Biochemical modulation of growth, lipid quality and productivity in mixotrophic cultures of Chlorella sorokiniana

The genus Chlorella is a widely employed microalga for biodiesel, as it can be grown using photo/mixo/heterotrophic mode of cultivation. The present investigation was undertaken with the hypothesis that addition of different substrates (amino acids, carbon sources, vitamins) along with reducing agents may aid in diverting Acetyl CoA to malonyl CoA or fatty acid biosynthesis, under mixotrophic conditions in Chlorella sorokiniana. Preliminary investigations undertaken with two reducing agents individually (sodium thiosulphate and methyl viologen) along with selected substrates revealed the promise of sodium thiosulphate (1%) in enhancing lipid accumulation significantly. Further, the role of inclusion of twelve substrates and sodium thiosulphate revealed that supplementation with tryptophan (0.1%) recorded 57.28% enhancement in lipid productivity on 4th day. Highest values of lipid productivity of 33% were recorded on 8th day in 0.1% glucose supplemented medium containing sodium thiosulphate. Fatty Acid Methyl Ester (FAME) profiles generated revealed significant reduction in the content of Poly unsaturated fatty acids (PUFA) and enhanced Mono unsaturated fatty acids (MUFA) (especially oleic acid) in the treatments involving tryptophan, Vitamin B12, sodium pyruvate and glucose. This study reveals the promise of using sodium thiosulphate along with selected substrate for enriching the quality and quantity of lipids, which can be valuable for exploiting algae as a source of biodiesel.