Papillation in Bacillus anthracis colonies: a tool for finding new mutators.

Colonies of Bacillus anthracis Sterne allow the growth of papillation after 6 days of incubation at 30°C on Luria-Bertani medium. The papillae are due to mutations that allow the cells to overcome the barriers to continued growth. Cells isolated from papillae display two distinct gross phenotypes (group A and group B). We determined that group A mutants have mutations in the nprR gene including frameshifts, deletions, duplications and base substitutions. We used papillation as a tool for finding new mutators as the mutators generate elevated levels of papillation. We discovered that disruption of yycJ or recJ leads to a spontaneous mutator phenotype. We defined the nprR/papillation system as a new mutational analysis system for B. anthracis. The mutational specificity of the new mutator yycJ is similar to that of mismatch repair-deficient strains (MMR⁻) such as those with mutations in mutL or mutS. Deficiency in recJ results in a unique specificity, generating only tandem duplications.