Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Synechococcus”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,009 records · Page 56Linked to original sources
PubMed2007

labA: a novel gene required for negative feedback regulation of the cyanobacterial circadian clock protein KaiC.

In the cyanobacterium Synechococcus elongatus PCC 7942, circadian timing is transmitted from the KaiABC-based central oscillator to the transcription factor RpaA via the KaiC-interacting histidine kinase SasA to activate transcription, thereby generating rhythmic circadian gene expression. However, KaiC can also repress circadian gene expression, including its own. The mechanism and significance of this negative feedback regulation have been unclear. Here, we report a novel gene, labA (low-amplitude and bright), that is required for negative feedback regulation of KaiC. Disruption of labA abolished transcriptional repression caused by overexpression of KaiC and elevated the trough levels of circadian gene expression, resulting in a low-amplitude phenotype. In contrast, overexpression of labA significantly lowered circadian gene expression. Furthermore, genetic analysis indicated that labA and sasA function in parallel pathways to regulate kaiBC expression, whereas rpaA functions downstream from labA for kaiBC expression. These results suggest that temporal information from the KaiABC-based oscillator diverges into a LabA-dependent negative pathway and a SasA-dependent positive pathway, and then converges onto RpaA to generate robust circadian gene expression. It is likely that quantitative information of KaiC is transmitted to RpaA through LabA, whereas SasA mediates the state of the KaiABC-based oscillator.

Amino Acid Sequence↗
PubMed2006

Iron deficiency in cyanobacteria causes monomerization of photosystem I trimers and reduces the capacity for state transitions and the effective absorption cross section of photosystem I in vivo.

The induction of the isiA (CP43') protein in iron-stressed cyanobacteria is accompanied by the formation of a ring of 18 CP43' proteins around the photosystem I (PSI) trimer and is thought to increase the absorption cross section of PSI within the CP43'-PSI supercomplex. In contrast to these in vitro studies, our in vivo measurements failed to demonstrate any increase of the PSI absorption cross section in two strains (Synechococcus sp. PCC 7942 and Synechocystis sp. PCC 6803) of iron-stressed cells. We report that iron-stressed cells exhibited a reduced capacity for state transitions and limited dark reduction of the plastoquinone pool, which accounts for the increase in PSII-related 685 nm chlorophyll fluorescence under iron deficiency. This was accompanied by lower abundance of the NADP-dehydrogenase complex and the PSI-associated subunit PsaL, as well as a reduced amount of phosphatidylglycerol. Nondenaturating polyacrylamide gel electrophoresis separation of the chlorophyll-protein complexes indicated that the monomeric form of PSI is favored over the trimeric form of PSI under iron stress. Thus, we demonstrate that the induction of CP43' does not increase the PSI functional absorption cross section of whole cells in vivo, but rather, induces monomerization of PSI trimers and reduces the capacity for state transitions. We discuss the role of CP43' as an effective energy quencher to photoprotect PSII and PSI under unfavorable environmental conditions in cyanobacteria in vivo.

Bacterial Proteins↗
PubMed2004

Insertion of the cytochrome b5 heme-binding loop into an SH3 domain. Effects on structure and stability, and clues about the cytochrome's architecture.

Under native conditions, apocytochrome b(5) exhibits a stable core and a disordered heme-binding region that refolds upon association with the cofactor. The termini of this flexible region are in close proximity, suggesting that loop closure may contribute to the thermodynamic properties of the apocytochrome. A chimeric protein containing 43 residues encompassing the cytochrome loop was constructed using the cyanobacterial photosystem I accessory protein E (PsaE) from Synechococcus sp. PCC 7002 as a structured scaffold. PsaE has the topology of an SH3 domain, and the insertion was engineered to replace its 14-residue CD loop. NMR and optical spectroscopies showed that the hybrid protein (named EbE1) was folded under native conditions and that it retained the characteristics of an SH3 domain. NMR spectroscopy revealed that structural and dynamic differences were confined near the site of loop insertion. Variable-temperature 1D NMR spectra of EbE1 confirmed the presence of a kinetic unfolding barrier. Thermal and chemical denaturations of PsaE and EbE1 demonstrated cooperative, two-state transitions; the stability of the PsaE scaffold was found only moderately compromised by the insertion, with a DeltaT(m) of 8.3 degrees C, a DeltaC(m) of 1.5 M urea, and a DeltaDeltaG degrees of 4.2 kJ/mole. The data implied that the penalty for constraining the ends of the inserted region was lower than the approximately 6.4 kJ/mole calculated for a self-avoiding chain. Extrapolation of these results to cytochrome b(5) suggested that the intrinsic stability of the folded portion of the apoprotein reflected only a small detrimental contribution from the large heme-binding domain.

Binding Sites↗
PubMed2005

Identification of cyanobacterial cell division genes by comparative and mutational analyses.

We performed comparative and mutational analyses to define more comprehensively the repertoire of genes involved in cyanobacterial cell division. Genes ftsE, ftsI, ftsQ, ftsW, and (previously recognized) ftsZ, minC, minD, minE and sulA were identified as homologues of cell division genes of Gram-negative and Gram-positive bacteria. Transposon mutagenesis of Synechococcus elongatus PCC 7942 identified five additional genes, cdv1, cdv2, cdv3, ftn6 and cikA, involved in cell division. cdv1 encodes a presumptive periplasmic peptidyl-prolyl cis-trans isomerase. cdv2 has similarity to ylmF which, like divIVA, lies within the Gram-positive bacterial ylm gene cluster whose members have functions associated with division. Conservation of other ylm genes in cyanobacteria suggests that cyanobacteria and Gram-positive bacteria share specific division proteins. Two ylm homologues are also found in algal and plant genomes. cdv3 has low but significant similarity to divIVA, suggesting that minE and cdv3 both mediate division-site determination in cyanobacteria. In contrast, Gram-positive bacteria lack minE, and (Gram-negative) proteobacteria lack divIVA. ftn6, of unknown function, and the circadian input kinase, cikA, are specific to cyanobacteria. In S. elongatus, unlike in other bacteria, FtsZ rings are formed at sites occupied by nucleoids. Thus, the division machinery of cyanobacteria differs in its composition and regulation from that of Gram-negative and Gram-positive bacteria.

Bacillus subtilis↗
PubMed2005

Transcriptional regulation of the circadian clock operon kaiBC by upstream regions in cyanobacteria.

In the cyanobacterium, Synechococcus elongatus PCC 7942, the kaiBC operon is upregulated by the KaiA protein and downregulated by the KaiC protein to generate circadian oscillation. We investigated the regulation of kaiBC transcription. A primer extension and deletion analyses of the upstream region mapped the sufficient promoter region (SPR) to base pairs -55 to +1 (the transcription start site, TSS) and identified a constitutive negative regulatory region upstream of the SPR (base pairs -897 to -56) that extended into the coding sequence of kaiA. Base-pair substitution within the SPR identified a sequence from -52 to -28 that was the essential element for transcription. Most of the examined sequences drove rhythmic expression of a luxAB reporter that was similar to the expression driven by the kaiBC promoter (PkaiBC) and responded to the overexpression of kaiA or kaiC, even in a promoter activity range of 1-8000%. These results indicate that circadian feedback regulation by KaiA and KaiC is addressed to a global step preceding transcription driven by PkaiBC. However, increasing or decreasing the intrinsic activity of PkaiBC greatly affected the rhythm, suggesting that constitutive adjustment of PkaiBC activity by the sequences identified here is essential for the oscillator.

Bacterial Proteins↗
PubMed2006

The pseudo-receiver domain of CikA regulates the cyanobacterial circadian input pathway.

CikA (circadian input kinase) is a component of the cyanobacterial circadian clock that aids in synchronizing the endogenous oscillator with the external environment. cikA mutants of the prokaryotic circadian model organism Synechococcus elongatus PCC 7942 fail to reset the phase of the circadian rhythm of gene expression after an environmental time cue, and also exhibit reduced amplitude and shortened period of circadian oscillation. CikA has histidine protein kinase (HPK) activity that is modulated in vitro by GAF and pseudo-receiver (PsR) domains. Here we show that the PsR domain negatively regulates HPK activity in vivo and also serves as an interaction module to dock CikA at a specific subcellular location. Phenotypes conferred by alleles that encode CikA variants showed that all domains except the featureless N-terminus are required for CikA function. Overexpression of all alleles that encode the PsR domain, whether or not the HPK is functional, caused a dominant arrhythmic phenotype, whereas overexpressed variants that lack PsR did not. Subcellular localization of intact CikA identified a polar focus whereas a variant without PsR showed uniform distribution in the cell, consistent with a model in which PsR mediates interaction with other input pathway components.

Bacterial Proteins↗
PubMed2005

The Calvin cycle in cyanobacteria is regulated by CP12 via the NAD(H)/NADP(H) ratio under light/dark conditions.

In Synechococcus PCC7942 cells grown in the dark, the concentrations of NAD(H) and NADP(H) were 128+/-2.5 and 483+/-4.0 microm, respectively, while those in the cells under light conditions were 100+/-5.0 and 649+/-7.0 microm, respectively. Analysis of gel filtration indicated that the change of the ratio of NADP(H) to NAD(H) in cyanobacterial cells under light/dark conditions controls the reversible dissociation of the PRK/CP12/GAPDH complex (approximately 520 kDa) consisting of phosphoribulokinase (PRK), CP12, and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). S. 7942 CP12 lacked the two Cys residues essential for formation of the N-terminal peptide loop in the CP12 of higher plants, but the N-terminal region of S. 7942 CP12 had the ability to be associated with PRK. The growth of mutant cells in which the CP12 gene was disrupted by a kanamycin resistance cartridge gene was almost the same as that of wild-type cells under continuous light conditions. However, under the light/dark cycle (12 h/12 h), the growth of CP12-disrupted mutant cells was significantly inhibited compared with that of wild-type cells. The mutant cells showed a decreased rate of O2 consumption and an increased level of ribulose 1,5-bisphosphate compared with wild-type cells in the dark. These data suggest that under light and dark conditions, the oligomerization of CP12 with PRK and GAPDH regulates the activities of both enzymes and thus the carbon flow from the Calvin cycle to the oxidative pentose phosphate cycle.

Amino Acid Sequence↗
PubMed2005

Biogeochemical processes in the saline meromictic Lake Kaiike, Japan: implications from molecular isotopic evidences of photosynthetic pigments.

Stable carbon and nitrogen isotopic compositions were determined for individual photosynthetic pigments isolated and purified from the saline meromictic Lake Kaiike, Japan, to investigate species-independent biogeochemical processes of photoautotrophs in the natural environment. In the anoxic monimolimnion and benthic microbial mats, the carbon isotopic compositions of BChls e and isorenieratene related to brown-coloured strains of green sulfur bacteria are substantially ( approximately 10 per thousand) depleted in (13)C relative to those found in the chemocline. In conjunction with 16S rDNA evidence reported previously, it strongly suggests that Pelodyctyon luteolum inhabited and photosynthesized in the anoxic monimolimnion and benthic microbial mats by using (13)C-depleted regenerated CO(2). By contrast, both Chl a and BChl a in the monimolimnion and microbial mats have similar isotopic compositions as they do in the chemocline, implying that the source organisms live only in the chemocline. In the chemocline, the nitrogen isotopic compositions of BChl e homologues ranges from -7.7 to-6.5 per thousand, whereas that of BChl a is -2.1 per thousand. These isotopic compositions suggest that green sulfur bacteria Chlorobium phaeovibrioides would conduct nitrogen fixation in the chemocline, whereas purple sulfur bacteria Halochromatium sp. and cyanobacteria Synechococcus sp. may assimilate nitrite.

Bacteria↗
PubMed2006

New models for circadian systems in microorganisms.

Microorganisms provide important model systems for studying circadian rhythms, and they are overturning established ideas about the molecular mechanisms of rhythmicity. The transcription/translation feedback model that has been accepted as the basis of circadian clock mechanisms in eukaryotes does not account for old data from the alga Acetabularia demonstrating that transcription is not required for rhythmicity. Moreover, new results showing in vitro rhythmicity of KaiC protein phosphorylation in the cyanobacterium Synechococcus, and rhythmicity in strains of the fungus Neurospora carrying clock gene null mutations, require new ways of looking at circadian systems.

Acetabularia↗
PubMed2004

No transcription-translation feedback in circadian rhythm of KaiC phosphorylation.

An autoregulatory transcription-translation feedback loop is thought to be essential in generating circadian rhythms in any model organism. In the cyanobacterium Synechococcus elongatus, the essential clock protein KaiC is proposed to form this type of transcriptional negative feedback. Nevertheless, we demonstrate here temperature-compensated, robust circadian cycling of KaiC phosphorylation even without kaiBC messenger RNA accumulation under continuous dark conditions. This rhythm persisted in the presence of a transcription or translation inhibitor. Moreover, kinetic profiles in the ratio of KaiC autophosphorylation-dephosphorylation were also temperature compensated in vitro. Thus, the cyanobacterial clock can keep time independent of de novo transcription and translation processes.

Bacterial Proteins↗
PubMed2006

Dimethylsulfoniopropionate uptake by marine phytoplankton.

Dimethylsulfoniopropionate (DMSP) accounts for most of the organic sulfur fluxes from primary to secondary producers in marine microbial food webs. Incubations of natural communities and axenic cultures with radio-labeled DMSP showed that dominant phytoplankton groups of the ocean, the unicellular cyanobacteria Prochlorococcus and Synechococcus and diatoms, as well as heterotrophic bacteria take up and assimilate DMSP sulfur, thus diverting a proportion of plankton-produced organic sulfur from emission into the atmosphere.

Bacteria↗
PubMed2007

Counting low-copy number proteins in a single cell.

We have designed a microfluidic device in which we can manipulate, lyse, label, separate, and quantify the protein contents of a single cell using single-molecule fluorescence counting. Generic labeling of proteins is achieved through fluorescent-antibody binding. The use of cylindrical optics enables high-efficiency (approximately 60%) counting of molecules in micrometer-sized channels. We used this microfluidic device to quantify beta2 adrenergic receptors expressed in insect cells (SF9). We also analyzed phycobiliprotein contents in individual cyanobacterial cells (Synechococcus sp. PCC 7942) and observed marked differences in the levels of specific complexes in cell populations that were grown under nitrogen-depleted conditions.

Animals↗
PubMed1961

Some characteristics of a thermophilic blue-green alga.

An alga identified as Synechococcus lividus has an exponential growth rate of nine doublings per day at 52 degrees C with illumination of 1500 foot-candles. It uses nitrate or urea as a nitrogen source and does not use acetate or glucose. It seems a promising organism for atmospheric regeneration in sealed cabins.

Eukaryota↗
PubMed2006

Marine and freshwater cyanophages in a Laurentian Great Lake: evidence from infectivity assays and molecular analyses of g20 genes.

While it is well established that viruses play an important role in the structure of marine microbial food webs, few studies have directly addressed their role in large lake systems. As part of an ongoing study of the microbial ecology of Lake Erie, we have examined the distribution and diversity of viruses in this system. One surprising result has been the pervasive distribution of cyanophages that infect the marine cyanobacterial isolate Synechococcus sp. strain WH7803. Viruses that lytically infect this cyanobacterium were identified throughout the western basin of Lake Erie, as well as in locations within the central and eastern basins. Analyses of the gene encoding the g20 viral capsid assembly protein (a conservative phylogenetic marker for the cyanophage) indicate that these viruses, as well as amplicons from natural populations and the ballast of commercial ships, are related to marine cyanophages but in some cases form a unique clade, leaving questions concerning the native hosts of these viruses. The results suggest that cyanophages may be as important in freshwater systems as they are known to be in marine systems.

Bacteriophages↗
PubMed2006

Luminescent whole-cell cyanobacterial bioreporter for measuring Fe availability in diverse marine environments.

A Synechococcus sp. strain PCC 7002 Fe bioreporter was constructed containing the isiAB promoter fused to the Vibrio harveyi luxAB genes. Bioreporter luminescence was characterized with respect to the free ferric ion concentration in trace metal-buffered synthetic medium. The applicability of the Fe bioreporter to assess Fe availability in the natural environment was tested by using samples collected from the Baltic Sea and from the high-nutrient, low-chlorophyll subarctic Pacific Ocean. Parallel assessment of dissolved Fe and bioreporter response confirmed that direct chemical measurements of dissolved Fe should not be considered alone when assessing Fe availability to phytoplankton.

Bacterial Proteins↗
PubMed2006

Biotransformation of Hg(II) by cyanobacteria.

The biotransformation of Hg(II) by cyanobacteria was investigated under aerobic and pH-controlled culture conditions. Mercury was supplied as HgCl(2) in amounts emulating those found under heavily impacted environmental conditions where bioremediation would be appropriate. The analytical procedures used to measure mercury within the culture solution, including that in the cyanobacterial cells, used reduction under both acid and alkaline conditions in the presence of SnCl(2). Acid reduction detected free Hg(II) ions and its complexes, whereas alkaline reduction revealed that meta-cinnabar (beta-HgS) constituted the major biotransformed and cellularly associated mercury pool. This was true for all investigated species of cyanobacteria: Limnothrix planctonica (Lemm.), Synechococcus leopoldiensis (Racib.) Komarek, and Phormidium limnetica (Lemm.). From the outset of mercury exposure, there was rapid synthesis of beta-HgS and Hg(0); however, the production rate for the latter decreased quickly. Inhibitory studies using dimethylfumarate and iodoacetamide to modify intra- and extracellular thiols, respectively, revealed that the former thiol pool was required for the conversion of Hg(II) into beta-HgS. In addition, increasing the temperature enhanced the amount of beta-HgS produced, with a concomitant decrease in Hg(0) volatilization. These findings suggest that in the environment, cyanobacteria at the air-water interface could act to convert substantial amounts of Hg(II) into beta-HgS. Furthermore, the efficiency of conversion into beta-HgS by cyanobacteria may lead to the development of applications in the bioremediation of mercury.

Biodegradation, Environmental↗
PubMed2005

Differential sunlight sensitivity of picophytoplankton from surface Mediterranean Coastal Waters.

We tested the sensitivity of coastal picophytoplankton exposed to natural sunlight in short-term experiments. Cell abundance and cell-specific chlorophyll fluorescence were significantly reduced in Prochlorococcus spp. but not in Synechococcus, whereas picoeukaryotes had an intermediate response. These results are the first direct evidence of a differential sensitivity to sunlight of these ubiquitous marine members of unicellular phytoplankton.

Animals↗
PubMed2005

Nitrate and phosphate affect cultivability of cyanobacteria from environments with low nutrient levels.

Nitrate and phosphate concentrations higher than those found in the natural environment slowed down growth of two strains of non-bloom-forming, phycoerythrin-rich Synechococcus spp. isolated from mesotrophic subalpine lakes. The results make clear why isolation of these picocyanobacteria in standard cultivation media was difficult. At low concentrations, closely related strains exhibited distinct growth characteristics with respect to these two nutrients, possibly explaining differences in their seasonal appearance in the natural environment.

Bacteriological Techniques↗