title: A polyketide interferes with cellular differentiation in the symbiotic cyanobacterium Nostoc punctiforme.
abstract: Nostoc punctiforme is a filamentous cyanobacterium capable of forming symbiotic associations with a wide range of plants. The strain exhibits extensive phenotypic characteristics and can differentiate three mutually exclusive cell types: nitrogen-fixing heterocysts, motile hormogonia and spore-like akinetes. Here, we provide evidence for a crucial role of an extracellular metabolite in balancing cellular differentiation. Insertional mutagenesis of a gene of the polyketide synthase gene cluster pks2 led to the accumulation of short filaments carrying mostly terminal heterocysts under diazotrophic conditions. The mutant has a strong tendency to form biofilms on solid surfaces as well as in liquid culture. The pks2(-) strain keeps forming hormogonia over the entire growth curve and shows an early onset of akinete formation. We could isolate two fractions of the wild-type supernatant that could restore the capability to form long filaments with intercalary heterocysts. Growth of the mutant cells in the neighbourhood of wild-type cells on plates led to a reciprocal influence and a partial reconstruction of wild-type and mutant phenotype respectively. We postulate that extracellular metabolites of Nostoc punctiforme act as life cycle governing factors (LCGFs) and that the ratio between distinct factors may guide the differentiation into different life stages.
authors.affiliation: Molecular Environments Group, Department of Arctic and Marine Biology, Faculty of Biosciences, Fisheries and Economics, University of Tromsø, 9037 Tromsø, Norway. Okinawa Institute of Science and Technology, Evolutionary Systems Biology Unit, 1919-1 Tancha, Onna-son, Okinawa 904-0412, Japan. Leibniz Institute for Natural Product Research and Infection Biology, Hans Knöll Institute, Beutenbergstr. 11a, 07745 Jena, Germany. University of Potsdam, Institute for Biochemistry and Biology, Karl-Liebknecht-Str. 24/25, 14476 Potsdam-Golm, Germany.
authors.forename: Anton
authors.initials: A
authors.lastname: Liaimer
authors.forename: Holger
authors.initials: H
authors.lastname: Jenke-Kodama
authors.forename: Keishi
authors.initials: K
authors.lastname: Ishida
authors.forename: Katrin
authors.initials: K
authors.lastname: Hinrichs
authors.forename: Janne
authors.initials: J
authors.lastname: Stangeland
authors.forename: Christian
authors.initials: C
authors.lastname: Hertweck
authors.forename: Elke
authors.initials: E
authors.lastname: Dittmann