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Cover Picture: A Gene Cluster Encoding Rhizoxin Biosynthesis in “Burkholderia rhizoxina”, the Bacterial Endosymbiont of the Fungus Rhizopus microsporus (ChemBioChem 1/2007)
The cover picture shows a confocal scanning micrograph of bacterial endosymbionts (Burkholderia rhizoxina) residing in the mycelium of the plant-pathogenic fungus Rhizopus microsporus, stained with a fluorescent dye. This symbiosis is a unique example in which a fungus harbors bacteria for the production of a virulence factor, the potent antimitotic macrolide rhizoxin. The entire 82 kb gene cluster that encodes rhizoxin biosynthesis has been located, cloned, and sequenced, and its identity has been confirmed by a targeted gene inactivation in the genome of the cultured endosymbionts. Analyses of the gene cluster revealed that rhizoxin polyketide assembly involves a giant trans-AT PKS-NRPS thiotemplate system with some unusual features. The elucidation of rhizoxin biosynthesis sheds more light on an unparalleled phytopathogenic symbiosis and sets the basis for engineering new derivatives of the potential antitumor drug. Further details can be found in the article by C. Hertweck et al. on p. 41 ff.