Nitrogen control in cyanobacteria.
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TLDR
Nitrogen control in cyanobacteria is mediated by NtcA, a transcriptional regulator which belongs to the CAP (the catabolite gene activator or cyclic AMP [cAMP] receptor protein) family and is therefore different from the well-characterized Ntr system.Abstract:
Nitrogen is a quantitatively important bioelement which is incorporated into the biosphere through assimilatory processes carried out by microorganisms and plants. Numerous nitrogencontaining compounds can be used by different organisms as sources of nitrogen. These include, for instance, inorganic ions like nitrate or ammonium and simple organic compounds like urea, amino acids, and some nitrogen-containing bases. Additionally, many bacteria are capable of fixing N 2. Nitrogen control is a phenomenon that occurs widely among microorganisms and consists of repression of the pathways of assimilation of some nitrogen sources when some other, more easily assimilated source of nitrogen is available to the cells. Ammonium is the preferred nitrogen source for most bacteria, but glutamine is also a very good source of nitrogen for many microorganisms. Two thoroughly investigated nitrogen control systems are the NtrB-NtrC two-component regulatory system found in enterics and some other proteobacteria (80) and the GATA family global nitrogen control transcription factors of yeast and some fungi (75). Novel nitrogen control systems have, however, been identified in bacteria other than the proteobacteria, like Bacillus subtilis (26), Corynebacterium glutamicum (52), and the cyanobacteria. The cyanobacterial system is the subject of this review. The cyanobacteria are prokaryotes that belong to the Bacteria domain and are characterized by the ability to perform oxygenic photosynthesis. Cyanobacteria have a wide ecological distribution, and they occupy a range of habitats, which includes vast oceanic areas, temperate soils, and freshwater lakes, and even extreme habitats like arid deserts, frigid lakes, or hot springs. Photoautotrophy, fixing CO 2 through the Calvin cycle, is the dominant mode of growth of these organisms (109). A salient feature of the intermediary metabolism of cyanobacteria is their lack of 2-oxoglutarate dehydrogenase (109). As a consequence, they use 2-oxoglutarate mainly as a substrate for the incorporation of nitrogen, a metabolic arrangement that may have regulatory consequences. Notwithstanding their rather homogeneous metabolism, cyanobacteria exhibit remarkable morphological diversity, being found as either unicellular or filamentous forms and exhibiting a number of cell differentiation processes, some of which take place in response to defined environmental cues, as is the case for the differentiation of N 2-fixing heterocysts (109). Nitrogen control in cyanobacteria is mediated by NtcA, a transcriptional regulator which belongs to the CAP (the catabolite gene activator or cyclic AMP [cAMP] receptor protein) family and is therefore different from the well-characterized Ntr system. Interestingly, however, the signal transduction P II protein, which plays a key role in Ntr regulation, is found in cyanobacteria but with characteristics which differentiate it from proteobacterial P II. In the following paragraphs, we shall first briefly summarize our current knowledge of the cyanobacterial nitrogen assimilation pathways and of what is known about their regulation at the protein level. This description will introduce most of the known cyanobacterial nitrogen assimilation genes. We shall then describe the ntcA gene and the NtcA protein themselves to finally discuss NtcA function through a survey of the NtcA-regulated genes which participate in simple nitrogen assimilation pathways or in heterocyst differentiation and function.read more
Citations
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References
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Sequence analysis of the genome of the unicellular cyanobacterium Synechocystis sp. strain PCC6803. II. Sequence determination of the entire genome and assignment of potential protein-coding regions.
Takakazu Kaneko,Shusei Sato,Hirokazu Kotani,Ayako Tanaka,Erika Asamizu,Yasukazu Nakamura,Nobuyuki Miyajima,Makoto Hirosawa,Masahiro Sugiura,Shigemi Sasamoto,Takaharu Kimura,Tsutomu Hosouchi,Ai Matsuno,Akiko Muraki,Naomi Nakazaki,Kaoru Naruo,Satomi Okumura,Sayaka Shimpo,Chie Takeuchi,Tsuyuko Wada,Akiko Watanabe,Manabu Yamada,Miho Yasuda,Satoshi Tabata +23 more
TL;DR: The sequence determination of the entire genome of the Synechocystis sp.
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Biological Nitrogen Fixation
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TL;DR: Highlights in biological nitrogen fixation during the last fifty years are highlighted.
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The Molecular Biology of Cyanobacteria
TL;DR: This work focuses on the study of the structure and function of the Photosystem II Reaction Center in Cyanobacteria, which consists of Chloroplast Origins and Evolution, and its role in the Evolution of the Universal Enzyme.
Journal ArticleDOI
Trichodesmium, a Globally Significant Marine Cyanobacterium
TL;DR: N2 fixation by Trichodesmium is likely a major input to the marine and global nitrogen cycle.
Journal ArticleDOI
Crystal structure of a CAP-DNA complex: the DNA is bent by 90 degrees.
TL;DR: The 3 angstrom resolution crystal structure of the Escherichia coli catabolite gene activator protein (CAP) complexed with a 30-base pair DNA sequence shows that the DNA is bent by 90 degrees.
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