DIVERSITY OF LIPIDS IN ALGAE

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1 DIVERSITY OF LIPIDS IN ALGAE Aakanksha 1, Shilpi Samantray 2, Supriya Guruprasad 2 & T.V Ramachandra 2 1 Birla Institute of Technology, Ranchi 2 Energy & Wetland Research Group, Centre for Ecological Sciences, Indian Institute of Science, Bangalore 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 22 nd -24 th December 2010 Page 1

2 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 22 nd -24 th December 2010 Page 2

3 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, C16:1, C20:5ω3 and C22:6ω3; in eustigmatophyta,,c20:3 and C20:4 ω3; in chlorophyta,, and C18:3ω3; in cryptophyta, C20:1, C18:3ω3, 18:4 and C20:5; in dinophyta, C18:5ω3 and C22:6ω3; in cyanophyta, C16:1, 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. 22 nd -24 th December 2010 Page 3

4 Table 1: Showing the various lipid classes in different algae Fatty acid Bacillariophyta Eustigmatophyta Chlorophyta Haptophyta Cyanophyta Cryptophyta Dinophyta C10:0 + C11:0 + C12:0 + C14: C14:1 C14:2 + C15: C16:1ω5 + C16:1ω C16:1ω C16:2ω C16:2ω C16:3 + + C17: ω ω nd -24 th December 2010 Page 4

5 ω13 + ω C18:3ω C18:3ω C18:4ω C18:5ω3 + + C20:0 + C20:1 + C20:4ω C20:5ω C22:5ω3 + + C22:6ω3 + + C24:0 + Table 2: The major TAGs which are found in algal lipids are listed in the table below C16:1 C20:1 C16:1 C16:1 C14:0 C14:0 22 nd -24 th December 2010 Page 5

6 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. 22 nd -24 th December 2010 Page 6

7 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 % 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 22 nd -24 th December 2010 Page 7

8 promising source of lipid. The lipid classes are present in all the algal species are, C16:1ω7, ω9, 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 Basova, M.M. (2005) Fatty acid composition of lipids in microalgae. Int. J. Algae, 7, 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, 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, Borowitzka, M. (1988) Fats, oils and hydrocarbons. In Microalgal Biotechnology (Borowitzka, M.A. and Borowitzka, L.J., eds).cambridge, UK: Cambridge University Press, pp 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, Cobelas, M.A. and Lechado, J.Z. (1989) Lipids in microalgae. A review. I. Biochemistry. Grasas y Aceites, 40, Craigie,J.S., and Mclaclam, J. (1964). Excretion of colored ultraviolet-absorbing substances by Marine algae. Can.J.Bot. 42: Falkowski, P.G. and Owens, T.G. (1980) Light shade adaptation: two strategies in marine phytoplankton. Plant Physiol. 66, 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, 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 nd -24 th December 2010 Page 8

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