Effect of irradiance on the cell density, size and lipid accumulation of Neochloris oleoabundans

Resumen

Neochloris oleoabundans (Chlorophyceae) has shown potential as source of lipids for biodiesel production. Nevertheless, scant information is available about the effect of light intensity on the growth and biochemical composition of this microalga. Furthermore, no reports are available related to the effect of irradiance on its cell size. The aim of this work was to evaluate the effect of three different light intensities (50, 94 and 136 μmol m-2s-1), on the cell density and cell size of N. oleoabundans cultivated in a modified BBM, as well as to evaluate the presence of intracellular lipids using Sudan III. It was found that cell density was highest at 136 μmol m-2s-1 and cell productivity was sustained throughout the duration of the experimental period (15 days), under such conditions. The average cell density registered at the highest light intensity was 4.1 x105 cells mL-1. The cell productivity at the end of day 1 in which a maximum specific growth rate was observed (1.30 d-1), was 3.1x105 cells mL-1 d-1. Cell size was affected significantly by light intensity, being higher at the lowest (10.92 ±1.26 μm ) and medium (11.88 ±1.12 μm) levels tested , compared to the size observed at the highest level (5.25 ±1.26 μm). To the best of our knowledge, there are no other reports on cell size changes as a response to different irradiance levels for this type of microalgae. Furthermore, irradiance did affect lipid accumulation: cultures exposed at the highest light intensity, showed a higher percentage of stained cells with Sudan III. This lipophilic dye turned out to be a fast and easy to use screening dye for lipids presence in microalgae.