The genetics and molecular biology of carotenoid biosynthesis in mucorales

Cap?tulo de libro

[EN] Carotenoids are synthesized by most photosynthetic organisms like cyanobacteria, algae and plants and some non-photosynthetic such as certain fungi, yeasts and bacteria. Animals and humans cannot synthesize them and acquire them through diet. The usefulness of carotenoids in nature is very diverse. In oxidative photo-synthetic organisms carotenoids are essential compounds with different functions, the protection against photo-oxidation being the most important. In animals, carotenoids and their derivatives are involved in different biological processes, such as vitamin A in nutrition, retinol used as antenna pigment, rhodopsin in the retinal cells, retinal pigment used as an antenna and retinoic acid to regulate various cellular processes. In humans, carotenoids taken in the diet may protect against cancer, chronic diseases and immune illnesses. A number of carotenoids are used in the animal and human food industries to intensify the colour of salmon or trout flesh, egg yolk and human food colorant. The market for commercial carotenoids has been mainly based on products of chemical synthesis, but today the interest in carotenoids of biological origin is growing because of the public concern over the safety of artificial food colorants. This preference for carotenoids of natural origin has led to a search for natural sources of such compounds. In this sense, some Mucorales as Blakesleea trispora, Mucor circinelloides and Phycomyces blakesleeanus are being studied as carotenoid producers. In these fungi, all the enzymatic activities needed to synthesize ?-carotene are encoded by two closely linked genes divergently orientated in a cluster like organization that seems to be characteristic of Zygomycetes. The biosynthesis of carotene is much more conserved than its regulation, as is often the case in the evolution of metabolic pathways. In this sense, Phycomyces is feed-back regulated by the end-product, while in Mucor and Blakeslea this regulation has not been described.