whether or not a clear zone resulting from plastic decomposition is formed around the microorganisms. However, while this method is effective for cell-dividing microorganisms such as bacteria and yeast because the formation of a clear zone is easy to confirm, in the case of filamentous fungi (molds) that undergo hyphal elongation, it can be difficult to confirm the formation of a clear zone depending on the degree of hyphal elongation and color.

[0007] Therefore, the inventors conducted extensive research and created a culture medium containing dissolved biodegradable plastic and undissolved biodegradable plastic chunks as a carbon source, and used it to cultivate plastic-degrading microorganisms.By detecting whether the biodegradable plastic chunks had been decomposed, they were able to successfully screen plastic-degrading microorganisms, thereby completing the present invention.

[0008] Patent Document 1 discloses a method for producing a biodegradable plastic-degrading enzyme, which includes a step of screening yeast, filamentous fungi, or bacteria for those capable of degrading biodegradable plastics. However, this method screens based on the presence or absence of clear zone formation, and does not describe or suggest confirming the decomposition ability by culturing plastic-degrading microorganisms in a culture medium containing biodegradable plastic chunks and detecting whether the biodegradable plastic chunks have been decomposed.

[0009] Furthermore, although Non-Patent Document 1 describes that the ability of filamentous fungi to decompose plastics can be confirmed based on the formation of a clear zone, the formation of a clear zone is somewhat difficult to confirm, and there is no mention or suggestion of confirming the decomposition ability by culturing plastic-decomposing microorganisms in a culture medium containing biodegradable plastic blocks and detecting whether the biodegradable plastic blocks have been decomposed.

[0010] The present invention has been made in view of the above circumstances, and aims to provide a culture medium, a method for screening microorganisms, and a screening kit that enable suitable screening of plastic-degrading microorganisms. [Means for solving the problem]

[0011] In order to achieve the above-mentioned objective, the culture medium of the present invention is a culture medium for screening plastic-degrading microorganisms, and is configured to contain dissolved biodegradable plastic and undissolved biodegradable plastic chunks as carbon sources. In addition, in the culture medium of the present invention, the biodegradable plastic preferably has an ester bond in its chemical structure. In the culture medium of the present invention, the biodegradable plastic is preferably polycaprolactone.

[0012] Furthermore, the culture medium of the present invention is preferably one based on Zapeck agar medium. In addition, in the culture medium of the present invention, the content of the biodegradable plastic relative to the culture medium is preferably 0.1 to 1.0% (w / v). In addition, in the culture medium of the present invention, the plastic-degrading microorganism is preferably a filamentous fungus.

[0013] In addition, the microorganism screening method of the present invention is a method for screening plastic-degrading microorganisms, and is a method comprising a culture step of culturing plastic-degrading microorganisms in a culture medium containing dissolved biodegradable plastic and undissolved biodegradable plastic blocks as carbon sources, and a detection step of detecting whether the biodegradable plastic blocks have been decomposed. In addition, in the detection step of the microorganism screening method of the present invention, it is preferable that the decomposition of the biodegradable plastic mass is detected by calculating the change in size of the biodegradable plastic mass based on a microscopic photograph.

[0014] Furthermore, in the method for screening microorganisms of the present invention, when the microorganism is a filamentous fungus, it is preferable that in the detection step, the decomposition area of ​​the biodegradable plastic mass is calculated based on the following formula. Decomposition area = (area of ​​biodegradable plastic mass - area of ​​biodegradable plastic mass after number of days of culture from the arrival of mycelia) / number of days of culture from the arrival of mycelia

[0015] In addition, the screening kit of the present invention is configured to be used for screening plastic-degrading microorganisms, and includes a culture medium containing dissolved biodegradable plastic and undissolved biodegradable plastic chunks as a carbon source, and a culture container. The screening kit of the present invention is preferably configured to be used as a science teaching material. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a culture medium, a method for screening microorganisms, and a screening kit that enable suitable screening of plastic-degrading microorganisms. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is an explanatory diagram showing an image of a culture medium for screening plastic-degrading microorganisms according to an embodiment of the present invention. [Figure 2] FIG. 1 is an explanatory diagram showing an image of decomposition of undissolved plastic chunks by culturing microorganisms in a culture medium according to an embodiment of the present invention. [Figure 3] FIG. 1 is a diagram showing the formation of undissolved plastic masses at different plastic concentrations in a culture medium according to an embodiment of the present invention, relating to Test 1. [Figure 4] FIG. 10 is a graph showing the decomposition of undissolved plastic chunks at different sucrose concentrations by culturing microorganisms in a culture medium according to an embodiment of the present invention, in Test 2. [Figure 5] FIG. 10 is a graph showing esterase activity at different sucrose concentrations when various microorganisms are cultured in a culture medium according to an embodiment of the present invention, for Test 3. [Figure 6] FIG. 10 is a graph showing the decomposition area of ​​undissolved plastic chunks by culturing various microorganisms in a culture medium according to an embodiment of the present invention, for Test 4. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the culture medium, microbial screening method, and screening kit of the present invention will be described in detail, although the present invention is not limited to the specific details of the following embodiments and examples described later.

[0019] The culture medium of this embodiment is a culture medium for screening plastic-degrading microorganisms, and is characterized by containing dissolved biodegradable plastic and undissolved biodegradable plastic chunks as carbon sources. The culture medium of this embodiment will be described based on the image shown in Figure 1. Note that the components described for the culture medium can also be used for the same components used in the microorganism screening method and screening kit of this embodiment.

[0020] As shown in Figure 1, the culture medium of this embodiment can be formed based on an agar medium or the like, and is formed by forming undissolved biodegradable plastic chunks in the medium. These biodegradable plastic chunks are usually formed in a state where they sink to the bottom of the medium. Specifically, the culture medium in Figure 1 was obtained by adding polycaprolactone (PCL) to Czapek agar medium, suspending it under heating and stirring, then adding agar and autoclaving.

[0021] The biodegradable plastic used in the culture medium of this embodiment is preferably one having an ester bond in its chemical structure, although not particularly limited thereto. Examples of biodegradable plastics that can be used include polycaprolactone, polylactic acid, polylactic acid / polycaprolactone copolymer, polyglycolic acid, polylactic acid / polyether copolymer, butanediol / long-chain dicarboxylic acid copolymer, polybutylene adipate / terephthalate copolymer, polytetramethylene adipate-co-terephthalate, polyethylene terephthalate succinate, polybutylene succinate, polybutylene succinate adipate, and polyvinyl alcohol. Polycaprolactone is particularly preferred.

[0022] The size of the biodegradable plastic chunks in this embodiment is not particularly limited, but is preferably one that does not interfere with the cultivation of plastic-degrading microorganisms, for example, a diameter of 0.1 mm to 5 mm is preferred. Furthermore, the size of the biodegradable plastic chunks is more preferably 0.3 mm to 2 mm, and even more preferably 0.5 mm to 1 mm. The size of the biodegradable plastic mass can be adjusted by the content of the biodegradable plastic relative to the culture medium, and by heat stirring after mixing them.

[0023] The content of biodegradable plastic in the culture medium is preferably 0.1 to 10.0% (w / v), and more preferably 0.5 to 1.0% (w / v), from the viewpoint of improving the work efficiency of medium preparation and reducing consumption of reagents and equipment.

[0024] The plastic-degrading microorganisms to be screened using the culture medium of this embodiment are not particularly limited as long as they are microorganisms with the ability to decompose plastics, but filamentous fungi (molds) can be particularly suitable for use, as they can be difficult to screen by confirming the formation of a clear zone. As filamentous fungi, for example, those belonging to the genera Glomerella, Aspergillus, Fusarium, and Alternaria can be suitably used.

[0025] Next, the decomposition of biodegradable plastic masses by culturing microorganisms in the culture medium of this embodiment will be explained based on the image shown in FIG. The photograph on the left side of Figure 2 shows a biodegradable plastic mass (polycaprolactone mass) formed in the culture medium of this embodiment, and shows the state after culturing a filamentous fungus (Aspergillus flavus (NBRC6343)) in this culture medium for 8 days. Hyphae extend from the colony of the filamentous fungus. The photograph on the upper right side of the figure shows the biodegradable plastic mass, and the photograph on the lower right side of the figure shows the state after culturing the filamentous fungus for 20 days, in which the biodegradable plastic mass has been decomposed.

[0026] The microorganism screening method of this embodiment is based on the decomposition of biodegradable plastic blocks by such plastic-degrading microorganisms, and is a method for screening plastic-degrading microorganisms, characterized by having a culture step in which plastic-degrading microorganisms are cultured in a culture medium containing dissolved biodegradable plastic and undissolved biodegradable plastic blocks as carbon sources, and a detection step in which it is detected whether the biodegradable plastic blocks have been decomposed.

[0027] In other words, in the microorganism screening method of this embodiment, the presence or absence of the microorganism in the culture medium can be confirmed by detecting the presence or absence of decomposition of the biodegradable plastic mass in the detection process.

[0028] In addition, the microorganism screening method of this embodiment is preferably a method in which, in the detection step, the change in size of the biodegradable plastic mass is calculated based on microscopic photographs to detect the decomposition of the biodegradable plastic mass. That is, since the biodegradable plastic mass is usually formed at the bottom of the culture medium, when the culture is carried out in a container such as a transparent petri dish, the state can be observed from the bottom side of the container.

[0029] For this reason, for example, it is possible to take microscopic photographs of the biodegradable plastic before and after culturing the microorganisms in a culture medium, import these photographs into a computer, calculate the change in size of the biodegradable plastic chunks, and automatically determine whether or not decomposition has occurred. Alternatively, the state of the biodegradable plastic can be visually observed from the bottom side of the container to determine whether or not the biodegradable plastic chunks have decomposed.

[0030] Furthermore, in the method for screening microorganisms of this embodiment, when the microorganism is a filamentous fungus, it is preferable that in the detection step, the decomposition area of ​​the biodegradable plastic mass is calculated based on the following formula. Decomposition area = (area of ​​biodegradable plastic mass - area of ​​biodegradable plastic mass after number of days of culture from the arrival of mycelia) / number of days of culture from the arrival of mycelia According to the method for screening microorganisms of this embodiment, it is possible to quantitatively measure the plastic-degrading ability of each plastic-degrading microorganism.

[0031] In addition, the screening kit of this embodiment is characterized by comprising a culture medium containing dissolved biodegradable plastic and undissolved biodegradable plastic chunks as a carbon source, and a culture container, and is used to screen plastic-degrading microorganisms. The culture vessel is preferably transparent so that it is easy to check whether the biodegradable plastic block has decomposed, but the material is not particularly limited and it may be made of synthetic resin or glass. The shape of the vessel may be open, such as a petri dish, or closed, such as a bag. It is also preferable that the screening kit of this embodiment be used as a science teaching material.

[0032] As described above, the culture medium, microbial screening method, and screening kit of this embodiment make it possible to suitably screen plastic-degrading microorganisms. Furthermore, in particular with filamentous fungi, the presence or absence of plastic decomposition can be confirmed based on the decomposition of biodegradable plastic blocks, regardless of the presence or absence of clear zone formation, and it is also possible to quantitatively evaluate the decomposition ability. [Example]

[0033] Tests conducted to confirm the effects of the culture medium, microbial screening method, and screening kit according to the embodiments of the present invention will be described below. [Test 1] A test was conducted to prepare a culture medium according to the present embodiment. The culture medium was obtained by suspending polycaprolactone (PCL) as a carbon source in a Zapeck liquid medium while heating, adding agar, and autoclaving. The culture medium was prepared with a polycaprolactone content (PCL concentration (w / v)) of 10%, 5%, 3%, 1%, 0.5%, and 0.1%, and these were designated as the culture media of Examples 1 to 6, respectively.

[0034] Multiple samples were prepared with PCL concentrations (w / v) of 10%, 5%, 3%, 1%, and 0.5%, and in Figure 3, the upper photograph shows the medium with the most residual dissolution. The lower photograph shows one of the media suitable for testing. Only one sample was prepared with a PCL concentration (w / v) of 0.1%, and a medium suitable for testing containing only a few biodegradable plastic chunks was obtained. The corresponding upper and lower rows show photographs of the same medium.

[0035] Specifically, PCL was added as a single carbon source to a previously prepared sucrose-free Czapek medium (1000 ml of purified water, in that order, containing 33 g of NaNO, 1 g of K2HPO4, 0.5 g of MgSO4·7H2O, 0.5 g of KCL, and 0.01 g of FeSO4·7H2O, pH 7.3) to achieve the above concentrations. The mixture was heated and stirred using a heat stirrer (set to around 280°C), and the pellet was crushed and suspended with a spatula to obtain a liquid medium. Next, agar was added to the liquid medium to a concentration of 1.5% (w / v), autoclaved, and then dispensed into 90 mm diameter petri dishes and allowed to solidify at room temperature to obtain an agar medium.

[0036] As a result, as shown in Figure 3, biodegradable plastic masses suitable for screening could be obtained in culture media with any PCL concentration (w / v). When the PCL concentration (w / v) was 10%, 5%, or 3%, the PCL was somewhat difficult to dissolve, resulting in significant loss due to residual dissolution. Furthermore, when the PCL concentration (w / v) was 0.1%, the number of biodegradable plastic chunks was small, resulting in a slight decrease in screening efficiency. Therefore, it was found that the content of polycaprolactone in the culture medium (PCL concentration (w / v)) is preferably 0.1% to 10%, and more preferably 0.5% to 1%.

[0037] [Test 2] A test was conducted to confirm the effect of sucrose on the culture medium of this embodiment. Specifically, PCL was added as a carbon source to the Czapek medium described above in Test 1 at 0.5% (w / v) and sucrose at 0, 0.03, and 3% (w / v), respectively. The mixture was heated and stirred using a heat stirrer (set to approximately 280°C), and the pellets were crushed and suspended with a spatula to obtain a liquid medium. Next, agar was added to the liquid medium at 1.5% (w / v), autoclaved, and dispensed into 90 mm diameter Petri dishes and solidified at room temperature to obtain the agar mediums of Examples 7, 8, and Comparative Example 1 for each sucrose concentration. Biodegradable plastic chunks were present in the resulting agar medium.

[0038] In addition, a filamentous fungus of the genus Aspergillus (Aspergillus flavus (NBRC6343)) was cultured on PDA (Potato Dextrose Agar) medium, and a fungal disk was prepared by punching out the grown colony with a cork borer having a diameter of 5 mm. Then, a bacterial disk was placed in contact with each agar medium, and static culture was initiated at 30°C in the dark, and the state of the biodegradable plastic mass was observed under a microscope over time. FIG. 4 shows photographs showing the state of decomposition of biodegradable plastic blocks before inoculation and on the 8th day of culture for each example and comparative example.

[0039] As shown in Figure 4, when the sucrose concentration was 0% and 0.03%, the biodegradable plastic blocks were decomposed, confirming the presence of plastic-degrading microorganisms. On the other hand, when the sucrose concentration was 3%, no decomposition of the biodegradable plastic blocks was observed. The reason that no decomposition of the biodegradable plastic blocks was observed when the sucrose concentration was 3% is presumed to be due to the inhibition of carbon catabolites, and it is thought that sucrose, a disaccharide that is easily decomposed, was preferentially decomposed, thereby inhibiting the decomposition of the biodegradable plastic.

[0040] As described above, the culture medium of this embodiment may contain a carbon source other than biodegradable plastic, but it was found that a sucrose concentration of 3% would not yield a culture medium suitable for screening, whereas a sucrose concentration of at least 0% to 0.03% would yield a culture medium suitable for screening.

[0041] [Test 3] A test was conducted to confirm the effect of sucrose on the culture medium of this embodiment based on esterase activity. In other words, plastic-degrading microorganisms decompose biodegradable plastics by hydrolyzing the ester bonds in the chemical structure of biodegradable plastics with esterases. Therefore, the presence or absence of esterase activity was confirmed in extracts of plastic-degrading microorganisms.

[0042] First, as in Experiment 2, PCL was added as a carbon source to Czapek medium at 0.5% (w / v) and sucrose at 0, 0.03, and 3% (w / v), respectively, and the mixture was heated and stirred using a heat stirrer. The pellet was crushed and suspended with a spatula to obtain liquid medium. The liquid medium was dispensed into a total of nine flasks, three for each sucrose concentration.

[0043] In addition, filamentous fungi of the genus Glomerella (NBRC107004), Aspergillus flavus (NBRC6343), and Fusarium oxysporum (NBRC9971) were cultured on Potato Dextrose Agar (PDA) medium, and mycelial disks were punched out of the grown colonies with a 5 mm cork borer to prepare mycelial disks. These mycelial disks were then placed in liquid media containing 0%, 0.03%, and 3% (w / v) sucrose.

[0044] Liquid media containing a filamentous fungus of the genus Glomerella and having sucrose concentrations of 0%, 0.03%, and 3% (w / v) were designated Example 9, Example 10, and Comparative Example 2, respectively. Liquid media containing a filamentous fungus of the genus Aspergillus and having sucrose concentrations of 0%, 0.03%, and 3% (w / v) were designated Example 11, Example 12, and Comparative Example 3, respectively. Liquid media containing a filamentous fungus of the genus Fusarium and having sucrose concentrations of 0%, 0.03%, and 3% (w / v) were designated Example 13, Example 14, and Comparative Example 4, respectively.

[0045] After static cultivation at 25°C in the dark for 16 days, the cultured cells and the culture filtrate were separated and collected, and the culture filtrate was used as a crude enzyme solution for an esterase activity measurement test. Esterase activity in the crude enzyme solution was measured using p-nitrophenyl butylate (pNPB, C4) as a substrate. The esterase hydrolyzed pNPB to produce 4-nitrophenol, which could be measured spectrophotometrically at 405-410 nm. The pNPB substrate solution was prepared by mixing pNPB with isopropanol to a concentration of 10 mM. 890 μl of buffer (50 mM Tris-HCl, pH 7.5) was mixed with 100 μl of the crude enzyme solution, and 10 μl of the pNPB substrate solution was added. The mixture was then allowed to stand for 60 minutes, and the absorbance of 1 ml of the reaction solution at 405 nm was measured at room temperature using a spectrophotometer (Thermo Fisher Scientific, Nanodrop 2000C).

[0046] As a result, as shown in FIG. 5, the esterase activity of each sample was 1.0605 for Example 9, 1.0005 for Example 10, 0.1565 for Comparative Example 2, 0.3425 for Example 11, 0.306 for Example 12, 0.1175 for Comparative Example 3, 0.2024 for Example 13, 0.3165 for Example 14, and 0.095 for Comparative Example 4. As described above, in the culture medium of this embodiment, when the sucrose concentration is 3%, the production and secretion of esterase is suppressed, and when the sucrose concentration is at least 0% to 0.03%, the effect of sucrose is absent or slight, and it was found that a culture medium suitable for use in screening can be obtained.

[0047] [Test 4] A test was conducted to quantitatively measure the decomposition ability of various microorganisms when they were cultured in the culture medium of this embodiment to decompose undissolved plastic chunks. Specifically, multiple petri dishes containing agar medium with a PCL concentration of 0.5% (w / v) were prepared in the same manner as in Test 1. Visually identifiable PCL clumps with a diameter of approximately 500 μm present in the agar medium were selected and marked on the back of the petri dish.

[0048] In addition, filamentous fungi from the genus Glomerella (Glomerella cingulate (NBRC107001), Glomerella cingulate (NBRC107004)), Aspergillus (Aspergillus flavus (NBRC6343)), Fusarium (Fusarium oxysporum (NBRC9971), Fusarium sacchari (JCM9676)), and Alternaria (Alternaria alternate (NBRC106339)) were cultured on PDA medium, and fungal disks were prepared by punching out the grown colonies with a 5 mm diameter cork borer.

[0049] Next, the bacterial disk was placed in contact with the center of the agar medium surface, and after static cultivation at 30°C in the dark for a predetermined number of days, the biodegradable plastic in the culture medium was photographed using a microscope with a built-in CCD camera. The decomposition area of ​​polycaprolactone per day (μm2) was calculated using the following formula: 2 ) was calculated. Decomposition area = (area of ​​biodegradable plastic mass - area of ​​biodegradable plastic mass after number of days of culture from the arrival of mycelia) / number of days of culture from the arrival of mycelia

[0050] The results are shown in Figure 6. In each example, the minimum and maximum decomposition area are shown based on the results of microbial culture and decomposition area calculations performed individually a predetermined number of times. The number of petri dishes used in each example was three in Examples 15, 16, 18, and 19, two in Example 17, and one in Example 20. The polycaprolactone decomposition area of ​​the filamentous fungus of the genus Glomerella in Example 15 (Glomerella cingulate (NBRC107001)) was 624 to 1082, and the polycaprolactone decomposition area of ​​the filamentous fungus of the genus Glomerella in Example 16 (Glomerella cingulate (NBRC107004)) was 6092 to 17863. The polycaprolactone decomposition area of ​​the filamentous fungus of the genus Aspergillus in Example 17 (Aspergillus flavus (NBRC6343)) was 41156 to 41241.

[0051] Furthermore, the polycaprolactone decomposition area of ​​the Fusarium oxysporum (NBRC9971) in Example 18 was 13,816 to 25,236, and the polycaprolactone decomposition area of ​​the Fusarium sacchari (JCM9676) in Example 19 was 7,574 to 15,773. The polycaprolactone decomposition area of ​​the filamentous fungus of the genus Alternaria in Example 20 (Alternaria alternate (NBRC106339)) was 33,365.

[0052] As described above, it has been confirmed that the culture medium, microbial screening method, and screening kit of this embodiment not only make it possible to suitably screen plastic-degrading microorganisms, but also enable quantitative evaluation of the decomposition ability of plastic-degrading microorganisms.

[0053] The present invention is not limited to the above embodiments and examples, and various modifications are possible within the scope of the present invention. For example, the culture vessel is not limited to a petri dish, and any vessel capable of confirming the decomposition of biodegradable plastic blocks can be used. Furthermore, the plastic-degrading microorganisms are not limited to those described above, and any vessel capable of decomposing biodegradable plastics can be used. [Industrial Applicability]

[0054] The present invention can be suitably used for screening plastic-degrading microorganisms, and can be effectively used in particular for evaluating the plastic-degrading ability of filamentous fungi.

Claims

1. A culture medium for screening plastic-degrading microorganisms, comprising: The carbon source contains dissolved biodegradable plastic and undissolved biodegradable plastic chunks, The biodegradable plastic has an ester bond in its chemical structure, The plastic-degrading microorganism is a filamentous fungus. A culture medium characterized by:

2. 2. The culture medium according to claim 1, wherein the biodegradable plastic is polycaprolactone.

3. 3. The culture medium according to claim 1, wherein the culture medium is based on Zapeck agar.

4. 4. The culture medium according to claim 1, wherein the content of the biodegradable plastic relative to the culture medium is 0.1 to 1.0% (w / v).

5. A method for screening plastic-degrading microorganisms, comprising: a culturing step of culturing plastic-degrading microorganisms in a culture medium containing dissolved biodegradable plastic and undissolved biodegradable plastic chunks as a carbon source; A detection step of detecting whether the biodegradable plastic mass has been decomposed, The biodegradable plastic has an ester bond in its chemical structure, The plastic-degrading microorganism is a filamentous fungus. A method for screening microorganisms, comprising:

6. A method for screening microorganisms as described in claim 5, characterized in that in the detection step, the change in size of the biodegradable plastic mass is calculated based on a microscopic photograph to detect the decomposition of the biodegradable plastic mass.

7. 7. The method for screening microorganisms according to claim 6, wherein in the detection step, the decomposition area of ​​the biodegradable plastic mass is calculated based on the following formula: Decomposition area = (area of ​​biodegradable plastic mass - area of ​​biodegradable plastic mass after number of days of culture from the arrival of mycelia) / number of days of culture from the arrival of mycelia

8. A screening kit comprising a culture medium containing dissolved biodegradable plastic and undissolved biodegradable plastic chunks as a carbon source, and a culture vessel, wherein the biodegradable plastic has an ester bond in its chemical structure, and characterized in that the screening kit is used to screen for plastic-degrading microorganisms that are filamentous fungi.

9. 9. The screening kit according to claim 8, which is used as a science teaching material.

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