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PubMed1995

Two enzymes together capable of cysteine biosynthesis are encoded on a cyanobacterial plasmid.

The cyanobacterium Synechococcus sp. PCC 7942 contains two endogenous, genetically cryptic plasmids of 8.0 and 48.5 kb, which have been designated pANS and pANL, respectively. Characterization of the 3.8 kb Ba6 BamHI fragment of pANL identified three open reading frames which were transcriptionally regulated by sulfur availability and the protein CysR. One of these genes, designated srpG, encodes a protein which exhibits 67% amino acid identity to the Escherichia coli enzyme O-acetyl-L-serine (thio)-lyase A. Overlapping the 3' end of srpG is a second gene, designated srpH, which encodes a protein with similarity to the amino-terminal region of serine acetyltransferase enzymes. DNA hybridization results indicate that there is second copy of srpG in Synechococcus sp. PCC 7942, which is consistent with previous isoenzyme studies on O-acetyl-L-serine (thiol)-lyase in cyanobacteria. The introduction of srpG and srpH into E. coli cysKcysM and cysE mutant strains, respectively, results in the complementation of the lesion in cysteine biosynthesis. Additionally, the E. coli cysK cysM strain containing srpG is able to utilize sulfate more efficiently than thiosulfate, indicating that SrpG is probably a type A O-acetyl-L-serine (thiol)-lyase. The possible function of these genes in the adaptation of cyanobacteria to sulfur stress is discussed.

Acetyltransferases↗
PubMed1977

Adaptation by hot spring phototrophs to reduced light intensities.

Photosynthesis was measured by the 14C method on natural as well as low light adapted populations of Chloroflexus (a photosynthetic bacterium) and Synechococcus (a blue-green alga) from hot springs in Yellowstone National Park (Wyoming U.S.A.), to test the ability of these phototrophs to photosynthesize at a variety of light intensities. The herbicide 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU) was used to distinguish uptake of the blue-green alga from that of the photosynthetic bacterium, while measurements of chlorophyll a and bacteriochlorophyll c served to quantitate the standing crops of these organisms. Natural populations of Synechococcus were found to be slightly inhibited by full sunlight intensities (summer values can surpass 90000 Lux), whereas the Chloroflexus populations were not. Populations of both phototrophs subjected to reduced light intensities through the use of neutral density filters were found to adapt to low light, and then become severely inhibited by high light intensities. Adaptation to various light regimes may be an important ecological phenomenon to the survival of these hot spring phototrophs.

Adaptation, Biological↗
PubMed1996

Cyanobacteria carrying an smt-lux transcriptional fusion as biosensors for the detection of heavy metal cations.

The metal-responsive smt operator/promoter region of Synechococcus PCC7942 was fused to the luxCDABE genes of Vibrio fischeri. Plasmid DNA (pJLE23) carrying this fusion conferred metal ion-inducible luminescence to transformed cyanobacteria. Synechococcus PCC7942 (pJLE23) was sensitive to ZnCl2 concentrations within a range of 0.5-4 microM as demonstrated by induction of luminescence. Trace levels of CuSO24 and CdCl2 were also detected.

Bacterial Proteins↗
PubMed2004

The biogeography and phylogeny of unicellular cyanobacterial symbionts in sponges from Australia and the Mediterranean.

The distribution, host associations, and phylogenetic relationships of the unicellular cyanobacterial symbionts of selected marine sponges were investigated with direct 16s rDNA sequencing. The results indicate that the symbionts of the marine sponges Aplysina aerophoba, Ircinia variabilis, and Petrosia ficiformis from the Mediterranean, four Chondrilla species from Australia and the Mediterranean, and Haliclona sp. from Australia support a diversity of symbionts comprising at least four closely related species of Synechococcus. These include the symbionts presently described as Aphanocapsa feldmannii from P. ficiformis and Chondrilla nucula. A fifth symbiont from Cymbastela marshae in Australia is an undescribed symbiont of sponges, related to Oscillatoria rosea. One symbiont, Candidatus Synechococcus spongiarum, was found in diverse sponge genera in the Mediterranean Sea and the Indian, Pacific, and Southern oceans, whereas others were apparently more restricted in host association and distribution. These results are discussed in terms of the biodiversity and biogeographic distributions of cyanobacterial symbionts.

Animals↗
PubMed2007

Histidine ligands in bacterial metallothionein enhance cluster stability.

The cyanobacterial metallothionein (MT) SmtA is the prototype for bacterial MTs and protects against elevated levels of zinc. In contrast to mammalian MTs, bacterial MTs coordinate to metal ions not only via cysteine sulfurs, but unusually for MTs, also via histidine nitrogens. To investigate whether histidine coordination in these metal-sulfur clusters provides advantages over S-coordination only, we mutated the two metal-binding histidine residues in the cyanobacterial MT SmtA from Synechococcus PCC7942 to cysteines. We show that the mutant proteins are still capable of binding up to four zinc ions as is the wild-type protein. However, the mutations perturb protein folding and metal-binding dynamics. Interestingly, several homologues of SmtA also show variations in these two residues. We conclude that histidine residues in Synechococcus PCC7942 SmtA have a stabilising effect due to electrostatic interactions that impact on protein folding and metal cluster charge, and are involved in fine-tuning the reactivity of the bound metal ions.

Amino Acid Sequence↗
PubMed2005

Community phylogenetic analysis of moderately thermophilic cyanobacterial mats from China, the Philippines and Thailand.

Most community molecular studies of thermophilic cyanobacterial mats to date have focused on Synechococcus occurring at temperatures of approximately 50-65 degrees C. These reveal that molecular diversity exceeds that indicated by morphology, and that phylogeographic lineages exist. The moderately thermophilic and generally filamentous cyanobacterial mat communities occurring at lower temperatures have not previously been investigated at the community molecular level. Here we report community diversity in mats of 42-53 degrees C recovered from previously unstudied geothermal locations. Separation of 16S rRNA gene-defined genotypes from community DNA was achieved by DGGE. Genotypic diversity was greater than morphotype diversity in all mats sampled, although genotypes generally corresponded to observed morphotypes. Thirty-six sequences were recovered from DGGE bands. Phylogenetic analyses revealed these to form novel thermophilic lineages distinct from their mesophilic counterparts, within Calothrix, Cyanothece, Fischerella, Phormidium, Pleurocapsa, Oscillatoria and Synechococcus. Where filamentous cyanobacterial sequences belonging to the same genus were recovered from the same site, these were generally closely affiliated. Location-specific sequences were observed for some genotypes recovered from geochemically similar yet spatially separated sites, thus providing evidence for phylogeographic lineages that evolve in isolation. Other genotypes were more closely affiliated to geographically remote counterparts from similar habitats suggesting that adaptation to certain niches is also important.

China↗
PubMed2000

Diel Patterns of Regulation of rbcL Transcription in a Cyanobacterium and a Prymnesiophyte.

Diel patterns of rbcL transcription, ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) activity, and whole cell carbon fixation were compared in the marine cyanobacterium Synechococcus PCC7002 and the chromophytic prymnesiophyte Pavlova gyrans. Both organisms were grown on a 12:12 light-dark cycle, with the light period starting at 0700. Strong diel patterns in these three aspects of carbon fixation occurred in both organisms, with maximal levels in the light period and minima in the dark. In Synechococcus, maximal rbcL transcript abundance occurred at noon and was followed by rapid disappearance. RubisCO enzyme activity and whole cell carbon fixation were elevated at 1600, and they disappeared over the next 8 hours. In contrast, in Pavlova, rbcL transcript abundance was maximal at 1600, and it was maintained at 66% of this level into the dark period (2000). Whole cell carbon fixation and RubisCO activity were elevated into the dark period (at 2000), being 77% and 81%, respectively, of the maximum. A similar diel pattern of cyanobacterial-like and chromophyte-like rbcL transcription has been observed in natural phytoplankton populations. These studies suggest that chromophytes are more adapted to take advantage of carbon fixation late in the day than cyanophytes.

Journal Article↗
PubMed1990

Reconstitution of electron transport in photosystem I with PsaC and PsaD proteins expressed in Escherichia coli.

A fusion protein, denoted PsaC1, which contains an amino-terminal extension of five amino acids (MEHSM...) and is derived from an in vitro modified form of the psaC gene of Synechococcus sp. PCC 7002, has been over-expressed in Escherichia coli. The product of the psaD gene of Nostoc sp. PCC 8009 has similarly been over-expressed. The PsaC1 and PsaD proteins can be combined with the photosystem I core protein of Synechococcus sp. PCC 6301 to reconstitute electron transport from P700 to the terminal FA/FB acceptors. Reconstitution was found to be absolutely dependent on reinsertion of the iron-sulfur clusters in the PsaC1 apoprotein and on the presence of the PsaD protein. This implies that the PsaC1 holoprotein does not bind solely to the PsaA/PsaB heterodimer but rather that its interaction with these proteins is mediated through the PsaD protein.

Amino Acid Sequence↗
PubMed1992

Immobilized ferredoxins for affinity chromatography of ferredoxin-dependent enzymes.

An immobilized ferredoxin more stable than the conventional immobilized spinach ferrodoxin was prepared by reacting CNBr-Sepharose with ferredoxins isolated from barley and Synechococcus vulcanus, a thermophilic blue-green alga. The dissociation constants of immobilized ferredoxin from spinach, barley and S. vulcanus for spinach ferredoxin-NADP reductase were 0.922, 2.505 and 5.209 microM, respectively, whereas those for barley ferredoxin-NADP reductase were 1.159, 0.579 and 2.851 microM, respectively. The order of stability was S. vulcanus greater than barley greater than spinach. The immobilized ferredoxin was applied to the simultaneous detection of ferredoxin-dependent enzymes in spinach chloroplasts. Over 20 polypeptides were detected. Synechococcus ferredoxin could also be immobilized on a Toyopearl gel and repeatedly used in an automated high-performance liquid chromatographic system.

Chemical Phenomena↗
PubMed1996

A cDNA clone from Arabidopsis thaliana encoding plastidic ferredoxin:sulfite reductase.

A cDNA with an open reading frame of 1929 bp (termed sir) was isolated from a lambda ZapII library of Arabidopsis thaliana leaf tissue. The polypeptide sequence deduced from the cDNA is homologous to the ferredoxin-dependent sulfite reductase (EC 1.8.7.1) from Synechococcus PCC7942 and distantly related to the hemoprotein subunit of Escherichia coli NADPH-dependent sulfite reductase (EC 1.8.1.2). A molecular mass of 71.98 kDa can be predicted for a ferredoxin sulfite reductase from A. thaliana. The polypeptide consists of 642 amino acids including a transit peptide of 66 residues (6.72 kDa) that is assumed to direct the protein into the plastid. For expression and enzymatic characterization of a putative A. thaliana ferredoxin sulfite reductase, the DNA of the transit peptide was deleted by a PCR method. The truncated cDNA clone was expressed as his-tag fusion protein. The modified gene product was enzymatically inactive but specific cross-reaction with polyclonal antibodies against ferredoxin sulfite reductase from Synechococcus is seen as confirmation of its identity as higher plant ferredoxin sulfite reductase.

Amino Acid Sequence↗
PubMed2005

Cyanobacterial psbA families in Anabaena and Synechocystis encode trace, constitutive and UVB-induced D1 isoforms.

Cyanobacteria cope with UVB induced photoinhibition of Photosystem II by regulating multiple psbA genes to boost the expression of D1 protein (in Synechocystis sp. PCC6803), or to exchange the constitutive D1:1 protein to an alternate D1:2 isoform (in Synechococcus sp. PCC7942). To define more general patterns of cyanobacterial psbA expression, we applied moderately photoinhibitory UVB to Anabaena sp. PCC7120 and tracked the expression of its five psbA genes. psbAI, encoding a D1:1 protein isoform characterized by a Gln130, represented the majority of the psbA transcript pool under control conditions. psbAI transcripts decreased upon UVB treatment but the total psbA transcript pool increased 3.5 fold within 90 min as a result of sharply increased psbAII, psbAIV and psbAIII transcripts encoding an alternate D1:2 protein isoform characterized by Glu130, similar to that of Synechococcus. Upon UVB treatment the relaxation of flash induced chlorophyll fluorescence showed a characteristic acceleration of a decay phase likely associated with the exchange from the D1:1 protein isoform encoded by psbAI to the alternate D1:2 isoform encoded by psbAIV, psbAII and psbAIII. Throughout the UVB treatment the divergent psbA0 made only a trace contribution to the total psbA transcript pool. This suggests a similarity to the divergent psbAI gene from Synechocystis, whose natural expression we demonstrate for the first time at a trace level similar to psbA0 in Anabaena. These trace-expressed psbA genes in two different cyanobacteria raise questions concerning the functions of these divergent genes.

Amino Acid Sequence↗
PubMed2001

Fluorescent probes for non-invasive bioenergetic studies of whole cyanobacterial cells.

Fluorescent DeltapH and DeltaPsi indicators have been screened for the non-invasive monitoring of bioenergetic processes in whole cells of the cyanobacterium Synechocystis sp. PCC 6803. Acridine yellow and Acridine orange proved to be the best DeltapH indicators for the investigation of thylakoid and cytoplasmic membrane energization: While Acridine yellow indicated only cytosolic energization, Acridine orange showed signals from both the thylakoid lumen and the cytosol that could be separated kinetically. Both indicators were applied successfully to monitor cellular energetics, such as the interplay of linear and cyclic photosynthetic electron transport, osmotic adaptation and solute transport across the cytoplasmic membrane. In contrast, useful membrane potential indicators were more difficult to find, with Di-4-ANEPPS and Brilliant cresyl blue being the only promising candidates for further studies. Finally, Acridine yellow and Acridine orange could also be applied successfully for the thermophilic cyanobacterium Synechococcus elongatus. Different from Synechocystis sp. PCC 6803, where both respiration and ATP hydrolysis could be utilized for cytoplasmic membrane energization, proton extrusion at the cytoplasmic membrane in Synechococcus elongatus was preferentially driven by ATP hydrolysis.

Acridine Orange↗
PubMed1989

Spectroscopic studies of cyanobacterial phycobilisomes lacking core polypeptides.

Synechococcus sp. PCC 7002 (Agmenellum quadruplicatum PR6) genes encoding two highly conserved phycobilisome core polypeptides, a small linker polypeptide (LC8, apcC) and the allophycocyanin-B alpha-subunit (alpha APB, apcD), respectively, were interrupted by insertion of restriction fragments carrying the neomycin phosphotransferase gene of Tn5. The interrupted genes were used to transform Synechococcus sp. PCC 7002 to kanamycin resistance. The apcC- mutant assembled phycobilisomes lacking the LC8 polypeptide and the apcD- mutant assembled phycobilisomes lacking alpha APB. No other differences between the compositions of the mutant and wild-type phycobilisomes were detected. The apcC- strain grew about 25% more slowly than the wild-type, and its phycobilisomes dissociated more rapidly in 0.33 M Na/K-PO4 (pH 8.0) or in 0.75 M Na/K-PO4 at pH 8.0, at 40 degrees C, than did those of the wild-type. The phycobilisomes of this mutant were indistinguishable from those of the wild-type with respect to absorption and circular dichroism spectra, as well as time-resolved fluorescence emission. Steady-state emission spectra indicate a small decrease in long wavelength (680 nm) emission from the apcC- phycobilisomes and a complementary increase in shorter wavelength (665 nm) emission, relative to wild-type phycobilisomes. Strain apcD- phycobilisomes appear to be functionally indistinguishable from those of the wild-type, in spite of the absence of the two alpha APB subunits which bear terminal acceptor bilins. The only spectroscopic difference was seen in the steady-state fluorescence emission, for which the emission of the mutant was about 15% higher than that of the wild-type and was slightly blue-shifted. A phenotype has yet to be found for the apcD- mutation.

Cloning, Molecular↗
PubMed2001

Time-resolved fluorescence emission measurements of photosystem I particles of various cyanobacteria: a unified compartmental model.

Photosystem I (PS-I) contains a small fraction of chlorophylls (Chls) that absorb at wavelengths longer than the primary electron donor P700. The total number of these long wavelength Chls and their spectral distribution are strongly species dependent. In this contribution we present room temperature time-resolved fluorescence data of five PS-I core complexes that contain different amounts of these long wavelength Chls, i.e., monomeric and trimeric photosystem I particles of the cyanobacteria Synechocystis sp. PCC 6803, Synechococcus elongatus, and Spirulina platensis, which were obtained using a synchroscan streak camera. Global analysis of the data reveals considerable differences between the equilibration components (3.4-15 ps) and trapping components (23-50 ps) of the various PS-I complexes. We show that a relatively simple compartmental model can be used to reproduce all of the observed kinetics and demonstrate that the large kinetic differences are purely the result of differences in the long wavelength Chl content. This procedure not only offers rate constants of energy transfer between and of trapping from the compartments, but also well-defined room temperature emission spectra of the individual Chl pools. A pool of red shifted Chls absorbing around 702 nm and emitting around 712 nm was found to be a common feature of all studied PS-I particles. These red shifted Chls were found to be located neither very close to P700 nor very remote from P700. In Synechococcus trimeric and Spirulina monomeric PS-I cores, a second pool of red Chls was present which absorbs around 708 nm, and emits around 721 nm. In Spirulina trimeric PS-I cores an even more red shifted second pool of red Chls was found, absorbing around 715 nm and emitting at 730 nm.

Chlorophyll↗
PubMed2000

Constitutive expression of a small heat-shock protein confers cellular thermotolerance and thermal protection to the photosynthetic apparatus in cyanobacteria.

The role of a small heat-shock protein (Hsp) in the acquisition of thermotolerance in cyanobacteria was investigated. Synechococcus sp. PCC 7942 was transformed with an expression vector carrying the coding sequence of the hspA gene encoding a small heat-shock protein from Synechococcus vulcanus under the control of the tac promoter. The transformant which was shown to constitutively express HspA displayed improved viability compared with the reference strain upon transfer from 30 to 50 degrees C in the light. When the heat shock was given in darkness, the survival rate in the reference strain increased greatly, approaching a level similar to that for the HspA expressing strain after heat shock in the light. Expression of HspA increased thermal resistance of photosystem II (PS II) and protected phycocyanin from heat-induced photobleaching. Our results are indicative of a central role for HspA in amelioration of the harmful effect of light during heat stress and identified the possible sites of action of the small Hsp in vivo to be the PS II complex and the light-harvesting phycobilisomes.

Adaptation, Physiological↗
PubMed1998

A role for the signal transduction protein PII in the control of nitrate/nitrite uptake in a cyanobacterium.

In the cyanobacterium Synechococcus sp. strain PCC 7942, ammonium exerts a rapid and reversible inhibition of the nitrate and nitrite uptake, and the PII protein (GlnB) is differentially phosphorylated depending on the intracellular N/C balance. RNA/DNA hybridizations, as well as nitrate and nitrite uptake experiments, were carried out with the wild-type strain and a PII-null mutant. The transcriptional control by ammonium of the expression of the nir-nrt ABCD-narB operon remained operative in the mutant but, in contrast to the wild-type strain, the mutant took up nitrate and nitrite even in the presence of ammonium. Moreover, the wild-type phenotype was restored by insertion of a copy of the wild-type glnB gene in the genome of the PII-null mutant. These results indicate that the unphosphorylated form of PII is involved in the short-term inhibition by ammonium of the nitrate and nitrite uptake in Synechococcus sp. strain PCC 7942.

Ammonium Chloride↗
PubMed2003

Positive and negative selection of mutant forms of prokaryotic (cyanobacterial) ribulose-1,5-bisphosphate carboxylase/oxygenase.

A system for biological selection of randomly mutagenized ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) genes from the cyanobacterium Synechococcus PCC6301 was designed in which a Rubisco deletion mutant of the photosynthetic bacterium Rhodobacter capsulatus served as a host. Trans-complementation with the Synechococcus PCC6301 rbcLS genes enabled anaerobic photoautotrophic growth of the R.capsulatus deletion strain with 5% CO(2), but not with 1.5% CO(2) in the atmosphere, and this strain could not grow under aerobic chemoautotrophic conditions. Phenotypic differences between the R.capsulatus host strain complemented with the wild-type rbcLS genes and transconjugates carrying mutated genes were used to identify mutants that were able to complement to photoautotrophic growth with 1.5% CO(2). These "positive" mutant proteins were unaffected for any measured kinetic properties, with a single exception. A mutant with a valine substitution at phenylalanine 342 had an increased affinity for ribulose-1,5-bisphosphate. Mutants with changes in the affinity for CO(2) were isolated through negative selection, in which mutants incapable of complementing R.capsulatus to photoautotrophic growth with 5% CO(2) were identified. Mutations at aspartate 103 resulted in enzymes that were greatly affected for different kinetic parameters, including an increased K(m) for CO(2). This study demonstrated that random mutagenesis and bioselection procedures could be used to identify mutations that influence important properties of bacterial Rubisco; these residues would not have been identified by other methods.

Bacterial Proteins↗
PubMed2001

Circadian rhythms in microalgae.

Circadian rhythms have been described in a variety of microalgae. In each group, some model organisms arose and most detailed studies have been done with them. They include the cyanobacterium ("blue-green alga") Synechococcus and eukaryotic microalgae Gonyaulax polyedra (Dinophyta), Chlamydomonas reinhardtii (Chlorophyta), and Euglena gracilis (Euglenophyta). This review focuses on recent approaches to depict molecular components of the circadian system and the mechanisms of regulation in these organisms. In Synechococcus, the identification of the kailocus, which represents a central part of its oscillatory system, is discussed, as well as diverse approaches based on a luminescent reporter gene, which is driven by a clock-controlled cyanobacterial promoter. In eukaryotic microalgae, the diversity of genes/proteins that are controlled by the circadian clock is described and the kind of regulation (transcriptional and translational control) is emphasized. The role and function of conserved clock-controlled RNA-binding proteins such as CCTR from Gonyaulaxor Chlamy 1 from Chlamydomonas are discussed.

Animals↗