TABLE 1.

Relative activity of nitrogenase in wild-type and mutant strains^a

Condition and no. of days in BG110	Nitrogenase activity (%) for indicated strain
	Wild type	prpA mutant (A.3)	pknE mutant (8.1)
Anaerobic
2	100	21.7	26.4
4	100	21.8	26.9
Aerobic
2	100	2.2	13.1
4	100	3.4	10.6

^aCells were cultured for 2 or 4 days in BG11₀, and then the standard acetylene reduction assay was performed (13, 31) with 20% acetylene either in air (aerobic conditions) or in argon in the presence of 10 μM dichlorodimethylurea (anaerobic conditions). The amount of ethylene produced was used to compare the activity of nitrogenase of the two mutants relative to that in the wild-type strain. The values shown are the means of at least three measurements in the exponential phase of ethylene production.