The nifB gene expression is enhanced in the fnr mutant strains from H. seropedicae.
(A) The activity of the nifB::lacZ fusion (primary y axis) was assayed using cells cultured in NFbHP-Malate liquid medium supplemented with 5 mM NH4Cl (6 ml in 25 ml bottles under air). Every two hours samples were taken for determination of β-galactosidase activity of the wild type strain (SmR1) (black bars), the double fnr1 and fnr3 deletion strain (MB13) (red bars) and the triple fnr deletion strain (MB231) (blue bars). Samples were also taken for measuring the growth (O.D600-nm – secondary y axis) of the strains SmR1 (dotted black lines – squares), MB13 (dotted red lines – triangles) and MB231 (dotted blue lines – circles). (B) Activity of the nifB::lacZ fusion measured under the initial oxygen concentrations of 4.0% (light grey bars), 6.0% (blue bars), 8.0% (orange bars) and 20.8% (black bars) in liquid medium without addition of fixed nitrogen as describe in Methods.