CO2 as main carbon source for isoprenoid biosynthesis via the mevalonate-independent methylerythritol 4-phosphate route in the marine diatoms Phaeodactylum tricornutum and Nitzschia ovalis

Isoplenoid biosynthesis was investigated in the two diatoms Phaeodactylum tricornutum and Nitzschia ovalis by labeling experiments performed in mixotrophic growth conditions with sodium [1-C-13]acetate, (CO2)-C-13, [1-C-13]glucose, sodium [3-C-13]pyruvate and 1-deoxy-D-[5,5-H-2(2)]xylulose. A clear dichotomy was found. Acetate was the preferred carbon source for the formation of the sterols in the cytoplasm via the mevalonate pathway. Carbon dioxide was the main source for phytol biosynthesis in the chloroplasts via the mevalonate-independent methylerythritol 4-phosphate pathway. The two diatoms showed the same compartmentation for isoprenoid biosynthesis as that previously found in higher plants, the red alga Porphyridium cruentum and the Chrysophyte Ochromonas danica. (C) 2000 Elsevier Science Ltd. All rights reserved.