Genes from a Dietzia sp. for synthesis of C40 and C50 β-cyclic carotenoids

Dietzia sp. CQ4 accumulated the C40 β-cyclic carotenoids (canthaxanthin and echinenone) and the C50 β-cyclic carotenoid (C.p.450 monoglucoside). A plant-type lycopene β-cyclase gene crtL was identified for β-cyclization of the C40 carotenoids. A carotenoid synthesis gene cluster was identified away from the crtL gene, which contained the crtEBI genes for the synthesis of lycopene followed by the lbtABC genes for lycopene elongation and β-cyclization of the C50 carotenoids. This C50 β-cyclic carotenoid synthesis gene cluster from Dietzia sp. CQ4 showed high homology with the gene clusters for synthesizing the C50 ε-cyclic carotenoids (decaprenoxanthin and glucosides) from Corynebacterium glutamicum and Agromyces mediolanus. One unique feature of the C50 β-cyclic carotenoid synthesis genes in Dietzia sp. CQ4 was that the gene encoding a C50 carotenoid β-cyclase subunit and the gene encoding the lycopene elongase appeared to be fused as a single gene (lbtBC). Expression of the gene (lbtA) encoding another subunit of the C50 carotenoid β-cyclase and the lbtBC gene in lycopene-accumulating Escherichia coli produced almost exclusively the C50 β-cyclic carotenoid C.p.450. One gene (crtX) with high homology to glycosyl transferases was transcribed in the opposite orientation downstream of the lbtBC gene. The crtX gene was likely involved in C.p.450 glucosylation in Dietzia sp. CQ4. The pathway analogous to the synthesis of the C50 ε-cyclic carotenoids was proposed for the synthesis of the C50 β-cyclic carotenoids.