De novo synthesis of astaxanthin: From organisms to genes

Astaxanthin is a ketocarotenoid with stronger antioxidant activity than vitamin E and coenzyme Q10, and with pharmacological effects against cancer, cardiovascular disease, diabetes, inflammation, and others. Increased astaxanthin supplementation in foods, nutraceuticals, and cosmetic products has resulted in tremendous growth in the demand for natural astaxanthin. Astaxanthin is found widely in aquatic animals and some other organisms, but its de novo synthesis is limited to several bacteria, protists, fungi, algae and plants. Metabolic engineering offers approaches to create systems for high-efficiency production of astaxanthin, which will require in-depth dissection of the astaxanthin synthesis enzymes in the available organisms. Here, we review the de novo synthesis of astaxanthin in bacteria, protists, fungi, algae and plants, and the functional enzymes of specific organisms. A protein-sequence based phylogenetic tree was established to reveal the evolutionary relationships of astaxanthin synthesis proteins across organisms. This review will provide valuable information for the metabolic engineering of astaxanthin bioreactors.