Metabolic and morphological changes of an oil accumulating trebouxiophycean alga in nitrogen-deficient conditions (original) (raw)
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Plant Biotechnology Journal, 2016
The great need for more sustainable alternatives to fossil fuels has increased our research interests in algal biofuels. Microalgal cells, characterized by high photosynthetic efficiency and rapid cell division, are an excellent source of neutral lipids as potential fuel stocks. Various stress factors, especially nutrient-starvation conditions, induce an increased formation of lipid bodies filled with triacylglycerol in these cells. Here we review our knowledge base on glycerolipid synthesis in the green algae with an emphasis on recent studies on carbon flux, redistribution of lipids under nutrient-limiting conditions and its regulation. We discuss the contributions and limitations of classical and novel approaches used to elucidate the algal triacylglycerol biosynthetic pathway and its regulatory network in green algae. Also discussed are gaps in knowledge and suggestions for much needed research both on the biology of triacylglycerol accumulation and possible avenues to engineer improved algal strains.
Qualitative and quantitative estimation of algal lipids for biofuel production
International Journal of Chemical Studies, 2020
The current rising demand for energy, global warming, and depletion of fossil fuels have led to increased consideration of alternate renewable biofuel sources. Microalgae serve as an excellent feedstock for biofuel production. Many qualitative and quantitative methods are available for lipid estimation from microalgae. In this review, we describe the various lipid estimation methods. Among the various methods discussed viz., conventional, and non-conventional methods, Nile red method offers a high throughput technique for rapid screening of high neutral lipid producing microalgae.
PLoS ONE, 2014
Many species of microalgae produce greatly enhanced amounts of triacylglycerides (TAGs), the key product for biodiesel production, in response to specific environmental stresses. Improvement of TAG production by microalgae through optimization of growth regimes is of great interest. This relies on understanding microalgal lipid metabolism in relation to stress response in particular the deprivation of nutrients that can induce enhanced TAG synthesis. In this study, a detailed investigation of changes in lipid composition in Chlorella sp. and Nannochloropsis sp. in response to nitrogen deprivation (Ndeprivation) was performed to provide novel mechanistic insights into the lipidome during stress. As expected, an increase in TAGs and an overall decrease in polar lipids were observed. However, while most membrane lipid classes (phosphoglycerolipids and glycolipids) were found to decrease, the non-nitrogen containing phosphatidylglycerol levels increased considerably in both algae from initially low levels. Of particular significance, it was observed that the acyl composition of TAGs in Nannochloropsis sp. remain relatively constant, whereas Chlorella sp. showed greater variability following N-deprivation. In both algae the overall fatty acid profiles of the polar lipid classes were largely unaffected by Ndeprivation, suggesting a specific FA profile for each compartment is maintained to enable continued function despite considerable reductions in the amount of these lipids. The changes observed in the overall fatty acid profile were due primarily to the decrease in proportion of polar lipids to TAGs. This study provides the most detailed lipidomic information on two different microalgae with utility in biodiesel production and nutraceutical industries and proposes the mechanisms for this rearrangement. This research also highlights the usefulness of the latest MS-based approaches for microalgae lipid research.
We hypothesize that, in algae, carbon allocation to lipids depends on the combined effects of the metabolic constraints imposed by the genotype (i.e., species-specific differences in composition) and on the acclimation responses (phenotype) to changes in the stoichiometry of available inorganic carbon (for photosynthesis) and nitrogen (primarily for amino acids, protein, and nucleic acid synthesis). We thus cultured three taxonomically distinct algae, the green alga Dunaliella salina, the diatom Thalassiosira pseudonana, and the dinoflagellate Protoceratium reticulatum, at four nitrate concentrations and constant inorganic carbon. Since energy availability also directly impacts carbon partitioning, we studied the effect of irradiance on the oil quality of P. reticulatum. We used Fourier transform infrared (FTIR) spectroscopy to study carbon allocation and biomass reduction level and gas chromatography for fatty acid analysis. The fatty acid complements of the three species were different; within each species, growth conditions substantially altered oil quality. We ranked the oils in terms of their suitability as biodiesels, using international standards as reference. We believe that this approach may help to identify the appropriate combination of taxa and culture conditions for algal biodiesel production and in general offers insight on carbon allocation to fatty acids.
PLOS ONE, 2018
Algae are often promoted as feedstock organisms to produce a sustainable petroleum fossil fuel alternative. However, to induce lipid accumulation most often requires a severe stress that is difficult to induce in large batch cultures. The objective of this study is to analyze and mathematically model heat stress on growth, chlorophyll content, triacylglyceride, and starch synthesis in algae. We initially screened 30 algal species for the most pronounced induction of lipid droplets from heat stress using confocal microscopy and mass spectroscopy techniques. One species, Coccomyxa subellipsoidea C169, was selected and subjected to further biochemical analyses using a jacketed bioreactor amended with 1% CO 2 at 25˚C, 30˚C, 32˚C, 33˚C, 34˚C, 35˚C, and 36˚C. Lipid and starch accumulation was less extreme than N stress. Growth was reduced above 25˚C, but heat stress induced lipid droplet synthesis was negatively correlated with growth only past a demonstrated threshold temperature above 32˚C. The optimal temperature for lipid accumulation was 35˚C, which led to 6% of dry weight triglyceride content and a 72% reduction from optimal growth after 5 days. Fatty acid influx rates into triglycerides and 15 N labeling of amino acids and proteins indicate that heat stress is mechanistically distinct from N stress. Thus, this study lends support to a novel hypothesis that lipid droplet triglycerides result from a redistribution of carbon flux as fatty acids to neutral storage lipids over membrane or other lipids.
Potential of lipid metabolism in marine diatoms for biofuel production
Biotechnology for Biofuels, 2015
Background: Diatoms are an ecologically relevant group of microalgae that are not commonly considered for bio-oil production even if they are responsible for massive blooms at sea. Seventeen diatom species were screened for their capacity to produce biomass and lipids, in relation to their growth rate. Triglyceride levels were also assessed as a preferential source of biofuels. Results: Using statistical analysis, two centric diatoms, Thalassiosira weissflogii and Cyclotella cryptica, were selected as good candidates for oil production. Lipid levels significantly increased when the two diatoms were cultivated in a two-stage process under nitrogen limitation. The effect was less pronounced in cultures where silicon was reduced to 20% of the standard supply. Nitrogen limitation did not affect growth rates but led to lipid remodeling and de novo synthesis of triacylglycerols. Conclusions: Triacylglycerols in T. weissflogii and C. cryptica can account for up to 82% and 88% of total glycerolipids, thereby suggesting that the two species are promising candidates for large-scale experimentation for biofuel production.
Journal of Applied Phycology, 2020
Lipid-accumulating microalgae are an emerging feedstock for production of liquid biofuel because of their high biomass and lipid productivity. The potential of the green microalgae, Chlorolobion sp. (BIOTECH 4031) and Chlorella sp. (BIOTECH 4026), for biodiesel production was evaluated by analyzing the effect of nitrogen starvation (0.375-1.500 g L −1 NaNO 3) on growth response, oil yield, and fatty acid methyl ester (FAME) profiles of the two algal strains. Maximum biomass yields for Chlorolobion sp. and Chlorella sp. were obtained after 20 days of cultivation using the control medium (1.5 g L −1 NaNO 3) with 0.873 g L −1 and 0.757 g L −1 , respectively. An increasing trend in the total lipid yield was observed under a nitrogen-starved culture condition (0.375 g L −1 NaNO 3). When the amount of nitrate was limited, the mean oil contents of Chlorolobion sp. and Chlorella sp. were 31.61 and 28.77% with lipid productivity of 227.84 and 151.14 mg L −1 day −1 , respectively. Nitrogen starvation caused an increase in the lipid yield and a decrease in biomass production of the two microalgae. The FAME profile of the obtained algal biodiesel shows a high concentration of saturated fatty acid (SAFA) and monounsaturated fatty acid (MUFA) methyl esters which are desirable for biodiesel production. The fuel properties of biodiesel from the two microalgae were predicted based on the molecular properties of fatty acid methyl esters using empirical equations showing that the biodiesel properties of the two microalgae satisfied the set specifications of biodiesel standards EN 14214 (European) and ASTM D6751 (American). The quality properties of biodiesel obtained for Chlorolobion sp. were low density (0.89 g cm −3), low kinematic viscosity (2.79 mm 2 s −1), cetane number (65.17), and oxidation stability (8.93 h). On the other hand, Chlorella sp. has low density (0.88 g cm −3), low kinematic viscosity (2.78 mm 2 s −1), good cetane number (68.79), and oxidation stability (10.44 h). Hence, Chlorolobion sp. (BIOTECH 4031) and Chlorella sp. (BIOTECH 4026) have potential as raw material for production of biodiesel with superior fuel quality.
Lipid productivity as a key characteristic for choosing algal species for biodiesel production
Journal of Applied Phycology, 2009
Microalgae are a promising alternative source of lipid for biodiesel production. One of the most important decisions is the choice of species to use. High lipid productivity is a key desirable characteristic of a species for biodiesel production. This paper reviews information available in the literature on microalgal growth rates, lipid content and lipid productivities for 55 species of microalgae, including 17 Chlorophyta, 11 Bacillariophyta and five Cyanobacteria as well as other taxa. The data available in the literature are far from complete and rigorous comparison across experiments carried out under different conditions is not possible. However, the collated information provides a framework for decision-making and a starting point for further investigation of species selection. Shortcomings in the current dataset are highlighted. The importance of lipid productivity as a selection parameter over lipid content and growth rate individually is demonstrated.
The versatility of algae and their lipid metabolism
Biochimie, 2009
Eukaryotic algae are a very diverse group of organisms that are key components of ecosystems ranging from deserts to the Antarctic. They account for over half of the primary production at the base of food chains. The lipids of different classes are varied and contain unusual compounds not found in other phyla. In this short review, we introduce the major cellular lipids and their fatty acids and then describe how the latter (particularly the polyunsaturated fatty acids, PUFAs) are synthesised. The discovery of different elongases and desaturases important for PUFA production is detailed and their application for biotechnology described. Finally, the potential for algae in commercial applications is discussed, particularly in relation to the production of very long chain PUFAs and biofuel.