Diatom cultivation and biotechnologically relevant products. Part II: current and putative products.

While diatoms are widely present in terms of diversity and abundance in nature, few species are currently used for biotechnologically applications. Most studies have focussed on intracellularly synthesised eicosapentaenoic acid (EPA), a polyunsaturated fatty acid (PUFA) used for pharmaceutical applications. Applications for other intracellular molecules, such as total lipids for biodiesel, amino acids for cosmetic, antibiotics and antiproliferative agents, are at the early stage of development. In addition, the active principle component must be identified amongst the many compounds of biotechnological interest. Biomass from diatom culture may be applied to: (1). aquaculture diets, due to the lipid- and amino-acid-rich cell contents of these microorganisms, and (2). the treatment of water contaminated by phosphorus and nitrogen in aquaculture effluent, or heavy metal (bioremediation). The most original application of microalgal biomass, and specifically diatoms, is the use of silicon derived from frustules in nanotechnology. The competitiveness of biotechnologically relevant products from diatoms will depend on their cost of production. Apart from EPA, which is less expensive when obtained from Phaeodactylum tricornutum than from cod liver, comparative economic studies of other diatom-derived products as well as optimisation of culture conditions are needed. Extraction of intracellular metabolites should be also optimised to reduce production costs, as has already been shown for EPA. Using cell immobilisation techniques, benthic diatoms can be cultivated more efficiently allowing new, biotechnologically relevant products to be investigated.