Abstract
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.Electronic supplementary materialThe online version of this article (doi:10.1186/2193-1801-1-33) contains supplementary material, which is available to authorized users.
Highlights
The last few decades have seen a growing interest in using microalgae, cyanobacteria and other photosynthetic bacteria as potential producers of renewable fuels, such as biodiesel, biohydrogen and biogas
Microalgae exhibit a great variability in lipid content; oil content can reach up to 80%, and levels of 20-50% are quite common (Powell and Hill 2009)
Supplementation with sodium thiosulphate (1%) only, enhanced the lipid productivity from 16.66 (BBM) to 19.66% on 4th day and 23.66% in 8th day cultures, which is equivalent to 18% and 42% increase over control respectively
Summary
The last few decades have seen a growing interest in using microalgae, cyanobacteria and other photosynthetic bacteria as potential producers of renewable fuels, such as biodiesel, biohydrogen and biogas. Biodiesel production from microalgae is a relatively novel concept and these organisms offer the greatest photosynthetic efficiency, as a consequence of a minimum of internally competitive plant functions and limited nutrient requirements, besides exhibiting fast reproductive cycles. The total content of lipids in microalgae may vary from about 1–85% of the dry weight (i.e. lipid productivity), with values higher than 40% being typically achieved under stress conditions (Chisti 2007). Factors such as temperature, irradiance and, most markedly, nutrient availability have been shown to affect both lipid composition and lipid content in several algae (Takagi and Karseno 2006; Rao et al 2007). Many microalgae can accumulate lipids due to excess photosynthesis and some species can accu- reducing agent for diverting acetyl CoA to malonyl CoA mulate high amount of lipids under heterotrophic or en- and thereby towards lipid biosynthesis (Additional file 1: vironmental stress, such as nutrient deficiency or salt Figure S1)
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