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Lake 2010: Wetlands, Biodiversity and Climate Change
DIVERSITY OF LIPIDS IN ALGAE
Aakanksha1, Shilpi Samantray2, Supriya Guruprasad 2 & T.V Ramachandra2
1
Birla Institute of Technology, Ranchi
2
Energy & Wetland Research Group, Centre for Ecological Sciences, Indian Institute of Science, Bangalore - 560012
ABSTRACT
The ability of algae to survive or proliferate over a wide range of environmental conditions is, to a large extent, reflected in the
tremendous diversity and unusual pattern of cellular lipids as well as its ability to modify lipid metabolism efficiently in
response to changes in environmental condition The potential of algae as a source of oil and fats stems from the traditional use
of algae as a source of food. The range of lipids of algae is always more complex than other microorganism due to presence of
photosynthetic apparatus. The major lipid components in all algal species were triglycerides, monogalactosyl, digalactosyl and
sulphoquinovosyl diglycerides, phosphatidyl glycerol, phosphatidyl choline (lecithin), and phosphatidyl ethanolamine; while
palmitoleic, palmitic, eicosapentaenoic and eicosate-traenoic acids were the major fatty acid constituents The compositions of
total lipids vary from species to species and also affected by the climatic conditions. Generally the conditions favoring the
maximum lipid production seemingly are not compatible with those required for yield optimization. The conditions used to
promote lipid accumulation in algae are the same as other microalgae i.e. deprivation of essential nutrient from the media. The
nutrient deficiency and other physico-chemical changes results in the accumulation of the neutral lipids. Triglycerides, a
major neutral lipid can be used for the production of the biodiesel from algae
INTRODUCTION
Algae are a large and diverse group of simple, typically autotrophic (sometimes heterotrophic also) organisms, ranging from
unicellular to multicellular forms. Algae are:
—
Cryptogamous
—
Ubiquitous
—
Prokaryotic or Eukaryotic
—
Photosynthetic
—
Reproduce asexually sometimes sexually also
—
They can be planktonic or benthic
They are sunlight driven cell factories that convert carbon dioxide to potential biofuels. Due to the fact that the oceans cover
over 70% of the earth’s surface, aquatic algae are major producers of oxygen and important users of carbon dioxide.
Phytoplankton is predominantly made up of unicellular algae. This phytoplankton is a major source of food for many animals,
large and small. Algae are distinguished on the basis of
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Lake 2010: Wetlands, Biodiversity and Climate Change
—
Size of the algal cell
—
Pigment color
—
Presence of flagella
—
life cycle of algae
—
Stored material
—
Cell wall composition:
Algae are classified in multiple major groups: cyanobacteria (cyanophyceae), green algae (chlorophyceae), diatoms
(bacillariophyceae), yellow-green algae (xanthophyceae), golden algae (chrysophyceae), red algae (rhodophyceae), brown
algae (phaeophyceae), dinoflagellates (dinophyceae) and ‘pico-plankton’ (prasinophyceae and Eustigmatophyceae) (Hu et
al.,2008 ). Algae are ubiquitous in nature, they can form heavy growths in sea ponds, lakes, reservoirs and slow-moving rivers
throughout the world; along with water bodies it can be found on the land surfaces, on tree barks. Algal population can be
affected by the environmental factors like seasonal changes, nutrients availability, light penetrations etc. Algae are primarily
made up of proteins, carbohydrates, fats, and nucleic acids in varying proportions. They contain large amount of proteins
about 47% of the total biomass. Microalgae have already been considered as a source of food proteins for a long time. Algae
are represented as an important source of dissolved organic carbon in water. The organic carbon is represented by
carbohydrates, polysaccharides, nitrogeneous and polyphenolic materials (Craigie and Melachlan, 1964). Carbohydrates one
of the major nutrients obtained from algae. Seaweeds contains about 50% of the total biomass as carbohydrate with little
amount of protein and fats. The algal carbohydrates are considered as important groups of cell constituents for storage material
and energy, also they can be considered as function of enviroment factors (EL-sharaff et al.,1983;). Lipid is the most important
constituent of algal with respect to its use as biodiesel and feedstocks. While the percentages can vary with the type of algae,
some types of algae are made up of up to 40% fatty acids based on their overall mass. It is this fatty acid that can be extracted
and converted into biofuels. The diversity of algal lipids and its ability to modify according to environment made algae
Ubiquitous (Thompson, 1996;). The lipids may include polar lipids, neutral lipids, wax esters, hydrocarbons etc. The chain
lengths of fatty acid varies from C-10 to C>20 depending on the species. Neutral lipids basically consist up of hydrocarbons
and triacylglycerols. (TAGs). TAGs can be used as a feedstock for the production of the biodiesel. The purpose of this review
is to overview the different classes of lipids in algae emphasizing the TAGs and the factors which causes accumulation of
TAG’s. (TAGs primarily composed of C14–C18 fatty acids that are saturated or mono-unsaturated).
LIPIDS OF ALGAE
Decreasing fuels and increasing pollution level made the algal Lipids of high concern because of its use for production of the
biodiesel. Lipids are basically all organic compounds which cannot be dissolved in water. The lipid can be classified into polar
lipids and neutral lipids. The polar lipids include sphingolipids, Glycolipids, phospholipids and sterols. Neutral lipids include
TAGs and Hydrocarbons. Hydrocarbons include about 5% of the total dry weight (Lee and Loeblich, 1971). Various strains of
algae are examined to determine the lipid content in their cell. Green algae are the most important oleaginous algae. In normal
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Lake 2010: Wetlands, Biodiversity and Climate Change
conditions algae synthesizes lipid mainly in the form of membrane lipids. They constitute about 5-20% of total dry cell weight.
The membrane lipids are mainly in the form of Glycosylglycerides which resides in Chloroplast of the cell and the other
membrane lipid is phosphoglycerides which resides in the plasma-membrane and endoplasmic reticulum (Guckert and
Cooksey, 1990; Harwood, 1998; Pohl and Zurheide, 1979a,b; Wada and Murata, 1998). In adverse conditions instead of
synthesizing membrane lipids algae starts synthesizing storage lipids. These storage lipids reside in the form of densely packed
bodies in the cytoplasm of the cell. However in certain green algae the formation and storage of these lipid bodies takes place
in inter-thylakoidal space of the chloroplast (Ben-Amotz et al., 1989). These neutral lipids are generally TAGs. TAGs can be
used as a feedstock for the production of the biodiesel. Algae synthesizes fatty acids as building blocks for the formation of
various types of lipid. Generally algae contain fatty acids having carbon number between 16 to 18 (Ohlrogge and Browse,
1995). Fatty acids are of two types saturated and unsaturated, and unsaturated fatty acids may vary in the number and position
of double bonds on the carbon chain backbone. Saturated and mono-unsaturated fatty acids are dominating in most algae
(Borowitzka, 1988). The dominating fatty acids in Bacillariophyta is C16:0, C16:1, C20:5ω3 and C22:6ω3;
in
eustigmatophyta C16:0 , C18:1,C20:3 and C20:4 ω3; in chlorophyta C16:0, C18:1, C18:2 and C18:3ω3; in cryptophyta
C16:0, C20:1, C18:3ω3, 18:4 and C20:5; in dinophyta C16:0, C18:5ω3 and C22:6ω3; in cyanophyta C16:0, C16:1, C18:1
C18:2 and C18:3ω3 (Cobelas and Lechado, 1989). There is a great variation between the fatty acids of the plant and algae.
TAGs constitute about 80% of the total lipids found in algal cell (Kathen, 1949; Klyachko- Gurvich, 1974; Suen et al., 1987;
Tonon et al., 2002; Tornabene et al., 1983). The TGAs having saturated and mono-unsaturated fatty acids are used for biofuels
production. Algal oils have been found to be very high in unsaturated fatty acids. Some of these unsaturated fatty acids that
are found in different algal species include: arachidonic acid, eicospentaenoic acid, docasahexaenoic acid, gamma-linolenic
acid, and linoleic acid. The PUFAs found in algae omega 3, omega 4, omega 5, omega 6, omega 7, omega 9 and mega 13.
Among this omega 3, omega 6 are the essential fatty acids which are used as the nutrient supplement for mariculture.
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Lake 2010: Wetlands, Biodiversity and Climate Change
Table 1: Showing the various lipid classes in different algae
Fatty acid
Bacillariophyta
Eustigmatophyta
Chlorophyta
Haptophyta
Cyanophyta
C10:0
+
C11:0
+
C12:0
+
C14:0
+
+
+
+
Cryptophyta
Dinophyta
+
+
C14:1
C14:2
+
C15:0
C16:0
+
+
+
+
+
+
+
C16:1ω5
C16:1ω7
+
+
+
+
+
+
C16:1ω9
+
+
+
C16:2ω4
+
+
C16:2ω7
+
+
C16:3
+
+
C17:0
+
C18:0
+
C18:1ω7
C18:1ω9
+
+
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+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
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Lake 2010: Wetlands, Biodiversity and Climate Change
C18:1ω13
+
C18:2ω6
+
+
+
+
+
+
C18:3ω3
+
+
+
+
+
+
+
C18:3ω6
+
+
+
+
+
+
+
C18:4ω3
+
+
+
+
+
+
C18:5ω3
+
+
C20:0
+
C20:1
+
C20:4ω6
+
C20:5ω3
+
+
+
+
+
C22:5ω3
+
+
C22:6ω3
+
+
+
+
C24:0
+
Table 2: The major TAGs which are found in algal lipids are listed in the table below
C16:0
C18:1
C18:1
C18:1
C18:2
C18:1
C16:0
C18:0
C18:0
C16:1
C20:1
C18:0
C18:1
C16:0
C18:1
C18:1
C16:0
C16:0
C18:1
C16:0
C18:1
C18:1
C16:0
C18:1
C18:1
C18:1
C18:0
C18:1
C18:0
C18:1
C18:1
C16:0
C18:0
C18:1
C16:1
C18:2
C16:0
C18:2
C16:1
C18:1
C18:1
C18:1
C18:1
C18:2
C18:0
C16:0
C16:0
C16:0
C18:1
C16:0
C18:2
C14:0
C16:0
C16:0
C18:1
C18:2
C18:1
C18:2
C18:0
C16:0
C18:1
C18:2
C18:0
C18:1
C16:0
C14:0
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Lake 2010: Wetlands, Biodiversity and Climate Change
C18:0
C18:2
C18:1
C18:1
C18:1
C18:1
C18:1
C16:0
C18:0
C18:1
C18:1
C18:0
C16:0
C18:2
C18:0
C18:1
C16:0
C18:1
C16:0
C18:0
C16:0
C18:1
C16:0
C18:1
C18:1
C16:0
C18:1
C18:1
C18:1
C18:1
C16:0
C16:0
C18:1
Table 3: Other uses of lipids of algae
FACTORS AFFECTING FATTY ACID COMPOSITION
Fatty acid composition of an algal cell is affected by different factors. In normal condition the fatty acid composition is
decided by the genetic make-up of the algal cell. It means in normal condition the lipid composition of the algae is strain
specific. In adverse situation the algal lipid becomes dependent on the environmental factors. these factors can be chemical
stimuli or physical stimuli. the chemical stimuli which affects lipid composition is nutrient deficiency, salinity and pH of the
media. Among physical factors which affect the lipid composition is light intensity and temperature. Along with these
chemical and physical stimuli the growth phase affects the fatty acid composition.
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Lake 2010: Wetlands, Biodiversity and Climate Change
Factors responsible for accumulation of TAGs and changes in fatty acid composition
Nutrients
Nutrient starvation is the most important factor which affects the lipid composition in algae. The nutrient which basically
affects the lipid composition is nitrogen, phosphate, silicate and sulfate. The concentration of the silicate affects the diatom
only (Roessler, 1988). During nitrogen deficiency the accumulation of TAGs starts increasing (Basova et al).
Temperature
Temperature has been found to have a major effect on the fatty acid composition of algae. It is found that with increasing
temperature, saturation of fatty acids starts increasing and with decreasing temperature unsaturation of fatty acid starts
increasing (Lynch and Thompson, 1982; Murata et al., 1975;). Temperature also affects the total lipid content of the
algal cell.
Light intensity
Light intensity affects the chemical composition of the algae (Falkowski and Owens, 1980; Richardson et al., 1983;).
Generally polar lipids formation is induced by the low light intensity (Brown et al., 1996; Napolitano, 1994). Light intensity
also affects the saturation and unsaturation of the fatty acids. High light intensity induces the formation of more saturated and
mono unsaturated fatty acids
Growth phase and physiological status
Growth cycle affects the lipid content of the algal cell. During logarithmic phase the amount of TAGs decreases and during
stationary phase there is a increase in TAGs (Mansour et al., 2003). During logarithmic phase of the growth the amount of
PUFAs increases (Bigogno et al., 2002). Aging of the culture also affects the fatty acid content and composition.
Conclusion
Algae are diverse group of organisms adapted to various ecological conditions. Many microalgae have the ability to produce
substantial amounts (e.g. 20–50% dry cell weight) of triacylglycerols (TAG) as a storage lipid under photo-oxidative stress or
other adverse environmental conditions. Chlorophyceae, green algae, are the strain most favored by researchers. However,
green algae tend to produce starches instead of lipids and require nitrogen to grow. They
have the advantage that they have very high growth rates at 30°C and at high light levels in aqueous solution. Bacilliarophya,
diatom algae, are also favored by researchers. One drawback is that the diatom algae require silicon to be present in the
growth medium. Different kinds of lipids are accumulated in the algal cells depending on the species or strains of the algae in
normal growth conditions. Unfavourable condition supports the accumulation of lipids specially TAGs. Microalgae are a
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Lake 2010: Wetlands, Biodiversity and Climate Change
promising source of lipid. The lipid classes are present in all the algal species are C16:0, C16:1ω7, C18:1ω9, C18:3ω3,
C18:3ω6. High lipid productivity is a key desirable characteristic of a species for production of biofuels. Based on the lipid
content decision can be made on the usage of the algae. Lipid constitute about 50-60% of the total dry weight. The proportion
of various lipid classes (particularly triglycerides) varies widely with environnemental conditions. A condition which causes
TAG accumulation include nutrient deficiency, light intensity, temperature, growth phase etc.. The two main types of lipids
found in algal cells are polar lipids and non polar lipids. The polar lipids form the part of structural lipids and non polar or
neutral lipids are storage in the algal cell. Fatty acids are the building blocks of the lipids. It can be saturated or unsaturated.
Storage lipids are basically made up of saturated and mono-saturated fatty acids. The polyunsaturated fatty acids (PUFAs)
which are generally the parts of the membrane lipids acts as an essential fatty acids. Specially ω 3 and ω 6 unsaturated fatty
acids, are the essential fatty acids. The storage lipids are used for the production of the biofuels whereas the essential fatty
acids like EPA, DHA are used as a nutrient supplement.
REFERENCES
ž Basova, M.M. (2005) Fatty acid composition of lipids in microalgae. Int. J. Algae, 7, 33–57.
ž Ben-Amotz, A., Shaish, A. and Avron, M. (1989) Mode of action of the massively accumulated b-carotene of
Dunaliella bardawil in protecting the alga against damage by excess irradiation. Plant Physiol. 91, 1040–1043.
ž Bigogno, C., Khozin-Goldberg, I., Boussiba, S., Vonshak, A. and Cohen, Z. (2002) Lipid and fatty acid composition
of the green oleaginous alga Parietochloris incisa, the richest plant source of arachidonic acid. Phytochemistry, 60,
497–503.
ž Borowitzka, M. (1988) Fats, oils and hydrocarbons. In Microalgal Biotechnology (Borowitzka, M.A. and
Borowitzka, L.J., eds).Cambridge, UK: Cambridge University Press, pp. 257–287.
ž Brown, M.R., Dunstan, G.A., Norwood, S.J. and Miller, K.A. (1996) Effects of harvest stage and light on the
biochemical composition of the diatom Thalassiosira pseudonana. J. Phycol. 32, 64–73.
ž Cobelas, M.A. and Lechado, J.Z. (1989) Lipids in microalgae. A review. I. Biochemistry. Grasas y Aceites, 40, 118–
145.
ž Craigie,J.S., and Mclaclam, J. (1964). Excretion of colored ultraviolet-absorbing substances by Marine algae.
Can.J.Bot. 42: 23-33.
ž Falkowski, P.G. and Owens, T.G. (1980) Light–shade adaptation: two strategies in marine phytoplankton. Plant
Physiol. 66, 592–595.
ž Guckert, J.B. and Cooksey, K.E. (1990) Triacylglyceride accumulation and fatty acid changes in Chlorella
(Chlorophyta) during high-pH induced cell cycle inhibition. J. Phycol. 26, 72–79.
ž Harwood, J.L. (1998) Membrane lipids in algae. In Lipids in Photosynthesis: Structure, Function and Genetics
(Siegenthaler, P.A. and Murata, N., eds). Dordrecht, The Netherlands: Kluwer Publishers, pp. 53–64.
22nd-24th December 2010
Page 8
Lake 2010: Wetlands, Biodiversity and Climate Change
ž .Hu, Q., Sommerfeld, M., Jarvis, E., Ghirardi, M., Posewitz, M., Seibert, M., Darzins, A., Microalgal Triacylglycerols
as Feedstocks for Biofuel Production: Perspectives and Advances. The Plant Journal. 2008. 54: 621-639.
ž Kathen, M. (1949) U¨ ber die Ermittelung der chemischen Konstitution von Algenlipoiden mit Hilfe der
Adsorptionsmethode. Arch.Mikrobiol. 14, 602–634.
ž Klyachko-Gurvich, G.L. (1974) Changes in the content and composition of triacylglyceride fatty acids during
restoration of Chlorella pyrenoidosa cells after nitrogen starvation. Soviet Plant Physiol. 21, 611–618.
ž Lee, R.F. and Loeblich, A.R. III (1971) Distribution of 21:6 hydrocarbon and its relationship to 22:6 fatty acid in
algae. Phytochemistry, 10, 593–602.
ž Lynch, D.V. and Thompson, G.A. (1982) Low temperature-inducedalterations in the chloroplast and microsomal
membranes of Dunaliella salina. Plant Physiol. 69, 1369–1375.
ž Mansour, M.P., Volkman, J.K. and Blackburn, S.I. (2003) The effect of growth phase on the lipid class, fatty acid
and sterol composition in the marine dinoflagellate, Gymnodinium sp. in batch culture. Phytochemistry, 63, 145–153.
ž Murata, N., Throughton, J.H. and Fork, D.C. (1975) Relationships between the transition of the physical phase of
membrane lipids and photosynthetic parameters in Anacystis nidulans
ž Napolitano, G.E. (1994) The relationship of lipids with light and chlorophyll measurement in freshwater algae and
periphyton. J. Phycol. 30, 943–950.
ž Ohlrogge, J. and Browse, J. (1995) Lipid biosynthesis. Plant Cell, 7, 957–970.
ž Pohl, P. and Zurheide, F. (1979b) Control of fatty acid and lipid formation in Baltic marine algae by environmental
factors. In Advances in the Biochemistry and Physiology of Plant Lipids (Appelqvist, L.A. and Liljenberg, C., eds).
Amsterdam: Elsevier, pp. 427–432.
ž Richardson, K., Beardall, J. and Raven, J.A. (1983) Adaptation of unicellular algae to irradiance: an analysis of
strategies. New Phytol. 93, 157–191.
ž Roessler, P.G. (1987) UDP-glucose pyrophosphorylase activity in the diatom Cyclotella cryptica: pathway of
chrysolaminarin biosynthesis. J. Phycol. 23, 494–498.
ž Suen, Y., Hubbard, J.S., Holzer, G. and Tornabene, T.G. (1987) Total lipid production of the green alga
Nannochloropsis sp. QII under different nitrogen regimes. J. Phycol. 23, 289–297.
ž Thompson, G.A. (1996) Lipids and membrane function in green algae. Biochim. Biophys. Acta, 1302, 17–45.
ž Tonon, T., Larson, T.R. and Graham, I.A. (2002) Long chain polyunsaturated fatty acid production and partitioning
to triacylglycerols in four microalgae. Phytochemistry 61, 15–24.
ž Tornabene, T.G., Holzer, G., Lien, S. and Burris, N. (1983) Lipid composition
of the nitrogen starved green alga Neochloris oleabundans. Enzyme Microbiol. Technol. 5, 435–440.
ž Wada, H. and Murata, N. (1998) Membrane lipids in cyanobacteria. In Lipids in Photosynthesis: Structure, Function
and Genetics(Siegenthaler, P.A. and Murata, N., eds). Dordrecht, The Netherlands: Kluwer Academic Publishers, pp.
65–81.
22nd-24th December 2010
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