Production of carotenoids by recombinant DNA technology
Biotechnology can be used to effect the production of carotenoids by natural organisms. Algae and yeast strains have been developed by classical strain improvement methods to produce several different carotenoids. However, the carotenoid productivity of these organisms is low compared to carotenoid production by chemical synthesis. One way to increase the production of carotenoids in biological systems is to use recombinant DNA techniques. The carotenoid biosynthetic pathway is especially amenable to manipulation by recombinant DNA techniques since all carotenoids share a common precursor. Effecting these key steps with genetic engineering methods can increase carotenoid productivity. In addition natural systems have a very widespread biosynthetic capability, and these systems can be used to synthesize novel carotenoids for particular applications. Recently, many genes coding for enzymes catalyzing specific steps in the biosynthesis of carotenoids have been isolated and characterized from bacteria, cyanobacteria, and higher plants. This paper will focus on the application of carotenoid biosynthetic genes to affect carotenoid production in bacteria and yeasts. I NTRO DUCT1 0 N Carotenoids are produced by a diverse group of organisms, ranging from bacteria to higher plants. Over 600 different carotenoids have been identified from natural sources. This biological diversity and synthetic capability have not been exploited to develop systems for the production of carotenoids. Currently only P-carotene and astaxanthin are produced from biological sources and sold widely to the food and feed industries. The key limitation to the use of biological systems to produce carotenoids is the low productivity of these systems compared to chemical syntheses. One way to increase the productivity of carotenoid synthesis is to use recombinant DNA technology. However, before recombinant DNA technology and genetic engineering can be used to increase the productivity, genes encoding the carotenoid biosynthetic enzymes need to be isolated and characterized. Until very recently, genes for the carotenoid biosynthetic enzymes had not been isolated. This situation has changed markedly over the past three years. Currently a number of the genes coding for carotenoid biosynthetic enzymes have been isolated from bacteria, fungi, cyanobacteria, green algae, and higher plants (Table 1 I . With the large number of genes now available for further study, systems can be tested to increase the production of carotenoids from biological sources. Results from these studies will fuel the development of processes for the production of carotenoids from a number of different host organisms and the full range of carotenoid compounds from biological sources will be accessible. The following will describe the characterization of carotenoid genes from Erwinia herbicola and the use of these genes to effect carotenoid synthesis in different host cells. 1057