Changes in the hydrocarbon-synthesizing activity during growth of Botryococcus braunii B70

► We demonstrated Botryococcus braunii B70 was classified into the B race. ► The hydrocarbon-synthesizing activity was high in early logarithmic growth phase, but it declined thereafter. ► The allocation of carbon might be the regulatory step in hydrocarbon biosynthesis during the early logarithmic growth phase. ► NADPH produced by the pentose phosphate pathway appeared to be involved in botryococcene biosynthesis. Botryococcus braunii is a green, colonial microalga that produces large amounts of hydrocarbons. B. braunii B70 was estimated to be B race by the incorporation of radioactivity from l-[methyl14C]-methionine into hydrocarbon. The hydrocarbon-synthesizing activity of B70 cells was determined by feeding experiments using 14C-compounds. NaH14CO3 incorporation rate into the hydrocarbon was high in the early logarithmic growth phase but it declined thereafter. Hydrocarbon-synthesizing activity from [2-14C] pyruvate in 15-day cells was 80% of that in 5-day cells. In contrast, hydrocarbon-synthesizing activity from NaH14CO3 and l-[methyl14C]-methionine decreased remarkably by 15days after inoculation. Hence, the allocation of carbon was a regulatory step in hydrocarbon biosynthesis during the early logarithmic growth phase. The high activity of pentose phosphate pathway in the early logarithmic growth was seemed to be the contribution of the supply of NADPH for botryococcene synthesis.