Table 1. Strains and plasmids used in this study.

Strain or plasmid	Genotype and relevant features	Source or reference
E. coli strain
XL1-Blue	recA endA1 gyrA96 thi-1 hsdR17 supE44 relA1 lac [F′ proAB lacZΔM15 : : Tn10]	Stratagene
XL1-Bluerat	recA endA1 gyrA96 thi-1 hsdR17 supE44 relA1 murA1 lac [F′ proAB lacZΔM15 : : Tn10], murA1 contains the murArat1 mutation corresponding to an amino acid substitution of L138Q	Bernhardt et al. (2001)
HfrH	λ- fhuA : : Tn10 lacIq relA1 spoT1 thi-1	Laboratory stock
HfrHrat	λ- fhuA : : Tn10 lacIq relA1 murA1 spoT1 thi-1	This study
HfrH lacZ : : Tn5	λ− lacIq1 lacZ : : Tn5 relA1 spoT1 thi-1	Laboratory stock
HfrH ΔmurA : : kan	λ- fhuA : : Tn10 lacIq relA1 ΔmurA : : kan spoT1 thi-1	This study
pZE12-murABs	ΔmurA : : kan transduced from strain ZK1745	Brown et al. (1995)
ER2738	(F′proA+B+ lacIq Δ(lacZ)M15 zzf : : Tn10) fhuA2 glnV Δ(lac-proAB) thi-1 Δ(hsdS-mcrB)5	New England Biolabs
Plasmid
pZE12-A2	Qβ A2 cloned under the PLlacO-1 promoter, which is IPTG-inducible	This study
pZE12-murA	E. coli murA cloned under the PLlacO-1 promoter, which is IPTG-inducible	Bernhardt et al. (2001)
pZE12-murAHis	An oligo-histidine tag (G2H6G2) was adjoined to the C terminus of murA	Reed et al. (2012)
pZE12-murABs	Bacillus subtilis murAA cloned under the PLlacO-1 promoter, which is IPTG-inducible	This study