Scientists engineered bacteria to produce bixin, a plant product used in many foods and cosmetics, after uncovering nature's genetic recipe for the pigment. Tomatoes capable of producing bixin, also known as annatto and used to add an orange touch to microwave popcorn and some cheeses, may arise from the advances reported in the 27 June issue of the journal, Science, published by AAAS, the science society.
This research may expand the supply of this economically important plant product used to add an orange touch to microwave popcorn and some cheeses, and texture and color to a variety of creams and cosmetics. Outside the laboratory, bixin is produced by a single, heavily-fruiting, small tropical tree, Bixa orellana.
First, the researchers figured out how the plant itself produces bixin. In addition to locating the three necessary genes, they demonstrated that lycopene is the physical precursor to bixin. Lycopene is the compound known to make tomatoes red.
Next, the authors moved to replicate this biosynthetic pathway in another organism.
"We chose to start with E. coli because you can insert all the genes at once. Tomatoes will be more complicated," explained senior author Bilal Camara from CNRS and Université Louis Pasteur in Strasbourg, France.
Bixin genes are not the only genetic ingredient. The scientists added these genes to E. coli already engineered to produce lycopene. When the E. coli growing in test tubes began to produce bixin, they did not change color because the lycopene had already turned these single-celled bacteria red.
Lycopene is an antioxidant that gives foods such as tomatoes, watermelon and pink grapefruit their red color. It has made recent headlines as scientists investigate lycopene as a compound that may reduce the risk for some kinds of cancer.
The next step, according to Camara, is to insert the genes that produce this pigment into tomatoes, or other fruit that produce large amounts of lycopene naturally.
"Tomatoes could become bixin factories," said Camara who explained that the three bixin genes would each have to be added to separate plants. These plants could be crossed to breed plants with the full complement of bixin genes. Alternatively, a vector allowing insertion of several genes could be used. Camara is hoping to have bixin-producing tomatoes in about two years.
Camara explained why he is focused on harnessing the power of living organisms to produce bixin.
"Living organisms can be engineered to constantly make the enzymes required for bixin synthesis. It's the best way," said Camara who explained that managing all the enzymes in a non-biological synthesis scenario would be difficult.
"The bixin produced in E. coli is exactly the same compound as the bixin harvested from the plant. There is no difference," said Camara.
Throughout the tropical world, people grow the plants that produce bixin on plantations. Others harvest the red seed pods from wild plants.
Bixin has been used by humans in such a wide range of products because it easily mixes and dissolves into both water-based and oil-based products destined for human consumption and human adornment. Indigenous tribes in the rainforests of South America have long used the seeds of Bixa orellana as a body paint and fabric dye. From Brazilian herbal medicine to jellies and soft drinks, the list of human uses for this yellow-orange pigment derived from the brilliantly red seed covers of Bixa orellana is long and varied.
Lycopene, the precursor to bixin, is a carotenoid. This class of compounds can be described as nature's advertisers. Scientists believe that lycopene's bright red color announces to the world that a tomato is ripe and ready consumption. The authors of this study have demonstrated how a tomato's advertisement (generated in E. coli) can be used to produce bixin, a colorful marketing tool of the plant Bixa orellana. And from this second advertisement, humans produce cosmetics – one of the social and sexual advertisments employed by humans.
Florence Bouvier and Bilal Camara are from Institut de Biologie Moléculaire des Plantes, CNRS, Université Louis Pasteur in Strasbourg, France. Odette Dogbo is from Université d'Abobo-Adjamé in Adibjan Côte d'Ivoire.
Funding for this research was provided in part by European Community grant QLK3-CT-2000-00809.
Materials provided by American Association For The Advancement Of Science. Note: Content may be edited for style and length.
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