Highly plastic genome of Microcystis aeruginosa PCC 7806, a ubiquitous toxic freshwater cyanobacterium.
BACKGROUND
The colonial cyanobacterium Microcystis proliferates in a wide range of freshwater ecosystems and is exposed to changing environmental factors during its life cycle. Microcystis blooms are often toxic, potentially fatal to animals and humans, and may cause environmental problems. There has been little investigation of the genomics of these cyanobacteria.


RESULTS
Deciphering the 5,172,804 bp sequence of Microcystis aeruginosa PCC 7806 has revealed the high plasticity of its genome: 11.7% DNA repeats containing more than 1,000 bases, 6.8% putative transposases and 21 putative restriction enzymes. Compared to the genomes of other cyanobacterial lineages, strain PCC 7806 contains a large number of atypical genes that may have been acquired by lateral transfers. Metabolic pathways, such as fermentation and a methionine salvage pathway, have been identified, as have genes for programmed cell death that may be related to the rapid disappearance of Microcystis blooms in nature. Analysis of the PCC 7806 genome also reveals striking novel biosynthetic features that might help to elucidate the ecological impact of secondary metabolites and lead to the discovery of novel metabolites for new biotechnological applications. M. aeruginosa and other large cyanobacterial genomes exhibit a rapid loss of synteny in contrast to other microbial genomes.


CONCLUSIONS
Microcystis aeruginosa PCC 7806 appears to have adopted an evolutionary strategy relying on unusual genome plasticity to adapt to eutrophic freshwater ecosystems, a property shared by another strain of M. aeruginosa (NIES-843). Comparisons of the genomes of PCC 7806 and other cyanobacterial strains indicate that a similar strategy may have also been used by the marine strain Crocosphaera watsonii WH8501 to adapt to other ecological niches, such as oligotrophic open oceans.
Institut Pasteur, Pasteur Genopole, F-75015, Paris, France. lfrangeu@pasteur.fr
Lionel
L
Frangeul
Philippe
P
Quillardet
Anne-Marie
AM
Castets
Jean-François
JF
Humbert
Hans C P
HC
Matthijs
Diego
D
Cortez
Andrew
A
Tolonen
Cheng-Cai
CC
Zhang
Simonetta
S
Gribaldo
Jan-Christoph
JC
Kehr
Yvonne
Y
Zilliges
Nadine
N
Ziemert
Sven
S
Becker
Emmanuel
E
Talla
Amel
A
Latifi
Alain
A
Billault
Anthony
A
Lepelletier
Elke
E
Dittmann
Christiane
C
Bouchier
Nicole Tandeau
NT
de Marsac
D000818:Animals; D015280:DNA Restriction-Modification Enzymes / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D021901:DNA, Intergenic / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics; D017753:Ecosystem; D019143:Evolution, Molecular; D005618:Fresh Water / Q000382:microbiology; D016680:Genome, Bacterial; D006801:Humans; D046931:Microcystis / Q000145:classification / Q000235:genetics* / Q000472:pathogenicity / Q000502:physiology; D008969:Molecular Sequence Data; D005810:Multigene Family; D010802:Phylogeny; D012091:Repetitive Sequences, Nucleic Acid; D013045:Species Specificity
D015280:DNA Restriction-Modification Enzymes; D004269:DNA, Bacterial; D021901:DNA, Intergenic; D004275:DNA, Ribosomal