CAROTENOID DIVERSITY - A MODULAR ROLE FOR THE PHYTOENE DESATURASE STEP

Carotenoids play a crucial role in light harvesting and are essential photoprotective agents in photosynthesis. It has also been suggested t hat their ability to scavenge harmful radicals may offer protection ag ainst cancer and heart disease. Key enzymes in the carotenoid biosynth etic pathway of the photosynthetic bacterium Rhodobacter sphaeroides c an be successfully replaced with the corresponding enzyme from the non -photosynthetic bacterium Erwinia herbicola. This results in the synth esis of carotenoids new to Rhodobacter. The response of the pathway to 'swapping' these enzymes may explain how a wide range of carotenoids can be produced with relatively minor changes to the basic biosyntheti c pathway.