The fast-growing strain of hydrocarbon-rich green alga Botryococcus braunii, BOT-22, is a vitamin B12 autotroph

Botryococcus braunii is one of the most promising microalgal feedstocks for biofuel production because it accumulates a large amount of hydrocarbons within the colony. Several researchers have used vitamin-free media for short-term culture experiments of B. braunii. However, vitamin requirements of B. braunii have never been explicitly described. Therefore, the consequences of long-term vitamin deficiency remain unclear. To investigate the vitamin B-12 (cobalamin) requirement of B. braunii, the growth characteristics and oil productivity were compared using an axenic strain B. braunii BOT-22, one of the fast-growing strains, with and without vitamin B-12 supplementation. The growth rate, maximum biomass concentration, and lipid content did not differ between cultures with and without vitamin B-12 supplements. In addition, an in silico survey of the transcriptomic dataset of B. braunii BOT-22 identified a putative gene fragment coding for the vitamin B-12-independent methionine synthetase (metE), which is a hallmark of the vitamin B-12 autotrophy in algae. In conclusion, these data suggest that B. braunii BOT-22 is a vitamin B-12 autotroph.