A new mutator strain of Bacillus subtilis.

Bacillus subtilis strain SB1207, widely used in our laboratory, was found to be highly temperature-sensitive and to exhibit a strong SOS-independent mutator phenotype at elevated temperatures. Both chromosomal and plasmid-borne genes were affected by the mutator. Lethality and mutator phenotype could not be attributed to a replication shut off or to thymine starvation. Due to the high frequency of base misincorporation, the mutator phenotype probably results from an editing defect rather than from a post-replication defect (mismatch repair).