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

Strain or plasmid	Genotype or relevant phenotype	Source or reference
P. mirabilis
wt	Wild-type N2; Tcr	[2]
hfq	wt derivative; hfq-knockout mutant; Kmr	[19]
micM	wt derivative; micM-knockout mutant; Kmr	This study
impR	wt derivative; impR-knockout mutant; Cmr	This study
hfq/impR	wt derivative; hfq/impR-knockout mutant; Kmr Cmr	This study
chbIGRov	wt containing pGEM-T Easy-chbBC-IGR; chbBC-IGR overexpressing strain; Ampr	This study
ImpRov	wt containing pGEM-T Easy-impR; impR overexpressing strain; Ampr	This study
hfqca	hfq mutant containing pGEM-T Easy-hfq; Hfq-complemented strain; Ampr	[19]
hfq/impRc	hfq/impR mutant containing pGEM-T Easy-impR; hfq/impR mutant complemented with ImpR; Ampr	This study
hfqca/impR	hfq/impR mutant containing pGEM-T Easy-hfq; hfq/impR mutant complemented with Hfq; Ampr	This study
micMc	micM mutant containing pGEM-T Easy-micM; MicM-complemented strain; Ampr	This study
E. coli
DH5α	fhuA2 lac(del)U169 phoA glnV44 Φ80' lacZ(del)M15 gyrA96 recA1 relA1 endA1 thi-1 hsdR17	Invitrogen
S17–1 λ pir	λ pir lysogen of S17–1 [thi pro hsdR - hsdM + recA RP4 2-Tc::Mu-Km::Tn7 (Tpr Smr)]; permissive host able to transfer suicide plasmids requiring the Pir protein by conjugation to recipient cells	[2]
Plasmids
pGEM-T Easy	High-copy TA cloning vector; Ampr	Promega
pUT-Km1	Suicide plasmid requiring the Pir protein for replication and containing a mini-Tn5 cassette containing Kmr gene	[2]
pACYC184	Low-copy cloning vector, P15A replicon; Cmr Tetr	[2]
pGEM-T Easy-chbBC-IGR	pGEM-T Easy containing intact chbBC-IGR sequence; Ampr	This study
pGEM-T Easy-impR (pImpR)	pGEM-T Easy containing intact impR sequence including its ribosome binding site only for overexpression or its promoter for complementation; Ampr	This study
pACYC184-chb-xylE	chb reporter plasmid, pACYC184 containing intact chb promoter sequence before xylE; Cmr	This study
pGEM-T Easy-micM	pGEM-T Easy containing intact micM sequence including its promoter; Ampr	This study