Effects of nitrogen and phosphorus limitation on lipid accumulation by Chlorella kessleri str. UTEX 263 grown in darkness

Growing algae in darkness for biodiesel production eliminates the challenges of evaporation and light penetration reported for open ponds and the costs and fouling that plague photobioreactors. The current study demonstrated that Chlorella kessleri str. UTEX 263 could grow heterotrophically in the dark on pure sugars or lignocellulosic hydrolysates of plant biomass. Hydrolysates of a prairie grass native to Kansas, Big Bluestem (Andropogon gerardii), supported the growth of C. kessleri in the dark. Nitrogen limitation stimulated the accumulation of biodiesel lipids by 10-fold in heterotrophic cultures grown on pure sugars or Big Bluestem hydrolysate. Limiting P in the growth medium also was shown to increase cellular lipid accumulation in C. kessleri. Iron limitation was not sufficient to increase cellular lipid content. Crude biomass extracts may have levels of N that cannot be easily removed, which are high enough to relieve N limitations in growth media. This initial study suggests that P might be more easily removed from biomass extracts than N for increasing cellular lipid production by nutrient limitation and further that native prairie grasses are potentially suitable as sources of lignocellulosic sugars.