Abstract
BackgroundIndividual nutrient depletion is widely used to induce lipid accumulation in microalgae, which also causes cell growth inhibition and decreases the total biomass. Thus, improving the lipid accumulation without biomass loss in the nutrient deficiency cells becomes a potential cost-effective treatment for cheaper biofuels.MethodsIn this study, the effects of different nutritional conditions on the growth and contents of lipids in Chlamydomonas reinhardtii were compared, and the metabolic profiles under different nutritional conditions were also investigated.ResultsWe showed that similar to other microalgae, nitrogen or phosphorus deficiency inhibited the growth of Chlamydomonas and combined nutrition deficiency reduced biomass by up to 31.7%, though lipid contents in cells (g/g dry weight [DW]) were significantly increased. The addition of sodium acetate countered this growth inhibition that resulted from nitrogen and phosphorus deficiency, with significantly increased biomass. Furthermore, the combination of 4 g/L sodium acetate supplementation with nitrogen and phosphorous deficiency increased total fatty acid yield (mg/L) by 93.0 and 150.1% compared to nutrient-depleted and normal culture conditions, respectively. Metabolite content was affected by the different nutritional conditions, especially metabolites that are involved in lipid metabolism, amino acid metabolism and metabolism of external substances.ConclusionFurther research into these metabolites could shed light onto the relationship between cell growth inhibition and fatty acid accumulation in Chlamydomonas.
Highlights
Individual nutrient depletion is widely used to induce lipid accumulation in microalgae, which causes cell growth inhibition and decreases the total biomass
Under the condition of nitrogen deficiency, the microalgae growth was still inhibited even after phosphorus was added. This is in agree with the previous study conducted in another green microalga Chlorella where the initial nitrogen concentration was the major nutrient factor of growth and this was unaffected by initial phosphorus concentrations [20,21,22]
We found that total FA (TFA) production per DW could be maximized by restricted access to both nitrogen and phosphorus and the addition of 4 g/L sodium acetate under the condition of nutrient deficiency could significantly increase both the biomass and TFA yield
Summary
Individual nutrient depletion is widely used to induce lipid accumulation in microalgae, which causes cell growth inhibition and decreases the total biomass. Improving the lipid accumulation without biomass loss in the nutrient deficiency cells becomes a potential cost-effective treatment for cheaper biofuels. The addition of organic carbon sources (such as glucose, ethanol, methanol, acetate) to the microalgal culture medium during cultivation can promote cell growth, and lipid yield (g/L) therein. Sodium acetate addition can increase the yield of intracellular FA in both C. reinhardtii [7] and another green microalga Haematococcus pluvialis [8]. Sodium acetate promotes the growth of Chlorella pyrenoidosa and increases its lipid yield [9]. It might be an effective method to improve the total yield of lipids while not reducing the biomass by heterotrophic or mixotrophic culture
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