DNA damage increases natural transformation.

A. Wild-type cells were treated at or above the MIC of ciprofloxacin (cipro), ampicillin (amp) (0.016 ug/ml [50]) or gentamicin (1 ug/ml, data not shown) for 2.5 hours and transformed with 20ng genomic DNA harboring an antibiotic resistance cassette and the fraction of cells transformed per CFU was determined. B. Wild-type cells were treated with the minimum inhibitory concentration (MIC) of ciprofloxacin for 2.5 hours and the fraction of cells transformed by genomic DNA per CFU was determined. Wild-type transformation frequency ranges between 10−7 and 10−4, depending on DNA concentration and experiment and for each panel, error bars are the standard deviation of the mean with at least three replicates for each point and a representative from two experiments is shown. C. Wild-type cells were treated with 10× MIC gentamicin for the indicated time and the fraction of cells transformed by genomic DNA per CFU was determined either by plating directly to selective medium or by plating to non-selective medium to allow translation of the selective marker prior to selection. D. Increased expression of comB4 (comB4IE) increases natural transformation. The fraction of wild-type cells and comB4IE cells transformed by genomic DNA was determined.