Environmental controls on growth and lipid content for the freshwater diatom, Fragilaria capucina: A candidate for biofuel production

The use of microalgae for biofuel production has the potential to reduce fossil fuel consumption. Ideal candidate species of microalgae for bio-oil production need both relatively high growth rates and lipid content. Here, we report on the effects of temperature, nutrients (N, Si), and salinity on growth rates and lipid content of the common freshwater diatom, Fragilaria capucina (Desm), isolated from western Lake Erie. At low NaCl salinity, growth rate increased rapidly from 10 to 20A degrees C, and then further increased slowly from 20 to 30A degrees C, with a maximum specific growth rate of 0.61 day(-1). Growth rate declined with increasing salinity (e.g., reduced by ca. 50 and 100% at 137 and 274 mmol L-1 NaCl, respectively), and increased with increased N and Si concentration until ca. 100 mu mol L-1 for each (with > 85% of maximum growth rate at 10 mu mol L-1). Lipid content (% total lipid per dry mass) in nutrient-replete cultures was 14% and (1) increased to > 30% at low N and, especially, low Si; (2) was lower at 30A degrees C vs. 20 or 10A degrees C; and (3) decreased with salinity. Thus, F. capucina accumulates lipid to high levels even under N, Si, and temperature levels that permit a high growth rate for this species, and hence, this species is a candidate for use in biofuel production.