Disrupting hierarchical control of nitrogen fixation enables carbon-dependent regulation of ammonia excretion in soil diazotrophs
Fig 5
Ps-NifA-E356K protein is able to escape NifL inhibition in P. stutzeri leading to carbon-dependent ammonia excretion.
The (A) Diagram depicting the modifications in the P. stutzeri nifA-E356K strain (Ps_EKc) compared to wild type P. stutzeri (Ps_WT). Drawings are not to scale. (B) Levels of nifH transcripts in the P. stutzeri Ps_EKc strain in the presence of 5 mM NH4Cl (+N) under 4% O2. (C) Nitrogenase activity in the P. stutzeri strain (Ps_EKc) in the presence of 5 mM NH4Cl (+N) under 8% O2. (D) Comparison of ammonia excretion profiles in different carbon sources. In all cases, the Ps_EKc strain was grown in UMS-PS supplemented with 30 mM glucose, 45 mM malate, 60 mM lactate or 60 mM glycerol (to provide balanced carbon equivalents). In (D) cells (O.D600 nm = 0.2) were incubated at an initial O2 concentration of 8% for 48 hours before ammonia quantification. N.D: not detected. Plots followed by different letters are statistically different according to ANOVA with post-hoc Tukey’s HSD.