報告書番号

U99015

タイトル（和文）

微生物によるCO２固定 ９． --夏季における適用を目指した高温耐性クロレラの探索とその光合成生産性--

タイトル（英文）

Microbial CO2 fixation 9. Isolation of high temperature tolerant Chlorella and its photosynthetic productivity

概要 （図表や脚注は「報告書全文」に掲載しております）

強い日射条件下での高生産性の維持とリアクターの冷却エネルギーの減少を目指して、高温かつ強光条件下で活発に増殖する微細藻類の利用を検討した。温泉水試料から微細藻類の単離を試みた結果、クロレラの高温性株を純粋分離できた。分離株は40度で生育を維持でき、NOとSO２を混合した10％CO２富化空気条件下でも良好な増殖を示した。分離株の光合成生産性を螺旋状チューブラーリアクターを用いて調べた結果、日本の標準的な日射条件を模擬した室内培養実験において、最大34.2g-乾物/m2-設置面積/日（12時間照射）の生産性を達成した。さらに、夏季の強光条件を模擬した実験でも高生産性を維持した。また、NOとSO２を混合した条件下でも高生産性を示した。以上の結果から、分離株は高い光合成生産性を持ち、実排ガスを用いた屋外培養への適用の際には、大きな利点を有していると考えられた。

概要 （英文）

We have been investigating the microalgal CO2 conversion technology in order to contribute to the mitigation of global warming. Previously, we examined a combined unit system of cone-shaped helical tubular photobioreactors (HTPs). It is important that the system is able to keep a high photosynthetic productivity under the open air conditions in midsummer causing a strong irradiance and increase of medium temperature. In this report, we isolated a high temperature tolerant Chlorella strain, and examined its growth characteristics and photosynthetic productivity. A high temperature tolerant Chlorella strain was isolated from a hot spring at Hakone, Kanagawa Prefecture in Japan. The isolate seemed to be Chlorella sorokiniana from the determination of 18S ribosomal RNA sequence, morphological and physiological characteristics. The effects of CO2 concentration in air, temperature, pH of medium, NO and SO2 on the growth of the isolate were examined. The isolate showed good growths in the conditions of CO2 enriched air from 10 to 15 %. Although the optimum temperature of the isolate was 35 ℃, the isolate had a good growth at 40 ℃. The optimum pH of medium was around 6.0. The isolate could grow under mixed gases composed of 10 % CO2, 100 ppm NO and 25 ppm SO2 in air. The isolate would be applicable to the stack gases containing SO2 from coal or oil power plants as well as those from LNG. The batch culture experiments were carried out using the cone-shaped HTP (diameter 0.8 m) to investigate the photosynthetic productivity of the isolate. The maximum photosynthetic productivity was 34.2 g-dry biomass・m-2-installation area・day-1 (12 h light / 12 h dark cycle) under an imitated average photosynthetic photon flux density of Japan (980 μmol・m-2・s-1). The productivity was corresponded to a photosynthetic efficiency of 8.64 % [photosynthetically active radiation (PAR, 400-700 nm)]. This value was much higher than that of Chlorella sp. HA-1 strain in the same culture condition. The good growth of the isolate was kept even at 42 ℃. A high photosynthetic productivity was kept under mixed gases composed of 10 % CO2, 100 ppm NO and 25 ppm SO2 in air. A high photosynthetic productivity of 49.9 g・m-2・day-1 was obtained under an imitated strong irradiance at midday in summer (1,737 μmol・m-2・s-1). These results showed that the isolate had quite high photosynthetic productivities under high temperature and high light intensity conditions. In order to convert CO2 in the stack gases from thermal power plants to valuable biomass, the isolate had an advantage for the practical application in a summer season.

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