Stationary phase mutagenesis in B. subtilis: a paradigm to study genetic diversity programs in cells under stress

One of the experimental platforms to study programs increasing genetic diversity in cells under stressful or nondividing conditions is adaptive mutagenesis, also called stationary phase mutagenesis or stress-induced mutagenesis. In some model systems, there is evidence that mutagenesis occurs in genes that are actively transcribed. Some of those genes may be actively transcribed as a result of environmental stress giving the appearance of directed mutation. That is, cells under conditions of starvation or other stresses accumulate mutations in transcribed genes, including those transcribed because of the selective pressure. An important question concerns how, within the context of stochastic processes, a cell biases mutation to genes under selection pressure? Because the mechanisms underlying DNA transactions in prokaryotic cells are well conserved among the three domains of life, these studies are likely to apply to the examination of genetic programs in eukaryotes. In eukaryotes, increasing genetic diversity in differentiated cells has been implicated in neoplasia and cell aging. Historically, Escherichia coli has been the paradigm used to discern the cellular processes driving the generation of adaptive mutations; however, examining adaptive mutation in Bacillus subtilis has contributed new insights. One noteworthy contribution is that the B. subtilis' ability to accumulate chromosomal mutations under conditions of starvation is influenced by cell differentiation and transcriptional derepression, as well as by proteins homologous to transcription and repair factors. Here we revise and discuss concepts pertaining to genetic programs that increase diversity in B. subtilis cells under nutritional stress.