Efficacy of EDTA and Phosphorous on Biomass Yield and Total Lipid Accumulation in Two Green Microalgae with Special Emphasis on Neutral Lipid Detection by Flow Cytometry

Abstract

Chlorella ellipsoidea and Chlorococcum infusionum , promising microalgae for biodiesel feedstock production, were treated with ethylenediaminetetraacetate (EDTA) and phosphorous to induce stress which was then followed by flow cytometry to study the enhanced intracellular neutral lipid content. Treatment resulted in up to a threefold increase in total lipid content of Chlorella (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mn fontstyle="italic">41.8</mml:mn><mml:mo>±</mml:mo><mml:mn fontstyle="italic">1.9</mml:mn></mml:math>% at 16 days of incubation period) and more than twofold increases in Chlorococcum (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M2"><mml:mn fontstyle="italic">31.3</mml:mn><mml:mo>±</mml:mo><mml:mn fontstyle="italic">1.0</mml:mn></mml:math>% at 18 days of incubation period) under phosphorous starvation in the culture. It was observed that maximum biomass yields in Chlorella and Chlorococcum were <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M3"><mml:mn fontstyle="italic">1.56</mml:mn><mml:mo>±</mml:mo><mml:mn fontstyle="italic">0.06</mml:mn></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M4"><mml:mn fontstyle="italic">2.17</mml:mn><mml:mo>±</mml:mo><mml:mn fontstyle="italic">0.12</mml:mn></mml:math> g/L at 1.5 g/L of phosphorous after 20 and 18 days of incubation periods, respectively. The qualitative analyses of neutral lipid bodies under stress conditions were performed by confocal microscopy and revealed bright golden-yellow lipid droplets in stress exposed cells. Significant increase of monounsaturated fatty acids under the nutrient limited conditions was suitable to produce biodiesel. The maximum biomass (g/L) and lipid content (% dry cell weight) at different stresses showed significant results (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M5"><mml:mi>p</mml:mi><mml:mo>&lt;</mml:mo><mml:mn fontstyle="italic">0.05</mml:mn></mml:math>) by single-factor Analysis of Variance (ANOVA) followed by Duncan’s Multiple Range Test (DMRT).