Herbicide-resistant mutants of Botryococcus braunii race B (strain BOT-22)

The freshwater green alga Botryococcus braunii produces long-chain hydrocarbon oil in large quantities and secretes these from the cells. To exploit B. braunii as a source of next-generation biofuel, development of cost-effective cultivation systems are required. One of the most cost-effective methods for large-scale production is to simply grow B. braunii in open ponds. However, trials to cultivate B. braunii in open ponds often fail due to thriving of other green algal and cyanobacterial species because of the relatively slow growth of B. braunii. We previously demonstrated that herbicides are effective in control of contaminating algae. In order to use herbicide-assisted cultivation systems, we generated herbicide-resistant mutants of an oil-rich strain of B. braunii race B (strain BOT-22) by ethyl methanesulfonate mutagenesis. We isolated 44 glufosinate-resistant and 21 methyl viologen-resistant mutant lines. Some of these mutant lines exhibited vigorous growth and oil production in herbicide-containing liquid media, suggesting that they can be directly used in herbicide-containing cultivation systems.