Growth of oil accumulating microalga Neochloris oleoabundans under alkaline–saline conditions

► Oil accumulating microalgae cultivated under alkaline–saline conditions are a potential feedstock for biofuel production. ► Alkaline–saline media low concentrated in calcium and phosphate have minimum precipitation and still sustain algal growth. ► Lipid accumulation in microalgae is not only dependent on the nitrogen supply but also on the alkalinity of the medium. The effect of elevated pH and salt concentration on the growth of the freshwater microalga Neochloris oleoabundans was investigated. A study was conducted in 24-well plates on the design of a growth medium and subsequently applied in a photobioreactor. An artificial seawater medium with reduced Ca2+ and PO43- could prevent mineral precipitation at high pH levels. Growth was characterized in this new medium at pH8.1 and at pH10.0, with 420mM of total salts. Specific growth rates of 0.08h−1 at pH8.1 and 0.04h−1 at pH10.0 were obtained under controlled turbidostat cultivation. The effect of nitrogen starvation on lipid accumulation was also investigated. Fatty acids content increased not only with nitrogen limitation but also with a pH increase (up to 35% in the dry biomass). Fluorescence microscopy gave visual proof that N. oleoabundans accumulates oil bodies when growing in saline conditions at high pH.