Regulation Of The Nitrogen Fixation Genes In The Heterocystous Cyanobacterium Anabaena Sp Strain Pcc 7120 PDF Download
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| Author | : Krithika Kumar |
| Publisher | : |
| Total Pages | : |
| Release | : 2012 |
| Genre | : |
| ISBN | : |
Download Regulation of the Nitrogen Fixation Genes in the Heterocystous Cyanobacterium Anabaena Sp. Strain PCC 7120 Book in PDF, ePub and Kindle
Many multicellular cyanobacteria produce specialized nitrogenfixing heterocysts. During diazotrophic growth of Anabaena (Nostoc) sp. strain PCC 7120, a regulated developmental pattern of single heterocysts separated by about 10 to 20 photosynthetic vegetative cells is maintained along filaments. Heterocyst structure and metabolic activity function together to accommodate oxygensensitive nitrogen fixation, catalyzed by nitrogenase. In this work, we show that the promoter of the nifHDK genes that encode nitrogenase, lies upstream from the intergenic region between nifH and nifU. Excision of the fdxN element is required for transcription of the nifHDK genes. Fluorescence microscopy of reporter strain PnifHD-gfp, in the chromosomal nif locus indicated that expression of nifHDK is blocked in mutants that are unable to excise the fdxN element after nitrogen deprivation. We proposed that a promoter upstream of the element, likely PnifB, is required for transcription of the nifHDK genes. Indeed, the PnifHD-gfp reporter at an ectopic site did not show GFP fluorescence. A PnifB-gfp reporter was expressed specifically in heterocysts indicating that a promoter for the nifB gene lies in the intergenic region upstream of nifB. A stem loop structure located in the intergenic region between nifH and nifU may act as a processing site for production of nifHDK transcripts. We also provide evidence that DevH, a transcriptional regulator, is involved in regulating the nifBfdxNnifSUHDK genes. DevH is a protein belonging to the cAMP receptor protein (CRP) family of proteins that are widespread in bacteria and regulate genes in response to a gamut of physiological conditions. We show that DevH binds specifically to the nifB upstream region but not to the immediate upstream region of nifH. We predict that DevH binds to an NtcAlike binding site upstream of nifB and functions as an activator of the nifB-fdxN-nifSUHDK genes. Finally, we show that sigE, which is expressed at 16 hours after nitrogen deprivation, is required for normal expression of some heterocyst specific genes, including nifHDK. A sigE mutant shows delayed and reduced expression of nifHDK and some middle and late genes. We hypothesize that DevH in concert with SigE upregulates the expression of nifHDK in heterocysts after nitrogen deprivation.
| Author | : Werner Klipp |
| Publisher | : Springer Science & Business Media |
| Total Pages | : 313 |
| Release | : 2006-01-28 |
| Genre | : Science |
| ISBN | : 1402021798 |
Download Genetics and Regulation of Nitrogen Fixation in Free-Living Bacteria Book in PDF, ePub and Kindle
Genetics and Regulation of Nitrogen-Fixing Bacteria This book is the second volume of a seven-volume series, which covers all fields of research related to nitrogen fixation - from basic studies through applied aspects to environmental impacts. Volume II provides a comprehensive and detailed source of information concerning the genetics and regulation of biological nitrogen fixation in free-living prokaryotes. This preface attempts to provide the reader with some insight into how this volume originated, how it was planned, and then how it developed over the several years of its production. Once the editorial team was established, the first job was to decide which of the many free-living diazotrophs that have been subjected to genetic analysis should be included in this volume. Would we need to develop specific criteria for selection or would the organisms, in effect, select themselves? Of course, Klebsiella pneumoniae and Azotobacter vinelandii, which have served (and still serve) as the main model organisms for the genetic analysis of diazotrophy, plus some of the other bacteria described in this volume, did indeed select themselves. However, there was considerable discussion surrounding well-characterized fixing species, like Azorhizobium caulinodans and Herbaspirillum seropedicae, both of which are able to fix atmospheric N under free-living conditions.
| Author | : James W. Golden |
| Publisher | : |
| Total Pages | : 16 |
| Release | : 2004 |
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| ISBN | : |
Download Regulation of Development and Nitrogen Fixation in Anabaena Book in PDF, ePub and Kindle
The nitrogen-fixing filamentous cyanobacterium Anabaena sp. strain PCC 7120 is being used as a simple model of microbial development and pattern formation in a multicellular prokaryotic organism. Anabaena reduces atmospheric nitrogen to ammonia in highly specialized, terminally differentiated cells called heterocysts. Anabaena is an important model system because of the multicellular growth pattern, the suspected antiquity of heterocyst development, and the contribution of fixed nitrogen to the environment. We are especially interested in understanding the molecular signaling pathways and genetic regulation that control heterocyst development. In the presence of an external source of reduced nitrogen, the differentiation of heterocysts is inhibited. When Anabaena is grown on dinitrogen, a one-dimensional developmental pattern of single heterocysts separated by approximately ten vegetative cells is established to form a multicellular organism composed of two interdependent cell types. The goal of this project is to understand the signaling and regulatory pathways that commit a vegetative cell to terminally differentiate into a nitrogen-fixing heterocyst. Several genes identified by us and by others were chosen as entry points into the regulatory network. Our research, which was initially focused on transcriptional regulation by group 2 sigma factors, was expanded to include group 3 sigma factors and their regulators after the complete Anabaena genome sequence became available. Surprisingly, no individual sigma factor is essential for heterocyst development. We have used the isolation of extragenic suppressors to study genetic interactions between key regulatory genes such as patS, hetR, and hetC in signaling and developmental pathways. We identified a hetR R223W mutation as a bypass suppressor of patS overexpression. Strains containing the hetR R223W allele fail to respond to pattern formation signals and overexpression of this allele results in a lethal phenotype because all cells differentiate a few days after nitrogen step-down. Our continued analysis of these genes will provide a better understanding of how a simple prokaryotic organism can perform both photosynthetic carbon fixation and nitrogen fixation simultaneously by separating these processes in different cell types.
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| Release | : 2004 |
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Download Characterization of Two Genes Up-regulated During Heterocyst Development in the Cyanobacterium Anabaena Sp. Strain PCC 7120 Book in PDF, ePub and Kindle
Anabaena sp. strain PCC 7120 is a cyanobacterium that carries out photosynthesis in a manner similar to plants and is capable of nitrogen fixation. This organism has developed a necessary spatial separation of the incompatible processes of photosynthesis and nitrogen fixation, as nitrogen fixation is sensitive to oxygen that is produced during photosynthesis. A differentiated cell type, called a heterocyst, is formed when Anabaena is in an environment lacking nitrogen, and these cells are the sites of nitrogen fixation. Heterocyst formation occurs about every tenth cell along a filament of photosynthetic vegetative cells after 24-36 hours of nitrogen starvation. A screen for sequences up-regulated at the transcript level during heterocyst development in Anabaena identified adjacent loci alr4311 and all4312. The sequence of alr4311 suggests it encodes the ATP-binding protein of an ABC transporter complex, while that of all4312 suggests it encodes the response regulator of a two-component regulatory system. Phylogenetic analysis of the predicted protein sequences of alr4311 and all4312 indicated that both of these proteins have orthologs in Nostoc punctiforme and Anabaena variabilis, two filamentous, diazotrophic cyanobacteria. Additionally, alr4311 appears to be most similar to ABC transporters involved in the import of cobalt, while all4312 was most similar to uncharacterized response regulators. The transcripts of alr4311 and all4312 are expressed at low levels in vegetative cells, and increase in abundance after nitrogen starvation and the induction of heterocyst development. Northern analysis and real-time RT-PCR showed that expression of alr4311 and all4312 are induced as early as 3 hours after initiation of differentiation, and expression levels of both genes remain elevated through the first 24 hours of development. Expression of both of these genes was blocked in an ntcA mutant, and significantly decreased in a hetR mutant. alr4311 was shown to be part of an.
| Author | : Britt Lee Flaherty |
| Publisher | : |
| Total Pages | : 125 |
| Release | : 2012 |
| Genre | : |
| ISBN | : 9781267832580 |
Download Transcriptional Regulation of Heterocyst Development in Anabaena Sp. Strain PCC 7120 Book in PDF, ePub and Kindle
Fixed nitrogen is a limited resource for growth in the environment and the fixation of atmospheric nitrogen is vital to nutrient cycling and growth. Cyanobacteria are a group of photosynthetic bacteria that evolved 4.5 billion years ago to harvest sunlight as energy. Cyanobacteria have since evolved a wide array of metabolic capabilities over time, including the ability to fix atmospheric nitrogen. Anabaena sp. strain PCC 7120, hereafter Anabaena, is a species of cyanobacteria that fixes atmospheric N2 into ammonia by forming specialized nitrogen-fixing cells called heterocysts. Heterocysts form only in the absence of a source of fixed nitrogen and are evenly spaced along a filament of Anabaena cells. We studied the gene expression networks that regulate heterocyst development through deep sequencing, employing both RNA-seq on a nitrogen-deprived culture as well as ChIP-seq on key transcription factors involved in heterocyst development. Deep sequencing gave us a global view of gene expression in response to nitrogen deprivation in Anabaena. Our RNA-seq work identified new genes involved in heterocyst development, mapped operon structure and transcript length, and discovered abundant antisense transcription in the genome. In particular, we identified antisense transcription in the coding region of the gene nblA, which codes for a small peptide that triggers the proteolysis of the photosynthetic machinery in response to nutrient stress. Furthermore, we used ChIP-seq to identify the regulon of two transcription factors, HetR and DevH, in response to nitrogen deprivation. Our work on HetR, a transcription factor with known roles in regulating heterocyst development, identified many new HetR targets, including genes involved in HetR's role during nitrogen deprivation and during vegetative cell growth. Our work on DevH, a transcription factor required for forming the heterocyst-specific cell wall, also identified new DevH targets, including many genes involved in cell wall formation and transcriptional regulators. This work adds to our understanding of transcriptional networks that regulate heterocyst development in Anabaena. Furthermore, our study provides insight into gene structure and transcriptional regulation in cyanobacteria as a whole.
| Author | : Pritty B. Borthakur |
| Publisher | : |
| Total Pages | : 194 |
| Release | : 2008 |
| Genre | : Anabaena |
| ISBN | : |
Download Characterization of Genes Involved in Heterocyst Differentiation and Pattern Formation in the Cyanobacterium Anabaena Sp. Strain PCC 7120 Book in PDF, ePub and Kindle
The goal of this research was to understand regulation of heterocyst differentiation in Anabaena sp. strain PCC 7120 by characterizing regulatory genes for heterocyst formation and their mutants. Anabaena is a filamentous cyanobacterium that forms specialized cells for nitrogen fixation, called heterocysts, which differentiate from vegetative cells at intervals of 10--12 cells. Two genes, patS and hetN, are known to suppress the differentiation of vegetative cells into heterocysts for establishing a de novo pattern and maintaining a pattern of heterocysts along the filament. A mutant, UHM100, was created to study the function of both genes by deleting patS and making expression of hetN conditional. This study has established that PatS and HetN are members of two separate heterocyst suppression pathways. In absence of nitrogen, inactivation of both patS and hetN increases heterocyst differentiation to nearly 100%, giving rise to a phenotype called 'multiple contiguous heterocysts' (Mch). UHM100 has an Mch phenotype even in the presence of combined nitrogen, which usually suppresses heterocyst differentiation. In absence of both patS and hetN, the expression of hetR, a master regulator of heterocyst differentiation, was observed in ~55% cells and was asynchronous. The distribution of heterocysts next to a vegetative cell in UHM 100 was found to be nonrandom. These results suggest that besides PatS and HetN, there are other factors that influence pattern formation in Anabaena PCC 7120. A heterocyst-deficient (Hef) spontaneous mutant, NSM6, was isolated from UHM 100. A novel gene, alr9018, from the Anabaena Epsilon plasmid complemented NSM6 and restored the Mch phenotype of this mutant. Transconjugants of Anabaena PCC 7120 containing the cloned alr9018 gene fixed 50% more N2 than PCC 7120, suggesting that multiple copies of alr9018 enhance heterocyst development. This is the first report showing that the Epsilon plasmid of Anabaena PCC 7120 contains genes involved in heterocyst differentiation. Expression of alr9018 was observed in both vegetative cells and heterocysts. Similar to alr9018, hetR could also restore the Mch phenotype in NSM6, suggesting functional similarity between a1r9018 and hetR. The Alr9018 protein contains an NTPase domain, which is a characteristic of proteins involved in signal transduction.
| Author | : |
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| Release | : 2008 |
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Download Regulation of Development and Nitrogen Fixation in Anabaena Book in PDF, ePub and Kindle
The regulation of development and cellular differentiation is important for all multicellular organisms. The nitrogen-fixing filamentous cyanobacterium Anabaena (also Nostoc) sp. PCC 7120 (hereafter Anabaena) provides a model of multicellular microbial development and pattern formation. Anabaena reduces N2 to ammonia in specialized terminally differentiated cells called heterocysts. A one-dimensional developmental pattern of single heterocysts regularly spaced along filaments of photosynthetic vegetative cells is established to form a multicellular organism composed of these two interdependent cell types. This multicellular growth pattern, the distinct phylogeny of cyanobacteria, and the suspected antiquity of heterocyst development make this an important model system. Our long-term goal is to understand the regulatory network required for heterocyst development and nitrogen fixation. This project is focused on two key aspects of heterocyst regulation: one, the mechanism by which HetR controls the initiation of differentiation, and two, the cis and trans acting factors required for expression of the nitrogen-fixation (nif) genes. HetR is thought to be a central regulator of heterocyst development but the partners and mechanisms involved in this regulation are unknown. Our recent results indicate that PatS and other signals that regulate heterocyst pattern cannot interact, directly or indirectly, with a R223W mutant of HetR. We plan to use biochemical and genetic approaches to identify proteins that interact with the HetR protein, which will help reveal the mechanisms underlying its regulation of development. Our second goal is to determine how the nif genes are expressed. It is important to understand the mechanisms controlling nif genes since they represent the culmination of the differentiation process and the essence of heterocyst function. The Anabaena genome lacks the genes required for expression of nif genes present in other organisms such as rpoN (sigma 54) and nifA. We will use nifH-gfp reporter fusions to define the upstream sequences that are required for nifH expression and for genetic experiments to identify the trans-acting factors required for nifH regulation.
| Author | : Rodrigo Andres Mella Herrera |
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| Total Pages | : |
| Release | : 2010 |
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Download Heterocyst Morphogenesis and Gene Expression in Anabaena Sp. PCC 7120 Book in PDF, ePub and Kindle
Many multicellular cyanobacteria produce specialized nitrogen-fixing heterocysts. During diazotrophic growth of the model organism Anabaena (Nostoc) sp. strain PCC 7120, a regulated developmental pattern of single heterocysts separated by about 10 to 20 photosynthetic vegetative cells is maintained along filaments. Heterocyst structure and metabolic activity function to accommodate the oxygen-sensitive process of nitrogen fixation. This dissertation focuses on my research on heterocyst development, including morphogenesis, transport of molecules between cells in a filament, differential gene expression, and pattern formation. We using microarray experiments we found that conR (all0187) gene is necessary for normal septum-formation of vegetative cells, diazotrophic grow, and heterocyst morphogenesis. In our studies we characterized the expression of sigma factors genes in Anabaena PCC 7120 during heterocyst differentiation, and we found that the expression of sigC, sigG and sigE is localized primarily in heterocysts. Expression studies using sigE mutant showed that nifH is under the control of this specific sigma factor.
| Author | : T. A. Sarma |
| Publisher | : CRC Press |
| Total Pages | : 803 |
| Release | : 2012-12-18 |
| Genre | : Science |
| ISBN | : 1466559411 |
Download Handbook of Cyanobacteria Book in PDF, ePub and Kindle
This handbook acquaints readers with the exciting developments in various areas of cyanobacterial research in the backdrop of the publication of complete genome sequence of the cyanobacterium Synechocystis sp. strain PCC 6803 in 1996. It begins with a summary of the current knowledge on the taxonomy, phylogeny and evolution of cyanobacteria followe
| Author | : Yuping Cai |
| Publisher | : |
| Total Pages | : 372 |
| Release | : 1991 |
| Genre | : Anabaena |
| ISBN | : |
Download Molecular Genetic Approaches Towards the Understanding of Heterocyst Differentiation and Pattern Formation in the Cyanobacterium Anabaena Sp Book in PDF, ePub and Kindle
