Salmon farming increased substantially in the 1980s, which created a large market for astaxanthin, the principal pigment of salmon. Carotenoids are the most widely distributed class of pigments in ...

Astaxanthin from Microbial Sources

The two major functions of carotenoids in photosyn- thetic microorganisms and plants are the absorption of energy for use in photosynthesis and the protection of chlorophyll from photodamage. The synthesis of vari- ous carotenoids, therefore, is a crucial metabolic proc- ess underlying these functions. In this second review, the nature of these biosynthetic pathways is discussed in detail. In their elucidation, molecular biological techniques as well as conventional enzymology have played key roles. The reasons for some of the ci.s-t Tans isomerizations in the pathway are obscure, however, and much still needs to be learned about the regula- tion of carotenoid biosynthesis. Recent important find- ings, as summarized in this review, have laid the groundwork for such studies. ABSTRACT The crucial roles of carotenoids and their metabolites in photooxidative protection and photosynthesis, not to mention nutrition, vision, and cellular differentiation, make them an important and complex class of biological pigments. Significant ad- vances within the last few years have enhanced our understanding of the genetics and molecular biology of carotenoid biosynthesis in bacteria, fungi, algae, and plants. All of the genes involved in carotenoid biosynthesis from Rhodobacter capsulatus, an anoxygenic photosynthetic bacterium, and from sev- eral species of Erwinia, nonphotosynthetic bacteria, have been molecularly characterized. Recent studies have revealed that two early enzymes of carotenoid biosynthesis, geranylgeranyl pyrophosphate synthase and phytoene synthase, are structurally and function- ally related in all carotenogemc organisms. In con- trast, the subsequent conversion of phytoene, the first C40 carotenoid, to p-carotene requires two de- saturases and one cyclase in oxygenic photosynthetic organisms (cyanobacteria, algae, and higher plants) but only one structurally distinct desaturase and a structurally distinct cyclase in other carotenogemc bacteria and in fungi. Studies of the enzymes that introduce oxygen-containing functional groups into carotenes to produce xanthophylls, the vast majority of all carotenoids, are still in their infancy. This review summarizes the most recent developments in carotenoid biosynthesis from a molecular genetic standpoint.-Armstrong, G. A., Hearst, J. E. Genet- ics and molecular biology of carotenoid pigment biosynthesis. F14SEBJ. 10, 228-237 (1996)

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Carotenoids 2: Genetics and molecular biology of carotenoid pigment biosynthesis.

Microbial sources of carotenoid pigments used in foods and feeds

Vitamins and related biofactors belong to those few chemicals with a direct positive appeal to people. There is indeed a large need for extra vitamins, other than those derived from plant and animal food sources, due to unbalanced food habits or processing, food shortage or disease. Added vitamins are now either prepared chemically or biotechnologically via fermentation or bioconversion processes. Several vitamins and related biofactors are now only or mainly produced chemically (vitamin A, cholecalciferol (D3), tocopherol (E), vitamin K2, thiamine (B1), niacin (PP or B3), pantothenic acid (B5), pyridoxine (B6), biotin (H or B8), folic acid (B9) or via extraction processes (beta-carotene or provitamin A, provitamin D3, tocopherol, vitamin F-group). However, for several of these compounds microbiological or algal methods also exist or are rapidly emerging. Others are produced practically exclusively via fermentation (ergosterol or provitamin D2, riboflavin (B2), cyanocobalamin (B12), orotic acid (B13), vitamin F-group, ATP, nucleosides, coenzymes, etc. or via microalgal culture (beta-carotene, E, F). Both chemical and microbial processes are run industrially for vitamin B2 while vitamin C (ascorbic acid) is produced via a combination of chemical reactions and fermentation processes. A survey is given here of the current state of vitamin production, with emphasis on developments and strategies for improved biotechnological production and its significance, as compared to existing chemical processes. The screening or construction of vitamin hyperproducing microbial strains is a difficult task; pathway elucidation and metabolic (de)regulation need further study; r-DNA technology has only recently been introduced; improved fermentation processes and immobilised biocatalysts bioconversions for the synthesis of chiral vitamin compounds or intermediates or derivatives are gaining importance; the recovery and purification of these vitamin compounds from their fermentation broths remains equally complex.

Production of vitamins, coenzymes and related biochemicals by biotechnological processes.

The industrial production of beta-carotene with the zygomycete Blakeslea trispora involves the joint cultivation of mycelia of opposite sex in the presence of beta-ionone and other chemical activators. We have obtained improved strains by mutation and heterokaryosis. We chose wild strains on the basis of their growth and carotene content in single and mated cultures. Following exposure of their spores to N-methyl-N'-nitro-N-nitrosoguanidine, we obtained high-carotene mutants, which were more productive than their parents but similar to them in having beta-carotene as the main product. Further increases in carotene content were obtained after a new round of mutagenesis in one of the mutants. The production was shifted to lycopene in cultures incubated in the presence of nicotine and in lycopene-rich mutants derived from the wild strains. The highest production levels were achieved in intersexual heterokaryons, which contained mutant nuclei of opposite sex. These contained up to 39 mg of beta-carotene or 15 mg of lycopene per g (dry mass) under standard laboratory conditions in which the original wild strains contained about 0.3 mg of beta-carotene per g (dry mass). Beta-ionone did not increase the carotene content of these strains. Not all wild strains lent themselves to these improvements, either because they produced few mutants or because they did not increase their carotene production in mated cultures.

Mutants and Intersexual Heterokaryons of Blakeslea trispora for Production of β-Carotene and Lycopene

Humans,like most other animals, need carotenoids but cannot synthesize them. Our main suppliers are the fruits and vegetables, with lesser, mostly indirect contributions from fungi, algae, and bacteria. Carotenoid production is rarely the main objective of a culture, but colourful products rich in carotenoids are obtained from various plants and algae. The oldest example is saffron (Crocus sativus), still planted in La Mancha, Spain, and elsewhere for the stigmas of its flowers. Many fields of central Mexico become bright orange in the summer with the flowers of cempasuchil (Tagetes tenuifolia, a kind of marigold), whose dried petals are fed to chicken for meat and egg yolk colour. Annatto is extracted from the seeds of a tropical tree, Bixa orellana. The most familiar carotenoid-rich product is probably paprika, a powder made by grinding red peppers (Capsicum annuum).

E. Cerdá-Olmedo

Papers

Production of Carotenoids with Fungi