The Smallest Known Genomes of Multicellular and Toxic Cyanobacteria: Comparison, Minimal Gene Sets for Linked Traits and the Evolutionary Implications

PLoS One

Allan Cembella¹  Alejandro A. Murillo¹  Karina Stucken¹  Maik Friedel²  Mónica Vásquez²  Katia Soto-Liebe²  Uwe John³  Juan J. Fuentes-Valdés³  Alvaro M. Plominsky³  Gernot Glöckner³ 

[1] Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany;Department of Molecular Genetic and Microbiology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Santiago, Chile;Millenium Nucleus EMBA, Santiago, Chile

关键词: Cyanobacteria;    Comparative genomics;    Genomic libraries;    Cell differentiation;    Anabaena;    Evolutionary genetics;    Diazo compounds;    Genome evolution;   

DOI  :  10.1371/journal.pone.0009235

学科分类：医学（综合）

来源: Public Library of Science

【 摘 要 】

Cyanobacterial morphology is diverse, ranging from unicellular spheres or rods to multicellular structures such as colonies and filaments. Multicellular species represent an evolutionary strategy to differentiate and compartmentalize certain metabolic functions for reproduction and nitrogen (N2) fixation into specialized cell types (e.g. akinetes, heterocysts and diazocytes). Only a few filamentous, differentiated cyanobacterial species, with genome sizes over 5 Mb, have been sequenced. We sequenced the genomes of two strains of closely related filamentous cyanobacterial species to yield further insights into the molecular basis of the traits of N2 fixation, filament formation and cell differentiation. Cylindrospermopsis raciborskii CS-505 is a cylindrospermopsin-producing strain from Australia, whereas Raphidiopsis brookii D9 from Brazil synthesizes neurotoxins associated with paralytic shellfish poisoning (PSP). Despite their different morphology, toxin composition and disjunct geographical distribution, these strains form a monophyletic group. With genome sizes of approximately 3.9 (CS-505) and 3.2 (D9) Mb, these are the smallest genomes described for free-living filamentous cyanobacteria. We observed remarkable gene order conservation (synteny) between these genomes despite the difference in repetitive element content, which accounts for most of the genome size difference between them. We show here that the strains share a specific set of 2539 genes with >90% average nucleotide identity. The fact that the CS-505 and D9 genomes are small and streamlined compared to those of other filamentous cyanobacterial species and the lack of the ability for heterocyst formation in strain D9 allowed us to define a core set of genes responsible for each trait in filamentous species. We presume that in strain D9 the ability to form proper heterocysts was secondarily lost together with N2 fixation capacity. Further comparisons to all available cyanobacterial genomes covering almost the entire evolutionary branch revealed a common minimal gene set for each of these cyanobacterial traits.

【 授权许可】

CC BY