TABLE 4.

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

Strain (relevant genotype)	Reporter gene fusion	β-Galactosidase activity (Miller units)b
		Aerobic	Anaerobic
			Fermentative	With nitrate	With nitrite
BSIP1192 (wild type)	PalsS-lacZ1	<10	610	190	600
THB357 (ΔresDE)	PalsS-lacZ1	<10	740	880	940
THB457 (fnr)	PalsS-lacZ1	<10	390	380	330
THB557 (ΔnarGH)	PalsS-lacZ1	<10	530	630	790
MMB112 (fnr ΔnarGH)	PalsS-lacZ1	<10	270	280	250
MMB113 (fnr ΔresDE)	PalsS-lacZ1	<10	410	390	440
BSIP1194 (alsR)	PalsS-lacZ1	<10	40	20	30
BSIP1173 (alsS)	PalsS-lacZ2	<10	610	200	610
BSIP1187 (wild type)	PalsS-lacZΔfnr	<10	<10	<10	<10

^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%.