Streptomyces are ubiquitous Gram-positive soil bacteria exhibiting a complex life cycle and are responsible for producing most natural antibiotics used today in medicine. The genome of Streptomyces is also remarkable by several traits: a very large size with about 8 Mb, a high GC content (70-74%) and a linear structure. In addition, several Streptomyces species (if not all), including Streptomyces ambofaciens, are prone to frequent mutations which affect morphological and biochemical differentiation. These spontaneous mutations are associated to the formation of large genomic rearrangements affecting the terminal regions. Comparison of the Streptomyces coelicolor A3(2) (Bentley et al., 2002) and Streptomyces avermitilis (Ikeda et al., 2003) genome reveals that the subtelomeric regions (about 2 Mb) are highly variable for gene organisation and encoded functions between the two species while the 6.5 Mb central core is highly conserved. Our sequencing project of the S. ambofaciens chromosomal ends shows a similar situation between S. ambofaciens and S. coelicolor A3(2) despite a very close phylogenetic relationship. Therefore, the terminal regions of the chromosome could be a "hot spot" for gene replacement following horizontal transfer. Interestingly, most of the gene clusters for secondary metabolite biosynthesis are located in these regions.
References
Bentley et al., 2002, Nature, 417, 141-7.
Ikeda et al., 2003, Nat. Biotechnol., 21, 526-31.
