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 t ricornutum and Nitzschia ovalis by labeling experiments performed in mixotr ophic growth conditions with sodium [1-C-13]acetate, (CO2)-C-13, [1-C-13]gl ucose, 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 format ion of the sterols in the cytoplasm via the mevalonate pathway. Carbon diox ide was the main source for phytol biosynthesis in the chloroplasts via the mevalonate-independent methylerythritol 4-phosphate pathway. The two diato ms showed the same compartmentation for isoprenoid biosynthesis as that pre viously found in higher plants, the red alga Porphyridium cruentum and the Chrysophyte Ochromonas danica. (C) 2000 Elsevier Science Ltd. All rights re served.