Genome and transcriptome divergence in Bacillus subtilis after 6,000 generations of evolution

Ten populations were evolved for 6,000 generations. Five had strong selection for sporulation, imposed partially by their cultivation in sporulation-inducing medium, while the other five populations had relaxed selection for sporulation, by cultivating them in sporulation-repressing medium. Batch cultures were diluted 1:100 daily for approximately 892 days. In the five populations with relaxed selection for sporulation, sporulation ability was eventually lost. Keywords: comparative genome hybridization and transcriptome divergence Genomic DNA from all ten populations, and ancestors, was isolated, labeled and hybridized to microarrays. Only one hybridization was performed for each experimental population, with evolved and ancestral DNA hybridized to the slide. RNA hybridizations were done by chosing one strain that was evolved in sporulation-repressing medium and one strain that was evolved in sporulation-inducing medium. Two biological replicates were performed, as well as a dye swap for each biological replicate. Evolved and ancestral strains were grown in identical medium and RNA was isolated at the onset of stationary phase.