TABLE 3.

Regulation of lctEP expression by oxygen tension and nitrate, the regulatory loci resDE, fnr, and alsR, and the nitrate reductase genes narGHJI^a

Strain (relevant genotype)	Fusion	β-Galactosidase activity (Miller units)b
		Aerobic	Anaerobic
			Fermentative	With nitrate	With nitrite
BSIP1185 (wild type)	PlctE-lacZ1	<10	730	140	630
THB361 (ΔresDE)	PlctE-lacZ1	15	180	130	170
THB461 (fnr)	PlctE-lacZ1	<10	330	320	320
THB561 (ΔnarGH)	PlctE-lacZ1	<10	630	620	610
BSIP1188 (alsR)	PlctE-lacZ1	<10	60	30	60
BSIP1190 (lctE)	PlctE-lacZ2	<10	780	510	600
MMB110 (fnr ΔnarGH)	PlctE-lacZ1	<10	480	470	320
MMB110 (fnr ΔresDE)	PlctE-lacZ1	20	220	240	170
BSIP1191 (lctP)	PlctP-lacZ	<10	380	40	390
BSIP1189 (wild type)	PlctE-lacZΔfnr	<10	1,200	520	1,430
MMB114 (fnr)	PlctE-lacZΔfnr	<10	1,315	1,230	1,020
MMB115 (resDE)	PlctE-lacZΔfnr	30	450	320	460
MMB116 (ΔnarGH)	PlctE-lacZΔfnr	<10	1,220	1,210	1,480

^aConstruction of the various B. subtilis strains carrying the indicated lacZ fusions is described in Materials and Methods. The indicated strains were grown either aerobically or anaerobically with 50 mM glucose as a carbon source and ammonia as a nitrogen source, with the indicated additions (10 mM nitrate or nitrite), to the mid-exponential growth phase as outlined in detail before (8, 20). 

^bβ-Galactosidase activities were assayed as described before (16, 20). The results represent averages from at least five independent experiments performed in triplicate, with a standard error of less than 10%.