TABLE 1.

Complementation of an fnr mutant of B. subtilis 168 by fnr_Bl introduced by transformation with plasmid pMW93 (fnr_Bl⁺)

Strain	Nitrate reductase (U/g of protein)a		Increase (fold)
	Aerobic growth	Anaerobic growth
B. subtilis 168	1.6	131	82
B. subtilis 168 fnr::Spcr	0.2	2.6	13
B. subtilis 168 fnr::Spcr (pMW93)	≤0.2	180	900
B. licheniformis	1.4	134	96

^aMeasured in cell extracts with reduced benzyl viologen (averages of three independent assays) (9). Growth occurred in mineral medium with Casamino Acids (9) and 20 mM glucose (aerobic growth) or 20 mM glucose plus 20 mM nitrate (anaerobic growth).