ical Institute at Goethe University, Frankfurt, Germany, and coworkers [Nat Biotechnol, 18,843 (2000)].They took nonmodified genes for a variety of carotenoid biosynthetic enzymes from arotenoids, a family of colorful an chemistry Claudia Schmidt-Dannert different bacteria and combined them in tioxidant natural products, are and postdoc Daisuke Umeno of the Uni plasmids, which were then introduced marketed commercially for a versity of Minnesota, St. Paul, and pro into bacterial host cells. When the mixed genes were coexrange of industrial and medical applica fessor of chemical engineering and bio tions, although they are not easy to iso chemistry Frances H. Arnold of Califor pressed in the bacterial host, 12 different late or synthesize. Three independent nia Institute of Technology—used a carotenoid compounds were produced, research groups have now developed DNA-shuffling technique to breed bac four of which had never previously been genetic engineering techniques that teria that produce novel carotenoids isolated or synthesized chemically. And should make it a whole lot easier to ob [Nat. Biotechnol, 18, 750 (2000)]. The the antioxidative activity of these four ca tain known carotenoids in substantial technique involved taking gene frag rotenoids was relatively high, "making quantities and to create some entirely ments from different bacterial species them interesting pharmaceutical candi new ones as well. and combining them to form a large va dates," according to the researchers. Genetics professor Joseph HirschCarotenoids are essential to microbi riety of carotenoid genes, which were berg and coworkers at the Hebrew Uni al, plant, and animal life, note postdoc then expressed in bacterial host cells. Joseph M. Jez and associate professor One of the resulting products, a carot versity of Jerusalem, in Israel, adopted a Joseph P. Noel of the Structural Biology enoid called torulene, is not produced somewhat different approach to engi Laboratory at the Salk Institute for Bio by any known bacteria. According to the neering of carotenoid biosynthesis by logical Studies, La Jolla, Calif., in a writ researchers, the DNA-shuffling ap producing the compounds in tobacco ten commentary on the three Nature proach "may allow the discovery and plants rather than in bacteria [Nat. Bio Biotechnology scientific papers that de production, in simple laboratory organ technol, 18, 888 (2000)]. They manipu scribe the techniques. The compounds isms, of new compounds that are essen lated tobacco's carotenoid biosynthetic act as protective antioxidants in photo- tially inaccessible from natural sources pathway by adding a ketolase enzyme from red algae. synthetic plants and in organisms— or by synthetic chemistry." including people—that eat carotenoidThe modified plant biosynthesized A related strategy was used by pro containing foods. As vitamin A precur fessor Gerhard Sandmann of the Botan- astaxanthin, a compound responsible for sors, they play an essential role in the the characteristic pink coloring of salm visual system. They serve as important on, trout, and shrimp. Astaxanthin pro colorants of flowers, fruits, and vegeta duced by chemical synthesis is currently bles, such as tomatoes and carrots. And marketed commercially for use in salmon they are marketed commercially for use farming. However, it is also of interest for in a variety of cosmetics and foods. potential medical applications because it has been shown to boost immune func SRI Consulting, Menlo Park, Calif., es tion in humans, reduce oral cancer in timates the 1999 world market for carot rats, and inhibit breast cancer in mice. enoids at $750 million to $800 million per year, with Roche and BASF the main glo The approach developed by Hirschbal suppliers. Nevertheless, only a hand berg and coworkers not only provides a ful of carotenoid compounds can current way to produce astaxanthin in tobacco ly be synthesized in substantial quanti but could also be applicable to the pro ties, extracted from natural sources, or duction of novel carotenoids in other obtained by microbial fermentation. types of plants. "It's not clear yet if the biotechnological production of caroten In earlier efforts to increase the avail oids can become cheaper than chemical ability of carotenoids, one research group synthesis," Hirschberg tells C&EN. used recombinant DNA technology to "However, the biotechnology approach create β-carotene-containing rice as a has other advantages: 'cleaner' produc means to fight vitamin A deficiency—a tion, renewable sources, and the ability serious public health problem in poor to provide natural products," such as countries—and another created trans specific carotenoid enantiomers. genic tomatoes with enhanced carote noid content. Monsanto, which owns key According to Jez and Noel, the three patents on β-carotene-enriched rice, an papers "give us a glimpse of what the fu nounced earlier this month that it would ture holds for carotenoid biosynthesis allow thericeto be produced on a royaltyin hosts amenable to large-scale fermen free basis as a means to help alleviate vita Top: Artists rendering of bacteria tation and in plants. . . . Ultimately, a colored by genetic engineering of their min A deficiencies worldwide. combination of methodologies is most Now, three research groups have de carotenoid biosynthetic pathways. likely to lead to more diverse libraries of veloped new genetic engineering routes Bottom: Colorful extracts from bacterial novel carotenoids and a kaleidoscope of cells that Schmidt-Dannert, Umeno, and to carotenoid compounds. One group— Arnold engineered to produce new opportunities." consisting of assistant professor of bio carotenoids. Stu Borman
Building Better Carotenoids Three Ways
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AUGUST 14,2000 C&EN
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