title: Two distinct crt gene clusters for two different functional classes of carotenoid in Bradyrhizobium.
abstract: Aerobic photosynthetic bacteria possess the unusual characteristic of producing different classes of carotenoids. In this study, we demonstrate the presence of two distinct crt gene clusters involved in the synthesis of spirilloxanthin and canthaxanthin in a Bradyrhizobium strain. Each cluster contains the genes crtE, crtB, and crtI leading to the common precursor lycopene. We show that spirilloxanthin is associated with the photosynthetic complexes, while canthaxanthin protects the bacteria from oxidative stress. Only the spirilloxanthin crt genes are regulated by light via the control of a bacteriophytochrome. Despite this difference in regulation, the biosyntheses of both carotenoids are strongly interconnected at the level of the common precursors. Phylogenetic analysis suggests that the canthaxanthin crt gene cluster has been acquired by a lateral gene transfer. This acquisition may constitute a major selective advantage for this class of bacteria, which photosynthesize only under conditions where harmful reactive oxygen species are generated.
authors.affiliation: Institut de Recherche pour le Développement, Centre de Coopération Internationale en Recherche Agronomique pour le Développement, Agro-Montpellier, France. giraud@mpl.ird.fr
authors.forename: Eric
authors.initials: E
authors.lastname: Giraud
authors.forename: Laure
authors.initials: L
authors.lastname: Hannibal
authors.forename: Joël
authors.initials: J
authors.lastname: Fardoux
authors.forename: Marianne
authors.initials: M
authors.lastname: Jaubert
authors.forename: Philippe
authors.initials: P
authors.lastname: Jourand
authors.forename: Bernard
authors.initials: B
authors.lastname: Dreyfus
authors.forename: James N
authors.initials: JN
authors.lastname: Sturgis
authors.forename: Andre
authors.initials: A
authors.lastname: Verméglio
mesh_terms: D020369:Bradyrhizobium / Q000235:genetics*; D016644:Canthaxanthin / Q000096:biosynthesis* / Q000737:chemistry; D002338:Carotenoids / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D008027:Light; D000077276:Lycopene; D008956:Models, Chemical; D008969:Molecular Sequence Data; D005810:Multigene Family; D009154:Mutation; D018384:Oxidative Stress; D010269:Paraquat / Q000494:pharmacology; D010802:Phylogeny; D010860:Pigments, Biological; D017382:Reactive Oxygen Species; D013050:Spectrometry, Fluorescence; D024341:Xanthophylls / Q000031:analogs & derivatives* / Q000096:biosynthesis*
chemical_list: D010860:Pigments, Biological; D017382:Reactive Oxygen Species; D024341:Xanthophylls; D002338:Carotenoids; D016644:Canthaxanthin; C055255:spirilloxanthin; D010269:Paraquat; D000077276:Lycopene