TABLE 1.

β-Galactosidase activities of a transcriptional nprA-lacZ gene fusion in R. capsulatus B10^a

Compound	β-Galactosidase activity (Miller units)b
	0.1 mM	0.2 mM
None	1	1
Nitrofurazone	10	30
Nitrofurantoine	18	ND
Furazolidone	9	48
CB1954	21	75
2-Aminofluorene	19	116
Benzo[a]pyrene	18	25
2,4-Dinitrotoluene	54	90
3,5-Dinitrobenzoate	52	62
2,4-Dinitrophenol	105	144
Salicylate	30	33
Paraquat	ND	25

^aCells were harvested at an A₆₈₀ of about 0.5, and β-galactosidase activity was assayed as described in Materials and Methods. Cells were cultured under diazotrophic conditions with 30 mM malate as the carbon source and in the presence of different compounds at a final concentration of 0.1 mM or 0.2 mM. The compounds used were nitrofuran derivatives that are substrates of NfsA and NfsB of E. coli (27); the prodrug CB1954, which is a substrate of NfsB of E. coli (7); 2-aminofluorene and benzo[a]pyrene, substrates of SnrA of Salmonella enterica (13); several dinitroaromatics, substrates of the nitroreductase of R. capsulatus E1F1 (4); salicylate, a MarR repressor, as 2,4-dinitrophenol (2); and paraquat, a SoxR activator (9).

^bND, not determined. The β-galactosidase activity data are means of the values obtained in three independent experiments with variations of <15%.