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Control of nitrogen fixation and ammonia excretion in Azorhizobium caulinodans. PLoS Genet 2022; 18:e1010276. [PMID: 35727841 PMCID: PMC9249168 DOI: 10.1371/journal.pgen.1010276] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2022] [Revised: 07/01/2022] [Accepted: 05/26/2022] [Indexed: 11/19/2022] Open
Abstract
Due to the costly energy demands of nitrogen (N) fixation, diazotrophic bacteria have evolved complex regulatory networks that permit expression of the catalyst nitrogenase only under conditions of N starvation, whereas the same condition stimulates upregulation of high-affinity ammonia (NH3) assimilation by glutamine synthetase (GS), preventing excess release of excess NH3 for plants. Diazotrophic bacteria can be engineered to excrete NH3 by interference with GS, however control is required to minimise growth penalties and prevent unintended provision of NH3 to non-target plants. Here, we tested two strategies to control GS regulation and NH3 excretion in our model cereal symbiont Azorhizobium caulinodans AcLP, a derivative of ORS571. We first attempted to recapitulate previous work where mutation of both PII homologues glnB and glnK stimulated GS shutdown but found that one of these genes was essential for growth. Secondly, we expressed unidirectional adenylyl transferases (uATs) in a ΔglnE mutant of AcLP which permitted strong GS shutdown and excretion of NH3 derived from N2 fixation and completely alleviated negative feedback regulation on nitrogenase expression. We placed a uAT allele under control of the NifA-dependent promoter PnifH, permitting GS shutdown and NH3 excretion specifically under microaerobic conditions, the same cue that initiates N2 fixation, then deleted nifA and transferred a rhizopine nifAL94Q/D95Q-rpoN controller plasmid into this strain, permitting coupled rhizopine-dependent activation of N2 fixation and NH3 excretion. This highly sophisticated and multi-layered control circuitry brings us a step closer to the development of a "synthetic symbioses” where N2 fixation and NH3 excretion could be specifically activated in diazotrophic bacteria colonising transgenic rhizopine producing cereals, targeting delivery of fixed N to the crop while preventing interaction with non-target plants. Inoculation of cereal crops with associative diazotrophic bacteria that convert atmospheric nitrogen (N2) into ammonia (NH3) could be used to sustainably improve delivery of nitrogen to crops. However, due to the costly energy demands of N2 fixation, bacteria restrict excess production of NH3 and release to the plants. Diazotrophs can be engineered for excess NH3 production and release, however genetic control is required to minimise growth penalties and prevent unintended provision of NH3 to non-target weed species. Here, we engineer coupled control of N2 fixation and NH3 release in response to the signalling molecule rhizopine supplemented in vitro. This control circuitry represents a prototype for the future development of a “synthetic symbiosis” where bacterial N2 fixation and NH3 excretion could be specifically activated following colonisation of transgenic rhizopine producing cereals in the field, minimising bacterial energy requirements and preventing provision of NH3 to non-target plants.
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Abstract
Inoculation of cereals with diazotrophic (N2-fixing) bacteria offers a sustainable alternative to the application of nitrogen fertilizers in agriculture. While natural diazotrophs have evolved multilayered regulatory mechanisms that couple N2 fixation with assimilation of the product NH3 and prevent release to plants, genetic modifications can permit excess production and excretion of NH3. However, a lack of stringent host-specificity for root colonization by the bacteria would allow growth promotion of target and nontarget plants species alike. Here, we exploit synthetic transkingdom signaling to establish plant host-specific control of the N2-fixation catalyst nitrogenase in Azorhizobium caulinodans occupying barley roots. This work demonstrates how partner-specific interactions can be established to avoid potential growth promotion of nontarget plants. Engineering N2-fixing symbioses between cereals and diazotrophic bacteria represents a promising strategy to sustainably deliver biologically fixed nitrogen (N) in agriculture. We previously developed novel transkingdom signaling between plants and bacteria, through plant production of the bacterial signal rhizopine, allowing control of bacterial gene expression in association with the plant. Here, we have developed both a homozygous rhizopine producing (RhiP) barley line and a hybrid rhizopine uptake system that conveys upon our model bacterium Azorhizobium caulinodans ORS571 (Ac) 103-fold improved sensitivity for rhizopine perception. Using this improved genetic circuitry, we established tight rhizopine-dependent transcriptional control of the nitrogenase master regulator nifA and the N metabolism σ-factor rpoN, which drove nitrogenase expression and activity in vitro and in situ by bacteria colonizing RhiP barley roots. Although in situ nitrogenase activity was suboptimally effective relative to the wild-type strain, activation was specific to RhiP barley and was not observed on the roots of wild-type plants. This work represents a key milestone toward the development of a synthetic plant-controlled symbiosis in which the bacteria fix N2 only when in contact with the desired host plant and are prevented from interaction with nontarget plant species.
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Huergo LF, Chandra G, Merrick M. PIIsignal transduction proteins: nitrogen regulation and beyond. FEMS Microbiol Rev 2013; 37:251-83. [DOI: 10.1111/j.1574-6976.2012.00351.x] [Citation(s) in RCA: 141] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2012] [Revised: 07/26/2012] [Accepted: 07/26/2012] [Indexed: 01/12/2023] Open
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Huergo LF, Souza EM, Steffens MBR, Yates MG, Pedrosa FO, Chubatsu LS. Regulation of glnB gene promoter expression in Azospirillum brasilense by the NtrC protein. FEMS Microbiol Lett 2003; 223:33-40. [PMID: 12798997 DOI: 10.1016/s0378-1097(03)00346-x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
Abstract
In Azospirillum brasilense the glnB and glnA genes are clustered in an operon regulated by three different promoters: two located upstream of glnB (glnBp1-sigma(70), and glnBp2-sigma(N)) and one as yet unidentified promoter, in the glnBA intergenic region. We have investigated the expression of the glnB gene promoter using glnB-lacZ gene fusions, mutation analysis, heterologous expression and DNA band-shift assays. Deletion of the glnB promoter region showed that NtrC-binding sequences were essential for glnB expression under nitrogen limitation. The A. brasilense NtrC protein activated transcription of glnB-lacZ fusions in the heterologous genetic background of Escherichia coli. Expression of glnB-lacZ fusions in two A. brasilense ntrC mutants differed from that in the wild-type strain. In vitro studies also indicated that the purified NtrC protein from E. coli was able to bind to the glnB promoter region of A. brasilense. Our results show that the NtrC protein activates glnBglnA expression under nitrogen limitation in A. brasilense.
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Affiliation(s)
- Luciano F Huergo
- Department of Biochemistry and Molecular Biology, Universidade Federal do Paraná, CP 19046, 81531-990, PR, Curitiba, Brazil
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Martin DE, Reinhold-Hurek B. Distinct roles of P(II)-like signal transmitter proteins and amtB in regulation of nif gene expression, nitrogenase activity, and posttranslational modification of NifH in Azoarcus sp. strain BH72. J Bacteriol 2002; 184:2251-9. [PMID: 11914357 PMCID: PMC134945 DOI: 10.1128/jb.184.8.2251-2259.2002] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
P(II)-like signal transmitter proteins, found in Bacteria, Archaea, and plants, are known to mediate control of carbon and nitrogen assimilation. They indirectly regulate the activity of key metabolic enzymes and transcription factors by protein-protein interactions with signal transduction proteins. Many Proteobacteria harbor two paralogous P(II)-like proteins, GlnB and GlnK, whereas a novel third P(II) paralogue (GlnY) was recently identified in Azoarcus sp. strain BH72, a diazotrophic endophyte of grasses. In the present study, evidence was obtained that the P(II)-like proteins have distinct roles in mediating nitrogen and oxygen control of nif gene transcription and nitrogenase activity. Full repression of nif gene transcription in the presence of a combined nitrogen source or high oxygen concentrations was observed in wild-type and glnB and glnK knockout mutants, revealing that GlnB and GlnK can complement each other in mediating the repression. In contrast, in a glnBK double mutant strain in the presence of only GlnY, nif gene transcription was still detectable, albeit at a lower level, on nitrate or 20% oxygen. As another level of control, nitrogenase activity was regulated by at least three types of mechanisms in strain BH72: covalent modification of dinitrogenase reductase (NifH), probably by ADP-ribosylation, and two other, unknown means. Functional inactivation upon ammonium addition (switch-off) required the putative high-affinity ammonium transporter AmtB and GlnK, but not GlnB or GlnY. Functional inactivation in response to anaerobiosis did not depend on AmtB, GlnK, or GlnB. In contrast, covalent modification of NifH required both GlnB and GlnK and AmtB as response to ammonium addition, whereas it required either GlnB or GlnK and not AmtB when cells were shifted to anaerobiosis. In a glnBK double mutant expressing only GlnY, NifH modification was completely abolished, further revealing functional differences between the three P(II) paralogues.
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Affiliation(s)
- Dietmar E Martin
- Group Symbiosis Research, Max Planck Institute for Terrestrial Microbiology, D-35043 Marburg, Germany
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Dombrecht B, Marchal K, Vanderleyden J, Michiels J. Prediction and overview of the RpoN-regulon in closely related species of the Rhizobiales. Genome Biol 2002; 3:RESEARCH0076. [PMID: 12537565 PMCID: PMC151178 DOI: 10.1186/gb-2002-3-12-research0076] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2002] [Revised: 09/16/2002] [Accepted: 10/18/2002] [Indexed: 11/24/2022] Open
Abstract
BACKGROUND In the rhizobia, a group of symbiotic Gram-negative soil bacteria, RpoN (sigma54, sigmaN, NtrA) is best known as the sigma factor enabling transcription of the nitrogen fixation genes. Recent reports, however, demonstrate the involvement of RpoN in other symbiotic functions, although no large-scale effort has yet been undertaken to unravel the RpoN-regulon in rhizobia. We screened two complete rhizobial genomes (Mesorhizobium loti, Sinorhizobium meliloti) and four symbiotic regions (Rhizobium etli, Rhizobium sp. NGR234, Bradyrhizobium japonicum, M. loti) for the presence of the highly conserved RpoN-binding sites. A comparison was also made with two closely related non-symbiotic members of the Rhizobiales (Agrobacterium tumefaciens, Brucella melitensis). RESULTS A highly specific weight-matrix-based screening method was applied to predict members of the RpoN-regulon, which were stored in a highly annotated and manually curated dataset. Possible enhancer-binding proteins (EBPs) controlling the expression of RpoN-dependent genes were predicted with a profile hidden Markov model. CONCLUSIONS The methodology used to predict RpoN-binding sites proved highly effective as nearly all known RpoN-controlled genes were identified. In addition, many new RpoN-dependent functions were found. The dependency of several of these diverse functions on RpoN seems species-specific. Around 30% of the identified genes are hypothetical. Rhizobia appear to have recruited RpoN for symbiotic processes, whereas the role of RpoN in A. tumefaciens and B. melitensis remains largely to be elucidated. All species screened possess at least one uncharacterized EBP as well as the usual ones. Lastly, RpoN could significantly broaden its working range by direct interfering with the binding of regulatory proteins to the promoter DNA.
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Affiliation(s)
- Bruno Dombrecht
- Centre of Microbial and Plant Genetics, Katholieke Universiteit Leuven, 3001 Heverlee, Belgium
| | - Kathleen Marchal
- ESAT-SCD, Katholieke Universiteit Leuven, 3001 Heverlee, Belgium
| | - Jos Vanderleyden
- Centre of Microbial and Plant Genetics, Katholieke Universiteit Leuven, 3001 Heverlee, Belgium
| | - Jan Michiels
- Centre of Microbial and Plant Genetics, Katholieke Universiteit Leuven, 3001 Heverlee, Belgium
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Benelli EM, Buck M, de Souza EM, Yates MG, Pedrosa FO. Uridylylation of the PII protein from Herbaspirillum seropedicae. Can J Microbiol 2001; 47:309-14. [PMID: 11358170 DOI: 10.1139/w01-018] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The PII protein is apparently involved in the control of NifA activity in Herbaspirillum seropedicae. To evaluate the probable role of PII in signal transduction, uridylylation assays were conducted with purified H. seropedicae PII and Escherichia coli GlnD, or a cell-free extract of H. seropedicae as sources of uridylylating activity. The results showed that alpha-ketoglutarate and ATP stimulate uridylylation whereas glutamine inhibits uridylylation. Deuridylylation of PII-UMP was dependent on glutamine and inhibited by ATP and alpha-ketoglutarate. PII uridylylation and (or) deuridylylation in response to these effectors suggests that PII is a nitrogen level signal transducer in H. seropedicae.
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Affiliation(s)
- E M Benelli
- Department of Biochemistry, Federal University of Parana, Curitiba, Brazil
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Ye ZH, Yang ZY, Chan GY, Wong MH. Growth response of Sesbania rostrata and S. cannabina to sludge-amended lead/zinc mine tailings. A greenhouse study. ENVIRONMENT INTERNATIONAL 2001; 26:449-455. [PMID: 11392765 DOI: 10.1016/s0160-4120(01)00026-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Legumes are ideal for revegetation of metal-mined wastelands which lack nitrogen (N). A greenhouse study was conducted to investigate the feasibility of using Sesbania rostrata and S. cannabina for the reclamation of lead/zinc (Pb/Zn) mine tailings and to evaluate the effects of organic amendment using sewage sludge (0%, 25%, 50%, and 75%, v/v). The results showed that both species could continue to grow on the highly toxic tailings substrata for at least 80 days, although their growth suffered from adverse effects. That S. rostrata with stem and root nodules had better growth (biomass, growth rates, and biomass of nodules) than S. cannabina suggested that S. rostrata is a better choice as a pioneer species for revegetation of the mine tailings. Stem nodules had less obvious adverse effects imposed by tailings than root nodules. Application of sewage sludge increased contents of total carbon (C), N, phosphorus (P), and potassium (K), and reduced total Zn, Pb, Cd, and DTPA-extractable Pb and Cd in tailings substrata. These, in turn, reduced metal (Zn, Pb, and Cd) uptake and accumulation in plant tissues, and improved plant growth performance, including biomass, growth rates, stem nodulation. Fifty percent (v/v) of sludge application rate was the best loading rate for plant growth.
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Affiliation(s)
- Z H Ye
- Institute for Natural Resource and Environmental Management, and Department of Biology, Hong Kong Baptist University, Kowloon Tong, Kowloon, Hong Kong, SAR, People's Republic of China
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Arcondéguy T, Jack R, Merrick M. P(II) signal transduction proteins, pivotal players in microbial nitrogen control. Microbiol Mol Biol Rev 2001; 65:80-105. [PMID: 11238986 PMCID: PMC99019 DOI: 10.1128/mmbr.65.1.80-105.2001] [Citation(s) in RCA: 312] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The P(II) family of signal transduction proteins are among the most widely distributed signal proteins in the bacterial world. First identified in 1969 as a component of the glutamine synthetase regulatory apparatus, P(II) proteins have since been recognized as playing a pivotal role in control of prokaryotic nitrogen metabolism. More recently, members of the family have been found in higher plants, where they also potentially play a role in nitrogen control. The P(II) proteins can function in the regulation of both gene transcription, by modulating the activity of regulatory proteins, and the catalytic activity of enzymes involved in nitrogen metabolism. There is also emerging evidence that they may regulate the activity of proteins required for transport of nitrogen compounds into the cell. In this review we discuss the history of the P(II) proteins, their structures and biochemistry, and their distribution and functions in prokaryotes. We survey data emerging from bacterial genome sequences and consider other likely or potential targets for control by P(II) proteins.
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Affiliation(s)
- T Arcondéguy
- Department of Microbiology, John Innes Centre, Norwich, United Kingdom
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Martin DE, Hurek T, Reinhold-Hurek B. Occurrence of three PII-like signal transmitter proteins in the diazotrophic proteobacterium Azoarcus sp. BH72. Mol Microbiol 2000; 38:276-88. [PMID: 11069654 DOI: 10.1046/j.1365-2958.2000.02095.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PII-like signal transmitter proteins are involved in the regulation of ammonium assimilation and nitrogen fixation. We report the identification of three PII-like proteins in the diazotrophic, endophytic proteobacterium Azoarcus sp. BH72, encoded by glnB (monocistronically transcribed) or in the glnKamtB and glnYamtY operons. Phylogenetic analysis revealed that glnB, glnK and glnY represent distinct lineages within the Proteobacteria. A combined approach of two-dimensional gel electrophoresis, Western blotting with paralogue-specific antibodies, N-terminal sequencing and marker exchange mutagenesis allowed us to analyse PII protein expression of Azoarcus sp. BH72 in vivo. GlnK and GlnB were present on all nitrogen sources. Knock-out mutant analysis revealed that GlnB was the only detectable PII protein in a glnK- background, whereas GlnY was only present in a glnK/glnB- double mutant. Nitrogen limitation enhanced transcript abundance of glnK strongly, glnY moderately and glnB not at all in wild-type, glnB-/glnK- or glnK- backgrounds respectively. Phenotypic characterization of knock-out mutants revealed that, unlike in other Proteobacteria, neither glnK nor glnB were essential for nitrogen fixation. As the growth of a double mutant was drastically impaired only on minimal media, both proteins are probably involved in the control of ammonium and nitrate assimilation. The PII-like proteins differed from each other in details of N-sensing. They were covalently modified by uridylylation upon nitrogen limitation, as shown by mass spectrometry; however, the modification patterns in relation to the supplied nitrogen source differed. The novel paralogue GlnY was unusual, as it only occurred in the uridylylated state in vivo and thus lacked a deuridylylation response to nitrogen excess.
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Affiliation(s)
- D E Martin
- Max-Planck-Institute for Terrestrial Microbiology, Group Symbiosis Research, D-35043 Marburg, Germany
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Barrios H, Valderrama B, Morett E. Compilation and analysis of sigma(54)-dependent promoter sequences. Nucleic Acids Res 1999; 27:4305-13. [PMID: 10536136 PMCID: PMC148710 DOI: 10.1093/nar/27.22.4305] [Citation(s) in RCA: 294] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Promoters recognized by the RNA-polymerase with the alternative sigma factor sigma(54) (Esigma54) are unique in having conserved positions around -24 and -12 nucleotides upstream from the transcriptional start site, instead of the typical -35 and -10 boxes. Here we compile 186 -24/-12 promoter sequences reported in the literature and generate an updated and extended consensus sequence. The use of the extended consensus increases the probability of identifying genuine -24/-12 promoters. The effect of several reported mutations at the -24/-12 elements on RNA-polymerase binding and promoter strength is discussed in the light of the updated consensus.
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Affiliation(s)
- H Barrios
- Departamento de Reconocimiento Molecular y Bioestructura, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos 62271, México
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12
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Cheng J, Johansson M, Nordlund S. Expression of P(II) and glutamine synthetase is regulated by P(II), the ntrBC products, and processing of the glnBA mRNA in Rhodospirillum rubrum. J Bacteriol 1999; 181:6530-4. [PMID: 10515946 PMCID: PMC103791 DOI: 10.1128/jb.181.20.6530-6534.1999] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have studied the transcription of the glnB and glnA genes in Rhodospirillum rubrum with firefly luciferase as a reporter enzyme. Under NH(4)(+) and N(2) conditions, glnBA was cotranscribed from a weak and a strong promoter. In nitrogen-fixing cultures, activity of the latter was highly enhanced by NtrC, but transcription from both promoters occurred under both conditions. There is no promoter controlling transcription of glnA alone, supporting our proposal that the glnA mRNA is produced by processing.
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Affiliation(s)
- J Cheng
- Department of Biochemistry, Arrhenius Laboratories for Natural Sciences, Stockholm University, S-106 91 Stockholm, Sweden
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Lee HM, Vázquez-Bermúdez MF, de Marsac NT. The global nitrogen regulator NtcA regulates transcription of the signal transducer PII (GlnB) and influences its phosphorylation level in response to nitrogen and carbon supplies in the Cyanobacterium synechococcus sp. strain PCC 7942. J Bacteriol 1999; 181:2697-702. [PMID: 10217756 PMCID: PMC93707 DOI: 10.1128/jb.181.9.2697-2702.1999] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The PII protein is encoded by a unique glnB gene in Synechococcus sp. strain PCC 7942. Its expression has been analyzed in the wild type and in NtcA-null mutant cells grown under different conditions of nitrogen and carbon supply. RNA-DNA hybridization experiments revealed the presence of one transcript species 680 nucleotides long, whatever the nutrient conditions tested. A second transcript species, 620 nucleotides long, absent in the NtcA null mutant, was observed in wild-type cells that were nitrogen starved for 2 h under both high and low CO2 and in the presence of nitrate under a high CO2 concentration. Primer extension analysis indicated that the two transcript species are generated from two tandem promoters, a sigma70 Escherichia coli-type promoter and an NtcA-dependent promoter, located 120 and 53 nucleotides, respectively, from the glnB initiation codon. The NtcA-dependent promoter is up-regulated under the conditions mentioned above, while the sigma70 E. coli-type promoter displays constitutive levels of transcripts in the NtcA null mutant and slightly different levels in the wild-type cells, depending on the nitrogen and carbon supplies. In general, a good correlation between the amounts of the two transcript species and that of the PII protein was observed, as revealed by immunodetection with specific antibodies. The phosphorylation level of PII in the wild type is inversely correlated with nitrogen availability and directly correlated with higher CO2 concentration. This regulation is correspondingly less stringent in the NtcA null mutant cells. In contrast, the dephosphorylation of PII is NtcA independent.
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Affiliation(s)
- H M Lee
- Département de Biochimie et Génétique Moléculaire, Unité de Physiologie Microbienne, Institut Pasteur, 75724 Paris Cedex 15, France
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Michel-Reydellet N, Kaminski PA. Azorhizobium caulinodans PII and GlnK proteins control nitrogen fixation and ammonia assimilation. J Bacteriol 1999; 181:2655-8. [PMID: 10198037 PMCID: PMC93699 DOI: 10.1128/jb.181.8.2655-2658.1999] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We herein report that Azorhizobium caulinodans PII and GlnK are not necessary for glutamine synthetase (GS) adenylylation whereas both proteins are required for complete GS deadenylylation. The disruption of both glnB and glnK resulted in a high level of GS adenylylation under the condition of nitrogen fixation, leading to ammonium excretion in the free-living state. PII and GlnK also controlled nif gene expression because NifA activated nifH transcription and nitrogenase activity was derepressed in glnB glnK double mutants, but not in wild-type bacteria, grown in the presence of ammonia.
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Affiliation(s)
- N Michel-Reydellet
- Unité de Physiologie Cellulaire, Centre National de la Recherche Scientifique, Unité Recherche Associée 1300, Département des Biotechnologies, Institut Pasteur, 75724 Paris Cedex 15, France
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15
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Mandon K, Michel-Reydellet N, Encarnación S, Kaminski PA, Leija A, Cevallos MA, Elmerich C, Mora J. Poly-beta-hydroxybutyrate turnover in Azorhizobium caulinodans is required for growth and affects nifA expression. J Bacteriol 1998; 180:5070-6. [PMID: 9748438 PMCID: PMC107541 DOI: 10.1128/jb.180.19.5070-5076.1998] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Azorhizobium caulinodans is able to fix nitrogen in the free-living state and in symbiosis with the tropical legume Sesbania rostrata. The bacteria accumulate poly-beta-hydroxybutyrate (PHB) under both conditions. The structural gene for PHB synthase, phbC, was inactivated by insertion of an interposon. The mutant strains obtained were devoid of PHB, impaired in their growth properties, totally devoid of nitrogenase activity ex planta (Nif-), and affected in nucleotide pools and induced Fix- nodules devoid of bacteria. The Nif- phenotype was the consequence of the lack of nifA transcription. Nitrogenase activity was partially restored to a phbC mutant by constitutive expression of the nifA gene. However, this constitutive nifA expression had no effect on the nucleotide content or on growth of the phbC mutant. It is suggested that PHB is required for maintaining the reducing power of the cell and therefore the bacterial growth. These observations also suggest a new control of nifA expression to adapt nitrogen fixation to the availability of carbon and reducing equivalents.
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Affiliation(s)
- K Mandon
- Departamento de Ecología Molecular, Centro de Investigación sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, Mexico
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16
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Hanson TE, Forchhammer K, de Marsac NT, Meeks JC. Characterization of the glnB gene product of Nostoc punctiforme strain ATCC 29133: glnB or the PII protein may be essential. MICROBIOLOGY (READING, ENGLAND) 1998; 144 ( Pt 6):1537-1547. [PMID: 9639924 DOI: 10.1099/00221287-144-6-1537] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Bacterial PII proteins, encoded by glnB genes, are central signalling molecules in nitrogen regulatory pathways and are modulated by post-translational modification in response to the cellular nitrogen status. The glnB gene was cloned from the filamentous heterocyst-forming cyanobacterium Nostoc punctiforme strain ATCC 29133 (PCC 73102) by heterologous hybridization to a Synechococcus sp. strain PCC 7942 gene fragment. Expression of the cloned gene was verified by hybridization to N. punctiforme total RNA and a single cross-reactive polypeptide was observed in immunoblots of N. punctiforme extracts probed with anti-Synechococcus 7942 PII antiserum. Modification of the purified N. punctiforme PII protein by a Synechococcus 7942 PII kinase was observed, but modified forms of PII were not detected in extracts of N. punctiforme from a variety of incubation conditions. The N. punctiforme glnB gene could not be disrupted by targeted gene replacement unless a second copy of glnB was provided in trans, suggesting that the gene or gene product is essential for growth under the conditions tested.
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Affiliation(s)
- Thomas E Hanson
- Section of Microbiology, University of California, One Shields Avenue, Davis, CA 95616, USA
| | - Karl Forchhammer
- Lehrstuhl für Mikrobiologie der Universität München, Maria-Ward-Str. 1a, D-80638 München, Germany
| | - Nicole Tandeau de Marsac
- Unité de Physiologie Microbienne, Département de Biochimie et Génétique Moléculaire, Institut Pasteur, 28 rue du Docteur Roux, 75724 Paris Cedex 15, France
| | - John C Meeks
- Section of Microbiology, University of California, One Shields Avenue, Davis, CA 95616, USA
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