TABLE 3.

Effects of an fnr::Ω mutation on NifL activity in K. pneumoniae UN4495

Strain	Relevant genotypea	Nitrogen source	Presence of oxygen	Expression of nifH′-′lacZ (U/ml/OD600 U)b	Doubling time (h)
UN 4495	Wild type	Glutamine	−	4,400 ± 100	3.5
UN 4495	Wild type	Glutamine	+	220 ± 10	2.0
RAS18	fnr mutant	Glutamine	−	400 ± 20	4.0
RAS18	fnr mutant	Glutamine	+	100 ± 10	2.2
RAS19	fnr mutant/Ptet-fnrc	Glutamine	−	3,800 ± 50	3.8
RAS20	fnr mutant/pACYC184	Glutamine	−	660 ± 30	4.2
RAS26	Wild type/Ptac-nifL mutant nifA	Ammoniumd	−	2,350 ± 100	3.7
RAS26	Wild type/Ptac-nifL mutant nifA	Ammoniumd	+	2,100 ± 100	1.7
RAS27	fnr mutant/Ptac-nifL mutant nifA	Ammoniumd	−	2,200 ± 50	4.1
RAS27	fnr mutant/Ptac-nifL mutant nifA	Ammoniumd	+	2,150 ± 150	1.6
RAS28	Wild type/Ptac-nifLA	Glutamine	−	2,400 ± 30	4.0
RAS28	Wild type/Ptac-nifLA	Glutamine	+	160 ± 5	1.6
RAS29	fnr mutant/Ptac-nifLA	Glutamine	−	430 ± 30	3.6
RAS29	fnr mutant/Ptac-nifLA	Glutamine	+	310 ± 30	1.6
RAS30	4495ΔnifLA/Ptac-nifLA	Glutamine	−	2,450 ± 30	4.1

^anifL mutant nifA, nifL^C184S/C187S nifA (see Materials and Methods); Ptac, under the control of the tac promoter. 

^bData are presented as mean values (± standard errors) of three independent experiments. 

^cK. pneumoniae fnr is expressed under the control of the tet promoter (Ptet). 

^dGrown in the presence of 10 mM ammonium to repress chromosomal nifLA induction.