Culture system and culture method

Abstract

To provide a novel culture technique capable of culturing algae at high density.SOLUTION: A culture system comprises: a first culture vessel which has a first culture chamber to which light from a light source is made incident, and in which first algae having negative phototaxis are cultured inside thereof, and emits light having passed through the first culture chamber to the outside; and a second culture vessel which has a second culture chamber in which second algae having positive phototaxis or weaker negative phototaxis comparing to the first algae are cultured inside thereof, in which the light emitted from the first culture vessel is made incident to the second culture chamber.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a culture system and a culture method.

Background Art

[0002] Algae are cultured to produce useful substances. The oil produced by algae can be used, for example, as a raw material for biofuels. In addition, the carbohydrates produced by algae can be used, for example, as raw materials for fuel additives, pharmaceuticals, cosmetics, and plastic products.

[0003] When algae are cultured, the cell density increases with the passage of the culture time, light does not reach the deep part of the culture tank, and the growth rate of the algae decreases. Various efforts have been made to prevent the decrease in the growth rate of algae. As an example, it has been proposed to isolate an algal strain in which the amount of light-harvesting pigment is less than that of the wild type and culture this algal strain. Since such an algal strain has a small amount of light-harvesting pigment, the algae present near the surface of the culture solution do not absorb more light than necessary, and the irradiated light can efficiently reach the deep part of the culture tank.

[0004] For example, Non-Patent Document 1 discloses randomly modifying genes and isolating an algal strain with a small amount of light-harvesting pigment from among them. Specifically, Non-Patent Document 1 describes a transformant of Chlamydomonas reinhardtti that has a smaller amount of chlorophyll per cell and a larger ratio a / b of chlorophyll a to chlorophyll b compared to the wild type. Chlorophyll b serves as an antenna for collecting light, that is, as a light-harvesting pigment. On the other hand, chlorophyll a serves as a reaction center directly involved in the electron transfer reaction of photosynthesis and as a light-harvesting pigment.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

[0006] Algae are known to vary the amount of light-harvesting pigments according to various environmental factors such as nutritional conditions, thereby adapting to environmental changes. For this reason, as in Non-Patent Document 1, there is concern that if the amount of light-harvesting pigments in algae is suppressed low or made constant by genetic modification, the adaptability of the algae to environmental changes will be reduced.

[0007] Therefore, an object of the present invention is to provide a new culture technique capable of culturing algae at high density. Means for Solving the Problems

[0008] According to a first aspect of the present invention, a first culture container having a first culture chamber inside which light from a light source is incident and in which a first alga having negative phototaxis is cultured, and which emits the light transmitted through the first culture chamber to the outside; a second culture container having a second culture chamber inside which a second alga having positive phototaxis or having a weaker negative phototaxis than the first alga is cultured, and the light emitted from the first culture container is incident on the second culture chamber A culture system comprising is provided.

[0009] According to a second aspect of the present invention, causing light from a light source to be incident on a first culture chamber for culturing a first alga having negative phototaxis; The light that has passed through the first culture chamber is made to enter a second culture chamber for culturing a second type of algae that has positive phototaxis or has a weak negative phototaxis compared to the first type of algae. A culture method including this is provided.

Advantages of the Invention

[0010] According to the present invention, a new culture technique capable of culturing algae at high density is provided.

Brief Description of the Drawings

[0011]

Figure 1

Embodiments for Carrying Out the Invention

[0012] The inventors of the present invention have completed the present invention based on a new idea. That is, the algae culture tank is divided into several spaces in the vertical direction, algae showing different phototaxes are arranged for each space, and light is irradiated from above the culture tank to culture the algae. When such culture is performed, the algae arranged in the space on the upper surface side of the culture tank move to a specific region within the space according to phototaxis, so that a region where no algae exist is generated within the space. For example, algae showing negative phototaxis are arranged in the space on the upper surface side of the culture tank, algae showing positive phototaxis are arranged in the space on the bottom surface side of the culture tank, and light is irradiated from directly above the culture tank to culture the algae. In this case, since the algae arranged in the space on the upper surface side of the culture tank move to the corner region within the space according to negative phototaxis, a region where no algae exist is generated in the central portion of the space. As a result, the light can reach the space on the bottom surface side of the culture tank without being blocked by the light-collecting pigments of the algae arranged in the space on the upper surface side of the culture tank. As a result, it becomes possible to culture algae at high density not only in the space on the upper surface side of the culture tank but also in the space on the bottom surface side of the culture tank.

[0013] "Phototaxis" refers to the property of an organism to move in response to light stimuli. The property of moving towards light is called "positive phototaxis", and the property of moving away from light is called "negative phototaxis".

[0014] Hereinafter, embodiments of the present invention will be described. The embodiments described below are more specific forms of any of the above aspects. The matters described below can be incorporated into each of the above aspects alone or in combination.

[0015] <1. Culture System> The culture system according to the embodiment will be described with reference to FIG. 1. FIG. 1 is a cross-sectional view of the culture system according to the embodiment.

[0016] The culture system shown in FIG. 1 includes a light source 40, a first culture container 11 that has a first culture chamber 12 inside which light from the light source 40 is incident and that cultures the first algae 13 having negative phototaxis, and that emits the light transmitted through the first culture chamber 12 to the outside, a second culture container 21 that has a second culture chamber 22 inside which the second algae 23 having positive phototaxis or having a weaker negative phototaxis than the first algae is cultured, and that emits the light incident on the second culture chamber 22 from the first culture container 11 and that emits the light transmitted through the second culture chamber 22 to the outside, a third culture container 31 that has a third culture chamber 32 inside which the third algae 33 having a stronger positive phototaxis than the second algae 23 when the second algae 23 has positive phototaxis, or having positive phototaxis or having a weaker negative phototaxis than the second algae 23 when the second algae 23 has negative phototaxis is cultured, and that emits the light incident on the third culture chamber 32 from the second culture container 21, and is provided with.

[0017] As shown in Fig. 1, the culture system includes a culture tank 10 composed of a first culture container 11, a second culture container 21, and a third culture container 31, and a light source 40 disposed above the culture tank 10. Here, the culture tank 10 is configured to stack the first culture container 11, the second culture container 21, and the third culture container 31 in three tiers. That is, the second culture container 21 faces the light source 40 with the first culture container 11 in between, and the third culture container 31 faces the light source 40 with the first culture container 11 and the second culture container 21 in between.

[0018] Alternatively, the culture tank 10 may be configured to partition one culture container into three spaces in the vertical direction by a partitioning member. In this case, the partitioning member may be a light-transmissive plate that completely blocks the movement of algal cells and the culture solution, or a light-transmissive membrane that completely blocks the movement of algal cells but allows the movement of the culture solution.

[0019] The light from the light source 40 is incident on the first culture container 11. The light from the light source 40 is light that can be used by algae for photosynthesis. Specifically, the light from the light source 40 is light that can be absorbed by the light-harvesting pigments of algae. The light-harvesting pigments refer to pigments that function as antennas for collecting light among photosynthetic pigments. The light-harvesting pigments vary depending on the biological species. For example, green algae have chlorophyll a and chlorophyll b as light-harvesting pigments. As the light source 40, for example, a white light source or a white light-emitting diode can be used.

[0020] The internal space of the first culture container 11 is called the first culture chamber 12, the internal space of the second culture container 21 is called the second culture chamber 22, and the internal space of the third culture container 31 is called the third culture chamber 32. The first culture chamber 12 contains a first culture solution, where the first algae 13 are cultured. Similarly, the second culture chamber 22 contains a second culture solution, where the second algae 23 are cultured. Similarly, the third culture chamber 32 contains a third culture solution, where the third algae 33 are cultured.

[0021] The shapes of the first culture chamber 12, the second culture chamber 22, and the third culture chamber 32 are not particularly limited. For example, they may have the shape of a flat cylinder or a flat rectangular parallelepiped. When the first culture chamber 12 has a flat shape, light can reach the second culture chamber 22 and the third culture chamber 32 efficiently. That is, it is preferable that the dimension of the first culture chamber 12 in the incident direction of light from the light source 40 is smaller than the dimension in the direction perpendicular to the aforementioned incident direction. In addition to the first culture chamber 12, when the second culture chamber 22 also has a flat shape, light can reach the third culture chamber 32 even more efficiently. Further, when the third culture chamber 32 has a flat shape, the third algae 33 tend to gather on the liquid surface of the third culture solution, and the light from the light source 40 can be utilized efficiently.

[0022] The algae used as the first algae 13, the second algae 23, and the third algae 33 are typically microalgae. Microalgae are, for example, photosynthetic eukaryotes, which are single-celled organisms or colonies thereof. Microalgae are, for example, single-celled green algae such as Chlamydomonas reinhardtti and Botryococcus, single-celled red algae such as Cyanidioschyzon merolae, diatoms such as Phaeodactylum, or colonies thereof. Microalgae do not have to be eukaryotes and may be prokaryotes that perform photosynthesis, such as bacteria such as cyanobacteria.

[0023] The first algae 13, the second algae 23, and the third algae 33 may be of the same biological species or different biological species from each other. Also, the first culture solution, the second culture solution, and the third culture solution are not particularly limited as long as the algae in each culture solution can be cultured, and they may be the same or different from each other.

[0024] The light source 40 irradiates light from above the culture tank 10. In this embodiment, the light source 40 is a point light source. The light source 40 is not particularly limited as long as it can irradiate light with a high intensity on the central region of the first culture chamber 12 and irradiate light with a low intensity on the corner region of the first culture chamber 12. It may be an area light source or sunlight. When a point light source is used as the light source 40, in the central region of the first culture chamber 12, the light from the light source 40 can be irradiated with a higher intensity, and in the corner region of the first culture chamber 12, the light from the light source 40 can be irradiated with a lower intensity. In this case, when the first algae 13 exhibits positive phototaxis, the first algae 13 can be easily gathered in the central region of the first culture chamber 12, and when the first algae 13 exhibits negative phototaxis, the first algae 13 can be easily gathered in the corner region of the first culture chamber 12.

[0025] That is, it is preferable that the liquid surface of the first culture solution in the first culture chamber 12 facing the light source 40 is configured to include a region where the light from the light source 40 is incident with a higher intensity and a region where the light from the light source 40 is incident with a lower intensity or where the light from the light source 40 is not incident.

[0026] Alternatively, a shielding plate that blocks or weakens the light from the light source 40 may be installed between the liquid surface of the first culture solution in the first culture chamber 12 and the light source 40 to create a region in the first culture chamber 12 where the light from the light source 40 is irradiated with a lower intensity and a region where the light from the light source 40 is irradiated with a higher intensity. For example, a shielding plate that blocks or weakens the light from the light source 40 may be installed between the liquid surface of the first culture solution in the first culture chamber 12 and the light source 40 so that almost no light from the light source 40 enters the corner region of the first culture chamber 12 and the light from the light source 40 only enters the central region of the first culture chamber 12. In this case, when the first algae 13 exhibits positive phototaxis, it is easy to gather in the central region of the first culture chamber 12, and when the first algae 13 exhibits negative phototaxis, it is easy to gather in the corner region of the first culture chamber 12.

[0027] (The first example) According to one example, as the first alga 13, an alga showing negative phototaxis can be arranged, as the second alga 23, an alga showing a weaker negative phototaxis compared to the first alga 13 can be arranged, and as the third alga 33, an alga showing positive phototaxis can be arranged. For example, as the first alga 13, Chlamydomonas reinhardtti CC-124 strain, as the second alga 23, a strain maintained at the Chlamydomonas Resource Center of the United States among Chlamydomonas reinhardtti CC-125 strains, and as the third alga 33, a strain maintained in the field of cell motility research in Japan among Chlamydomonas reinhardtti CC-125 strains (commonly known as CC-125 Tokyo strain) can be used.

[0028] In the case of this example, when light from the light source 40 enters the first culture chamber 12 from directly above the culture tank 10, the first alga 13 showing negative phototaxis moves toward the side wall of the first culture container 11 so as to avoid light and gathers in the corner region of the first culture chamber 12. The light that has passed through the first culture chamber 12 enters the second culture chamber 22. However, since the first alga 13 has gathered in the corner region of the first culture chamber 12, light of higher intensity enters the central region of the second culture chamber 22. In the second culture chamber 22, the second alga 23 showing weak negative phototaxis moves toward the side wall of the second culture container 21 so as to avoid light and gathers in the corner region of the second culture chamber 22. At this time, since the second alga 23 shows a weaker negative phototaxis than the first alga 13, as shown in FIG. 1, compared to the first alga 13, it is sparsely present not only in the corner region of the second culture chamber 22 but also in a region slightly closer to the center of the second culture chamber 22. The light that has passed through the second culture chamber 22 enters the third culture chamber 32. However, since almost all of the first alga 13 and many of the second alga 23 have gathered in the corner regions of each culture chamber, light of higher intensity enters the central region of the third culture chamber 32. In the third culture chamber 32, the third alga 33 showing positive phototaxis moves seeking light and gathers on the liquid surface in the central region of the third culture chamber 32.

[0029] Alternatively, in the above example, the third alga 33 may have a weaker negative phototaxis compared to the second alga 23.

[0030] (Second example) According to another example, as the first alga 13, an alga showing negative phototaxis can be arranged, as the second alga 23, an alga showing positive phototaxis can be arranged, and as the third alga 33, an alga showing stronger positive phototaxis compared to the second alga 23 can be arranged. For example, as the first alga 13, Chlamydomonas reinhardtti strain CC-124, as the second alga 23, the strain maintained at the Chlamydomonas Resource Center of the United States among Chlamydomonas reinhardtti strain CC-125, and as the third alga 33, the strain maintained in the field of cell motility research in Japan among Chlamydomonas reinhardtti strain CC-125 can be used.

[0031] In the case of this example, when light from the light source 40 enters the first culture chamber 12 from directly above the culture tank 10, the first alga 13 showing negative phototaxis moves toward the side wall of the first culture container 11 so as to avoid light and gathers in the corner region of the first culture chamber 12. The light that has passed through the first culture chamber 12 enters the second culture chamber 22. However, since the first alga 13 has gathered in the corner region of the first culture chamber 12, light of higher intensity enters the central region of the second culture chamber 22. In the second culture chamber 22, the second alga 23 showing positive phototaxis moves in search of light and gathers on the liquid surface in the central region of the second culture chamber 22. The light that has passed through the second culture chamber 22 enters the third culture chamber 32. However, since the second alga 23 has gathered on the liquid surface in the central region of the second culture chamber 22, the intensity of the light entering the central region of the third culture chamber 32 decreases. However, in the third culture chamber 32, since the third alga 33 shows stronger positive phototaxis than the second alga 23, it can move in search of light and gather on the liquid surface in the central region of the third culture chamber 32.

[0032] Whether the algae exhibit positive or negative motility can be determined by irradiating the algae in the culture solution with light and observing the behavior of the algae. Also, when multiple types of algae exhibit the same motility and it is desired to determine the strength of the motility, it can be determined by irradiating each type of algae with light under the same conditions and observing the behavior of the algae.

[0033] (Modification example of the culture system) In the above embodiment, a culture system including a culture tank partitioned into three culture chambers has been described. However, a culture system including a culture tank partitioned into multiple culture chambers is included in the scope of the present invention. For example, a culture system including a culture tank partitioned into 2 to 5 culture chambers can be cited as a representative example of the culture system of the present invention.

[0034] Modification example 1: The culture system of Modification example 1 includes a culture tank partitioned into two culture chambers. This culture system has the same structure as the culture system according to the above embodiment shown in FIG. 1, except that the third culture container 31 is omitted. In this case, it is preferable to arrange algae showing negative phototaxis as the first algae 13 and algae showing positive phototaxis as the second algae 23.

[0035] Modification example 2: The culture system of Modification example 2 includes a culture tank partitioned into four culture chambers. This culture system has the same structure as the culture system according to the above embodiment shown in FIG. 1, except that a fourth culture container is added under the third culture container 31, and when the third algae shows positive phototaxis, algae showing stronger positive phototaxis than the third algae are used as the fourth algae cultured in the fourth culture container, and when the third algae shows negative phototaxis, algae showing positive phototaxis are used.

[0036] <2. Culture method> Using the above culture system, algae can be cultured at high density. That is, according to another aspect, causing the light from the light source 40 to enter the first culture chamber 12 for culturing the first algae 13 having negative phototaxis, The light that has passed through the first culture chamber 12 is made to enter a second culture chamber 22 for culturing a second alga 23 that has positive phototaxis or has a weak negative phototaxis as compared with the first alga 13. A culturing method including this is provided.

[0037] In the above culturing method, when the second alga 23 has positive phototaxis, it has a stronger positive phototaxis as compared with the second alga 23, and when the second alga 23 has negative phototaxis, the light that has passed through the second culture chamber 22 may further be made to enter a third culture chamber 32 for culturing a third alga 33 that has positive phototaxis or has a weak negative phototaxis as compared with the second alga 23.

[0038] Also, as described in the above explanation of the culturing system, when the light source 40 is a point light source, in the central region of the first culture chamber 12, the light from the light source 40 is irradiated with a higher intensity, and in the corner region of the first culture chamber 12, the light from the light source 40 is irradiated with a lower intensity. In this case, when the first alga 13 exhibits positive taxis, it is likely to gather in the central region of the first culture chamber 12, and when the first alga 13 exhibits negative taxis, it is likely to gather in the corner region of the first culture chamber 12.

[0039] That is, in the above culturing method, it is preferable that the light from the light source 40 is made to enter the first culture chamber 12 such that the liquid surface of the culture solution in the first culture chamber 12 facing the light source 40 includes a region where the light from the light source 40 is incident with a higher intensity and a region where the light from the light source 40 is incident with a lower intensity or the light from the light source 40 does not enter.

[0040] The above culturing method can be carried out according to the above explanation of the culturing system.

[0041] <3. Effects> According to the culturing technique of the present invention, when culturing algae by combining algae having different phototactic properties with a culture tank provided with a plurality of culture chambers in the vertical direction, light can be efficiently transmitted to the deep part of the culture tank. Therefore, algae can be cultured at high density not only in the culture chamber on the upper surface side of the culture tank but also in the culture chamber on the bottom surface side of the culture tank. As a result, material production using algae can be efficiently performed.

[0042] On the other hand, as described in the background art section, conventionally, algae have been cultured at high density using a transformant with a small amount of light-harvesting pigment as the algae. In this conventional method, since the amount of light-harvesting pigment in the algae is suppressed low or made constant by genetic modification, the adaptability of the algae to environmental changes is low. In contrast, since the culturing technique of the present invention does not use a transformant with a small amount of light-harvesting pigment as the algae, the adaptability of the algae to environmental changes does not decrease.

[0043] Also, in the conventional method, even if the amount of light-harvesting pigment in the algae is reduced, the irradiated light is still absorbed by the algae present near the surface of the culture solution, and the growth rate of the algae present in the deep part of the culture tank decreases to some extent. Also, if the amount of light-harvesting pigment in the algae is reduced too much by genetic modification, the growth of the algae is delayed. In contrast, as described above, since the culturing technique of the present invention can efficiently transmit light to the deep part of the culture tank, the growth rate of the algae present in the deep part of the culture tank is not decreased. Also, since the culturing technique of the present invention does not perform genetic modification to reduce the amount of light-harvesting pigment in the algae, the growth of the algae is not delayed.

[0044] In addition, since the conventional method uses a recombinant, the place where it can be implemented is limited to a facility capable of culturing the recombinant. In contrast, since the culturing technique of the present invention does not use a recombinant, there is no limitation on the place where it can be implemented.

[0045] <4. Preferred Embodiment> The preferred embodiments are summarized below. [1] It has a first culture chamber inside which light from a light source is incident and in which a first type of algae having negative phototaxis is cultured, and a first culture container that has the first culture chamber inside and emits the light that has passed through the first culture chamber to the outside. A second culture container that has a second culture chamber inside which a second type of algae having positive phototaxis or having a weaker negative phototaxis compared to the first type of algae is cultured, and the light emitted by the first culture container is incident on the second culture chamber. A culture system comprising the above. [2] The culture system according to [1], further comprising the light source. [3] The culture system according to [1] or [2], wherein the liquid level of the culture solution in the first culture chamber facing the light source is configured to include a region where the light from the light source is incident with a higher intensity and a region where the light from the light source is incident with a lower intensity or where the light from the light source does not enter. [4] The culture system according to any one of [1] to [3], wherein the dimension of the first culture chamber in the incident direction of the light from the light source is smaller than the dimension in the direction perpendicular to the incident direction. [5] The culture system according to any one of [1] to [4], wherein the second culture container faces the light source with the first culture container sandwiched therebetween. [6] It further comprises a third culture container that has a third culture chamber inside which a third type of algae is cultured. The second culture container emits the light that has passed through the second culture chamber to the outside. The light emitted by the second culture container is incident on the third culture chamber of the third culture container. [7] Incident light from a light source into a first culture chamber for culturing a first type of algae having negative phototaxis.

[0046] [7] Causing light from a light source to be incident on a first culture chamber for culturing a first type of algae having negative phototaxis. Causing the light that has passed through the first culture chamber to enter a second culture chamber for culturing a second type of alga that has positive phototaxis or has a weak negative phototaxis compared to the first type of alga A culture method including this [8] The light from the light source is made to enter the first culture chamber such that the liquid surface of the culture solution in the first culture chamber facing the light source includes a region where the light from the light source enters with a higher intensity and a region where the light from the light source enters with a lower intensity or where the light from the light source does not enter, according to the culture method described in [7]. [9] The first culture chamber has a dimension in the incident direction of the light from the light source that is smaller compared to the dimension in the direction perpendicular to the incident direction, according to the culture method described in [7] or [8].

[10] The second culture chamber faces the light source with the first culture chamber in between, according to the culture method described in any one of [7] to [9].

[11] When the second type of alga has positive phototaxis, it has a stronger positive phototaxis compared to the second type of alga, and when the second type of alga has negative phototaxis, it further includes causing the light that has passed through the second culture chamber to enter a third culture chamber for culturing a third type of alga that has positive phototaxis or has a weak negative phototaxis compared to the second type of alga, according to the culture method described in any one of [7] to

[10] .

Example

[0047] In this example, algae were cultured using the culture system of Modification 1, that is, the culture chamber system obtained by removing the third culture container 31 from the culture system shown in FIG. 1.

[0048] As the first culture container 11 and the second culture container 21, a T25 cell culture flask (culture area: 25 cm 2 , volume: 60 cm 3 ) was used. The culture tank 10 was prepared by stacking the first culture container 11 on top of the second culture container 21.

[0049] About 50 mL of culture solution was put into the first culture container 11 together with Chlamydomonas reinhardtti CC-124 strain showing negative phototaxis, and about 50 mL of culture solution was put into the second culture container 21 together with Chlamydomonas reinhardtti CC-125 Tokyo strain showing positive phototaxis.

[0050] From directly above the first culture container 11, white cold light was irradiated at an intensity of > 3,000 μmol photons m -2 s -1 for 30 minutes, and the behavior of Chlamydomonas in the first culture container 11 and the second culture container 21 was observed.

[0051] The algal cells of the CC-124 strain showing negative phototaxis gathered in the corner of the first culture chamber 12 so as to escape from the light. On the other hand, the algal cells of the CC-125 Tokyo strain showing positive phototaxis gathered near the liquid surface of the culture solution in search of light and formed striped patterns. This is because when the algal cells of the CC-125 Tokyo strain became too dense near the liquid surface of the culture solution, they sedimented, and when they sedimented to a certain depth, they rose toward the liquid surface of the culture solution, repeating this sedimentation and rising, that is, because the "bioconvection" phenomenon occurred.

[0052] In this example, since the algal cells of the CC-124 strain showing negative phototaxis gathered in the corner of the first culture chamber 12, light of higher intensity could be made to enter the central region of the second culture chamber 22 from the light source 40. For this reason, algae could be cultured at high density not only in the first culture chamber 12 but also in the second culture chamber 22.

Explanation of Signs

[0053] 10…culture tank, 11…first culture container, 12…first culture chamber, 13…first algae, 21…second culture container, 22…second culture chamber, 23…second algae, 31…third culture container, 32…third culture chamber, 33…third algae, 40…light source

Claims

1. A first culture container having therein a first culture chamber for culturing a first alga that has negative phototaxis and into which light from a light source is incident, and that emits the light transmitted through the first culture chamber to the outside; A second culture container having therein a second culture chamber for culturing a second alga that has positive phototaxis or has a negative phototaxis weaker than that of the first alga, wherein the light emitted from the first culture container is incident on the second culture chamber; A culture system comprising the same.

2. The culture system according to claim 1, further comprising the light source.

3. The culture system according to claim 1, wherein the liquid level of the culture solution in the first culture chamber facing the light source is configured to include a region where the light from the light source is incident at a higher intensity and a region where the light from the light source is incident at a lower intensity or where the light from the light source does not enter.

4. The culture system according to claim 1, wherein the dimension of the first culture chamber in the incident direction of the light from the light source is smaller than the dimension in the direction perpendicular to the incident direction.

5. The culture system according to claim 1, wherein the second culture container faces the light source with the first culture container interposed therebetween.

6. Further comprising a third culture container having therein a third culture chamber for culturing a third alga, wherein the second culture container emits the light transmitted through the second culture chamber to the outside, the third culture container has the light emitted from the second culture container incident on the third culture chamber, and the third alga has a positive phototaxis stronger than that of the second alga when the second alga has positive phototaxis, and has positive phototaxis or has a negative phototaxis weaker than that of the second alga when the second alga has negative phototaxis. The culture system according to claim 1.

7. Incident light from a light source into a first culture chamber for culturing a first alga having negative phototaxis; And incident the light transmitted through the first culture chamber into a second culture chamber for culturing a second alga having positive phototaxis or having a negative phototaxis weaker than that of the first alga. A culture method comprising the same.

8. The light from the light source is made to enter the first culture chamber facing the light source such that the liquid surface of the culture solution in the first culture chamber includes a region where the light from the light source enters with a higher intensity and a region where the light from the light source enters with a lower intensity or where the light from the light source does not enter. The culture method according to claim 7.

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