title: Ces locus embedded proteins control the non-ribosomal synthesis of the cereulide toxin in emetic Bacillus cereus on multiple levels.
abstract: The emetic toxin cereulide produced by Bacillus cereus is synthesized by the modular enzyme complex Ces that is encoded on a pXO1-like megaplasmid. To decipher the role of the genes adjacent to the structural genes cesA/cesB, coding for the non-ribosomal peptide synthetase (NRPS), gene inactivation- and overexpression mutants of the emetic strain F4810/72 were constructed and their impact on cereulide biosynthesis was assessed. The hydrolase CesH turned out to be a part of the complex regulatory network controlling cereulide synthesis on a transcriptional level, while the ABC transporter CesCD was found to be essential for post-translational control of cereulide synthesis. Using a gene inactivation approach, we show that the NRPS activating function of the phosphopantetheinyl transferase (PPtase) embedded in the ces locus was complemented by a chromosomally encoded Sfp-like PPtase, representing an interesting example for the functional interaction between a plasmid encoded NRPS and a chromosomally encoded activation enzyme. In summary, our results highlight the complexity of cereulide biosynthesis and reveal multiple levels of toxin formation control. ces operon internal genes were shown to play a pivotal role by acting at different levels of toxin production, thus complementing the action of the chromosomal key transcriptional regulators AbrB and CodY.
authors.affiliation: Department of Microbiology, Central Institute for Food and Nutrition Research (Zentralinstitut für Ernährungs- und Lebensmittelforschung), Technische Universität München Freising, Germany.
authors.forename: Genia
authors.initials: G
authors.lastname: Lücking
authors.affiliation: Functional Microbiology, Institute of Microbiology, Department of Pathobiology, University of Veterinary Medicine Vienna Vienna, Austria.
authors.forename: Elrike
authors.initials: E
authors.lastname: Frenzel
authors.affiliation: Department of Microbiology, Central Institute for Food and Nutrition Research (Zentralinstitut für Ernährungs- und Lebensmittelforschung), Technische Universität München Freising, Germany.
authors.forename: Andrea
authors.initials: A
authors.lastname: Rütschle
authors.affiliation: Chair of Food Chemistry and Molecular Sensory Science, Technische Universität München Freising, Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Marxen
authors.affiliation: Chair of Food Chemistry and Molecular Sensory Science, Technische Universität München Freising, Germany.
authors.forename: Timo D
authors.initials: TD
authors.lastname: Stark
authors.affiliation: Chair of Food Chemistry and Molecular Sensory Science, Technische Universität München Freising, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Hofmann
authors.affiliation: Department of Microbiology, Central Institute for Food and Nutrition Research (Zentralinstitut für Ernährungs- und Lebensmittelforschung), Technische Universität München Freising, Germany ; Lehrstuhl für Mikrobielle Ökologie, Wissenschaftszentrum Weihenstephan, Technische Universität München Freising, Germany.
authors.forename: Siegfried
authors.initials: S
authors.lastname: Scherer
authors.affiliation: Functional Microbiology, Institute of Microbiology, Department of Pathobiology, University of Veterinary Medicine Vienna Vienna, Austria.
authors.forename: Monika
authors.initials: M
authors.lastname: Ehling-Schulz
keywords: Bacillus cereus; cereulide synthetase; ces gene cluster; cesC; cesD; cesH; cesP; regulation