Metabolic and gene expression changes triggered by nitrogen deprivation in the photoautotrophically grown microalgae Chlamydomonas reinhardtii and Coccomyxa sp. C-169

School of Natural Resources, University of Nebraska-Lincoln, Lincoln, NE 68588, USA.
Phytochemistry (Impact Factor: 2.55). 03/2012; 75:50-9. DOI: 10.1016/j.phytochem.2011.12.007
Source: PubMed


Microalgae are emerging as suitable feedstocks for renewable biofuel production. Characterizing the metabolic pathways involved in the biosynthesis of energy-rich compounds, such as lipids and carbohydrates, and the environmental factors influencing their accumulation is necessary to realize the full potential of these organisms as energy resources. The model green alga Chlamydomonas reinhardtii accumulates significant amounts of triacylglycerols (TAGs) under nitrogen starvation or salt stress in medium containing acetate. However, since cultivation of microalgae for biofuel production may need to rely on sunlight as the main source of energy for biomass synthesis, metabolic and gene expression changes occurring in Chlamydomonas and Coccomyxa subjected to nitrogen deprivation were examined under strictly photoautotrophic conditions. Interestingly, nutrient depletion triggered a similar pattern of early synthesis of starch followed by substantial TAG accumulation in both of these fairly divergent green microalgae. A marked decrease in chlorophyll and protein contents was also observed, including reduction in ribosomal polypeptides and some key enzymes for CO₂ assimilation like ribulose-1,5-bisphosphate carboxylase/oxygenase. These results suggest that turnover of nitrogen-rich compounds such as proteins may provide carbon/energy for TAG biosynthesis in the nutrient deprived cells. In Chlamydomonas, several genes coding for diacylglycerol:acyl-CoA acyltransferases, catalyzing the acylation of diacylglycerol to TAG, displayed increased transcript abundance under nitrogen depletion but, counterintuitively, genes encoding enzymes for de novo fatty acid synthesis, such as 3-ketoacyl-ACP synthase I, were down-regulated. Understanding the interdependence of these anabolic and catabolic processes and their regulation may allow the engineering of algal strains with improved capacity to convert their biomass into useful biofuel precursors.

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Available from: Edgar Cahoon, Sep 13, 2014
    • "Comparative analysis and principal component analysis of gene expression in differential conditions unveiled genes ACP, FATA, KASII, LPAAT, PAP and DGAT to be positively correlated with the storage lipid accumulation in all strains, stages and stress conditions. ACP, KASII, FATA are associated with de novo fatty acid biosynthesis where ACP is an essential cofactor for the de novo fatty acid biosynthesis carrying the acyl chains through the cycles of condensation, reduction, and dehydration steps in fatty acid biosynthesis [41], FATA has its role in the termination of fatty acid chain elongation by hydrolyzing the newly formed acyl-ACP into free fatty acids and ACP [42] [43] and KASII belongs to the KAS (β-ketoacyl-ACP-synthase) complex which aids in the condensation reactions in fatty acid synthesis by elongating 16:0- ACP to 18:0-ACP [40]. FATA has substrate specificity for monounsaturated acyl-ACPs [44]. "

    Algal Research 11/2015; 12:341-349. DOI:10.1016/j.algal.2015.09.006 · 5.01 Impact Factor
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    • "The supernatant was used to determine the protein concentration by the Bradford method. Different concentration of bovine serum albumin was used to prepare the calibration curve [21] "

    Algal Research 09/2015; DOI:10.1016/j.algal.2015.08.014 · 5.01 Impact Factor
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    • "triglycerides (TAG)) when subjected to different forms of stress such as nutrient starvation (e.g., nitrogen or phosphorous). Nitrogen starvation has been well documented to induce TAG accumulation widely, however, these conditions eventually terminate growth [4] [5] [6] [7]. "
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    ABSTRACT: The use of microalgae as a biofuel feedstock is highly desired, but current methods to induce lipid accumulation cause severe stress responses that limit biomass and, thus oil yield. To address these issues, a high throughput screening (HTS) method was devised to identify chemical inducers of growth and lipid accumulation. Optimization was performed to determine the most effective cell density, DMSO and Nile Red (NR) concentrations to monitor growth and lipid accumulation. The method was tested using 1717 compounds from National Cancer Institute (NCI) Diversity Set III and Natural Products Set II in Chlamydomonas reinhardtii. Cells were inoculated at low density and 10 μM of the test compound was added. After 72 h, cell density was measured at OD550 and lipid accumulation assessed using NR fluorescence. Primary screening identified 8 compounds with a hit rate of 0.47% and a robust Z′ discrimination factor (0.68 ± 0.1). Of these, Brefeldin A (BFA) was the most successful at inducing lipid accumulation and was used to evaluate secondary screens including measuring levels of fatty acids, photosynthetic pigments, proteins and carbohydrates. The effectiveness of BFA was confirmed in Chlorella sorokiniana UTEX 1230. This study demonstrates the power of chemical genomics approaches in biofuel research.
    Algal Research 09/2015; 11:74-84. DOI:10.1016/j.algal.2015.06.002 · 5.01 Impact Factor
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