Production of Bioactive Compounds by Cell and Tissue Cultures of Marine Seaweeds in Bioreactor System

Summary

Macrophytic marine algae, commonly known as seaweeds, are a source of unique natural products with medicinal properties. Of particular interest are bioactive compounds produced through the selective oxidation of fatty acids to eicosanoids and related oxylipins, or the selective halogenation of terpenoids to brominated/chlorinated monoterpenes [Carte, 1996]. Cell and tissue cultures established from anatomically-complex marine seaweeds have the potential to biologically synthesize these compounds in a controlled environment at a scale required for continued drug development or commercial production. In pursuit of this goal, over the past six years we have developed several unique phototrophic cell and tissue culture systems representing brown, green, and red seaweeds. These include a gametophyte cell suspension culture from the brown alga Laminaria saccharina [Qi & Rorrer, 1995; Rorrer et al., 1995; Zhi & Rorrer, 1996], a freely suspended tissue culture of the green alga Acrosiphonia coalita [Rorrer et al., 1996], an differentiated filament clump culture of the red alga Agardhiella subulata established by a callus-induction technique, and a freely suspended microplantlet culture established by controlled regeneration of filament clumps [Huang et al., 1997]. For example, the Agardhiella subulata cell and tissue culture system is illustrated in Figure 1.

The controlled cultivation of these culture systems has been demonstrated in stirred tank [Qi & Rorrer, 1995; Rorrer et al., 1996; Ramanan et Rorrer, unpublished], bubble column [Zhi & Rorrer, 1996], immobilized mesh [Huang et al., 1997], and tubular recycle photobioreactor systems [Mullikin & Rorrer, 1997]. Representative growth curves for the L. saccharina female gametophyte cell suspension culture system in stirred tank vs. tubular recycle photobioreactors are shown in Figure 2. Cell densities exceeding 2 g of dry cell weight per liter of culture were achieved with specific growth rates up to 0.2 day⁻¹ under selected conditions of light, mixing intensity, aeration, and mode of nutrient delivery. The L. saccharina gametophyte cell suspension culture system was further studied for bioactive compound production. This culture biologically synthesized three bioactive hydroxy fatty acids derived from regio-and stereoselective ω-6 lipoxygenase oxidation: 15-hydroxy-5,8,11,13-eicosatetranenoic acid (15-HETE) from arachidonic acid, 13-hydroxy-9,11-octadecadienoic acid (13-HODE) from linoleic acid, and 13-hydroxy-9,11-octadecatetraenoic acid (13-HOTDA) from stearidonic acid [Rorrer et al., 1997]. Feeding the culture with the precursors linoleic acid and γ-linolenic acid stimulated the production of all three hydroxy fatty acids up to 400% of the controls, as shown in Figure 3. All of our studies suggest that bioprocess technology for the controlled production of bioactive compounds from cell and tissue cultures of marine seaweeds in bioreactor systems holds significant promise for securing future supplies of novel drugs derived from marine seaweeds.