Most bacterial genomes described so far display a unique circular chromosome. However, a few exceptions to this generality exist: some bacteria carry more than one chromosome, some others carry linear chromosomes. Together with the linearity come telomeres and subtelomeres. In Streptomyces, the only bacterial genus in which linearity is the general rule, the unique chromosome has an invertron structure and shows a particularly high plasticity in the subtelomere region. This remarkable plasticity is probably the resultant of various mechanisms including: horizontal gene transfer, terminal sequence exchange between replicons (chromosomes and plasmids), illegitimate recombination. Analysis of the genetic instability under laboratory conditions as well as comparative genomics argue in favor of the high frequency of these recombination events and their preferred occurrence/selection in the subtelomere region.