Table 1. Bacterial strains and plasmids used in this study.

Strains and plasmids	Relevant genotype or description	Reference
Escherichia coli strains
MG1656	ΔlacMluI derivative of Escherichia coli MG1655 (K-12F– λ– ilvG−rfb-50 rph-1)	[35]
MG/pZE1	MG1656 carrying p6851 and pZE1 plasmids	This work.
MG/intI1	MG1656 carrying p6851 and pZE1intI1 plasmids	This work.
MG/intI1*	MG1656 carrying p6851 and pZE1intI1* plasmids	This work.
MG1656λatt::gfp	MG1656 containing the gfpmut3 gene at the λatt site; expression of gfpmut3 from Pλ promoter. Green fluorescent bacteria.	[36]
Plasmids
p6851	Cassette recombination reporter (pSU38::aac(6’)-Ib*::attCaadA7-cat(T4)-attCVCR2); CmR, KmR	[24]
Recombined p6851	Plasmid resulting from deletion of the resistance gene cassette cat(T4)-attCVCR2 in native p6851; expression of the resistance gene cassette aac(6’)-Ib* from PlacZ promoter; TobraR, KmR	This work.
pZE1	Promoterless derivative of pZE12 plasmid, carrying a multiple cloning site (mcs1); AmpR	[24]
pZE1intI1	attI site + intI1 gene from In40 class 1 integron cloned into pZE1 plasmid; this intI1 gene encodes the most active variant of the integrase, IntI1R32_H39; AmpR	[24,37]
pZE1intI1*	pZE1intI1 plasmid carrying the LexAmut2 mutation in the LexA binding site of the class 1 integron integrase promoter PintI1, leading to constitutive expression of the intI1 gene; AmpR	[24]

Cm^R: confers resistance to chloramphenicol; Km^R: confers resistance to kanamycin; Tobra^R: confers resistance to tobramycin; Amp^R: confers resistance to ampicillin