TABLE 2.

Expression of transcriptional napA-lacZ gene fusion in phototrophic and heterotrophic cultures of R. sphaeroides with different nitrogen sources^a

Addition	β-Galactosidase activity (Miller units)
	Anaerobic phototrophic cultures	Aerobic heterotrophic cultures
None (control)	65	190
KNO3	70	210
KNO3 + NH4Cl	73	215
NH4Cl	67	200
KNO3	88	205
KClO3	65	185

^aThe transcriptional napA-lacZ gene fusion was constructed as described in Materials and Methods. β-Galactosidase activity was measured in cells grown under anaerobic phototrophic or aerobic heterotrophic conditions in medium with malate as the carbon source and glutamate as the nitrogen source in the absence (control) or presence of KNO₃, KNO₃ plus NH₄Cl, NH₄Cl, KNO₂, or KClO₃. All these compounds were present at 10 mM except nitrite (1 mM).