Growth, Lipid Productivity and Cellular Mechanism of Lipid Accumulation in Microalgae Monoraphidium sp. Following Different Phosphorous Concentrations for Biofuel Production

Stress to an algal species can be caused by several factors ranging from temperature extremes to varying light intensities under which they accumulate lipids. Stress caused by nutrient limitation is known to induce maximum lipid accumulation in microalgae. In order to obtain an appropriate phosphate concentration exhibiting both high biomass and high lipid contents, four different concentrations of phosphate were implemented. Mechanism of lipid accumulation was also studied. Of the tested concentrations, no significant difference between growth rates was observed. Cultures with phosphate concentration 2.7 mg/l exhibited maximum increase in biomass productivity compared to control. But phosphate concentration 0.5 mg/l demonstrated the highest lipid productivity (8.75 mg/l/day), in accordance with lipid content (21.8%). Further, representation of TEM and fluorescent microscopic images depicted differences in lipid accumulation and sub-cellular ultrastructure at different concentrations of phosphate. Disappearance of phosphate and nitrate from the medium was also evaluated to study the efficient nutrient concentration and to better understand mechanism of lipid enhancement.