Docosahexaenoic acid accumulation in thraustochytrids: search for the rationale
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Thraustochytrid protists characteristically accumulate high amounts of lipids, much of which is comprised of the polyunsaturated fatty acid, docosahexaenoic acid (DHA). Since DHA is important in human health, thraustochytrids have attracted much attention from the point of view of biotechnology. However, the biological rationale of DHA production in the storage lipids of these organisms is not clear. We carried out three experiments to study this. (1) The fate of lipids in thraustochytrids during development was studied by staining lipids of vegetative cells with the fluorescent vital stain for lipids, namely Nile blue, following the growth of the cells. The fluorescent lipid bodies decreased in abundance in freshly formed motile limaciform amoeboid cells and subsequently disappeared when they moved away. When vegetative cells produced vast extensions of plasma membrane, the ectoplasmic net elements (EN), the fluorescent lipids appeared to be transported to them. (2) Changes in lipids and DHA during starvation were examined in cells with enhanced lipid and DHA contents and those in which they were not enhanced. Cells in which lipids and DHA were enhanced by refrigerating them for 48 h survived starvation for a longer period. Compared to cells that had not been refrigerated, total fatty acids, as well as DHA were marginally higher in pre-refrigerated cells, while palmitic acid levels were lower. Starvation of cells resulted in a gradual decrease of absolute concentrations and percentage levels of DHA after 8 days, while percentage of palmitic acid levels increased. (3) The relationship between DHA and specific gravity of cells was studied by comparing cells pre-refrigerated as above with those which were not pre-refrigerated. Refrigerated cells with increased lipids and DHA showed higher specific gravities than non-refrigerated cells. We suggest the following roles for storage lipids and DHA in thraustochytrids: (1) lipids serve as energy sources during movement of cells and for production of EN; (2) DHA in storage lipids become distributed in the plasma membrane when EN are formed; (3) DHA is preferably utilized as a fatty acid energy reserve during starvation and (4) an unknown mechanism results in negative buoyancy of cells when total lipids and DHA are marginally enhanced. DHA in storage lipids might be crucial to the survival of thraustochytrid cells.
KeywordsSpecific Gravity Palmitic Acid Fatty Acid Profile Storage Lipid Lipid Body
We are grateful to the Director of NIO for encouragement and support. The experiments that were performed comply with the current laws of India. This is NIO’s Contribution No. 4225.
- Decho AW (1990) Microbial exopolymer secretions in ocean environment: their role(s)in food webs and marine processes. Oceanogr Mar Biol Annu Rev 28:73–153Google Scholar
- Findlay RH, Fell JW, Coleman NK, Vestal JR (1986) Biochemical indicators of the role of fungi and thrausochytrids in mangrove detrital systems. In: Moss ST (ed) The biology of marine fungi. Cambridge University Press, Cambridge, pp 91–104Google Scholar
- Huang J, Aki T, Yokochi T, Nakahra T, Honda D, Kawamoto S, Shigeta S, Ono K, Suzuki O (2003) Grouping newly isolated docosahexaenoic acid-producing thraustochytrids based on their polyunsaturated fatty acid profiles and comparative analysis of 18S rRNA genes. Mar Biotechnol 5:450–457CrossRefGoogle Scholar
- Jain R, Raghukumar S, Chandramohan D (2004) Enhancement of the production of the polyunsaturated fatty acid, docosahexaenoic acid in thraustochytrid protists. Mar Biotechnol 6:S59–S65Google Scholar
- Lehninger AL (1978) Biochemistry. Kalyani Publishers, New DelhiGoogle Scholar
- Parrish CC, Abrajans TA, Budge SM, Helleur RJ, Hudson ED, Palshan K, Ramos C (2000) Lipids and phenolic biomarkers in marine ecosystems: analysis and application In: Wangersky P (ed) The handbook of environmental chemistry and marine chemistry, vol 5, part D. Springer, Berlin, pp 194–223Google Scholar
- Parsons TR, Maita Y, Lalli CM (1984) A manual of chemical and biological methods for sea water analysis. Oxford, Pergamon Press, pp 187Google Scholar
- Porter D (1990) Phylum Labyrinthulomycota. In: Margulis L, Corliss JO, Melkonian M, Chapman DJ (eds) Handbook of Protoctista. Jones and Bartlett, Boston, pp 388–398Google Scholar
- Sanders NK, Childress JJ (1988) Ion replacement as a buoyancy mechanisms in a pelagic deep-sea crustacean. J Exp Biol 138:333–343Google Scholar