Sammendrag
Carotenoids are membrane-protective antioxidant pigments produced by plants, algae, fungi and bacteria. The majority of all natural carotenoids are based on a symmetric C40 carbon backbone and only few C50 carotenoids have been discovered so far. Due to their chemical structure C50 carotenoids have a high potential for superior antioxidant and possible tumor-inhibiting activity and their biotechnological production is of interest for pharmaceutical, chemical, food and feed industries.Micrococcus luteus accumulates the g-cyclic C50 carotenoid sarcinaxanthin and we identified and cloned the corresponding biosynthetic gene cluster (crtEBIE2YgYh) from the “Fleming strain” NCTC2665. We elucidated the entire sarcinaxanthin biosynthetic pathway by heterologous overexpression of the complete and partial gene cluster in Escherichia coli host strains. Metabolic analysis by LC-MS and NMR revealed that sarcinaxanthin is synthesized from the precursor molecule farnesyl pyrophosphate via C40 lycopene, C45 nonaflavuxanthin, C50 flavuxanthin and C50 sarcinaxanthin. Glucosylation of sarcinaxanthin was shown to be accomplished by the crtX gene product [Netzer et al., 2010]. Another M. luteus strain, designated Otnes7, has recently been isolated from coastal waters of Mid-Norway. The isolate forms intensively colored colonies and analysis of extracted pigments revealed sarcinaxanthin as the major accumulated carotenoid [Stafsnes et al., 2010]. The sarcinaxanthin biosynthetic pathway genes crtE2YgYh were cloned and overexpressed in lycopene producing E. coli hosts to explore the potential of using Otnes7 derived genes to achieve effective heterologous production of sarcinaxanthin. The use of a fine-tunable broad-host-range vector system for heterologous overexpression resulted in significant higher sarcinaxanthin production compared to the use of corresponding genes derived from the wild type strain NCTC2665 [Lale et al., manuscript submitted].The sarcinaxanthin biosynthesis gene cluste