The Experts below are selected from a list of 264 Experts worldwide ranked by ideXlab platform
Sanfeng Chen - One of the best experts on this subject based on the ideXlab platform.
-
evolution and functional analysis of orf1 within Nif Gene cluster from paenibacillus graminis rsa19
International Journal of Molecular Sciences, 2019Co-Authors: Xiaomeng Liu, Haowei Zhang, Sanfeng ChenAbstract:Paenibacillus is a genus of Gram-positive, facultative anaerobic and endospore-forming bacteria. Genomic sequence analysis has revealed that a compact Nif (nitrogen fixation) Gene cluster comprising 9–10 Genes NifBHDKENX(orf1)hesANifV is conserved in diazotrophic Paenibacillus species. The evolution and function of the orf1 Gene within the Nif Gene cluster of Paenibacillus species is unknown. In this study, a careful comparison analysis of the compositions of the Nif Gene clusters from various diazotrophs revealed that orf1 located downstream of NifENX was identified in anaerobic Clostridium ultunense, the facultative anaerobic Paenibacillus species and aerobic diazotrophs (e.g., Azotobacter vinelandii and Azospirillum brasilense). The predicted amino acid sequences encoded by the orf1 Gene, part of the Nif Gene cluster NifBHDKENXorf1hesANifV in Paenibacillus graminis RSA19, showed 60–90% identity with those of the orf1 Genes located downstream of NifENX from different diazotrophic Paenibacillus species, but shared no sigNificant identity with those of the orf1 Genes from different taxa of diazotrophic organisms. Transcriptional analysis showed that the orf1 Gene was expressed under nitrogen fixation conditions from the promoter located upstream from NifB. Mutational analysis suggested that the orf1 Gene functions in nitrogen fixation in the presence of a high concentration of O2.
-
suppression of hesa mutation on nitrogenase activity in paenibacillus polymyxa wly78 with the addition of high levels of molybdate or cystine
PeerJ, 2019Co-Authors: Xiaomeng Liu, Xiyun Zhao, Sanfeng ChenAbstract:The diazotrophic Paenibacillus polymyxa WLY78 possesses a minimal nitrogen fixation Gene cluster consisting of nine Genes (NifB NifH NifD NifK NifE NifN NifX hesA and NifV). Notably, the hesA Gene contained within the Nif Gene cluster is also found within Nif Gene clusters among diazotrophic cyanobacteria and Frankia. The predicted product HesA is a member of the ThiF-MoeB-HesA family containing an N-terminal nucleotide binding domain and a C-terminal MoeZ/MoeB-like domain. However, the function of hesA Gene in nitrogen fixation is unknown. In this study, we demonstrate that the hesA mutation of P. polymyxa WLY78 leads to nearly complete loss of nitrogenase activity. The effect of the mutation can be partially suppressed by the addition of high levels of molybdate or cystine. However, the nitrogenase activity of the hesA mutant could not be restored by Klebsiella oxytoca NifQ or Escherichia coli moeB completely. In addition, the hesA mutation does not affect nitrate reductase activity of P. polymyxa WLY78. Our results demonstrate hesA is a novel Gene specially required for nitrogen fixation and its role is related to introduction of S and Mo into the FeMo-co of nitrogenase.
-
genome wide transcriptional analysis of the recombinant escherichia coli 78 7 carrying a Nif Gene operon of paenibacillus polymyxa wly78
2018Co-Authors: Haowen Shi, Sanfeng ChenAbstract:ObjectiveThe nitrogen fixation (Nif) Gene operon (NifBHDKEfNXhesANifV) of Paenibacillus polymyxa WLY78 encoding the nitrogenase enabled Escherichia coli to synthesize functional nitrogenase. The genome-wide transcriptional profiling of the recombinant E. coli 78-7 was examined for improving its nitrogenase activity. MethodsThe transcriptomic analysis of the recombinant E. coli 78-7 cultured under non-N2-fixing (air and 100 mmol/L NH4+) and N2-fixing (without O2 and NH4+) conditions was implemented. ResultsThese results reveal that Nif Genes were sigNificantly transcribed under both conditions, indicating that the negative regulation of Nif Gene transcription by O2 and NH4+ is bypassed in heteroGeneous E. coli. The non-Nif Genes specifically required for nitrogen fixation, such as mod, cys and feoAB encoding transporters of Mo, S, Fe and electron transporters, respectively, were transcribed at different levels in both conditions. The transcription levels of suf operon and isc system specific for the synthesis of the Fe-S cluster varied greatly. The Genes involved in nitrogen metabolism were notably up-regulated in N2-fixing conditions. ConclusionThese data suggest that the non-Nif Genes specifically required for nitrogen fixation in recombinant E. coli had obvious effects on its expression of nitrogenase. Our results will provide valuable exploration regarding the improvement for nitrogenase activity of heteroGeneous hosts.
-
a minimal nitrogen fixation Gene cluster from paenibacillus sp wly78 enables expression of active nitrogenase in escherichia coli
PLOS Genetics, 2013Co-Authors: Liying Wang, Lihong Zhang, Zhangzhi Liu, Dehua Zhao, Xiaomeng Liu, Bo Zhang, Jianbo Xie, Yuanyuan Hong, Sanfeng ChenAbstract:Most biological nitrogen fixation is catalyzed by molybdenum-dependent nitrogenase, an enzyme complex comprising two component proteins that contains three different metalloclusters. Diazotrophs contain a common core of nitrogen fixation Nif Genes that encode the structural subunits of the enzyme and components required to synthesize the metalloclusters. However, the complement of Nif Genes required to enable diazotrophic growth varies sigNificantly amongst nitrogen fixing bacteria and archaea. In this study, we identified a minimal Nif Gene cluster consisting of nine Nif Genes in the genome of Paenibacillus sp. WLY78, a gram-positive, facultative anaerobe isolated from the rhizosphere of bamboo. We demonstrate that the Nif Genes in this organism are organized as an operon comprising NifB, NifH, NifD, NifK, NifE, NifN, NifX, hesA and NifV and that the Nif cluster is under the control of a σ70 (σA)-dependent promoter located upstream of NifB. To investigate Genetic requirements for diazotrophy, we transferred the Paenibacillus Nif cluster to Escherichia coli. The minimal Nif Gene cluster enables synthesis of catalytically active nitrogenase in this host, when expressed either from the native NifB promoter or from the T7 promoter. Deletion analysis indicates that in addition to the core Nif Genes, hesA plays an important role in nitrogen fixation and is responsive to the availability of molybdenum. Whereas Nif transcription in Paenibacillus is regulated in response to nitrogen availability and by the external oxygen concentration, transcription from the NifB promoter is constitutive in E. coli, indicating that negative regulation of Nif transcription is bypassed in the heterologous host. This study demonstrates the potential for engineering nitrogen fixation in a non-nitrogen fixing organism with a minimum set of nine Nif Genes.
-
Comparison of the Paenibacillus sp. WLY78 Nif Gene cluster with representative clusters from diverse diazotrophic bacteria and archaea.
2013Co-Authors: Liying Wang, Lihong Zhang, Zhangzhi Liu, Dehua Zhao, Xiaomeng Liu, Bo Zhang, Jianbo Xie, Yuanyuan Hong, Sanfeng ChenAbstract:(A) Azotobacter vinelandii, (B) Heliobacterium chlorum, (C) Clostridium acetobutylicum W5, (D) Frankia sp. EAN1pec, (E) Methanococus maripaludis, (F) Anabaena variabilis ATCC 29413, (G) Klebsiella oxytoca M5al, (H) Paenibacillus sp. WLY78.
Thomas A. Bickle - One of the best experts on this subject based on the ideXlab platform.
-
Nif Gene expression studies in rhodobacter capsulatus ntrc independent repression by high ammonium concentrations
Molecular Microbiology, 1993Co-Authors: Philipp Hubner, Bernd Masepohl, Werner Klipp, Thomas A. BickleAbstract:The expression of Nif Genes in Rhodobacter capsulatus depends on the two regulatory Genes, rpoN and NifA, encoding a Nif-specific alternative sigma factor of RNA polymerase and a Nif-specific transcriptional activator, respectively. The expression of the rpoN Gene itself is also RPON/NifA dependent. In order to better characterize the regulation of Nif Gene induction, chromosomal NifH-, rpoN-, NifA1- and NifA2- lacZ fusions were constructed and the expression of these different Nif-lacZ fusions was determined under photoheterotrophic conditions at different starting ammonium concentrations. The two NifA Genes were found to be induced first, followed by NifH and finally by rpoN upon weak, medium and strong nitrogen starvation, respectively. This induction profile and the correlation between the expression of the different Nif Genes suggested that NifA1 expression is the limiting factor for Nif Gene induction. This hypothesis was tested by construction of different NifA1 overexpressing mutants. Contrary to the current model of Nif Gene expression in R. capsulatus, which predicted constitutive Nif Gene expression in such mutants, a strong repression of NifH and rpoN was found at high ammonium concentration. The low NifH expression under these conditions is unaffected by NifA2 and is not increased in a ntrC mutant, ruling out any role of NTRC as a mediator of this repression. This finding implies an additional, so far unidentified, regulation by fixed nitrogen in R. capsulatus. Changing the expression level of rpoN indicated that low levels of RPON are already sufficient for full NifH induction. The NifA1 and rpoN expression mutants were also tested for diazotrophic growth. Similar Generation times were determined for the mutants and for the wild type, but diazotrophic growth of the NifA1 over-expressing ntrC mutant RCM14 did not start until after a prolonged lag phase of two to three days.
-
expression of regulatory Nif Genes in rhodobacter capsulatus
Journal of Bacteriology, 1991Co-Authors: Philipp Hubner, John C. Willison, Paulette M. Vignais, Thomas A. BickleAbstract:Translational fusions of the Escherichia coli lacZ Gene to Rhodobacter capsulatus Nif Genes were constructed in order to determine the regulatory circuit of Nif Gene expression in R. capsulatus, a free-living photosynthetic diazotroph. The expression of NifH, NifA (copies I and II), and NifR4 was measured in different regulatory mutant strains under different physiological conditions. The expression of NifH and NifR4 (the analog of ntrA in Klebsiella pneumoniae) depends on the NifR1/R2 system (the analog of the ntr system in K. pneumoniae), on NifA, and on NifR4. The expression of both copies of NifA is regulated by the NifR1/R2 system and is modulated by the N source of the medium under anaerobic photosynthetic growth conditions. In the presence of ammonia or oxygen, moderate expression of NifA was detectable, whereas NifH and NifR4 were not expressed under these conditions. The implications for the regulatory circuit of Nif Gene expression in R. capsulatus are discussed and compared with the situation in K. pneumoniae, another free-living diazotroph.
Luis M. Rubio - One of the best experts on this subject based on the ideXlab platform.
-
formation of nitrogenase Nifdk tetramers in the mitochondria of saccharomyces cerevisiae
ACS Synthetic Biology, 2017Co-Authors: Stefan Burén, Gema Lopeztorrejon, Eric M Young, Elizabeth A Sweeny, Marcel Veldhuizen, Christopher A Voigt, Luis M. RubioAbstract:Transferring the prokaryotic enzyme nitrogenase into a eukaryotic host with the final aim of developing N2 fixing cereal crops would revolutionize agricultural systems worldwide. Targeting it to mitochondria has potential advantages because of the organelle’s high O2 consumption and the presence of bacterial-type iron–sulfur cluster biosynthetic machinery. In this study, we constructed 96 strains of Saccharomyces cerevisiae in which transcriptional units comprising nine Azotobacter vinelandii Nif Genes (NifHDKUSMBEN) were integrated into the genome. Two combinatorial libraries of Nif Gene clusters were constructed: a library of mitochondrial leading sequences consisting of 24 clusters within four subsets of Nif Gene expression strength, and an expression library of 72 clusters with fixed mitochondrial leading sequences and Nif expression levels assigned according to factorial design. In total, 29 promoters and 18 terminators were combined to adjust Nif Gene expression levels. Expression and mitochondrial ...
-
Diversity and Functional Analysis of the FeMo-Cofactor Maturase NifB
Frontiers Media S.A., 2017Co-Authors: Simon Arragain, Emilio Jiménez-vicente, Luis M. Rubio, Alessandro A. Scandurra, Stefan Burén, Carlos Echavarri-erasunAbstract:One of the main hurdles to engineer nitrogenase in a non-diazotrophic host is achieving NifB activity. NifB is an extremely unstable and oxygen sensitive protein that catalyzes a low-potential SAM-radical dependent reaction. The product of NifB activity is called NifB-co, a complex [8Fe-9S-C] cluster that serves as obligate intermediate in the biosyntheses of the active-site cofactors of all known nitrogenases. Here we study the diversity and phylogeny of naturally occurring NifB proteins, their protein architecture and the functions of the distinct NifB domains in order to understand what defines a catalytically active NifB. Focus is on NifB from the thermophile Chlorobium tepidum (two-domain architecture), the hyperthermophile Methanocaldococcus infernus (single-domain architecture) and the mesophile Klebsiella oxytoca (two-domain architecture), showing in silico characterization of their nitrogen fixation (Nif) Gene clusters, conserved NifB motifs, and functionality. C. tepidum and M. infernus NifB were able to complement an Azotobacter vinelandii (ΔNifB) mutant restoring the Nif+ phenotype and thus demonstrating their functionality in vivo. In addition, purified C. tepidum NifB exhibited activity in the in vitro NifB-dependent nitrogenase reconstitution assay. Intriguingly, changing the two-domain K. oxytoca NifB to single-domain by removal of the C-terminal NifX-like extension resulted in higher in vivo nitrogenase activity, demonstrating that this domain is not required for nitrogen fixation in mesophiles
-
expression of a functional oxygen labile nitrogenase component in the mitochondrial matrix of aerobically grown yeast
Nature Communications, 2016Co-Authors: Gema Lopeztorrejon, Hemant K. Verma, Jose Maria Buesa, José A. Hernández, Emilio Jimenezvicente, Luis M. RubioAbstract:The extreme sensitivity of nitrogenase towards oxygen stands as a major barrier to engineer biological nitrogen fixation into cereal crops by direct Nif Gene transfer. Here, we use yeast as a model of eukaryotic cell and show that aerobically grown cells express active nitrogenase Fe protein when the NifH polypeptide is targeted to the mitochondrial matrix together with the NifM maturase. Co-expression of NifH and NifM with Nif-specific Fe–S cluster biosynthetic proteins NifU and NifS is not required for Fe protein activity, demonstrating NifH ability to incorporate endogenous mitochondrial Fe–S clusters. In contrast, expression of active Fe protein in the cytosol requires both anoxic growth conditions and co-expression of NifH and NifM with NifU and NifS. Our results show the convenience of using mitochondria to host nitrogenase components, thus providing instrumental technology for the grand challenge of engineering N2-fixing cereals. The sensitivity of nitrogenase to oxygen is a major barrier to engineer biological nitrogen fixation into cereal crops by direct Nif Gene transfer. Here the authors use yeast to show that targeting nitrogenase Fe protein to the mitochondrial matrix overcomes the O2sensitivity impediment.
-
Expression of a functional oxygen-labile nitrogenase component in the mitochondrial matrix of aerobically grown yeast
Nature Communications, 2016Co-Authors: Gema López-torrejón, Emilio Jiménez-vicente, Hemant K. Verma, Jose Maria Buesa, José A. Hernández, Luis M. RubioAbstract:The extreme sensitivity of nitrogenase towards oxygen stands as a major barrier to engineer biological nitrogen fixation into cereal crops by direct Nif Gene transfer. Here, we use yeast as a model of eukaryotic cell and show that aerobically grown cells express active nitrogenase Fe protein when the NifH polypeptide is targeted to the mitochondrial matrix together with the NifM maturase. Co-expression of NifH and NifM with Nif-specific Fe-S cluster biosynthetic proteins NifU and NifS is not required for Fe protein activity, demonstrating NifH ability to incorporate endogenous mitochondrial Fe-S clusters. In contrast, expression of active Fe protein in the cytosol requires both anoxic growth conditions and co-expression of NifH and NifM with NifU and NifS. Our results show the convenience of using mitochondria to host nitrogenase components, thus providing instrumental technology for the grand challenge of engineering N2-fixing cereals.
-
challenges to develop nitrogen fixing cereals by direct Nif Gene transfer
Plant Science, 2014Co-Authors: Leonardo Curatti, Luis M. RubioAbstract:Some regions of the developing world suffer low cereal production yields due to low fertilizer inputs, among other factors. Biological N2 fixation, catalyzed by the prokaryotic enzyme nitrogenase, is an alternative to the use of synthetic N fertilizers. The molybdenum nitrogenase is an O2-labile metalloenzyme composed of the NifDK and NifH proteins, which biosyntheses require a number of Nif Gene products. A challenging strategy to increase cereal crop productivity in a scenario of low N fertilization is the direct transfer of Nif Genes into cereals. The sensitivity of nitrogenase to O2 and the apparent complexity of nitrogenase biosynthesis are the main barriers identified so far. Expression of active NifH requires the products of NifM, NifH, and possibly NifU and NifS, whereas active NifDK requires the products of NifH, NifD, NifK, NifB, NifE, NifN, and possibly NifU, NifS, NifQ, NifV, nafY, NifW and NifZ. Plastids and mitochondria are potential subcellular locations for nitrogenase. Both could provide the ATP and electrons required for nitrogenase to function but they differ in their internal O2 levels and their ability to incorporate ammonium into amino acids.
Xiaomeng Liu - One of the best experts on this subject based on the ideXlab platform.
-
evolution and functional analysis of orf1 within Nif Gene cluster from paenibacillus graminis rsa19
International Journal of Molecular Sciences, 2019Co-Authors: Xiaomeng Liu, Haowei Zhang, Sanfeng ChenAbstract:Paenibacillus is a genus of Gram-positive, facultative anaerobic and endospore-forming bacteria. Genomic sequence analysis has revealed that a compact Nif (nitrogen fixation) Gene cluster comprising 9–10 Genes NifBHDKENX(orf1)hesANifV is conserved in diazotrophic Paenibacillus species. The evolution and function of the orf1 Gene within the Nif Gene cluster of Paenibacillus species is unknown. In this study, a careful comparison analysis of the compositions of the Nif Gene clusters from various diazotrophs revealed that orf1 located downstream of NifENX was identified in anaerobic Clostridium ultunense, the facultative anaerobic Paenibacillus species and aerobic diazotrophs (e.g., Azotobacter vinelandii and Azospirillum brasilense). The predicted amino acid sequences encoded by the orf1 Gene, part of the Nif Gene cluster NifBHDKENXorf1hesANifV in Paenibacillus graminis RSA19, showed 60–90% identity with those of the orf1 Genes located downstream of NifENX from different diazotrophic Paenibacillus species, but shared no sigNificant identity with those of the orf1 Genes from different taxa of diazotrophic organisms. Transcriptional analysis showed that the orf1 Gene was expressed under nitrogen fixation conditions from the promoter located upstream from NifB. Mutational analysis suggested that the orf1 Gene functions in nitrogen fixation in the presence of a high concentration of O2.
-
suppression of hesa mutation on nitrogenase activity in paenibacillus polymyxa wly78 with the addition of high levels of molybdate or cystine
PeerJ, 2019Co-Authors: Xiaomeng Liu, Xiyun Zhao, Sanfeng ChenAbstract:The diazotrophic Paenibacillus polymyxa WLY78 possesses a minimal nitrogen fixation Gene cluster consisting of nine Genes (NifB NifH NifD NifK NifE NifN NifX hesA and NifV). Notably, the hesA Gene contained within the Nif Gene cluster is also found within Nif Gene clusters among diazotrophic cyanobacteria and Frankia. The predicted product HesA is a member of the ThiF-MoeB-HesA family containing an N-terminal nucleotide binding domain and a C-terminal MoeZ/MoeB-like domain. However, the function of hesA Gene in nitrogen fixation is unknown. In this study, we demonstrate that the hesA mutation of P. polymyxa WLY78 leads to nearly complete loss of nitrogenase activity. The effect of the mutation can be partially suppressed by the addition of high levels of molybdate or cystine. However, the nitrogenase activity of the hesA mutant could not be restored by Klebsiella oxytoca NifQ or Escherichia coli moeB completely. In addition, the hesA mutation does not affect nitrate reductase activity of P. polymyxa WLY78. Our results demonstrate hesA is a novel Gene specially required for nitrogen fixation and its role is related to introduction of S and Mo into the FeMo-co of nitrogenase.
-
a minimal nitrogen fixation Gene cluster from paenibacillus sp wly78 enables expression of active nitrogenase in escherichia coli
PLOS Genetics, 2013Co-Authors: Liying Wang, Lihong Zhang, Zhangzhi Liu, Dehua Zhao, Xiaomeng Liu, Bo Zhang, Jianbo Xie, Yuanyuan Hong, Sanfeng ChenAbstract:Most biological nitrogen fixation is catalyzed by molybdenum-dependent nitrogenase, an enzyme complex comprising two component proteins that contains three different metalloclusters. Diazotrophs contain a common core of nitrogen fixation Nif Genes that encode the structural subunits of the enzyme and components required to synthesize the metalloclusters. However, the complement of Nif Genes required to enable diazotrophic growth varies sigNificantly amongst nitrogen fixing bacteria and archaea. In this study, we identified a minimal Nif Gene cluster consisting of nine Nif Genes in the genome of Paenibacillus sp. WLY78, a gram-positive, facultative anaerobe isolated from the rhizosphere of bamboo. We demonstrate that the Nif Genes in this organism are organized as an operon comprising NifB, NifH, NifD, NifK, NifE, NifN, NifX, hesA and NifV and that the Nif cluster is under the control of a σ70 (σA)-dependent promoter located upstream of NifB. To investigate Genetic requirements for diazotrophy, we transferred the Paenibacillus Nif cluster to Escherichia coli. The minimal Nif Gene cluster enables synthesis of catalytically active nitrogenase in this host, when expressed either from the native NifB promoter or from the T7 promoter. Deletion analysis indicates that in addition to the core Nif Genes, hesA plays an important role in nitrogen fixation and is responsive to the availability of molybdenum. Whereas Nif transcription in Paenibacillus is regulated in response to nitrogen availability and by the external oxygen concentration, transcription from the NifB promoter is constitutive in E. coli, indicating that negative regulation of Nif transcription is bypassed in the heterologous host. This study demonstrates the potential for engineering nitrogen fixation in a non-nitrogen fixing organism with a minimum set of nine Nif Genes.
-
Comparison of the Paenibacillus sp. WLY78 Nif Gene cluster with representative clusters from diverse diazotrophic bacteria and archaea.
2013Co-Authors: Liying Wang, Lihong Zhang, Zhangzhi Liu, Dehua Zhao, Xiaomeng Liu, Bo Zhang, Jianbo Xie, Yuanyuan Hong, Sanfeng ChenAbstract:(A) Azotobacter vinelandii, (B) Heliobacterium chlorum, (C) Clostridium acetobutylicum W5, (D) Frankia sp. EAN1pec, (E) Methanococus maripaludis, (F) Anabaena variabilis ATCC 29413, (G) Klebsiella oxytoca M5al, (H) Paenibacillus sp. WLY78.
Philipp Hubner - One of the best experts on this subject based on the ideXlab platform.
-
Nif Gene expression studies in rhodobacter capsulatus ntrc independent repression by high ammonium concentrations
Molecular Microbiology, 1993Co-Authors: Philipp Hubner, Bernd Masepohl, Werner Klipp, Thomas A. BickleAbstract:The expression of Nif Genes in Rhodobacter capsulatus depends on the two regulatory Genes, rpoN and NifA, encoding a Nif-specific alternative sigma factor of RNA polymerase and a Nif-specific transcriptional activator, respectively. The expression of the rpoN Gene itself is also RPON/NifA dependent. In order to better characterize the regulation of Nif Gene induction, chromosomal NifH-, rpoN-, NifA1- and NifA2- lacZ fusions were constructed and the expression of these different Nif-lacZ fusions was determined under photoheterotrophic conditions at different starting ammonium concentrations. The two NifA Genes were found to be induced first, followed by NifH and finally by rpoN upon weak, medium and strong nitrogen starvation, respectively. This induction profile and the correlation between the expression of the different Nif Genes suggested that NifA1 expression is the limiting factor for Nif Gene induction. This hypothesis was tested by construction of different NifA1 overexpressing mutants. Contrary to the current model of Nif Gene expression in R. capsulatus, which predicted constitutive Nif Gene expression in such mutants, a strong repression of NifH and rpoN was found at high ammonium concentration. The low NifH expression under these conditions is unaffected by NifA2 and is not increased in a ntrC mutant, ruling out any role of NTRC as a mediator of this repression. This finding implies an additional, so far unidentified, regulation by fixed nitrogen in R. capsulatus. Changing the expression level of rpoN indicated that low levels of RPON are already sufficient for full NifH induction. The NifA1 and rpoN expression mutants were also tested for diazotrophic growth. Similar Generation times were determined for the mutants and for the wild type, but diazotrophic growth of the NifA1 over-expressing ntrC mutant RCM14 did not start until after a prolonged lag phase of two to three days.
-
expression of regulatory Nif Genes in rhodobacter capsulatus
Journal of Bacteriology, 1991Co-Authors: Philipp Hubner, John C. Willison, Paulette M. Vignais, Thomas A. BickleAbstract:Translational fusions of the Escherichia coli lacZ Gene to Rhodobacter capsulatus Nif Genes were constructed in order to determine the regulatory circuit of Nif Gene expression in R. capsulatus, a free-living photosynthetic diazotroph. The expression of NifH, NifA (copies I and II), and NifR4 was measured in different regulatory mutant strains under different physiological conditions. The expression of NifH and NifR4 (the analog of ntrA in Klebsiella pneumoniae) depends on the NifR1/R2 system (the analog of the ntr system in K. pneumoniae), on NifA, and on NifR4. The expression of both copies of NifA is regulated by the NifR1/R2 system and is modulated by the N source of the medium under anaerobic photosynthetic growth conditions. In the presence of ammonia or oxygen, moderate expression of NifA was detectable, whereas NifH and NifR4 were not expressed under these conditions. The implications for the regulatory circuit of Nif Gene expression in R. capsulatus are discussed and compared with the situation in K. pneumoniae, another free-living diazotroph.