Carotenogenic Microorganisms: A Product-Based Biochemical Characterization

Carotenoid production or occurrence—including derivatives biosynthesized from precursors—is widespread in nature in both the Prokaryota and Eucaryota superkingdoms and more than 600 different chemical structures are reported (
1
), most of them as tetraterpenoids (C
40
). Mammalian species lack the biochemical ability for carotenoid biosynthesis, but they convert some of them to vitamin A or perform other chemical modifications on the diet carotenoid input. At least four particular carotenoids (Fig. 1 ) are fully exploited for commercial applications because their production was consolidated through chemical synthesis: β-carotene (C
40
double cyclic ends), canthaxanthin (diketo-β-carotene), astaxanthin (dihydroxy-diketo-β-carotene), and apocarotenoic acid as its ethyl ester (C
32
; single cyclic end). As diluted organosolvent solutions (e.g., 2–4 μg/mL), these pigments display yellow to orange deep colors. The former nonoxygenated product, also obtained from plant sources like carrots and from genetically improved strains of the molds
Blakeslea trispora
(
2
) and
Phycomyces blakesleeanus
(
3
), is mainly employed in pharmaceutical multivitamin formulations or as a food additive in margarines. The three other xanthophyls (oxygenated carotenoids) are mainly used in aquaculture (salmonoid fish farming) and poultry purposes as an enhancer of meat and egg-yolk color. Cantaxanthin is the pink-orange natural pigment in the edible mushroom
Cantharellus cinnabarinus
(Agaricaceae) and in flamingo feathers. Astaxanthin is naturally found in the orange-red basidiomicetous yeast
Phaffia rhodozyma
(now
Xan-thophyllomyces dendrorhous
) (
4
), in the chlorophycean unicellular alga
Haematococcus pluvialis
(
5
), and in the marine bacterium
Agrobacterium aurantiacum
(
6
). The involved market appeal for carotenoids is strongly supported by scientific knowledge of their well-known biological activity for quenching and scavenging of free radicals (e.g., singlet oxygen and other active oxygen species), which are responsible for the undesirable effect of aging (
7
). This is the main reason for a consolidated market estimated about US$ 455 million for 2000 only for astaxanthin and cantaxanthin. Both contributions for this market—chemical synthesis and microbial source—are experiencing an increase, but in the second parcel, a doubling is seen every 4 yr (
8
).