title: Evolution of Anabaenopeptin Peptide Structural Variability in the CyanobacteriumPlanktothrix.
abstract: Cyanobacteria are frequently involved in the formation of harmful algal blooms wherein, apart from the toxic microcystins, other groups of bioactive peptides are abundant as well, such as anabaenopeptins (APs). The APs are synthesized nonribosomally as cyclic hexapeptides with various amino acids at the exocyclic position. We investigated the presence and recombination of the AP synthesis gene cluster (apnA-E) through comparing 125 strains of the bloom-forming cyanobacteriumPlanktothrixspp., which were isolated from numerous shallow and deep water habitats in the temperate and tropical climatic zone. Ten ecologically divergent strains were purified and genome sequenced to compare their entireapnA-Egene cluster. In order to quantifyapngene distribution patterns, all the strains were investigated by PCR amplification of 2 kbp portions of the entireapngene cluster without interruption. Within the 11 strains assigned toP. pseudagardhii, P. mougeotii, orP. tepida(Lineage 3), neitherapnA-Egenes nor remnants were observed. Within theP. agardhii/P. rubescensstrains from shallow waters (Lineage 1, 52 strains), strains both carrying and lackingapngenes occurred, while among the strains lacking theapnA-Egenes, the presence of the 5'end flanking region indicated a gene cluster deletion. Among the strains of the more derived deep water ecotype (Lineage 2, 62 strains),apnA-Egenes were always present. A high similarity ofapngenes of the genusPlanktothrixwhen compared with strains of the genusMicrocystissuggested its horizontal gene transfer during the speciation ofP. agardhii/P. rubescens. Genetic analysis of the first (A1-) domain of theapnAgene, encoding synthesis of the exocyclic position of the AP molecule, revealed four genotype groups that corresponded with substrate activation. Groups of genotypes were either related to Arginine only, the coproduction of Arginine and Tyrosine or Arginine and Lysine, or even the coproduction of Arginine, Tyrosine, and Lysine in the exocyclic position of the AP-molecule. The increased structural diversity resulted from the evolution ofapnAA1genotypes through a small number of positively selected point mutations that occurred repeatedly and independently from phylogenetic association.
authors.affiliation: Research Institute for Limnology, University of Innsbruck Mondsee, Austria.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Entfellner
authors.affiliation: Research Institute for Limnology, University of Innsbruck Mondsee, Austria.
authors.forename: Mark
authors.initials: M
authors.lastname: Frei
authors.affiliation: Research Institute for Limnology, University of InnsbruckMondsee, Austria; Miti Biosystems GmbH, Max F Perutz LaboratoriesWien, Austria.
authors.forename: Guntram
authors.initials: G
authors.lastname: Christiansen
authors.affiliation: Institute of Virology, Helmholtz Zentrum München München, Germany.
authors.forename: Li
authors.initials: L
authors.lastname: Deng
authors.affiliation: Bioinformatics and Systems Biology, Justus-Liebig-University Giessen, Germany.
authors.forename: Jochen
authors.initials: J
authors.lastname: Blom
authors.affiliation: Research Institute for Limnology, University of Innsbruck Mondsee, Austria.
authors.forename: Rainer
authors.initials: R
authors.lastname: Kurmayer
keywords: chemotype; cyanoHABs; cyanotoxins; ecotype; gene deletion; horizontal gene transfer; natural products; speciation