scholarly journals Azotobacter vinelandii NIFL is a flavoprotein that modulates transcriptional activation of nitrogen-fixation genes via a redox-sensitive switch.

1996 ◽  
Vol 93 (5) ◽  
pp. 2143-2148 ◽  
Author(s):  
S. Hill ◽  
S. Austin ◽  
T. Eydmann ◽  
T. Jones ◽  
R. Dixon
Keyword(s):  
Nitrogen Fixation ◽  
Transcriptional Activation ◽  
Azotobacter Vinelandii ◽  
Nitrogen Fixation Genes

Nitrogen fixation: key genetic regulatory mechanisms

2005 ◽  
Vol 33 (1) ◽  
pp. 152-156 ◽  
Author(s):  
I. Martinez-Argudo ◽  
R. Little ◽  
N. Shearer ◽  
P. Johnson ◽  
R. Dixon
Keyword(s):  
Nitrogen Fixation ◽  
Transcriptional Activation ◽  
Azotobacter Vinelandii ◽  
Regulatory Mechanisms ◽  
Excess Oxygen ◽  
Binary Complex ◽  
Fixed Nitrogen ◽  
Signal Transduction Protein ◽  
Sufficient Energy ◽  
Metabolic Signal

The necessity to respond to the level of fixed nitrogen and external oxygen concentrations and to provide sufficient energy for nitrogen fixation imposes common regulatory principles amongst diazotrophs. The NifL–NifA system in Azotobacter vinelandii integrates the signals of redox, fixed-nitrogen and carbon status to regulate nif transcription. Multidomain signalling interactions between NifL and NifA are modulated by redox changes, ligand binding and interaction with the signal-transduction protein GlnK. Under adverse redox conditions (excess oxygen) or when fixed nitrogen is in excess, NifL forms a complex with NifA in which transcriptional activation is prevented. Oxidized NifL forms a binary complex with NifA to inhibit NifA activity. When fixed nitrogen is in excess, the non-covalently modified form of GlnK interacts with NifL to promote the formation of a GlnK–NifL–NifA ternary complex. When the cell re-encounters favourable conditions for nitrogen fixation, it is necessary to deactivate the signals to ensure that the NifL–NifA complex is dissociated so that NifA is free to activate transcription. This is achieved through interactions with 2-oxoglutarate, a key metabolic signal of the carbon status, which binds to the N-terminal GAF (cGMP-specific and stimulated phosphodiesterases, Anabaena adenylate cyclases and Escherichia coliFhlA) domain of NifA.

Nitrogen fixation by cell-free extracts of Klebsiella pneumoniae

1968 ◽  
Vol 14 (1) ◽  
pp. 33-38 ◽  
Author(s):  
M. C. Mahl ◽  
P. W. Wilson
Keyword(s):  
Nitrogen Fixation ◽  
Klebsiella Pneumoniae ◽  
Azotobacter Vinelandii ◽  
Ammonium Ion ◽  
Michaelis Constant ◽  
Nitrogen Gas ◽  
Aerobacter Aerogenes ◽  
Free System ◽  
Evolving System ◽  
A Cell

A cell-free system which permits nitrogen fixation by extracts of Klebsiella pneumoniae M5al (formerly Aerobacter aerogenes) has been developed. It is, essentially, that system described by Bulen and associates for Azotobacter vinelandii, utilizing ATP as a source of energy and dithionite as a source of electrons. The Michaelis constant for fixation has been estimated to be 0.12 atm. The extracts possessed an ATP-dependent hydrogen evolving system. Hydrogen evolution from these extracts was less under nitrogen than under helium in the presence of ATP. Nitrogen gas appears to be the inducer of nitrogen fixation. In the absence of N2, no induction of nitrogenase occurs. Nitrogenase is absent in cells grown on NH4+-N. There is a lag of about 13 h after the introduction of N2 gas into a culture which has depleted its supply of NH4+-N before nitrogenase can be detected. For reasons discussed in the text, this conclusion must be regarded as tentative at this time. Ammonium ion appears to prevent the synthesis of new molecules of nitrogenase without affecting the activity of those already formed.

Expression of the nodulation and nitrogen fixation genes in Rhizobium meliloti during development

Genome ◽  
1989 ◽  
Vol 31 (1) ◽  
pp. 354-360 ◽  
Author(s):  
San Chiun Shen ◽  
Shui Ping Wang ◽  
Guan Qiao Yu ◽  
Jia Bi Zhu
Keyword(s):  
Nitrogen Fixation ◽  
Rhizobium Meliloti ◽  
Abnormal Development ◽  
Wild Type ◽  
Free Living ◽  
Nod Genes ◽  
Nodule Initiation ◽  
Fix Genes ◽  
Nitrogen Fixation Genes

Genes that specify nodulation (nod genes) are only active in the free-living rhizobia or in the nodule initiation state of rhizobia. As soon as the repression of nod genes occurs in the bacteroids of the nodule, nifA is induced, while ntrC is inactivated and thus the nifA-mediated nif/fix genes are turned on. Limitation of available oxygen brings about the induction of nifA, which reflects the actual status of nif/fix gene activities in symbiotic state of rhizobia. Oxygen thus appears to be a major symbiotic signal to the expression of bacteroid nif/fix genes. Mutation of nifA or shortage of nifA product in wild-type rhizobia caused by the inhibition of multicopy nifH/fixA promoters leads to an abnormal development of nodules and premature degradation of bacteroids in nodules.Key words: nitrogen fixation, nodulation, nif/fix regulation, nifA mutant.

The flavin transferase ApbE flavinylates the ferredoxin:NAD+-oxidoreductase Rnf required for N2 fixation in Azotobacter vinelandii

2021 ◽  
Author(s):  
Yulia V Bertsova ◽  
Marina V Serebryakova ◽  
Alexander A Baykov ◽  
Alexander V Bogachev
Keyword(s):  
Nitrogen Fixation ◽  
Azotobacter Vinelandii ◽  
Growth Defect ◽  
Deficient Mutant ◽  
Fixed Nitrogen ◽  
Oxidoreductase Activity ◽  
Threonine Residue ◽  
Ferredoxin Reductase ◽  
Relative Contribution ◽  
Fixation System

Abstract Azotobacter vinelandii, the model microbe in nitrogen fixation studies, uses the ferredoxin:NAD+-oxidoreductase Rnf to regenerate ferredoxin (flavodoxin) acting as an electron donor for nitrogenase. However, the relative contribution of Rnf into nitrogenase functioning is unknown because this bacterium contains another ferredoxin reductase, FixABCX. Furthermore, Rnf is flavinylated in the cell, but the importance and pathway of this modification reaction also remain largely unknown. We have constructed A. vinelandii cells with impaired activities of FixABCX and/or putative flavin transferase ApbE. The ApbE-deficient mutant could not produce covalently flavinylated membrane proteins and demonstrated a markedly decreased flavodoxin:NAD+ oxidoreductase activity and significant growth defect under diazotrophic conditions. The double ΔFix/ΔApbE mutation abolished the flavodoxin:NAD+ oxidoreductase activity and the ability of A. vinelandii to grow in the absence of fixed nitrogen source. ApbE flavinylated a truncated RnfG subunit of Rnf1 by forming a phosphoester bond between FMN and a threonine residue. These findings indicate that Rnf (presumably its Rnf1 form) is the major ferredoxin-reducing enzyme in the nitrogen fixation system and that the activity of Rnf depends on its covalent flavinylation by the flavin transferase ApbE.

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