The E2348/69 HsdMSR restriction-modification system is active. Transformation efficiency testing of E2348/69 and NH4. Equal numbers of WT (E2348/69) and ΔhsdR mutant (NH4) bacteria were transformed with pJW15 plasmid and the number of transformants obtained was divided by the μg of plasmid used in the transformation to obtain transformation efficiency. E2348/69 and NH4 were transformed with pJW15 isolated from either MC4100, an E. coli K-12 strain, E2348/69, or NH4. Each experiment was performed three times and the data represent the mean and standard deviation.