Expression of crl-lacZ and sdhA-lacZ gene fusions in Salmonella. Expression of the gene fusions in the Salmonella strains indicated was determined in cultures grown under different conditions. Cultures were grown overnight in LB medium (LB) at 37°C or 30°C or on LB agar at 30°C, as described previously (28). M9, minimal M9 medium with 20 mM glucose; M9+FeCl2, M9 with 100 μM ferrous chloride; M9+DP, M9 with the iron chelator 2,2′-dipyridyl (100 μM). β-Galactosidase activity was measured according to the method of Miller (31). (A) Expression of the crl-lacZ gene fusion in ATCCcrl-lacZ strains harboring pACYC184 and pACcrl-1 that expresses the crl gene under the control of the cat promoter of pACYC184 (40). (B) Expression of the crl-lacZ gene fusion in ATCCcrl-lacZ and ATCCfur crl-lacZ. (C) Expression of the sdhA-lacZ gene fusion in ATCCsdhA-lacZ-k and ATCCfur sdhA-lacZ-k and expression of the crl-lacZ gene fusion in ATCCcrl-lacZ and ATCCfur crl-lacZ. (D) Expression of the crl-lacZ gene fusion in ATCCcrl-lacZ, ATCCrpoS crl-lacZ, ATCCfur crl-lacZ and ATCCrpoSfur crl-lacZ.