Biochemical Genetics of Nitrogen Fixation

Brill, Winston J.

doi:10.1007/978-1-4684-4538-1_23

Cited by 38 publications

(42 citation statements)

References 136 publications

(159 reference statements)

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“…The MoFe protein, which is encoded by nifD and nifK genes, is a α 2 β 2 heterotetramer that contains P-cluster [8Fe-7S] and FeMo-co cluster [Mo-7Fe-9S-C-homocitrate] (Rubio and Ludden 2008;Seefeldt et al 2009). The nifD, nifH, and nifK genes are recognized as structural nif genes since they are responsible for encoding the aforementioned structural subunits (Brill 1983). …”

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confidence: 99%

Effect of GFP-tagging on nitrogen fixation and plant growth promotion of an endophytic diazotrophic strain ofPaenibacillus polymyxa

Padda¹,

Puri²,

Zeng³

et al. 2017

Botany

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Green fluorescent protein (GFP), a renowned marker protein, is typically believed to be inert in affecting the physiology of host bacteria. We analyzed the effects of GFP-tagging on the ability of an endophytic diazotroph, Paenibacillus polymyxa P2b-2R, to fix nitrogen and promote overall growth of corn plants. The growth response and the amount of nitrogen fixed by P2b-2Rgfp-inoculated plants were compared with uninoculated controls and P2b-2R-inoculated plants at three harvests. P2b-2Rgfp inoculation significantly increased the biomass of corn plants as compared to non-inoculated controls and P2b-2R-treated plants. In vitro tests revealed that strains P2b-2R and P2b-2Rgfp possess various plant-growth-promoting characteristics, namely phosphate solubilization, production of siderophores, IAA, ammonia, and enzymes like cellulase, protease, and catalase. P2b-2Rgfp-inoculated plants fixed 18% atmospheric nitrogen, significantly higher than P2b-2R-inoculated plants (15%). This difference led us to compare the expression of structural nif genes (nifH, nifD, nifK) of strains P2b-2R and P2b-2Rgfp. It was observed that expression levels of structural nif genes of strain P2b-2Rgfp were 1.5-fold higher than those of strain P2b-2R. These results indicate that GFP-tagging positively affects the efficacy of strain P2b-2R to promote plant growth and fix nitrogen, perhaps by increasing the expression levels of structural nif genes.

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confidence: 99%

Effect of GFP-tagging on nitrogen fixation and plant growth promotion of an endophytic diazotrophic strain ofPaenibacillus polymyxa

Padda¹,

Puri²,

Zeng³

et al. 2017

Botany

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“…Figure 3 shows that addition of sulfite to cell suspensions of Rhodopseudomonas capsulata (Fig. 3A) and Rhodopseudo- (3,6,7,13,14,18,21,24,25,27,39,47). The data presented in this paper, together with previously published similar findings (18,20,47), show that the reversible inhibition of acetylene reduction activity in vivo by oxygen, termed switch-off, is an inherent property of nitrogen fixation that should be added to the list of similarities among N2-fixing microorganisms.…”

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Mechanism of nitrogenase switch-off by oxygen

Goldberg¹,

Nadler²,

Hochman³

1987

J Bacteriol

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Oxygen caused a reversible inhibition (switch-off) of nitrogenase activity in whole cells of four strains of diazotrophs, the facultative anaerobe Klebsiella pneumoniae and three strains of photosynthetic bacteria (Rhodopseudomonas sphaeroides f. sp. denitrificans and Rhodopseudomonas capsulata strains AD2 and BK5). In K. pneumoniae 50% inhibition of acetylene reduction was attained at an 02 concentration of 0.37 ,uM. Cyanide (90 ,uM), which did not affect acetylene reduction but inhibited whole-cell respiration by 60 to 70%, shifted the 02 concentration that caused 50% inhibition of nitrogenase activity to 2.9 ,uM. A mutant strain of K. pneumoniae, strain AHll, has a respiration rate that is 65 to 75% higher than that of the wild type, but its nitrogenase activity is similar to wild-type activity. Acetylene reduction by whole cells of this mutant was inhibited 50% by 0.20 ,uM 02. Inhibition by CN-of 40 to 50% of the 02 uptake in the mutant shifted the 02 concentration that caused 50% inhibition of nitrogenase to 1.58 ,uM. Thus, when the respiration rates were lower, higher oxygen concentrations were required to inhibit nitrogenase. Reversible inhibition of nitrogenase activity in vivo was caused under anaerobic conditions by other electron acceptors. Addition of 2 mM sulfite to cell suspensions of R. capsulata B10 and R. sphaeroides inhibited nitrogenase activity. Nitrite also inhibited acetylene reduction in whole cells of the photodenitrifier R. sphaeroides but not in R. capsulata B10, which is not capable of enzymatic reduction of NO2-. Lower concentrations of N02-were required to inhibit the activity in N03-grown cells, which have higher activities of nitrite reductase. We suggest that the reversible inhibition of nitrogenase activity (switch-off) by oxygen is a particular case of the general phenomenon of diversion of electrons from nitrogenase to other electron acceptors.Oxygen interferes with biological nitrogen fixation at three different levels. At the genetic level, oxygen acts by repression of nitrogenase synthesis (2,32,41

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“…The production of active nitrogenase requires the expression of at least 15 linked genes arranged in seven operons (3,26). The nif genes are not expressed in the presence of fixed nitrogen (31,32,34), 02 (30), or temperatures above 37°C (5,14,35).…”

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Posttranscriptional control of Klebsiella pneumoniae nif mRNA stability by the nifL product

Collins¹,

Roberts²,

Brill³

1986

J Bacteriol

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Posttranscriptional control of nif mRNA stability was demonstrated by functional and chemical analyses, using specific probes for four niftranscripts. In the wild type, nif transcripts (except nijL4) were stable during derepression, with half-lives of approximately 30 min. They were dramatically destabilized by 02 or elevated temperature (41°C) and to a lesser extent by NH4'. In contrast, the nifLA message was not particularly stable, and posttranscriptional control was not evident. In NifL-strains, both forms of analysis indicated that the nifL product was involved in nif mRNA destabilization in the presence of 02 and NH4'.The complexity of mechanisms for control of gene expression in bacteria is exemplified by regulation of nitrogen fixation in Klebsiella pneumoniae. The production of active nitrogenase requires the expression of at least 15 linked genes arranged in seven operons (3,26). The nif genes are not expressed in the presence of fixed nitrogen (31,32,34), 02 (30), or temperatures above 37°C (5,14,35).Two levels of transcriptional control of nif gene expression have been established. Transcription of nifLA is repressed by NH4' (7,12,19,23,28,33) through the action of the general nitrogen regulatory system (ntr) but is not affected by 02, amino acids, or high temperature (7,11,20,35). The nifA product is required for transcription of all nif operons except nifLA (6,7,11,27). The nifL product turns off transcription of the other nif operons (not nifLA) in response to 02 and fixed N (7,15,24,25,27). Transcription of these operons is turned off at high temperature, but the nifL product is not involved. Rather, it appears that the nifA product is unable to exert positive control at high temperature (5-7, 35).Several papers have addressed the stability of nif mRNA under various conditions (16)(17)(18)26). These papers agree that most nif mRNAs are quite stable under derepressing conditions. In two of these, a significant reduction in chemmical (18) and functional (17, 18) stability of some nif transcripts was observed upon the addition of NH4+. Of these papers, one (17) concluded that the observed effects are not nif specific but reflect a general increase in bulk mRNA turnover. The other paper (18) Our results show that (i) the niftranscripts (except nifLA) are very stable in derepressing conditions, (ii) specific posttranscriptional control of nif mRNA stability is an important feature of the regulation of nif gene expression, and (iii) this specificity requires a nif-encoded protein, the nifL product, which is involved in nifmRNA destabilization in response to 02 and to a lesser extent NH4. The results of previous studies can be explained in light of the models that our results suggest.

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Biochemical Genetics of Nitrogen Fixation

Cited by 38 publications

References 136 publications

Effect of GFP-tagging on nitrogen fixation and plant growth promotion of an endophytic diazotrophic strain ofPaenibacillus polymyxa

Effect of GFP-tagging on nitrogen fixation and plant growth promotion of an endophytic diazotrophic strain ofPaenibacillus polymyxa

Mechanism of nitrogenase switch-off by oxygen

Posttranscriptional control of Klebsiella pneumoniae nif mRNA stability by the nifL product

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