In recent years, development has been advancing in the field of technologies for atmospheric carbon dioxide reduction, as a countermeasure against global warming. Research on renewable energy continues to progress as well from the point of view of the sense of crisis regarding fossil fuel depletion. Implemented renewable energy sources include solar photovoltaic power generation and wind power generation, but the use of photosynthetic organisms that convert water and carbon dioxide to hydrocarbons by light energy is also attracting interest.
Algae are photosynthetic organisms of interest as energy resources, with particular focus being directed toward green algae and diatoms. Most green algae have 15-17% lipids in their constituent components, the lipids being roughly classified as neutral lipids (30%), glycolipids (37%), phospholipids (26%) and non-fatty acid lipids (7%).
In recent years, particular interest has been focusing on the oil-producing green algae, Botryococcus braunii. The main components of the lipids produced by Botryococcus braunii are hydrocarbons composed of carbon and hydrogen, and they are known to store hydrocarbons such as straight-chain alkenes and triterpenes both intracellularly and extracellularly.
Botryococcus braunii is classified into race-A, race-B and race-L based on the structural characteristics of the produced hydrocarbons. By definition, race-A is a group that produces hydrocarbons with an odd number of carbons between 25 and 31, straight-chain, and having 2 or 3 double bonds in the molecule, race-B is a group producing hydrocarbons with a triterpene structure represented by CnH2n-10 (n=30-37), and race-L is a group that produces hydrocarbons having a tetraterpene lycopadiene (lycopadiene) (C40H78) structure.
The hydrocarbon contents of Botryococcus braunii strains belonging to each of these groups may be found in previously published reports. Variations exist between the strains in race-A, but the contents have been reported to be in the range of 0.4-61.0% (hydrocarbon weight with respect to cell dry weight) (Non-patent literature 1). In race-B, hydrocarbon content is generally 30-40% of cell dry weight, but some strains have been reported to produce only about 9 Non-patent literature (Non-patent literature 2). In race-L, 0.1% has been reported for an Indian strain and 8.0% for a Thai strain (Non-patent literature 3), which are low values compared to race-B. The hydrocarbons are mixtures of various carbon chain lengths and/or structures.
These hydrocarbons can be utilized without treatment, as heavy oils for production of thermal energy, but they are preferably used after further processing, as homogeneous hydrocarbon compositions to serve as materials for obtaining homogeneous compounds. There has also been a need for a strain having a simple hydrocarbon synthetic pathway, as a model for physiological research toward application of Botryococcus. 
In addition, while low-cost mass culturing methods have been established for realizing industrialization of Botryococcus, there has been a need for outdoor culturing using sunlight, in order to minimize costs. In this case, since light quantity is the major growth limiting factor, it is most efficient to carry out culturing in seasons and locations with high intensity of solar radiation, using pools with low water levels and thin bioreactors. When culturing is carried out by such methods, however, the water temperature increases, and therefore the existing Botryococcus strains whose optimum growth temperature is between 15° C. and 30° C. and cease growth at 35° C. or higher and above, cease to grow during periods of maximum intensity of solar radiation. In actual results, in Tsukuba city during July, 2006, with outdoor culturing in a reactor with a water level depth of 10 centimeters, the maximum water temperature reached 37° C. A strain with an optimum growth temperature at a high temperature of 35° C. or higher has therefore been desired.