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Targets of algal genetic modification

Genetic modification as a tool to improve algal performance is more and more considered a necessity to achieve new and economical viable productions systems (Wijffels and Barbosa, 2010; Greenwell et al., 2010; Hannon et al., 2010; Scott et al., 2010; Schuhmann et al., 2012).

Three types of targets can be distinguished for genetic modification of algae: improvement of photosynthetic efficiency, improvement of productivity of selected products and new products.

Improvement of photosynthetic efficiency

Biofuel production efficiency with algae is directly dependent on the solar photon capture and conversion efficiency of the system. However, daylight intensity is most of the time above the maximum photosynthetic efficiency of algae and therefore growth is reduced, a phenomenon known as photo inhibition. Research in this area focuses on the light harvesting antenna complex (LHC) (Mussgnug et al., 2007; Anastasios, 2009).

Improvement ofproductivity of selected products

The rising market demand for pigments from natural sources has promoted large-scale cultivation of microalgae for synthesis of such compounds. Genes encoding enzymes that are directly involved in specific carotenoid syntheses have been investigated and further development of transformation techniques will permit considerable increase of carotenoid cellular contents, and accordingly, contribute to increase the volumetric productivities of the associated processes (Guedes et al., 2011). One example of such a gene (a phytoene desaturase) has already been published (Steinbrenner and Sandmann, 2006). Table 4.2 gives an overview of carotenoids produced by selected microalgae.

Table 4.2. Carotenoids produced by selected microalgae

Microalga source

Active compound

Dunaliella salina

B-carotene

Haematococcus pluvialis

Astaxanthin, cantaxanthin, lutein

Chlorella vulgaris

Cantaxanthin, astaxanthin

Coelastrella striolata var. multistriata

Canthaxanthin, astaxanthin, p-carotene

Scenedesmus almeriensis

Lutein, p-carotene

Research on lipid production has increased in the past decades due to interest in developing algal biofuels. Genetic modification is part of the strategy to increase lipid production with algae. Target genes are lipid biosynthetic genes, lipid storage genes and lipid degradation genes. Obviously, the first two categories have to be enhanced while the third category of genes should be reduced (Radakovits et al., 2010; Scott et al., 2010).

Another interesting aspect is the modification of the lipid characteristics. This could increase the quality of the lipids with regards to suitability as diesel fuel feedstock but could also make the lipids suitable for other applications, like industrial applications, food or feed (Radakovits et al., 2010). Genes for this purpose will originate from the group of fatty acid modifying enzymes, such as desaturases and thioesterases, which have been studied in genetically modified plants in detail for a long time (Napier, 2007).

 
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