Lipid metabolism in algae
Project Contact: Neil Clarke, Genome Institute of Singapore
Lipids – defined broadly as small, hydrophobic or amphiphilic) molecules – are a chemically diverse class of biological compounds. Although they are generally built up in a simple way from ketoacyl units or isoprene units, they can be modified by cyclization, oxidation or reduction, and conjugation to other moieties to produce an enormous array of structures and functions. Indeed, much of the diversity of secondary metabolites in plants and algae derives from modifications in lipid metabolism. Functionally, lipids and lipid derivatives get used as hormones, as enzyme co-factors or co-factor precursors, as membranes and waxes, as energy storage molecules, as anti-oxidants, and as chromophores in photosynthesis and other processes. Economically, lipids have value in the pharmaceutical and specialty chemicals industries, as nutritional supplements for humans and for aquaculture, and as a source of renewable energy.
Plants and algae display great diversity in the identity and concentration of their lipids. This reflects the diversity of environments in which they live, and the great breadth of evolutionary history. Much of this diversity exists among the algae. The term algae includes green algae which are the most closely related to plants, but also red algae, which diverged before the common ancestor of plants and green algae. Red algae are nevertheless direct descendants of the same endosymbiosis of a cyanobacterium by a eukaryotic cell. Other algae, such as heterokonts, diatoms and other chromoalveolates, have a more complex evolutionary history. These organisms arose from secondary endosymbiotic events in which a photosynthetic eukaryote was engulfed by a different eukaryote, with subsequent loss (in most cases) of the nucleus of the engulfed organism.
A number of algal species are harvested or grown commercially for food and nutritional supplements, both for humans and for animals. The aquaculture industry, in particular, employs a number of algal species and products. Many algal species have also been investigated for their production of hydrocarbons and lipids, especially triacylglycerides, with an eye towards the use of algae as a feedstock for biofuels. In addition to the direct use of algae and their lipid products, genes encoding enzymes in algal lipid metabolism have been used to make transgenic plants that have modified lipid compositions.
While a number of algal genome sequences are known, most were chosen for their experimental tractability, not for their economic value or for the amount of that is known about their lipid compositions and metabolism. This project seeks to redress this problem by obtaining transcriptome information and lipidomic data on a dozen species that are commercially used, or for which some lipidomic data already exists to suggest the possible utility of the organism. Transcriptome sequences will be used to (i) infer lipid metabolic pathways to the extent possible (ii) identify interesting orthologs for heterologous expression and biochemical characterization and (iii) design custom microarrays for use in gene expression analyses of environmental effects, coupled with lipidomic analysis under the same conditions.
We will be performing transcriptome and lipid analyses on 13 species. These have been selected on the basis of commercial use or interest, partially characterized lipid characteristics, and phylogenetic diversity. The 13 species represent five phyla, ten classes and orders, and thirteen different families.