Evolution of the terminal regions of the Streptomyces linear chromosome.
Comparative analysis of the Streptomyces chromosome sequences, between Streptomyces coelicolor, Streptomyces avermitilis, and Streptomyces ambofaciens ATCC23877 (whose partial sequence is released in this study), revealed a highly compartmentalized genetic organization of their genome. Indeed, despite the presence of specific genomic islands, the central part of the chromosome appears highly syntenic. In contrast, the chromosome of each species exhibits large species-specific terminal regions (from 753 to 1,393 kb), even when considering closely related species (S. ambofaciens and S. coelicolor). Interestingly, the size of the central conserved region between species decreases as the phylogenetic distance between them increases, whereas the specific terminal fraction reciprocally increases in size. Between highly syntenic central regions and species-specific chromosomal parts, there is a notable degeneration of synteny due to frequent insertions/deletions. This reveals a massive and constant genomic flux (from lateral gene transfer and DNA rearrangements) affecting the terminal contingency regions. We speculate that a gradient of recombination rate (i.e., insertion/deletion events) toward the extremities is the force driving the exclusion of essential genes from the terminal regions (i.e., chromosome compartmentalization) and generating a fast gene turnover for strong adaptation capabilities.
Choulet
Frédéric
F
Laboratoire de Génétique et Microbiologie, UMR INRA 1128, IFR 110, Université Henri Poincaré Nancy 1, Faculté des Sciences et Techniques, Vandoeuvre-lès-Nancy, France.
Aigle
Bertrand
B
Gallois
Alexandre
A
Mangenot
Sophie
S
Gerbaud
Claude
C
Truong
Chantal
C
Francou
François-Xavier
FX
Fourrier
Céline
C
Guérineau
Michel
M
Decaris
Bernard
B
Barbe
Valérie
V
Pernodet
Jean-Luc
JL
Leblond
Pierre
P
D022004:Chromosome Structures; D002876:Chromosomes, Bacterial / Q000737:chemistry; D017124:Conserved Sequence; D019143:Evolution, Molecular; D040961:Genetic Drift; D014644:Genetic Variation; D016680:Genome, Bacterial; D013302:Streptomyces / Q000235:genetics*; D048372:Streptomyces coelicolor / Q000235:genetics; D026801:Synteny