Microalgae as a source of stable isotopically labeled compounds

Microalgae have the ability to convert inorganic compounds into organic compounds. When they are cultured in the presence of stable (non-radioactive) isotopes (i.e.¹³CO₂,¹⁵NO ₃ ^– ,²H₂O) their biomass becomes labeled with the stable isotopes, and a variety of stable isotopically-labeled compounds can be extracted and purified from that biomass.Two applications for stable isotopically-labeled compounds are as cell culture nutrients and as breath test diagnostics. Bacteria that are cultured with labeled nutrients will produce bacterial products that are labeled with stable isotopes. The presence of these isotopes in the bacterial products, along with recent developments in NMR technology, greatly reduces the time and effort required to determine the three-dimensional structure of macromolecules and the interaction of proteins with ligands. As breath test diagnostics, compounds labeled with¹³C are used to measure the metabolism of particular organs and thus diagnose various disease conditions. These tests are based on the principle that a particular compound is metabolized primarily by a single organ, and when that compound is labeled with¹³C, the appearance of¹³CO₂ in exhaled breath provides information about the metabolic activity of the target organ. Tests of this type are simple to perform, non-invasive, and less expensive than many conventional diagnostic procedures.The commercialization of stable isotopically labeled compounds requires that these compounds be produced in a cost-effective manner. Our approach is to identify microalgal overproducers of the desired compounds, maximize the product content of those organisms, and purify the resulting products.