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

The cyanobacterium Plectonema boryanum (IU 594-UTEX 594) fixes N2 only in the absence of combined N and of O2. We induced nitrogenase by transfer to anaerobic N-free medium and studied the effect of Mo starvation on nitrogenase activity and synthesis. Activity was first detected within 3 h after transfer by the acetylene reduction assay in controls, increasing for at least 25 h. Cells grown on nitrate and Mo and then transferred to N-free, Mo-free medium produced 8% of the control nitrogenase activity. Addition of W to the Mo-free medium reduced the activity to 0.5%. Under both Mo starvation conditions, nitrogenase protein components were synthesized. Component II of the cyanobacterial enzyme was detected by in vitro complementation with Mo-containing component I from Klebsiella pneumoniae or Azotobacter vinelandii but not Clostridium pasteurianum. Component I activity was restored by addition of Mo to cultures in which new enzyme synthesis was blocked by chloramphenicol. Acidified extracts of Plectonema induced in Mo-containing medium contained the Fe-Mo cofactor required to activate extracts of the Azotobacter mutant UW45 in vitro, but they did not activate extracts of Mo-starved Plectonema. Analysis of 35SO4(2-)-labeled proteins by polyacrylamide gel electrophoresis suggested that Mo is required for the conversion of a high-molecular-weight precursor to component I in Plectonema.
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PMID:Molybdenum independence of nitrogenase component synthesis in the non-heterocystous cyanobacterium Plectonema. 9 92

Pure cultures of the symbiotic cyanobacterium-bryophyte association with Anthoceros punctatus were reconstituted by using Nostoc sp. strain UCD 7801 or its 3-(3,4-dichlorophenol)-1,1-dimethylurea (DCMU)-resistant mutant strain, UCD 218. The cultures were grown under high light intensity with CO2 as the sole carbon source and then incubated in the dark to deplete endogenous reductant pools before measurements of nitrogenase activities (acetylene reduction). High rates of light-dependent acetylene reduction were obtained both before starvation in the dark and after recovery from starvation, regardless of which of the two Nostoc strains was reconstituted in the association. Rates of acetylene reduction by symbiotic tissue with the wild-type Nostoc strain decreased 99 and 96% after 28 h of incubation in the dark and after reexposure to light in the presence of 5 microM DCMU, respectively. Supplementation of the medium with glucose restored nitrogenase activity in the dark to a rate that was 64% of the illuminated rate. In the light and in the presence of 5 microM DCMU, acetylene reduction could be restored to 91% of the uninhibited rate by the exogenous presence of various carbohydrates. The rate of acetylene reduction in the presence of DCMU was 34% of the uninhibited rate of tissue in association with the DCMU-resistant strain UCD 218. This result implies that photosynthates produced immediately by the cyanobacterium can supply at least one-third of the reductant required for nitrogenase activity on a short-term basis in the symbiotic association. However, high steady-state rates of nitrogenase activity by symbiotic Nostoc strains appear to depend on endogenous carbohydrate reserves, which are presumably supplied as photosynthate from both A. punctatus tissue and the Nostoc strain.
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PMID:Physiological sources of reductant for nitrogen fixation activity in Nostoc sp. strain UCD 7801 in symbiotic association with Anthoceros punctatus. 193 24

Strains of aerobic, microaerobic, nonsymbiotic, and symbiotic dinitrogen-fixing bacteria were screened for the presence of alternative nitrogenase (N2ase) genes by DNA hybridization between genomic DNA and DNA encoding structural genes for components 1 of three different enzymes. A nifDK gene probe was used as a control to test for the presence of the commonly occurring Mo-Fe N2ase, a vnfDGK gene probe was used to show the presence of V-Fe N2ase, and an anfDGK probe was used to detect Fe N2ase. Hitherto, all three enzymes have been identified in Azotobacter vinelandii OP, and all but the Fe N2ase are present in Azotobacter chroococcum ATCC 4412 (MCD1). Mo-Fe N2ase and V-Fe N2ase structural genes only were confirmed in this strain and in two other strains of A. chroococcum (ATCC 480 and ATCC 9043). A similar pattern was observed with Azotobacter beijerinckii ATCC 19360 and Azotobacter nigricans ATCC 35009. Genes for all three systems are apparently present in two strains of Azotobacter paspali (ATCC 23367 and ATCC 23833) and also in Azomonas agilis ATCC 7494. There was no good evidence for the existence of any genes other than Mo-Fe N2ase structural genes in several Rhizobium meliloti strains, cowpea Rhizobium strain 32H1, or Bradyrhizobium japonicum. Nitrogenase and nitrogenase genes in Azorhizobium caulinodans behaved in an intermediate fashion, showing (i) the formation of ethane from acetylene under Mo starvation, a characteristic of alternative nitrogenases, and (ii) a surprising degree of cross-hybridization to the vnfDGK, but not the anfDGK, probe. vnfDGK- and anfDGK-like sequences were not detected in two saccharolytic Pseudomonas species or Azospirillum brasilense Sp7. The occurrence of alternative N2ases seems restricted to members of the family Azotobacteraceae among the aerobic and microaerobic diazotrophs tested, suggesting that an ability to cope with O2 when fixing N2 may be an important factor influencing the distribution of alternative nitrogenases.
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PMID:Detection of alternative nitrogenases in aerobic gram-negative nitrogen-fixing bacteria. 198 27

Frankia vesicles are differentiated during nitrogen starvation; they contain nitrogenase whether produced by free-living frankiae or by frankiae in actinorhizal root nodules. Vesicles are surrounded by envelopes of several monolayers of uncharacterized lipid. It has been suggested that the envelope limits diffusion of O2 into the vesicle cytoplasm, thereby preventing inactivation of nitrogenase. Whole vesicles were prepared on sucrose gradients and sonicated, and vesicle envelopes were isolated on top of a cushion of 40% sucrose. Transmission electron microscopy of potassium permanganate-fixed envelopes confirmed the purity of these preparations. Only the outer and inner envelope layers were visible in permanganate-fixed intact vesicles; the laminae were not visible in aldehyde-osmium-fixed, lead citrate-uranyl acetate-stained whole vesicles. However, the laminated nature of the envelope was clearly evident in sonicated vesicles and in envelope fragments fixed with KMnO4. The observations indicate that partial disruption of the vesicle envelope enables its visualization with permanganate fixation, and these observations open the way for further studies on the relationship of the vesicle surface to environmental conditions.
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PMID:Isolation and structure of the lipid envelopes from the nitrogen-fixing vesicles of Frankia sp. strain CpI1. 200 7

Experiments using plasmid-borne gene fusions and direct RNA measurements have revealed that expression from the nifA gene is induced in Rhizobium meliloti when the external oxygen concentration is reduced to microaerobic levels. Induction occurs in the absence of alfalfa and in the presence of fixed nitrogen and does not require ntrC. The production of functional nifA gene product (NifA) can be demonstrated by its ability to activate the nitrogenase promoter P1. Aerobic induction of nifA can also occur during nitrogen starvation at low pH, but in this case induction is dependent on ntrC and does not lead to P1 activation. The data indicate that reduced oxygen tension is potentially a major trigger for symbiotic activation of nitrogen fixation in Rhizobium species.
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PMID:The nifA gene of Rhizobium meliloti is oxygen regulated. 243 89

When the filamentous, nitrogen-fixing cyanobacterium Anabaena variabilis ATCC 29413 was subjected to nitrogen starvation under aerobic conditions, a complex series of events was initiated which resulted in heterocyst formation and derepression of the ability to fix dinitrogen. Using DNA-RNA hybridization techniques, we monitored the expression of several genes during nitrogen starvation and correlated changes in the mRNA levels with changes in enzyme activity, protein levels, and morphology. Nitrogenase mRNA was first observed after about 8.5 h of nitrogen starvation, as was nitrogenase activity. Late proheterocysts were present at that time. The level of nitrogenase mRNA increased for 5 to 6 h and then leveled off. Phycocyanin and allophycocyanin mRNA levels decreased rapidly within 1 h of nitrogen starvation; the levels increased later, as nitrogen starvation was alleviated, first by protein breakdown and then by nitrogen fixation. The average half-life of A. variabilis mRNA was determined by pulse-labeling techniques to be 16 to 18 min. Hybridization analysis showed that cpc and apc mRNAs also had half-lives of 16 to 18 min; the half-lives were not significantly different under nitrogen starvation conditions. Our results support the idea that the changes induced by nitrogen starvation are primarily the result of transcriptional regulation.
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PMID:Changes in gene expression during nitrogen starvation in Anabaena variabilis ATCC 29413. 249 42

The addition of DL-7-azatryptophan (AZAT), a tryptophan analog, to continuous cultures of Anabaena sp. strain CA grown with 10 mM nitrate as the nitrogen source resulted in the differentiation of heterocysts. Analysis of the intracellular amino acid pools of Anabaena sp. strain CA after the addition of AZAT showed a marked decline in the intracellular glutamate pool and a slight increase in the levels of glutamine. The in vitro activity of glutamate synthase, the second enzyme involved in primary ammonia assimilation in Anabaena spp., was partially inhibited by the presence of AZAT at concentrations which are effective in triggering heterocyst formation (15% inhibition at 10 microM AZAT and up to 85% inhibition at 1.0 mM AZAT). Azaserine, a glutamine analog and potent glutamate synthase inhibitor, had no effect on the triggering of heterocyst development from undifferentiated batch and continuous cultures of Anabaena sp. strain CA. However, the presence of 1.0 microM azaserine significantly decreased the intracellular glutamate pool and increased the glutamine pool. The addition of AZAT also caused a decrease in the C-phycocyanin content of Anabaena sp. strain CA as a result of its proteolytic degradation. AZAT also had an inhibitory effect on the nitrogenase activity of Anabaena sp. strain CA. All these results suggest that AZAT causes a general nitrogen starvation of Anabaena sp. strain CA filaments, triggering heterocyst synthesis.
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PMID:Nitrogen starvation mediated by DL-7-azatryptophan in the cyanobacterium Anabaena sp. strain CA. 310 56

Derepression of nitrogenase gene expression was studied at the mRNA and enzyme activity levels in anaerobic cultures of Anabaena variabilis 29413. Cells, previously grown with ammonium chloride, were incubated in the absence of fixed nitrogen compounds under an Ar atmosphere with dichlorophenyldimethyl-urea present to inhibit oxygen evolution. The appearance of nitrogenase mRNA (measured by dot blot hybridization analysis) and nitrogenase activity (measured as acetylene-reducing activity) was followed, and the cells were also observed by phase-contrast microscopy. Nitrogenase mRNA could be detected after 1.5 to 2.0 h of nitrogen starvation; enzyme activity appeared about 1 h later. Although enzyme activity increased for many hours, mRNA levels reached a steady state rapidly. Neither heterocysts nor proheterocysts formed under these conditions; however, the cells were observed to shrink and become chlorotic. When anaerobic, derepressed cultures were exposed to oxygen, nitrogenase mRNA levels decreased very rapidly.
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PMID:Regulation of nitrogenase gene expression in anaerobic cultures of Anabaena variabilis. 312 56

A histidine auxotrophic (hisA) mutant of Klebsiella pneumoniae is phenotypically Nif- when grown with 20 micrograms of histidine ml-1 but Nif+ when supplied with histidine at 100 micrograms ml-1. Reversion to Nif+ at 20 micrograms of histidine ml-1 occurs phenotypically by the addition of 2-thiazolyl-DL-alanine or genetically by mutation in hisG; 2-thiazolyl-DL-alanine inhibits and hisG encodes phosphoribosyl phosphotransferase, the first enzyme of the histidine biosynthetic pathway which consumes ATP. Physiological studies of the hisA mutant JS85 showed that after removal of NH4+ from a culture of the mutant grown with 20 micrograms of histidine ml-1, synthesis of nitrogenase polypeptides occurred at a rate similar to that in the wild type for about 3 h and acetylene reduction activity reached about 10% of the fully derepressed wild-type level. Shortly thereafter the concentration of intracellular adenylates decreased; in particular, ATP fell to about 10% of normal levels. Also, nitrogenase proteins (nifHDK products) and the nifJ gene product stopped being synthesized. These effects were not due to impairment of growth or protein synthesis by histidine starvation. Inhibition of phosphoribosyl phosphotransferase with 2-thiazolyl-DL-alanine restored nitrogenase activity and synthesis, indicating that the effect of the hisA mutation on nif expression was probably a consequence of lowered energy resources that occurred during anaerobic N starvation. The loss of ATP was not associated with nitrogenase synthesis or activity, since hisA nifA and hisA nifH double mutants underwent a loss of ATP in derepressing conditions. Transcription from the nifL, nifN, and nifH promoters was examined in hisA strains with Mu d(Ap lac) fusions in these nif genes. Transcription was not significantly influenced under conditions where adenylates were decreased in concentration. Also nif mRNA apparently accumulated in cultures unable to synthesize nitrogenase, suggesting that translational control of nif gene product synthesis occurs under unfavorable energetic conditions.
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PMID:Regulation of nitrogenase synthesis in histidine auxotrophs of Klebsiella pneumoniae with altered levels of adenylate nucleotides. 327 13

Cell-free extracts with high nitrogenase activity were prepared by sonic oscillation and French press treatment from the blue-gree alga Anabaena cylindrica. Extracts were prepared from cells grown on a 95% N(2)-5% CO(2) gas mixture followed by a period of nitrogen starvation under an atmosphere of 95% argon-5% CO(2). No increase in the specific activity of extracts was achieved by breaking heterocysts. Activity (assayed by acetylene reduction) was found to be dependent on adenosine triphosphate (ATP), an ATP-generating system, and a low-potential reductant. Na(2)S(2)O(2) employed as reductant supports higher rates of nitrogenase activity than reduced ferredoxin. The activity is associated with a small-particle fraction that can be sedimented by ultracentrifugation. In contrast to the particulate nitrogenase of Azotobacter, which is stable in air, the A. cylindrica nitrogenase is an oxygen sensitive as nitrogenase prepared from anaerobic bacteria.
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PMID:Nitrogenase activity in cell-free extracts of the blue-green alga, Anabaena cylindrica. 499 40


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