title: Toxicity phenotype does not correlate with phylogeny of Cylindrospermopsis raciborskii strains.
abstract: Cylindrospermopsis raciborskii is a species of freshwater, bloom-forming cyanobacterium. C. raciborskii produces toxins, including cylindrospermopsin (hepatotoxin) and saxitoxin (neurotoxin), although non toxin-producing strains are also observed. In spite of differences in toxicity, C. raciborskii strains comprise a monophyletic group, based upon 16S rRNA gene sequence identities (greater than 99%). We performed phylogenetic analyses; 16S rRNA gene and 16S-23S rRNA gene internally transcribed spacer (ITS-1) sequence comparisons, and genomic DNA restriction fragment length polymorphism (RFLP), resolved by pulsed-field gel electrophoresis (PFGE), of strains of C. raciborskii, obtained mainly from the Australian phylogeographic cluster. Our results showed no correlation between toxic phenotype and phylogenetic association in the Australian strains. Analyses of the 16S rRNA gene and the respective ITS-1 sequences (long L, and short S) showed an independent evolution of each ribosomal operon. The genes putatively involved in the cylindrospermopsin biosynthetic pathway were present in one locus and only in the hepatotoxic strains, demonstrating a common genomic organization for these genes and the absence of mutated or inactivated biosynthetic genes in the non toxic strains. In summary, our results support the hypothesis that the genes involved in toxicity may have been transferred as an island by processes of gene lateral transfer, rather than convergent evolution.
authors.affiliation: Laboratorio de Ecología Microbiana y Toxicología Ambiental, Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Alameda 340, 8331010 Santiago, Chile.
authors.forename: Karina
authors.initials: K
authors.lastname: Stucken
authors.forename: Alejandro A
authors.initials: AA
authors.lastname: Murillo
authors.forename: Katia
authors.initials: K
authors.lastname: Soto-Liebe
authors.forename: Juan J
authors.initials: JJ
authors.lastname: Fuentes-Valdés
authors.forename: Marco A
authors.initials: MA
authors.lastname: Méndez
authors.forename: Mónica
authors.initials: M
authors.lastname: Vásquez
mesh_terms: D000470:Alkaloids; D001427:Bacterial Toxins; D000087522:Cyanobacteria Toxins; D046891:Cylindrospermopsis / Q000145:classification* / Q000235:genetics / Q000472:pathogenicity* / Q000502:physiology; D004269:DNA, Bacterial / Q000032:analysis / Q000235:genetics; D021903:DNA, Ribosomal Spacer / Q000032:analysis / Q000235:genetics; D022761:Gene Transfer, Horizontal; D008969:Molecular Sequence Data; D010453:Peptide Synthases / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D010802:Phylogeny; D048630:Polyketide Synthases / Q000235:genetics / Q000378:metabolism; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012338:RNA, Ribosomal, 23S / Q000235:genetics; D012530:Saxitoxin / Q000235:genetics / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D013045:Species Specificity; D014498:Uracil / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D000470:Alkaloids; D001427:Bacterial Toxins; D000087522:Cyanobacteria Toxins; D004269:DNA, Bacterial; D021903:DNA, Ribosomal Spacer; D012336:RNA, Ribosomal, 16S; D012338:RNA, Ribosomal, 23S; C089595:cylindrospermopsin; D012530:Saxitoxin; D014498:Uracil; D048630:Polyketide Synthases; C087193:polyketide beta-ketoacylsynthase; D010453:Peptide Synthases; C104385:non-ribosomal peptide synthase