Nitrogen Limitation in Neochloris oleoabundans: A Reassessment of Its Effect on Cell Growth and Biochemical Composition

The aim of this work was to reassess the effect of nitrogen limitation (from 0 to 1 mM nitrate), on the growth and the biochemical composition of Neochloris oleoabundans cultures, where only the CO₂ available in the air was provided. Slight differences in the initial nitrate concentration, even minimal increments of 0.2 mM, significantly modify the microalgal response towards nitrogen limitation. This stress condition reduced cell proliferation, but increased cell mass values due to the simultaneous accumulation of two storage compounds: lipids, which contained up to a 55.9 % of total fatty acids; and carbohydrates, which may be primarily composed by starch. The highest biomass and lipid productivities of 98.24 and 43.24 mg/l/day, respectively, were attained at an initial nitrate concentration of 0.6 mM. The theoretical annual projection, based on these productivities, allowed the estimation of the liquid fuel energy yields, which are comparable or even higher than those calculated for several biomass feedstocks such as corn, oil palm, sugarcane, or even fast growing grasses, confirming the potential of nitrogen-limited N. oleoabundans biomass as an appropriate feedstock for biofuel purposes.