Adaptive (stationary-phase) mutagenesis occurs in the gram-positive bacterium 
Bacillus subtilis. Furthermore, taking advantage of B. subtilis as a paradigm 
for the study of prokaryotic differentiation and development, we have shown that 
this type of mutagenesis is subject to regulation involving at least two of the 
genes that are involved in the regulation of post-exponential phase prokaryotic 
differentiation, i.e., comA and comK. On the other hand, a functional RecA 
protein was not required for this type of mutagenesis. The results seem to 
suggest that a small subpopulation(s) of the culture is involved in adaptive 
mutagenesis and that this subpopulation(s) is hypermutable. The existence of 
such a hypermutable subpopulation(s) raises important considerations with 
respect to evolution, the development of specific mutations, the nature of 
bacterial populations, and the level of communication among bacteria in an 
ecological niche.