Influence of Medium Recipe on Biomass and Lipid Profile of an Aquatic Green Microalga Monoraphidium convolutum for Biodiesel Production

Changing the growth medium for microalgae causes a remarkable effect on cell metabolism. The growth and lipid content of Monoraphidium species, a promising source for biodiesel production, are significantly influenced by various nitrogen sources, phosphorus, and iron concentrations. Three different Monoraphidium species were isolated, identified and evaluated for their growth, lipid content and fatty acid profile on the Bold’s Basal medium. Monoraphidium convolutum exhibited the highest biomass (0.34g L^-1 ± 0.02) and lipid content (22.6± 1.6%). The effects of BG 11, Bold’s Basal and modified Navicula media on biomass and lipid production of M. convolutum were tested and compared. Different nitrogen sources; calcium nitrate, ammonium sulphate, ammonium acetate, and urea were tested for biomass production and lipid content. M. convolutum, which grew on ammonium acetate (12mg L^-1 N), maintained the highest lipid content (36± 0.6%), with a large amount of saturated fatty acid methyl esters. The effect of different phosphorous and iron concentrations on biomass and lipid accumulation of M. convolutum was separately tested. M. convolutum grown on phosphorous concentration equal to 0.475mg L^-1 recorded the highest lipid content (38.4± 1.5 %), with a high amount of monounsaturated, saturated, and polyunsaturated fatty acid methyl esters. On the other side, M. convolutum showed the highest lipid content (39.1± 0.14%) when grown on 0.75mg L^-1 Fe⁺³  with saturated > monounsaturated > polyunsaturated fatty acid methyl esters. Thus, it is advisable to optimize M. convolutum growth on a modified Navicula medium containing ammonium acetate and low phosphorous and iron concentrations to obtain high lipid content potential as a biodiesel feedstock.