A culture device for culturing euglena

Abstract

The present invention relates to a culture device. More particularly, the present invention relates to a culture device (100) for culturing Euglena, the culture device (100) comprising a first tank (la) and a second tank (lb); each of the first tank (la) and the second tank (lb) comprises an interior space for storing a mixture comprising Euglena and nutrients, wherein the interior space of the second tank (lb) is larger than the interior space of the first tank (la); and a conveying means (9) for transporting the Euglena stored in the interior space of the first tank (la) to the interior space of the second tank (lb), wherein each of the first tank (la) and the second tank (lb) comprises an agitating means (4) for agitating the mixture stored therein.

Description

[0001] A CULTURE DEVICE FOR CULTURING EUGLENA

[0002] FIELD OF INVENTION

[0003] The present invention relates to a culture device. More particularly, the present invention relates to a culture device for culturing Euglena.

[0004] BACKGROUND OF THE INVENTION

[0005] Euglena is known as a single-celled organism that is capable of photosynthesis and Euglena locomotion (so-called suzuri-mori motility). Euglena can be used as biofuel or biomass plastics because of its rich oil content. Euglena can also be used as a nutritional supplement or feed because of its rich nutritional content. In particular, Euglena powder has about 30% higher combustion energy than that of coal. For this reason, Euglena can be used as an alternative fuel to coal in thermal power plants. Technologies using Euglena can contribute to the realization of carbon neutrality.

[0006] For example, Japan Patent Application Publication Number JP2017148005A disclosed a method for extracting wax esters (WE) from Euglena obtained by culturing Euglena under aerobic conditions with light irradiation at a liquid temperature of about 27 °C to 35 °C and then culturing it at about 16 °C while undergoing hypoxic treatment. Under aerobic conditions, Euglena accumulates polysaccharide paramylon in its body. On the other hand, under anaerobic conditions, Euglena produces adenosine triphosphate (ATP) from the accumulated polysaccharide paramylon and produces WE as its metabolic product. It was necessary for the Euglena to perform photosynthesis in order to accumulate polysaccharide paramylon in the body of the Euglena. Therefore, when producing a large amount of the Euglena, it was necessary to set up a large area of shallow water tanks of about 20 cm in size and cultivate the Euglena in these tanks in order to ensure sunlight irradiation to the Euglena. As a result, the method required a large area of land to set up the tanks. In addition, the weather, such as sunlight hours, affected the cultivation speed.

[0007] On the other hand, International Patent Application Number W02020162502A1 disclosed a method for producing Euglena in the absence of sunlight irradiation. The amount of polysaccharide paramylon that accumulates in the body is increased by giving sugar to the Euglena. Next, by giving fatty acids with low carbon numbers, the oxygen respiratory system of the Euglena is stopped and anaerobic conditions are created. In the method, a small amount of the Euglena and nutrients are introduced into a tank. Then, the Euglena is cultured until it increases to a desired amount. The amount of the Euglena increases several hundred times or more in the tank between the start and the end of the culture. As the amount of the Euglena increases, a corresponding amount of the nutrients is required. For this reason, a large-capacity tank capable of storing up to the desired amount of the Euglena and nutrients in an amount corresponding to the amount of Euglena is required.

[0008] However, when a small amount of Euglena is stored in a large-capacity tank at the start of culture, the amount of the Euglena and nutrients is too small for the tank volume. As a result, the Euglena and nutrients could not be stirred sufficiently, and it was difficult to properly supply nutrients to the Euglena. As a result, it was difficult to mass-produce Euglena.

[0009] SUMMARY OF INVENTION

[0010] The present invention relates to a culture device for culturing Euglena, the culture device comprising a first tank and a second tank; each of the first tank and the second tank comprises an interior space for storing a mixture comprising Euglena and nutrients, wherein the interior space of the second tank is larger than the interior space of the first tank; and a conveying means for transporting the Euglena stored in the interior space of the first tank to the interior space of the second tank, wherein each of the first tank and the second tank comprises an agitating means for agitating the mixture stored therein.

[0011] Preferably, each of the agitating means is a pump to pump the Euglena present in the lower portion of the interior space of each of the first tank and the second tank to the upper portion of the interior space of each of the first tank and the second tank via a stirring means.

[0012] Preferably, the culture device further comprises additive supply means for supplying additives to the respective interior spaces of the first tank and the second tank.

[0013] Preferably, the volume of the interior space of the second tank is between 5 and 50 times the volume of the interior space of the first tank.

[0014] Preferably, each of the first tank and the second tank comprises a light-shielding material.

[0015] Preferably, the culture device further comprises an oxygen supply means for supplying oxygen into the mixture stored in the interior space of each of the first tank and the second tank.

[0016] BRIEF DESCRIPTION OF THE DRAWINGS

[0017] For the purpose of facilitating an understanding of the present invention, there is illustrated in the accompanying drawing the preferred embodiments from an inspection of which when considered in connection with the following description, the present invention, its construction and operation and many of its advantages would be readily understood and appreciated. Figure 1 shows a configuration of a culture device (100) in one embodiment of the present invention.

[0018] Figure 2 shows a cross-sectional view of the configuration associated with one of the representative tanks (la-lc) of Figure 1.

[0019] DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, the present invention shall be described according to the preferred embodiments of the present invention and by referring to the accompanying description and drawings. However, it is to be understood that limiting the description to the preferred embodiments of the present invention is merely to facilitate discussion of the present invention and it is envisioned that those skilled in the art may devise various modifications without departing from the scope of the appended claim.

[0021] The present invention relates to a culture device (100) for culturing Euglena. Referring to Figure 1 and Figure 2, the culture device 100 comprises a first tank (la) and a second tank (lb). Optionally, the culture device (100) further comprises a third tank (1c). Each of the tanks (la-lc) comprises a sensor (2), a ventilation hole (3), an agitation means (4), a stirring means (5), a first additive supply means (6), a second additive supply means (7), an oxygen supply means (8), a conveying means (9), and a conveyance means (10). The first tank (la) can be connected to a Euglena housing unit (11), whereas the second tank (lb) or the third tank (1c) can be connected to an extraction device (12). Additionally, the tanks (la-lc) can be connected to an additive tank (13), in which a control unit (14) controls the additives being supplied from the additive tank (13) to each of the tanks (la-lc). Each of the tanks (la-lc) has an interior space for storing a mixture containing the Euglena and nutrients. Preferably, the interior space of each of the tanks (la-lc) stores the mixture at a depth of 0.5 m or more. The interior space may be covered with a light-shielding material so that no light may enter the interior space. The Euglena stored in the interior space is not exposed to light to prevent photosynthesis such that the Euglena grows only by consuming the nutrients contained in the mixture.

[0022] Preferably, the mixture is controlled at a temperature of between 15 °C and 30 °C. More preferably, the mixture is controlled at a temperature of between 25 °C and 30 °C for promoting efficient storage of paramylon in the cells of Euglena.

[0023] Preferably, the first tank (la) has a volume capable of storing the mixture weighing 1 tonne or more. Preferably, the interior space of the second tank (lb) is larger than the interior space of the first tank (la). Preferably, the interior space of the third tank (1c) is larger than the interior space of the second tank (lb). The volume of the interior space of the second tank (lb) is preferably between 5 and 50 times larger than the volume of the interior space of the first tank (la). The volume of the interior space of the third tank (1c) should be between 5 and 50 times larger than the volume of the interior space of the second tank (lb). This allows the Euglena to be cultured in the corresponding tank (la-lc), which has an appropriately sized interior space according to the increase in the amount of the Euglena.

[0024] In an exemplary embodiment, the interior space of the first tank (la) has a volume that can store a mixture weighing 10 tonnes. The interior space of the second tank (lb) has a volume that can store a mixture weighing 100 tonnes. The interior space of the third tank (1c) has a volume that can store a mixture weighing 500 tonnes. Accordingly, 50 kg of the Euglena is cultured in the first tank (la) for approximately 6 days until 500 kg. Then, 500 kg of the Euglena is cultured in the second tank (lb) for approximately 6 days until 5,000 kg. Subsequently, 5,000 kg of the Euglena is cultured in the third tank (1c) for approximately 4 days until 25,000 kg.

[0025] Preferably, the culture device (100) further comprises an Euglena housing section (11) for containing a small amount of the Euglena, preferably 50 kg, before being introduced into the first tank (la). The Euglena housing section (11) and the interior space of the first tank (la) can be connected to each other by a first intermediate pipe (9a). The first intermediate pipe (9a) is preferably equipped with a first intermediate pump (10a). The Euglena housed in the Euglena housing unit (11) can be transported to the interior space of the first tank (la) at a first predetermined timing. This conveyance of the Euglena is carried out through the first intermediate pipe (9a) by the power of the first intermediate pump (10a). The transported Euglena is stored in the interior space of the first tank (la) and cultured to a predetermined amount.

[0026] The interior space of the first tank (la) and the interior space of the second tank (lb) can be connected to each other by a second intermediate pipe (9b). The second intermediate pipe (9b) can be equipped with a second intermediate pump (10b). The Euglena stored in the first tank (la) can be transported to the interior space of the second tank (lb) at a second predetermined timing. This conveyance of the Euglena is carried out through the second intermediate pipe (9b) by the power of the second intermediate pump (10b).

[0027] The interior space of the second tank (lb) and the interior space of the third tank (1c) can be connected to each other by a third intermediate pipe (9c). The third intermediate pipe (9c) can be equipped with a third intermediate pump (10c). The Euglena stored in the second tank (lb) can be transported to the interior space of the third tank (1c) at a third predetermined timing. This conveyance of the Euglena is carried out through the third intermediate pipe (9c) by the power of the third intermediate pump (10c).

[0028] Preferably, the extraction device (12) is used to extract fats, such as WE, from the Euglena. For example, the extraction device (12) comprises a device for drying the Euglena and a device for separating oil and fat components in the Euglena from the rest of the Euglena using differences in specific gravity.

[0029] The interior space of the third tank (1c) and the extraction device (12) can be connected to each other by a fourth intermediate pipe (9d). The fourth intermediate pipe (9d) can be equipped with a fourth intermediate pump (lOd). The Euglena stored in the third tank (1c) can be conveyed to the extraction device (12) at a fourth predetermined timing. This conveyance of the Euglena is carried out through the fourth intermediate pipe (9d) by the power of the fourth intermediate pump (lOd).

[0030] In one embodiment of the present invention, the Euglena is transported in the following order according to the increase in weight of the Euglena due to culture: Euglena housing unit (11), first tank (la), second tank (lb), third tank (1c), and extraction device (12).

[0031] Preferably, the additive tank (13) stores additives necessary for culturing the Euglena, such as a liquid medium suitable for culturing euglena, organic matter that serve as nutrients for euglena, and a WE fermentation accelerating substance. The additives are selectively added to each of tanks (la-lc) by the control unit (14).

[0032] The additive tank (13) and the interior space of the first tank (la) can be connected to each other by a first supply pipe (6a). The first supply pipe (6a) can be equipped with a first supply pump (7a). The additives stored in the additive tank (13) can be conveyed to the first tank (la) at a first predetermined supply interval. The additives can be conveyed through the first supply pipe (6a) under the power of the first supply pump (7a).

[0033] The additive tank (13) and the interior space of the second tank (lb) can be connected to each other by a second supply pipe (6b). The second supply pipe (6b) is equipped with a second supply pump (7b). The additives stored in the additive tank (13) can be conveyed to the second tank (lb) at a second predetermined supply interval. The additives can be conveyed through the second supply pipe (6b) by the power of the second supply pump (7b).

[0034] The additive tank (13) and the interior space of the third tank (1c) can be connected to each other by a third supply pipe (6c). The third supply pipe (6c) can be equipped with a third supply pump (7c). The additives stored in the additive tank (13) can be conveyed to the third tank (1c) at a third predetermined supply interval. The additives can be conveyed through third supply pipe (6c) by the power of the third supply pump (7c).

[0035] Preferably, the first tank (la) is further provided with a first sensor (2a), a first ventilation hole (3a), a first circulation pipe (5a), a first circulation pump (4a), and a first bubbling device (8a).

[0036] The first sensor (2a) may detect the liquid level of the mixture in the interior space of the first tank (la) and the amount of the Euglena in the mixture in the interior space of the first tank (la). The first sensor (2a) may further detect the pH of the mixture.

[0037] The first ventilation hole (3a) can be provided in the ceiling of the first tank (la). The first ventilation hole (3 a) can be opened and closed under the control of the control unit (14).

[0038] The first circulation pipe (5a) can connect the lower part and the upper part of the interior space of the first tank (la). Preferably, the first circulation pipe (5a) is equipped with the first circulation pump (4a). The Euglena present in the lower part of the interior space of the first tank (la) is pumped to the upper part of the interior space of the first tank (la) through the first circulation pipe (5a) by the power of the first circulation pump (4a) when required. This agitates the Euglena stored in the interior space of first tank (la)

[0039] The first bubbling device (8a) sucks air from outside the first tank (la) and releases it into the interior space of the first tank (la), thereby supplying oxygen into the mixture stored in the interior space of the first tank (la).

[0040] Preferably, the second tank (lb) is further provided with a second sensor (2b), a second ventilation hole (3b), a second circulation pipe (5b), a second circulation pump (4b), and a second bubbling device (8b).

[0041] The second sensor (2b) may detect the liquid level of the mixture in the interior space of the second tank (lb) and the amount of the Euglena in the mixture in the interior space of the second tank (lb).

[0042] The second ventilation hole (3b) can be provided in the ceiling of the second tank (lb). The second ventilation hole (3b) can be opened and closed under the control of the control unit (14).

[0043] The second circulation pipe (5b) and the second circulation pump (4b) create an agitation to the Euglena stored in the interior space of the second tank (lb).

[0044] The second bubbling device (8b) supplies oxygen into the mixture stored in the interior space of the second tank (lb).

[0045] Preferably, the third tank (1c) is further provided with a third sensor (2c), a third ventilation hole (3c), a third circulation pipe (5c), a third circulation pump (4c), and a third bubbling device (8c).

[0046] The third sensor (2c) may detect the liquid level of the mixture in the interior space of the third tank (1c) and the amount of the Euglena in the mixture in the interior space of the third tank (1c).

[0047] The third ventilation hole (3c) can be provided in the ceiling of the third tank (1c). The third ventilation hole (3c) can be opened and closed under the control of the control unit (14).

[0048] The third circulation pipe (5c) and the third circulation pump (4c) create an agitation to the Euglena stored in the interior space of the third tank (1c).

[0049] The third bubbling device (8c) supplies oxygen into the mixture stored in the interior space of the third tank (1c).

[0050] The control unit (14) is preferably provided to control the operation of the culture device (100) based on the inputs provided by each of the sensors (2a-2c). Preferably, the control unit (14) controls the opening and closing of each of the ventilation holes (3a-3c). Additionally, the control unit (14) can control the operation of each of the circulation pumps (4a-4c), supply pumps (7a-7c), and intermediate pumps (lOa-lOc). Besides, the control unit (14) can control the operation of each of the bubbling devices (8a-8c). Further, the control unit (14) can select the required additive from a plurality of additives stored in the additive tank (13) and adds the selected additive to the interior space of any one or more of the tank (la-lc).

[0051] The present invention further describes a method of culturing the Euglena, as depicted in Figure 3. In each of the tanks (la-lc), the Euglena is cultured in substantially the same way. In the following description, the method of culturing the Euglena in one representative tank 1 as depicted in Figure 2 will be explained. By carrying out the method as shown in Figure 3 in each of the tanks (la-lc), the culture device (100) gradually increases the amount of the Euglena and finally obtains the desired amount of the Euglena from which oils and fats, such as WE, are extracted from the Euglena.

[0052] According to Figure 3 with further reference to Figure 2, the Euglena is introduced into the interior space of the tank (1) or the Euglena housing unit (11) using the associated pump (10) (step SI), thereby forming the mixture containing the Euglena and nutrients. Then, stirring of the mixture MX is started by the stirring means (5). Unless otherwise specified, it is preferred that the mixture stored in the tank (1) is continuously stirred by the stirring means (5).

[0053] The Euglena used is one or more protozoa selected from the group consisting of species belonging to the genus Euglena (green lacewing) in zoological classification and mutant species thereof. The mutant species here also include cell lines (mutant strains) obtained by genetic methods, such as recombination, transduction, or transformation. Preferably, the Euglena is Euglena acus. Euglena caudala. Euglena chadefaudii. Euglena deses, Euglena gracilis (hereinafter referred to as 'Euglena gracilis"') Euglena gramdala. Euglena intermedia, Euglena mulab is, Euglena oxyuris, Euglena piride, Euglena proxima, Euglena spirogyra, Euglena vermiformis. or Euglena viridis.

[0054] The Euglena used may be collected from wild Euglena that are widely distributed in freshwater, such as ponds and swamps. The Euglena used should preferably be one or more protozoa selected from the group consisting of Euglena gracilis and mutant strains thereof, from the viewpoint that suitable culture conditions for the aforementioned Euglena have been studied in detail and are known and easy to culture.

[0055] The mixture preferably contains a culture medium capable of culturing the Euglena when the Euglena is seeded and kept under aerobic conditions at a medium temperature of between 15 °C and 35 °C. The culture medium may contain vitamin B12, ammonium salts, and other inorganic salts (compounds with phosphorus, potassium, iron, manganese, cobalt, zinc, copper, molybdenum, or nickel in their molecules). The culture medium may further contain other nutrients, such as sugars and amino acids. Examples of the culture medium include Kramer-Meyer, Huttner, or Koren-Huttner media. When the formulation is partially changed, another culture medium with an increased amount of organic matter, such as sugar, may be used with a view to saving time and effort in separately adding the organic matter to the medium in the next step S3, when culturing under aerobic conditions.

[0056] In addition, the culture medium may contain chelating agents or pH adjusters. Besides, the culture medium may contain a peptide-containing composition or ammonia water. The peptide-containing composition can include peptone, casamino acid, yeast extract, or com steep liquor. Further, the culture medium may contain one or more free amino acids or salts thereof. If the culture medium contains sugar, the sugar may be glucose, fructose, sucrose, maltose, or starch. Next, the Euglena is cultured under aerobic conditions in the presence of the organic matter (step S3). This causes the Euglena to produce and store paramylon in its own cells. Aerobic conditions are realized by supplying oxygen to the Euglena in the MX with the bubbling device (8).

[0057] The organic matter may be adjusted in step SI so that the mixture contains the required amount of the organic matter. Alternatively, the organic matter may be added to the mixture at an appropriate time depending on the cell density of the Euglena.

[0058] From the viewpoint of promoting fermentation of WE in step S5, it is preferable to keep the duration of step S3 (the duration of culturing the Euglena under aerobic conditions in the presence of the organic matter) to a duration of 0.5 to 0.8 times longer than the duration from the start of culture under these conditions to a steadystate phase. For example, if there are culture conditions that require 120 hours from the start of culturing the Euglena (when Euglena is introduced into the tank (1)) to the stationary phase, it is preferable to keep the duration of step S3 within the range of 60 hours to 96 hours.

[0059] Next, WE fermentation promoting substance is administered to the Euglena that has been aerobically cultured in step S3 in an acidic environment (step S5) and is storing paramylon in the cells. This causes the paramylon to be decomposed in the Euglena cells and promotes the production of WE. The acidic environment, in terms of promoting WE fermentation, requires the pH of the medium to be less than 7.0, preferably less than 6.0, and even more preferably less than 3.5 pH. From the viewpoint of avoiding the death of the Euglena, the pH of the medium should be 2.5 or higher. In step S5, the WE fermentation accelerating substance and the pH adjuster are preferably added to the mixture that has completed step S3. The WE fermentation accelerating substance and the pH adjuster may be introduced from the additive tank (13) by the additive supply means (6).

[0060] The WE fermentation accelerating substance is preferably one or more compounds selected from the group consisting of monovalent carboxylic acids having between 2 and 4 carbon atoms in the molecule, which may have aldehyde or hydroxy groups in the molecule, and salts thereof. Such low-molecular-weight organic compounds can easily penetrate into the Euglena cells by permeating cell membranes. In the Euglena cells, when an excessive supply of low-molecular-weight organic compounds that easily penetrate into the cell is supplied, aerobic respiration is inhibited (e.g., feedback inhibition) in the cell, and WE fermentation is easily promoted to acquire adenosine triphosphate (ATP) in place of aerobic respiration.

[0061] The WE fermentation accelerating substance may also include lower fatty acids, hydroxycarboxylic acids, or monovalent carboxylic acids with aldehyde groups in their molecules, which have between 2 and 4 carbon atoms in their molecules. The lower fatty acids may include propionic acid, butyric acid, or isobutyric acid. The hydroxycarboxylic acids may include glycolic acid, lactic acid, 2-hydroxybutyric acid, 3 -hydroxybutyric acid, or gamma-hydroxybutyric acid. The monovalent carboxylic acids having an aldehyde group in the molecule may include glyoxylic acid, pyruvic acid, 3-oxopropanoic acid, alpha-ketobutyric acid, or acetoacetic acid.

[0062] Next, the Euglena supplied with the WE fermentation accelerating substance is kept at room temperature for a predetermined period of time. This allows WE fermentation to take place in the cells of the Euglena (step S7). In nature, the Euglena cells that have stored paramylon through photosynthesis at the water surface may overwinter while undergoing WE fermentation to decompose paramylon by sinking to the water bottom during winter when sunlight is weak, so WE fermentation can proceed over time even at the water bottom temperature (about 4 °C). On the other hand, at temperatures exceeding 35 °C, metabolism is easily disturbed in the Euglena cells. From the viewpoint of promoting WE fermentation, "room temperature" is between 5 °C and 35 °C, preferably between 15 °C and 35 °C, and more preferably between 20 °C and 30 °C.

[0063] The predetermined time for keeping the Euglena at room temperature in step S7 is 6 hours or longer, preferably 12 hours or longer, and even more preferably 24 hours or longer. The predetermined time for keeping the Euglena at room temperature in step S7 is 96 hours or less, preferably 72 hours or less, and even more preferably 48 hours or less, from the viewpoint of avoiding taking a longer time than necessary. WE fermentation is prevented by the WE fermentation accelerating substance, and thus WE is produced even if the cells are kept under hypoxic conditions.

[0064] Next, the agitation of the mixture stored in the interior space of the tank (1) is stopped (step S9). This causes the Euglena to stay in the lower part of the interior space of the tank (1) due to the difference between the specific gravity of the Euglena in the mixture and the specific gravity of the components other than the Euglena. Then, the Euglena that remains in the lower part of the interior space of the tank (1) is discharged to a destination outside the tank (1). The discharge destination is another tank (1) having a larger interior space than the interior space of the previous tank (1) or the extraction device (12).

[0065] In the present invention, by storing the mixture containing the Euglena in the interior space of the first tank (la) and stirring it with the stirring means (5), the Euglena and nutrients can be sufficiently stirred and the nutrients can be appropriately supplied to the Euglena. This allows the Euglena to be cultured efficiently in the first tank (la). The increased amount of the Euglena in the interior space of the first tank (la) is then transported to the interior space of the second tank (lb), which is larger than the interior space of the first tank (la). By storing the mixture containing the Euglena in the interior space of the second tank (lb) that is appropriate for the increased amount of the Euglena and stirring it with the stirring means (5), the Euglena and nutrients can be sufficiently stirred and the nutrients can be appropriately supplied to the Euglena. As a result, the Euglena can be efficiently cultured in the second tank (lb).

[0066] Advantageously, the culture device (100) in the present invention is capable to mass produce the Euglena with an improved efficiency.

[0067] One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objects and obtain the ends and advantages mentioned, as well as those inherent therein. The embodiment described herein is not intended as limitations on the scope of the present invention.

Claims

CLAIMS1. A culture device (100) for culturing Euglena, the culture device (100) comprising: a first tank (la) and a second tank (lb); each of the first tank (la) and the second tank (lb) comprises an interior space for storing a mixture comprising Euglena and nutrients, wherein the interior space of the second tank (lb) is larger than the interior space of the first tank (la); and a conveying means (9) for transporting the Euglena stored in the interior space of the first tank (la) to the interior space of the second tank (lb), wherein each of the first tank (la) and the second tank (lb) comprises an agitating means (4) for agitating the mixture stored therein.

2. The culture device (100) as claimed in claim 1, wherein each of the agitating means (4) is a pump (4a, 4b) to pump the Euglena present in the lower portion of the interior space of each of the first tank (la) and the second tank (lb) to the upper portion of the interior space of each of the first tank (la) and the second tank (lb) via a stirring means (5).

3. The culture device (100) as claimed in claim 1 further comprising an additive supply means (6) for supplying additives to the respective interior spaces of the first tank (la) and the second tank (lb).

4. The culture device (100) as claimed in claim 1, wherein the volume of the interior space of the second tank (lb) is between 5 and 50 times the volume of the interior space of the first tank (la).

5. The culture device (100) as claimed in claim 1, wherein each of the first tank (la) and the second tank (lb) comprises a light-shielding material.

6. The culture device (100) as claimed in claim 1 further comprising an oxygen supply means (8) for supplying oxygen into the mixture stored in the interior space of each of the first tank (la) and the second tank (lb).

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