In analogy, a plausible hypothesis in the present study is that the chromosomes of S. avermitilis mutants SA1-8 and SA1-6 were formed compatibly, whereas chromosomes of SA1-7 and SA3-1 harbored incompatible junction. However, what makes a stable junction “”compatible”",

and what leads to “”incompatibility”" of two chromosome regions, remain to be clarified. Breakpoint analysis of the unstable chromosome of SA1-7 may shed some light on this issue. The inherent chromosome instability of Streptomyces likely reflects an evolutionary strategy for adapting to environmental changes by creating LY2835219 populations with altered genetic information [29]. Unfortunately, this “”strategy”" often results in reduced production of secondary metabolites which are desired in agricultural, pharmaceutical, and research industries. From this point of view, the present findings contribute to elucidation of mechanisms underlying genetic

GDC-0449 concentration instability in Streptomyces, and may help devising approaches to suppress or control such instability for industrial purposes. Conclusions S. avermitilis underwent chromosomal rearrangement events, including chromosomal arm replacement, internal deletions and circulation, by non-homologous recombination. The fact that major deletion in the central region of chromosome was observed in S. avermitilis suggests that genetic instability of the Streptomyces chromosome is uniform across the entire chromosome. Stability assay showed that the chromosome of some bald mutants derived from the wild-type strain was conserved, whereas other mutants underwent further chromosomal rearrangement. Methods Bacterial Doxorubicin strains and growth

conditions S. avermitilis ATCC31267 (wild-type strain) was used as starting strain and control. 76-9 was a high avermectin-producing strain derived from ATCC31267 by continuous mutagenesis, with the ability to sporulate. Spontaneous “”bald”" mutants (i.e., defective in production of aerial mycelia) of ATCC31267 and 76-9 were picked at random for further study, since the bald phenotype was stable. All strains were grown at 28°C on YMS solid medium for sporulation [30], or for isolation and growth of bald colonies. Cell Cycle inhibitor Preparation of DNA for PFGE analysis S. avermitilis was cultured at 28°C for 36 h in 25 mL YEME with 25% sucrose in a 250 mL flask, containing a coiled stainless steel spring to promote aeration and cell dispersion. Mycelia were harvested and used for making plugs, as described by Kieser et al [31]. For restriction analysis, 200 μl buffer (per manufacturer’s instructions) was added into 1.5 mL eppendorf tube containing one plug, incubated for 30 min at room temperature, and then the buffer was replaced with 300 μl fresh buffer containing 2 μl BSA (100 μg/mL) and 50 U AseI to digest the plug for 4 h at 37°C. PFGE runs were performed in a CHEF MAPPER XA system (Bio-Rad). Agarose gels were run in 0.5 × TBE buffer at 14°C.