Culture of the hydrocarbon producing microalga Botryococcus braunii strain Showa: Optimal CO2, salinity, temperature, and irradiance conditions

► Optimal growth in the medium with 0.2–5% CO2 and in freshwater conditions. ► Maximum specific growth rate of 0.5day−1 at 30°C and 850μmol photons m−2s−1. ► The highest specific growth rate for B. braunii ever reported. ► Positive correlation of hydrocarbon contents (29–39%) with specific growth rate. ► Hydrocarbon productivity increased with increased specific growth rate. Specific growth rates and hydrocarbon contents of Botryococcus braunii strain Showa were measured under a wide range of CO2, salinity, temperature, and irradiance conditions. The bubbling CO2 concentration of 0.2–5% and no addition of salinity were favorable conditions for growth. The strain cannot grow at 5°C and above 35°C under any irradiance levels. Maximum specific growth rate of 0.5day−1 (doubling time of 1.4days), the highest value reported for B. braunii in the past studies, was observed at 30°C and 850μmol photons m−2s−1. Since hydrocarbon productivity, shown as the product of hydrocarbon content and specific growth rate, increased with the increasing specific growth rate, we conclude that more efficient hydrocarbon production by the mass culture of strain Showa can be achieved by maintaining higher specific growth rate based on the culture conditions presented in this study.