Fig. 1: Principle behind the chromosomally-integrated inducible mutator strain.

In step 1, a mutS transgene was introduced under the control of a rhamnose-inducible promoter at a neutral site in the PAO1 chromosome. In step 2, the endogenous mutS gene was deleted. This yielded a strain where, in the absence of inducer (rhamnose) mutability was high (due to low intracellular MutS levels) whereas in the presence of inducer, mutation is suppressed.