JP3336439B2 - Chlorella microalgae that fix high concentration CO2 - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing C under high CO ₂ concentration conditions.
Chlorella microalgae that fix O ₂ can be used to fix high-concentration CO ₂ in fossil fuel combustion exhaust gas at thermal power plants, etc., and reduce greenhouse gas emissions from human activities. It relates to microalgae of the genus Chlorella that can contribute.

[0002]

BACKGROUND OF THE INVENTION Algae is a general term for lower plants that mainly grow in water and perform photosynthesis. Among them, microalgae mainly composed of single cells are called microalgae, but the types are extremely large. Among microalgae, Chlorella, Senedesmus, and Spirulina are currently used and industrialized as health foods.However, acetic acid and inorganic carbonates are mainly used as carbon sources for their cultivation. There have been few attempts to actively utilize the inherent CO ₂ fixation ability. Thus, in order to secure the CO ₂ fossil fuel combustion exhaust gas such as CO ₂ and thermal power plants exhaust gases of an industrial, example microalgae is used no. Further, the CO ₂ fixation product was immobilized CO ₂ in the flue gas feed and industrial SCP (Single Cell Protein, microbial proteins)
There are currently no industries to use. In the past, Tokugawa Biological Research Institute has cultivated microalgae with the exhaust gas burning city gas, but the amount of fixed CO ₂ is small,
In addition, the fuel cost is too high and it has not been industrialized.

[0003] The CO ₂ from fossil fuel combustion gas-fired power plants and the like in a large amount discharged, in order to industrially immobilized utilizing CO ₂ fixation ability of microalgae, directly exhaust gas to the culture tank The key is to use microalgae that function efficiently even under the introduced conditions. However, in the conventionally known microalgae strain, the concentration of CO _{2 that} can be enriched in the air blown into the culture tank was about 1 to 5% by volume (hereinafter, unless otherwise specified,% means volume%). . Exhaust gas from burning fossil fuels varies greatly depending on the combustion conditions, but the average value of the CO ₂ concentration in the exhaust gas from thermal power plants in Japan is currently around 16% for coal-fired power and 15% for oil-fired power. Before and after, about 11% by LNG thermal power (all based on dry gas). Thus, the CO ₂ concentration in the exhaust gas from a thermal power plant is about 10 to 15%. When these exhaust gases are directly blown into the culture tank,
Because of the high concentration of CO _{2, the} condition is such that ordinary microalgae cannot grow. In addition, in the case of diluting with air to obtain the optimal CO ₂ condition, the cost of the exhaust gas dilution system is a major factor in raising the CO ₂ fixing cost. In view of the above, in order to cultivate microalgae and fix CO ₂ by introducing exhaust gas directly into the culture tank, high concentration of C
It is necessary to search for and use microalgal strains that function even under O ₂ conditions. Those that grow even under relatively high CO ₂ conditions include nannochloris as a marine microalgae.
loris) NANNO2 strain [M. Negro et al., Appl. Biochem.
Biotechnol., 28/29, 877-886 (1991), N. Nishikawa
Et al., Energy conversion and management, Vol. 33, 553
-560 (1992)], Chlamydomonas as a freshwater microalgae
(Chlamydomonas) genus MGA-131 [Yamada et al., Journal of the Japanese Society of Agricultural Chemistry, Vol. 164, No. 3, p. 659 (1990)
], Chlorella vulgaris 21
1 / 8k strain [HJ Silva et al., J. Gen. Microbiol., 13
0, 2833-2838 (1984)]. The microalgae used for fixing CO ₂ in the exhaust gas were 10% discovered by Marine Biotechnology Institute, Inc.
The only known marine microalga Chlorococcum littorale that can grow at a CO ₂ concentration of 0.1 kg (August 31, 1990, Nikkei Inc.).

[0004] Microalgae are proteins that make up about half of the substances that make up their bodies, and can be used as industrial proteins or their raw materials, and can also be used as highly nutritious feeds. To prevent global warming due to an increase in greenhouse gas in the atmosphere, although it is important to suppress the release of greenhouse gases, the use of CO ₂ fixation product of microalgae as feed and industrial proteins An indirect greenhouse gas emission reduction effect described below is observed. That is, at present, feed grains used as livestock feed in the world account for over 40% of the total grain production,
During feed grain production, strong greenhouse gases such as nitrous oxide are emitted as methane is generated from composting cereal crop residues and nitrous oxide is caused from fertilizer decomposition. 1990 IP
According to the report of the CC (Intergovernmental Panel on Climate Change) meeting, on a 20-year scale, the greenhouse effect per unit weight of methane is about 60 times that of CO ₂ and that of nitrous oxide is about 270 times that of CO _2. Be powerful. However, if SCP production is performed by culturing microalgae, these greenhouse gases are hardly generated. Substituting SCP feed production for future increases in feed grain production can contribute to significantly reducing greenhouse gases generated when producing feed.
In addition, globally, forests are cultivated on a large scale in order to increase the production of feed grains, and carbon accumulated in forests is
_Although released as ₂ in the atmosphere, production of microalgae SCP does not accompany the cultivation of forests, and is expected to have the effect of suppressing the cultivation of forests. As described above, if microalgae are cultured while fixing CO ₂ in exhaust gas, an effect of indirectly suppressing the emission of greenhouse gases due to deforestation can also be expected.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of such a situation, and has a high concentration of C.
O ₂ can using cultured exhaust gas containing become such microalgae, CO ₂ fixation method using the exhaust gas or the like by the fine Hosomo, and the feed or industrial proteins consisting CO ₂ fixation product of the microalgae The task is to provide.

[0006]

As a result of various studies, the present inventors have separated and purified specific microalgae that fix and grow CO ₂ in a culture ventilated with air having a high CO ₂ concentration. It has been found that cultivation in which a gas simulating exhaust gas has been aerated does not promote the growth of the microalga or cause a decrease in the ability to fix CO ₂ , and further, the CO of the microalga is reduced.
_{(2) The} present invention was completed by knowing that the protein content in the immobilized product was as high as 40% by weight or more.

The present inventor paid attention to the following points in order to search for strains applicable to fix CO ₂ in exhaust gas. Although the CO ₂ concentration in the exhaust gas is three orders of magnitude higher than the concentration in the atmosphere, there are places such as soil where the CO ₂ concentration becomes higher depending on the time and conditions, such as soil, among the places where natural algae inhabit. Therefore, a search sample from the natural world was collected from paddy field water or soil having such a high CO ₂ concentration in addition to water from lakes and marshes.

[0008] That is, the present invention provides 5 to 20% by volume.
The CO ₂ concentration is stable viable Chlorella (Chlorel
la) Genus microalgae. In the present invention, “stable growth” means that the growth is equal to or higher than the growth under normal air ventilation conditions.

The present inventor uses lake water, paddy water, soil and the like from various collection sites as a separation source, and after pre-culture under low light, a specific mixed gas (CO ₂ = 15%, O ₂ = 2).
%, N ₂ = 83%), aerated and cultured, and further cloned and sterilized by a separation / purification method using a plate agar medium to obtain 6 new pure isolates of microalgae, which were then HA -1 strain, HA-2 strain, HC-1 strain, HC-2
Strains, HT-1 strain and HT-2 strain. These are strains that can grow even when cultured with aeration of a gas having a high CO ₂ concentration such as the exhaust gas from a thermal power plant. The morphology and life cycle of these isolates were observed using an optical microscope, and the genus levels were classified.The morphologies were all similar, the systematic differentiation was unicellular, the cell morphology was spherical, and the size was Is about 2-7 μm, grows by asexual reproduction forming autologous spores in the body, and the number of chloroplasts in the cell is 1
The individual had no flagella and no motility. From the above features,
All six new isolates were determined to belong to the genus Chlorella. At this time, no algae have been deposited at the Institute of Microbial Industry and Technology, and none of the above-mentioned isolates of the present invention has been deposited.

[0010] The microalgae of the present invention can grow without any special carbon source such as acetic acid or carbonate other than CO ₂ , and therefore can fix and assimilate CO ₂ . Therefore, the present invention relates to a method for fixing CO ₂ using the microalgae according to the present invention. In this method, it is preferable to aerate the culture solution with a gas having a CO ₂ concentration of 5 to 20%. Such gases may be, for example, various exhaust gases generated when fossil fuels are burned, and particularly include thermal power station exhaust gases. As a specific example, the microalga Chlorella HA-1 strain has a maximum growth in a culture in which air having a CO ₂ concentration of 10% is aerated, and a growth promoting effect by enrichment of CO ₂ is recognized. In the case of 15% CO ₂ , inhibition was observed due to an increase in the concentration of CO ₂ as compared with 10%, but the growth ability was maintained at a high level. This property indicates that if the exhaust gas is directly introduced into the culture tank and subjected to aeration culture, the growth of the HA-1 strain can be promoted or the culture can be performed without reducing the CO ₂ fixation ability.

The protein content contained in the microalgae, which is a CO ₂ fixed product, is 42 to 44% of the dry weight.
There is no great difference between the alga bodies cultured under the _two conditions. The fact that about half of the algal bodies of the microalgae of the present invention including the HA-1 strain and the like are proteins indicates that they can be used as highly nutrient feeds or industrial proteins (or raw materials thereof). Accordingly, the present invention relates to a feed or industrial protein comprising the CO ₂ fixed product of the microalgae according to the present invention.

[0012]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 Separation, Purification and Classification of Microalgae Lake water, paddy water or soil from various sampling sites (38 kinds in total).
1 In the case of soil, 1 g by wet weight was added to a large test tube containing 20 ml of MBM liquid medium (Table 1), and the mixture was incubated at 25 ° C. for 3 weeks under a fluorescent lamp (illuminance: 2500 lux). The light irradiation cycle was 12 hours under bright conditions (light irradiation) and 12 hours under dark conditions (no light irradiation).

[Table 1] (Footnote) * Composition of A-5 solution is as _{follows: H 3 BO 3 286mg MnSO 4} · 7H 2 O 250mg ZnSO 4 · 7H 2 O 22.2mg CuSO 4 · 5H 2 O 7.9mg Na 2 MoO ₄ 2.1 mg distilled water 1 liter Next, a mixed gas (CO ₂ = 15%, O ₂ = 2%, N ₂ =
83%) was passed through a test tube at an aeration rate of 60 ml / min or more, and microalgae grown under these conditions were accumulated and cultured. Light was irradiated using an incandescent lamp for photography (illuminance: about 11,000 lux). The cells were cultured at a temperature of 25 ° C. for 10 hours in a light condition and 14 hours in a dark condition for 5 days. The culture solution was subcultured in an MBM medium so that the absorbance at OD = 660 nm was about 0.03 to 0.05, and the culture was further integrated and cultured for 3 days under the above conditions. As a result of further repeating the subculture and the enrichment culture, a CO ₂ concentration of 15% was obtained.
An enriched culture sample containing microalgae that grows under the conditions described above was obtained. Microalgae were separated from the obtained enrichment culture sample by the following method. After serially diluting the enriched culture sample with sterile water,
The diluted solution was applied to a Detmer plate agar medium (Table 2),
The culture was allowed to stand still at 25 ° C. for 2 weeks under a fluorescent lamp (illuminance: 2500 lux). Light irradiation cycle is 12 hours under light condition, 1 under dark condition
Two hours. The grown colonies were subcultured on MBM agar medium (MBM liquid medium of Table 1 plus 1.5% agar) and MBM liquid medium.

TABLE 2 Composition of Detmer agar plate medium ─────────────────────── Ca (NO ₃ ) ₂ .4H ₂ O 1.0 g KCl 0.25 g _{MgSO 4 · 7H 2 O 0.25g KH} 2 PO 4 0.25g FeCl 3 0.002g agar 15g water 1 liter of water ─────────────────────── The transferred sample was checked for the presence of bacteria or the like on a nutrient agar medium or the like, and the separated sample was confirmed to be a clone free of other microorganisms. Further, the purified isolate was subjected to the growth test under the enrichment culture conditions described above again, and the growth ability under the enrichment culture conditions was confirmed. Microalgae that grow in this way a high concentration of CO ₂ of 15% as fixed is separated 6 strain which HA-1 strain, HA-2
Strains, HC-1, HC-2, HT-1 and HT-
It was named 2 strains. When the morphology and life cycle of these isolates were observed with an optical microscope, they were all determined to belong to the genus Chlorella. Table 3 summarizes the locations and forms of the sources of the above isolates. In addition, micrographs of these isolates are shown in FIGS. 1 to 6, and their color photographs are shown in Reference Photos 1 to 6. In the samples other than the above six isolates, microalgae strains capable of growing under the above conditions could not be isolated. In addition, the following nine NIES strain-preserving microalgae strains: Chloralla pyrenoidosa NIES
-226, Chloralla vulgaris NIES-227, Scenedesmus acu
minatus NIES-92, Scenedesmus acutusNIES-94, Chlamy
domonas augustae NIES-158, Chlamydomonas pulsatill
a NIES-122, Oscillatoria agardhii NIES-204, Spirul
ina platensis NIES-45, Spirulina subsalsa NIES-27
When the growth under the above-mentioned enrichment culture conditions was examined for Chloralla pyrenoid, clear growth was observed.
With osa NIES-226 alone, the other strains became white and died or hardly grew.

[Table 3] Sampling location and characteristics ^* Isolate sampling Ground (separated sample) Cell size Genus ─────────────────────────────────── HA-1 strain 2-7 μm Chlorella HA-2 strain, Kitaura Shirahama, Ibaraki Prefecture (lake) 2-8 μm Chlorella HC-1, 2-6 μm Chlorella HC-2, downstream of Chikugo River, Saga Prefecture 2-7μm Chlorella HT-1 strain Ayakami-cho, Kagawa prefecture (reservoir water) 2-6μm Chlorella HT-2 strain Zentsuji-shi, Kagawa prefecture (reservoir water) 2-7μm Chlorella II ─────────────────────────────── (Footnotes) * All six isolates are single-celled and spherical, and autologous vesicles Formation by growing by asexual reproduction. It has one chloroplast, has no flagella and has no motility. It is a green algae.

Example 2 Culture characteristics of microalgae isolates (a) Growth ratio Six isolates of Chlorella sp. Described in Example 1 and a control strain Ch
For loralla pyrenoidosaNIES-226 (National Institute for Environmental Studies strain-preserved microalgae), the relationship between CO ₂ concentration and growth rate was examined. The culture device used in this example is a culture tank,
Thermostat light irradiation system, is composed of CO ₂ enriched air supplying device, an optical illumination system and CO ₂ enriched air supplying device is controlled by the timer time. The culture tank was an acrylic cylindrical container having a height of 30 cm and an inner diameter of 8 cm. The outer wall was coated with white paint to prevent light from entering from the side. The light irradiation system includes a parallel beam type high brightness light source device UI-501C.
(Ushio Inc.) was used. In this device, ultraviolet light and infrared light are attenuated using a lens type filter and a cold mirror, respectively, and the wavelength characteristic is that visible light (400 to 700 nm) that can be used for photosynthesis is generated in a well-balanced manner. Can simulate. In the main culture device,
Light is irradiated from the top of the culture tank, and the light receiving area of the culture solution is 5
It was 0 cm ² . The average illuminance of the light receiving surface measured by the illuminometer is 55000 lux, which is equivalent to 1100 μE / m ² / sec, which is about half of the daytime illuminance in summer in the Kanto region. The CO ₂ enriched air supply device is composed of a pure CO ₂ gas cylinder, an air pump, a gas flow meter, and a solenoid valve.
The air pump and solenoid valve are linked to a timer, and air and CO
The mixing of the _two can be controlled. Adjusted C
O ₂ enriched air was supplied as fine bubbles through a glass filter (manufactured by Rika Kinoshita Co.) from the culture medium lower. In addition, the CO ₂ concentration of the CO ₂ -enriched air was periodically confirmed by an infrared absorption type CO ₂ analyzer LX-710 (manufactured by Iijima Electronics Co., Ltd.). The temperature of the culture tank was kept constant by a temperature controller (manufactured by Taiyo Corporation). The culture experiment was performed as follows. Four sets of the above-mentioned culture devices are installed, and each device is provided with air, air containing 5% CO ₂ , air containing 10% CO ₂ and 15% CO _{2 respectively.}
Was flowed at a flow rate of 0.25 liter / min.
An M4N medium (Table 4), which has a higher nutrient concentration than the MBM liquid medium and is more suitable for high-density culture, was used as a culture solution. The inoculum was obtained by isolating each of the isolates and control strains cultured in an M4N medium while aerating air.
The mixture was centrifuged at 00 rpm for 30 minutes, washed with distilled water, further centrifuged, and resuspended in distilled water. 950 ml of M4N medium was placed in the culture tank of each culture device, and 50 ml of the inoculum was inoculated. The amount of algal bodies in the inoculum was the same in a series of experiments for each strain, and the inoculum volume for each strain was approximately 80
To 110 mg. After inoculation, the cells were cultured at 25 ° C. for 1 week in each device while passing air containing CO ₂ at each concentration. The light irradiation cycle was a light condition of 12 hours and a dark condition of 12 hours, and ventilation was performed only during the light condition period. The cultivation was performed in an open system, not under aseptic conditions. After culturing, the entire amount of the culture was centrifuged, washed with distilled water, further centrifuged, and resuspended in distilled water. 1 suspension
It dried at 05 degreeC, and measured the amount of dry matter produced. The dry matter sample was further measured for carbon content and nitrogen content using a C / N coder NC-800 type (manufactured by Sumitomo Chemical Co., Ltd.).

[Table 4] The results are shown in FIGS. 7 to 13. As an index indicating the growth of the microalgae, the growth ratio, that is, the amount grown in one-week culture (the amount obtained by subtracting the inoculum dry weight from the final dry weight) was used as the inoculum dry weight. The divided value was used. Therefore, a value obtained by adding 1 to the growth ratio indicates how many times the amount of inoculated chlorella increased in one week. Under the conditions of this experiment, the rate of increase in chlorella dry weight over time was almost linear, and thus it was determined that the growth ratio could be used as an index indicating the growth rate. according to this,
The growth ratio of the Chlorella HA-1 strain of the present invention (FIG. 7) is 5%.
CO ₂ and similar in 10% CO _2, maintains the high values of those slightly decreased with 15% CO _{2, HA-2} strain (Fig. 8), HC-1 strain (Fig. 9) and HT-2 Stock (Figure 1
The three strains 2) showed a substantially constant high growth ratio from 5% CO ₂ to 15% CO ₂ , and the HT-1 strain (FIG. 11) increased the growth ratio with an increase in the CO ₂ concentration. Thus, these 5 strains are apparent growth promotion in the CO ₂ concentration of the same level as thermal power plant flue gas is 15% CO ₂ concentration of 10%, with respect to the CO ₂ concentration, using a thermal power plant flue gas directly Culture without the need for any dilution with air. Although the HC-2 strain (FIG. 10) is slightly inferior to the above five strains, the growth ratio is the highest at a CO ₂ concentration of 10%, and shows culture characteristics not found in conventional Chlorella microalgae. is there. In contrast, the control strain Chlora
lla pyrenoidosa NIES-226 (FIG. 13) has a growth ratio of about 3 times under the condition of aerated with 5% CO ₂ -enriched air compared with the case of aerated, and a clear growth promoting effect is recognized. 10% CO ₂ and 15% CO ₂
Under the conditions, growth was decreased. This indicates that, when cultivating flue gas from a thermal power plant using this algae, efficient culturing cannot be performed unless the flue gas is diluted with air.

(B) Growth rate, CO ₂ fixation rate, photosynthetic efficiency Next, from the experimental results in the preceding section (a), how much dry energy and fixed carbon quantity of irradiated solar energy are Table 5 summarizes whether or not the conversion has been performed. Table 5 shows the growth ratio of each isolate at the optimum CO ₂ concentration [see (a)], growth rate, CO ₂ fixation rate, and photosynthetic efficiency (PE).
The growth rate was converted from the amount of dry matter produced to the rate per day of the light irradiation area (unit: g dry matter / m ² / day).
The O ₂ fixation rate is calculated by multiplying the amount of dry matter produced by the amount of carbon obtained by measuring the C / N coder (unit: g carbon / m).
² / day), and photosynthetic efficiency was calculated from the amount of carbon incorporated into the algal cells of Chlorella, and was expressed as a percentage of the energy of irradiation light (ie, the chemical energy per gram of carbon of microalgae was calculated as 11.4K
Therefore, the carbon amount was multiplied by this value and divided by the irradiation energy of light; the irradiation light energy amount under the present experimental conditions = 2450 Kcal / m ² / day / culture tank).

[Table 5] Growth rate, CO ₂ fixation rate, photosynthetic efficiency of Chlorella isolates Test strain Optimal CO ₂ growth ratio Growth rate CO ₂ photosynthesis concentration Fixed rate Efficiency ──────────────────────────────── HA -1 10 5.90 17.1 7.80 3.62 HA-2 5 4.63 10.6 4.44 2.06 HC-1 10 4.86 14.0 6.29 2.92 HC-2 10 3.61 11.7 4.98 2.31 HT-1 15 5.74 12.9 6.10 2.83 HT-2 10 5.52 12.6 5.69 2.64 Control 5 4.74 15.4 6.83 3.17 に よ る Based on the results shown in Table 5. The control of Chloralla pyrenoid
The osa NIES-226 strain 5% CO ₂ condition, growth rate, CO
₂ Fixed speed is fast. E. FIG. Is also expensive. However, as indicated in the previous section (a), 57% compared to 10% CO ₂ in 5% CO _2, at high concentrations CO ₂ since the growth ratio is decreased to 15% in CO ₂ 40% Growth effect cannot be expected. In contrast, if isolates of the present invention, HA-1 strain with high-concentration CO ₂ conditions, growth rate, CO ₂ fixed speed and P. E. FIG. In both cases, the values under the 5% CO ₂ condition of the control were higher than those of the control, and the HC-1 strain and the HT-1 strain also showed values close to the values.
It can be obtained even at _two concentrations.

Example 3 Culture Characteristics of HA-1 Strain Regarding Culture Conditions The culture characteristics of the Chlorella sp. HA-1 strain that grew best among the above six isolates of the present invention were examined. The main factors affecting the growth of microalgae are light, medium composition, aerated CO ₂ concentration, aerated amount (stirring speed), temperature and medium pH.
₍₂₎ Four types of culture factors of concentration, aeration amount, temperature and medium pH were examined under different conditions. The culture was performed according to Example 2 except that the above conditions were changed. The results are shown in FIGS.
7 is shown. According to this, a CO ₂ concentration of 10% is optimal for growth, showing a fairly high growth ratio even at 20%, after which the growth ratio decreases as the CO ₂ concentration increases,
It hardly grew under the CO ₂ aeration condition (Fig. 1
4). In the experiment on the ventilation rate shown in FIG.
The growth was slightly better at 5 liters / minute and 0.5 liters / minute, but 0.10 liters / minute and 1.0 liters / minute.
The difference from the minute was small. In the experiment in which the temperature shown in FIG. 16 was examined, the growth ratio was low at 20 ° C.
The HA-1 strain was almost constant from ℃ to 35 ℃, indicating that the HA-1 strain was a mesophilic strain having a wide temperature adaptation range. The experiment on the medium pH shown in FIG. 17 showed that the optimum pH (initial medium) was about 4 to 5. However, with the culturing, the pH of the medium increased by about 0.6 after culturing for one week. When the pH was 3, it could not grow and died. However, since this strain grew actively even at pH 4, it was shown that the strain functions even at low pH. Since the pH of the medium is a factor that has a strong effect on the growth of chlorella like the CO ₂ concentration, the NO contained in the exhaust gas
Given the possible effects of acidic substances such as _X , low pH tolerance of the HA-1 strain is a useful trait. From the above results, the chlorella HA-1 strain can be efficiently cultured without strict control of the exhaust gas concentration, flow rate, temperature, and medium pH, which are important control items, when culturing using exhaust gas. You can do it. Considering a large-scale culture system, the culture system needs to be simple and easy to maintain, so that the Chlorella sp. HA-1 strain is suitable for a simple CO ₂ fixed culture system.

Example 4 Protein Content of Microalgae The protein content of microalgae, which is a CO ₂ fixed product of Chlorella sp. HA-1 strain obtained in Example 1, was analyzed. The analysis was performed according to the following procedure. First, the alga bodies were sonicated for 15 minutes to be crushed, and further added with 1N NaOH, and then heated at 100 ° C. for 10 minutes to extract proteins.
Albumin was measured using BioRad protein assay kit as a standard. Table 6 shows the results.
There was no significant difference in the protein content of the algal cells cultured under each CO ₂ condition, and 42 to 44% of the dry weight was protein.
This result indicates that nearly half of the algal cells of the HA-1 strain are proteins, and can be used as a highly nutrient feed or industrial protein or its raw material.

[Table 6] Protein content of HA-1 strain algal cells cultured under aeration at each CO ₂ concentration condition通 気 Aeration CO ₂ concentration (%) ０．０ 0.035 5 10 15 (air) ─────── ───────────────────────── Protein content (% per dry matter) 44.2 44.4 42.0 43.2 ────── ──────────────────────────

[0018]

As described in detail above, the present invention provides a
Stable growth at CO ₂ concentration as high as
This is a microalga of the genus Chlorella that fixes O ₂ . Therefore, the microalgae of the present invention can be used for CO2 such as thermal power plants.
_{2 Even if} the exhaust gas having a high concentration is directly introduced into the culture tank, the CO ₂ in the exhaust gas is fixed and can be stably grown. Further, the CO ₂ fixed product by the microalga of the present invention has a high protein content and can be effectively used as a feed for livestock and a raw material for industrial proteins. As described above, by using the microalgae of the present invention to fix CO _{2 in} exhaust gas and effectively use the fixed products, it is possible to prevent global warming due to greenhouse gases such as CO ₂ , increase population and improve living standards. The present invention greatly contributes to solving global environmental problems because it can solve food problems caused by the rise and prevent destruction and desertification of tropical forests.

[Brief description of the drawings]

FIG. 1 is a micrograph showing the morphology of a living organism of the Chlorella sp. HA-1 strain of the present invention.

FIG. 2 is a photomicrograph showing the morphology of the organism of the Chlorella sp. HA-2 strain of the present invention.

FIG. 3 is a photomicrograph showing the morphology of the organism of the Chlorella sp. HC-1 strain of the present invention.

FIG. 4 is a micrograph showing the morphology of the organism of the Chlorella sp. HC-2 strain of the present invention.

FIG. 5 is a micrograph showing the morphology of a living organism of Chlorella sp. HT-1 strain of the present invention.

FIG. 6 is a micrograph showing the morphology of a living organism of Chlorella HT-2 strain of the present invention.

FIG. 7 is a graph showing growth when the HA-1 strain is cultured with air having different CO ₂ concentrations being aerated.

FIG. 8 is a graph showing the growth when the HA-2 strain is cultured by passing air having different CO ₂ concentrations.

FIG. 9 is a graph showing growth when the HC-1 strain is cultured with air having different CO ₂ concentrations being aerated.

FIG. 10 shows that air with different CO ₂ concentration is ventilated and HC-2
It is a graph which shows growth when a strain is cultured.

FIG. 11 shows the flow of air having different CO ₂ concentrations to form HT-1.
It is a graph which shows growth when a strain is cultured.

FIG. 12 shows that HT-2 is produced by ventilating air having different CO ₂ concentrations.
It is a graph which shows growth when a strain is cultured.

FIG. 13 is a graph showing the growth when a control strain (Chloralla pyrenoidosa NIES-226) was cultured with air having different CO ₂ concentrations ventilated.

FIG. 14 is a graph showing the relationship between the CO ₂ concentration and the growth of the HA-1 strain.

FIG. 15 is a graph showing the relationship between the aeration rate and the growth of the HA-1 strain.

FIG. 16 is a graph showing the relationship between the temperature and the growth of the HA-1 strain.

FIG. 17 is a graph showing the relationship between the medium pH and the growth of the HA-1 strain.

Claims (6)

(57) [Claims] 1. A strain of Chlorella sp. HA-1 which can stably grow at a CO ₂ concentration of 5 to 20% by volume at a level equivalent to or higher than that of growth under normal atmospheric ventilation conditions. Chlorella microalgae. _{2. At} a CO ₂ concentration of 5 to 20% by volume , the
Equal to or better than growth under normal atmospheric ventilation conditions
And a chlorella HA-2 strain that can stably grow.
Chlorella microalgae. 3. At a CO ₂ concentration of 5 to 20% by volume , the
Equal to or better than growth under normal atmospheric ventilation conditions
And a Chlorella HC-1 strain that can stably grow.
Chlorella microalgae. 4. At a CO ₂ concentration of 5 to 20% by volume , the
Equal to or better than growth under normal atmospheric ventilation conditions
In addition, a stable Chlorella HC-2 strain
Chlorella microalgae. 5. The method according to claim 1, wherein the CO ₂ concentration is between 5 and 20% by volume.
Equal to or better than growth under normal atmospheric ventilation conditions
In addition, a chlorella HT-1 strain that can grow stably
Chlorella microalgae. 6. At a CO ₂ concentration of 5 to 20% by volume , the
Equal to or better than growth under normal atmospheric ventilation conditions
And a Chlorella HT-2 strain capable of stably growing.
Chlorella microalgae.