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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cells of the non-diazotrophic cyanobacterium Synechococcus sp. strain PCC 7942 acclimate to nitrogen deprivation by differentiating into non-pigmented resting cells, which are able to survive prolonged periods of starvation. In this study, the physiological properties of the long-term nitrogen-starved cells are investigated in an attempt to elucidate the mechanisms of maintenance of viability. Preservation of energetic homeostasis is based on a low level of residual photosynthesis; activities of photosystem II and photosystem I were approximately 0.1% of activities of vegetatively growing cells. The low levels of photosystem I activity were measured by a novel colorimetric assay developed from the activity staining of ferredoxin:NADP+ oxidoreductase. Photosystem II reaction centers, as determined by chlorophyll fluorescence measurements, exhibited normal properties, although the efficiency of light harvesting was significantly reduced compared with that of control cells. Long-term chlorotic cells carried out protein synthesis at a very low, but detectable level, as revealed by in vivo [35S]methionine labeling and two-dimensional gel electrophoresis. In conjunction with the very low levels of total cellular protein contents, this implies a continuous protein turnover during chlorosis. Synthesis of components of the photosynthetic apparatus could be detected, whereas factors of the translational machinery were stringently down-regulated. Beyond the massive loss of protein during acclimation to nitrogen deprivation, two proteins that were identified as SomA and SomB accumulated due to an induced expression following nitrogen reduction.
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PMID:Nitrogen starvation-induced chlorosis in Synechococcus PCC 7942. Low-level photosynthesis as a mechanism of long-term survival. 1135 Oct 86

A plasmid library of small genomic fragments from the cyanobacterium Anabaena sp. strain PCC 7120 was screened for sequences whose transcripts increase in abundance during a heterocyst development time course. A total of 350 clones were analyzed, representing 1-2% of the Anabaena sp. strain PCC 7120 genome. Twenty-seven clones (8%) showed some degree of up-regulation after nitrogen starvation. The increase in transcript abundance ranged from 1.2-fold to 3.5-fold. Further analysis of the expression of some of the sequences using Northern blots suggested that the up-regulation values calculated from the screen are underestimates. The collection of up-regulated clones includes novel genes, previously characterized genes, and genes identifiable by similarity to known genes. One of the novel genes has been shown to be required for heterocyst function, and the sequence similarities and expression patterns of some of the others suggest that they may play a role in heterocyst development.
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PMID:A screen for sequences up-regulated during heterocyst development in Anabaena sp. strain PCC 7120. 1140 41

Cyanobacteria respond to environmental stress conditions by degrading their phycobilisomes, the light harvesting complexes for photosynthesis. The expression of nblA, a key gene in this process, is controlled by the response regulator NblR in Synechococcus sp. PCC 7942. Here we show that, under nitrogen stress, nblA is also regulated by NtcA, the global regulator for nitrogen control. NtcA activation of nblA was found to be nitrogen-specific and did not take place under sulphur stress. Transcripts from the two major transcription start points (tsp) for the nblA gene were induced in response to nitrogen and sulphur starvation. The most active one (tspII) required both NblR and NtcA to induce full nblA expression under nitrogen starvation. NblR and NtcA bound in vitro to a DNA fragment from the nblA promoter region, suggesting that, under nitrogen stress, both NblR and NtcA activate the main regulated promoter (PnblA-2) by direct DNA-binding. The structure of PnblA-2 differs from that of the canonical NtcA-activated promoter and it is therefore proposed to represent a novel type of NtcA-dependent promoter. We analysed expression patterns from ntcA and selected NtcA targets in NtcA(-), NblR(-) and wild-type strains, and discuss data suggesting further interrelations between phycobilisome degradation and nitrogen assimilation regulatory pathways.
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PMID:Convergence of two global transcriptional regulators on nitrogen induction of the stress-acclimation gene nblA in the cyanobacterium Synechococcus sp. PCC 7942. 1153 55

Elemental manganese is essential for the production of molecular oxygen by cyanobacteria, plants, and algae. In the cyanobacterium Synechocystis sp. PCC 6803, transcription of the mntCAB operon, encoding a high affinity Mn transporter, occurs under Mn starvation (nm Mn) conditions but not in Mn-sufficient (microm Mn) growth medium. Using a strain in which the promoter of this operon directs the transcription of the luxAB reporter genes, we determined that inactivation of the slr0640 gene, which encodes a histidine kinase sensor protein component of a two-component signal transduction system, resulted in constitutive high levels of lux luminescence. Systematic targeted inactivation mutagenesis also identified slr1837 as the gene encoding the corresponding response regulator protein. We have named these two genes manS (manganese-sensor) and manR (manganese-regulator), respectively. A polyhistidine-tagged form of the ManS protein was localized in the Synechocystis 6803 cell membrane. Directed replacement of the conserved catalytic His-205 residue of this protein by Leu abolished its activity, although the mutated protein was present in cyanobacterial membrane. This mutant also showed suboptimal rates of Mn uptake under either Mn-starved or Mn-sufficient growth condition. These data suggest that the ManS/ManR two-component system plays a central role in the homeostasis of manganese in Synechocystis 6803 cells.
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PMID:A two-component signal transduction pathway regulates manganese homeostasis in Synechocystis 6803, a photosynthetic organism. 1203 66

An iron-rich protein was isolated from the Archaeon Halobacterium salinarum sharing a sequence identity of 35% with the starvation-induced DNA-binding protein, DpsA, of Synechecoccus sp. PCC 7942. It consists of 20 kDa subunits, forming a dodecameric structure. The protein exhibits a ferric iron loading of up to 103 Fe ions/mol of holoprotein. CD spectra are consistent with an alpha-helical contribution of 58%. The UV/visible spectrum provides no evidence for the presence of haem groups. This protein exhibits features of a non-haem-type bacterial ferritin although it shares only little sequence homology with non-haem bacterial ferritin.
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PMID:Characterization of a non-haem ferritin of the Archaeon Halobacterium salinarum, homologous to Dps (starvation-induced DNA-binding protein). 1219 73

The impact of nitrogen deficiency on the unicellular cyanobacterium Synechocystis sp. strain PCC 6803 and three nbl (non-bleaching) mutants (deltanblA1, deltanblA2 and deltanblB) was investigated. The deltanblA mutants entered a non-dividing, dormant state soon after the initiation of nitrogen starvation. The cells became larger, the membrane system was disorganized, and ribosomes were found near the membranes much less frequently. Photosystem II (PSII) activity declined to approximately 10% of the wild-type level and the amount of D1 protein declined precipitously, despite adequate psbA transcription; PSI activity declined, but more slowly. Transcription from PSII (except psbA), PSI and phycobilisome genes was very low. Fluorescence at 77K indicated many partially assembled or unassembled phycobilisomes. The level of transcript accumulation increased to normal by 4 h after the readdition of nitrogen to the culture. When NblA was present, the phycobilisomes were degraded to provide a nitrogen source for continued growth and metabolism. An important difference between the wild-type, mutant deltanblB, and the deltanblA mutants was seen in the rod linker proteins. Under nitrogen-deprivation condition, the L(R)33 and L(R)34.5 linker proteins were extensively degraded in the wild-type and deltanblB mutant, but remained intact in the deltanblA mutants.
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PMID:Characterization of Synechocystis sp. strain PCC 6803 and deltanbl mutants under nitrogen-deficient conditions. 1220 58

The effects of nitrogen starvation on photosynthetic efficiency were examined in three unicellular algae by measuring changes in the quantum yield of fluorescence with a pump-and-probe method and thermal efficiency (i.e. the percentage of trapped energy stored photochemically) with a pulsed photoacoustic method together with the inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea to distinguish photosystems I and II (PSI and PSII). Measured at 620 nm, maximum thermal efficiency for both photosystems was 32% for the diatom Thalassiosira weissflogii (PSII:PSI ratio of 2:1), 39% for the green alga Dunaliella tertiolecta (PSII:PSI ratio of 1:1), and 29% for the cyanobacterium Synechococcus sp. PCC 7002 (PSII:PSI ratio of 1:2). Nitrogen starvation decreased total thermal efficiency by 56% for T. weissflogii and by 26% for D. tertiolecta but caused no change in Synechococcus. Decreases in the number of active PSII reaction centers (inferred from changes in variable fluorescence) were larger: 86% (T. weissflogii), 65% (D. tertiolecta), and 65% (Synechococcus). The selective inactivation of PSII under nitrogen starvation was confirmed by independent measurements of active PSII using oxygen flash yields and active PSI using P700 reduction. Relatively high thermal efficiencies were measured in all three species in the presence of the PSII inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea, suggesting the potential for significant cyclic electron flow around PSI. Fluorescence or photoacoustic data agreed well; in T. weissflogii, the functional cross-sectional area of PSII at 620 nm was estimated to be the same using both methods (approximately 1.8 x 102 A2). The effects of nitrogen starvation occur mainly in PSII and are well represented by variable fluorescence measurements.
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PMID:Differential Effects of Nitrogen Limitation on Photosynthetic Efficiency of Photosystems I and II in Microalgae. 1222 11

The cyanobacterium Synechococcus PCC 7942 grown under iron starvation assembles a supercomplex consisting of a trimeric Photosystem I (PSI) complex encircled by a ring of 18 CP43' or IsiA light-harvesting complexes [Nature 412 (2001) 745]. Here we present a spectroscopic characterization by temperature-dependent absorption and fluorescence spectroscopy, site-selective fluorescence spectroscopy at 5 K, and circular dichroism of isolated PSI-IsiA, PSI and IsiA complexes from this cyanobacterium grown under iron starvation. The results suggest that the IsiA ring increases the absorption cross-section of PSI by about 100%. Each IsiA subunit binds about 16-17 chlorophyll a (Chl a) molecules and serves as an efficient antenna for PSI. Each of the monomers of the trimeric PSI complex contains two red chlorophylls, which presumably give rise to one exciton-coupled dimer and at 5 K absorb and fluoresce at 703 and 713 nm, respectively. The spectral properties of these C-703 chlorophylls are not affected by the presence of the IsiA antenna ring. The spectroscopic properties of the purified IsiA complexes are similar to those of the related CP43 complex from plants, except that the characteristic narrow absorption band of CP43 at 682.5 nm is missing in IsiA.
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PMID:Spectroscopic properties of PSI-IsiA supercomplexes from the cyanobacterium Synechococcus PCC 7942. 1246 Jun 85

Heterocyst-forming filamentous cyanobacteria, such as Anabaena variabilis ATCC 29413, require molybdenum as a component of two essential cofactors for the enzymes nitrate reductase and nitrogenase. A. variabilis efficiently transported (99)Mo (molybdate) at concentrations less than 10(-9) M. Competition experiments with other oxyanions suggested that the molybdate-transport system of A. variabilis also transported tungstate but not vanadate or sulfate. Although tungstate was probably transported, tungsten did not function in place of molybdenum in the Mo-nitrogenase. Transport of (99)Mo required prior starvation of the cells for molybdate, suggesting that the Mo-transport system was repressed by molybdate. Starvation, which required several generations of growth for depletion of molybdate, was enhanced by growth under conditions that required synthesis of nitrate reductase or nitrogenase. These data provide evidence for a molybdate storage system in A. variabilis. NtcA, a regulatory protein that is essential for synthesis of nitrate reductase and nitrogenase, was not required for transport of molybdate. The closely related strain Anabaena sp. PCC 7120 transported (99)Mo in a very similar way to A. variabilis.
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PMID:Transport of molybdate in the cyanobacterium Anabaena variabilis ATCC 29413. 1247 4

The cyanobacterium Synechocystis sp. strain PCC 6803 possesses two genes, named ppa and ppx, which, respectively, encode proteins involved in the hydrolysis of inorganic phosphate polymers, namely, inorganic pyrophosphatase (PPA, EC 3.6.1.1), an essential enzyme that hydrolyzes pyrophosphate, and exopolyphosphatase (PPX, EC 3.6.1.11), a processive enzyme that releases the terminal orthophosphate group from linear polyphosphates. Northern blots showed that both single-copy genes are induced by long-term inorganic phosphate (P(i)) starvation, transcript levels being markedly increased (ca. 10- and 20-fold, respectively) relative to P(i)-sufficient cells. Concurrent increases of both PPA and PPX specific activities and protein levels by P(i) deprivation were also observed. On the other hand, a knockout mutant was obtained by insertional mutagenesis of ppx, but it could not be achieved with ppa, thus indicating that PPA function is essential for cell viability. Moreover, whereas the ppx mutant exhibited under P(i)-sufficient conditions lower growth rates than the wild-type and was certainly devoid of PPX activity, it showed a severe reduction of the PPA levels. These results are the first evidence on the involvement of both PPA and PPX in a possible intracellular P(i)-recycling enzymatic process activated under P(i)-starvation.
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PMID:Concurrent transcriptional activation of ppa and ppx genes by phosphate deprivation in the cyanobacterium Synechocystis sp. strain PCC 6803. 1261 77


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