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PubMed1994

Foreign gene expression in marine cyanobacteria under pseudo-continuous culture.

Foreign gene expression in a marine cyanobacterium, Synechococcus NKBG 15041c, has been carried out in both batch and pseudo-continuous culture, using chloramphenicaol acetyltransferase (CAT) as a model peptide and the broad host range vector pKT230. CAT has been successfully expressed in marine cyanobacteria under kanamycin resistance gene promoter. Pseudo-continuous culture of these recombinant marine cyanobacteria has been done by varying the dilution rate. At a dilution rate between 0.01 to 0.02 h-1, highest productivity was achieved. Under these conditions, long-term pseudo-continuous culture of recombinant marine cyanobacteria was achieved for more than 600 h with CAT productivity 18-fold greater than that observed in batch culture.

Chloramphenicol O-Acetyltransferase↗
PubMed1989

Whole-cell biosensors for environmental monitoring.

Concern over the pollution risk to drinking water from industry and agriculture is growing, and the need for continuous on-line monitoring recognised. There is increasing use of living organisms as the sensitive agent to detect the presence of pollutants, and whole-cell biosensors are seen to have particular advantages in such environmental monitoring. The development of a mediated amperometric biosensor, incorporating the cyanobacterium Synechococcus as the biocatalyst, for on-line herbicide monitoring is described. The biosensor is able to detect a wide range of herbicides with sites of action on the photosynthetic electron transport chain, at concentrations down to 20 micrograms litre-1 and possesses a working life of up to 7 days. The use of alginate immobilisation of the biocatalyst to overcome the problems associated with obtaining a realistic shelf life for the biosensor is discussed.

Biosensing Techniques↗
PubMed1978

Some properties of allophycocyanin from a thermophilic blue-green alga.

Allophycocyanin was purified from the extremely thermophilic blue-green alga Synechococcus lividus. It was shown to be more stable to thermal or urea denaturation than allophycocyanin from a mesophilic organisms. Its amino acid composition and spectroscopic response to pH were investigated. An analysis was made of the relatively low fluorescence polarization of allophycocyanin compared to that of a comparable sized aggregate of the biliprotein, C-phycocyanin. A rather speculative conclusion was reached that suggests that the lower polarization of allophycocyanin may be caused by orientations or positioning of the chromophores that are more favorable for intra-protein energy transfer.

Journal Article↗
PubMed1996

Comparative thermodynamic elucidation of the structural stability of thermophilic proteins.

Differential scanning calorimetry, circular dichroism, and visible absorption spectrophotometry were employed to elucidate the structural stability of thermophilic phycocyanin derived from Cyanidium caldarium, a eucaryotic organism which contains a nucleus, grown in acidic conditions (pH 3.4) at 54 degrees C. The obtained results were compared with those previously reported for thermophilic phycocyanin derived from Synechococcus lividus, a procaryote containing no organized nucleus, grown in alkaline conditions (pH 8.5) at 52 degrees C. The temperature of thermal unfolding (t(d)) was found to be comparable between C. caldarium (73 degrees C) and S. lividus (74 degrees C) phycocyanins. The apparent free energy of unfolding (DeltaG([urea]=0)) at zero denaturant (urea) concentration was also comparable: 9.1 and 8.7 kcal/mole for unfolding the chromophore part of the protein, and 5.0 and 4.3 kcal/mole for unfolding the apoprotein part of the protein, respectively. These values of t(d) and DeltaG([urea]=0) were significantly higher than those previously reported for mesophilic Phormidium luridum phycocyanin (grown at 25 degrees C). These findings revealed that relatively higher values of t(d) and DeltaG([urea]=0) were characteristics of thermophilic proteins. In contrast, the enthalpies of completed unfolding (DeltaH(d)) and the half-completed unfolding (DeltaH(d)) 1 2 for C. caldarium phycocyanin were much lower than those for S. lividus protein (89 versus 180 kcal/mole and 62 versus 115 kcal/mole, respectively). Factors contributing to a lower DeltaH(d) in C. caldarium protein and the role of charged groups in enhancing the stability of thermophilic proteins were discussed.

Journal Article↗
PubMed1988

Cladistic analysis of ribosomal RNAs--the phylogeny of eukaryotes with respect to the endosymbiotic theory.

A strict cladistic analysis of 5S and 16S rRNA secondary and primary structure confirms particular hypotheses concerning the phylogeny of eukaryotes: plastids of Euglena, green algae and land plants, and the cyanelle of Cyanophora share a specific character and are closely related to cyanobacteria of the Synechococcus-type. Angiosperm mitochondria share specific signatures with the alpha subdivision of rhodobacteria. Cyanophora is a member of the Euglenozoa, the Oomycetes are derived from a group of heterokont algae.

Base Sequence↗
PubMed1990

Cloning, sequencing, and transcriptional analysis of the recA gene of Pseudomonas cepacia.

A recombinant plasmid carrying the recA gene of Pseudomonas cepacia complements a recA mutation of Escherichia coli and restores UV and methylmethane sulfonate resistance, as well as recombinational proficiency. The predicted amino acid (aa) sequence of P. cepacia RecA (347 aa; Mr, 37256) is highly homologous to the RecA proteins from Thiobacillus ferrooxidans (74% aa homology), Pseudomonas aeruginosa (72%), E. coli (71%), Anabaena variabilis (61%), and Synechococcus sp. strains PCC7002 (59%). The transcription of the recA gene in P. cepacia and E. coli, which starts at almost the same site, was enhanced slightly by UV irradiation in the former and markedly in the latter bacteria. An SOS box characteristic to LexA-regulated promoters, along with the -10 and -35 consensus sequences, was found in the 5' upstream region of the P. cepacia recA gene.

Amino Acid Sequence↗
PubMed1991

A small multigene family encodes the rod-core linker polypeptides of Anabaena sp. PCC7120 phycobilisomes.

The cpc operon of Anabaena sp. PCC7120 is shown to encode ten genes: 5'-cpcB-cpcA-cpcC-cpcD-cpcE-cpcF- cpcG1-cpcG2-cpcG3-cpcG4-3'. The 3' portion of this operon includes four tandemly repeated genes encoding phycocyanin (PC)-associated, rod-core linker polypeptides of the phycobilisomes (PBS). The products of these four genes are most similar at their N termini, and overall are 50-61% identical and 68-76% similar to one another. The four CpcG proteins of Anabaena sp. PCC7120 are 41-47% identical and 62-65% similar to the single CpcG rod-core linker protein in Synechococcus sp. PCC7002. The N-terminal domains of the polypeptides are also more distantly related to the conserved domains of other types of rod-linker polypeptides associated with PC, phycoerythrin, and allophycocyanin (AP). Three of these rod-core linker proteins (CpcG1, CpcG2, and CpcG4) were demonstrated to occur in isolated PBS by N-terminal amino acid sequence analyses. These results indicate that previously proposed models for the PBS of Anabaena sp. are incorrect. It is suggested that the PBS of Anabaena sp. have eight peripheral rods, each of which interacts with the AP of the core via a specific rod-core linker (CpcG) polypeptide.

Amino Acid Sequence↗
PubMed1994

The gene encoding cytochrome-c oxidase subunit I from Synechocystis PCC6803.

The gene (coxI or CoxA) encoding subunit I (COI) of cytochrome-c oxidase (cytochrome aa3) of Synechocystis PCC6803, Synechococcus PCC7942 (Anacystis nidulans R2) and Nostoc PCC8002 (Nostoc Mac), was identified by heterologous hybridization of chromosomal digests with a 17-bp oligodeoxyribonucleotide (probe C) derived from the coxI of Paracoccus denitrificans. A single genomic fragment was found to bind to probe C in all chromosomal digests. Due to its favorable signal-to-noise ratio, the genome of Synechocystis was chosen for the isolation and sequencing of this gene. A genomic DNA library in pUC18 was screened with probe C. The two probe C-positive plasmids, pDAUV1 and pDAUV2, contained a 1-kb overlapping region, with the conserved 17-bp sequence encoding the CuB-binding region of the COI polypeptide. These plasmids were subcloned into competent Escherichia coli DH5 alpha cells, and the nucleotide sequences were determined. The deduced amino acid (aa) sequences of Synechocystis COI and homologous proteins from a variety of prokaryotic and eukaryotic organisms showed an overall similarity of between 38.6 and 45.8%. Hydropathy plots revealed 12 potential transmembrane helices. All of the six histidines needed for the binding of heme a and the heme a3/CuB bimetallic center are present in the expected positions of the Synechocystis COI protein (533 aa, M(r) 59,390). A monospecific antibody raised against P. denitrificans COI gave an unequivocal immunological cross-reaction on Western blots of membrane preparations from Synechocystis, Anacystis and Nostoc, showing that the product of gene coxI is indeed synthesized and incorporated into cyanobacterial membranes.

Amino Acid Sequence↗
PubMed1996

Cloning, expression, purification and characterization of DNA topoisomerase I of Mycobacterium tuberculosis.

The complete gene encoding Topoisomerase 1 (Topo I) from Mycobacterium tuberculosis (MTb), Erdman strain, has been isolated and sequenced. The coding region of this gene is 2700 nt encoding a polypeptide of 900 amino acids with a calculated molecular mass of 99353 Da. The amino-acid sequence identity compared to E. coli and Synechococcus Topo I is 22 and 30%, respectively. The gene was expressed in E. coli BL21(DE3) and purified to near homogeneity. Recombinant MTb Topo I is enzymatically active, relaxing negatively supercoiled DNA in a magnesium-dependent, ATP-independent reaction. Spermidine, a typical inhibitor of prokaryotic type I DNA topoisomerase, inhibits the activity. Unlike the more well-characterized E. coli Topo I, MTb Topo I does not contain a zinc-finger DNA-binding motif in the C-terminal domain of the protein.

Amino Acid Sequence↗
PubMed2004

Relationship between uptake capacity and differential toxicity of the herbicide atrazine in selected microalgal species.

Microalgal species vary in their sensitivity to the triazine herbicide, atrazine. This study examined both atrazine uptake and cellular characteristics of microalgae to determine if either can be used to predict algal sensitivity. Standard toxicity tests were performed on five microalgal species, each representing a different algal division or habitat. Test species listed in order of increasing sensitivity were: Isochrysis galbana, Dunaliella tertiolecta, Phaeodactylum tricornutum, Pseudokirchneriella subcapitata, and Synechococcus sp. Each species was exposed to 14C-atrazine at its growth rate EC50 concentration (44-91 microg/L). At five time-points over 96 h, samples were filtered to collect algae and washed with unlabeled atrazine to displace labeled atrazine loosely absorbed to the cell surface. Radioactivity present on filters and in the growth medium was measured by liquid scintillation counting. Relationships between algal species-sensitivity to atrazine and compound uptake, cell dry weight, cell volume, and cell surface area were determined by linear regression analysis. Cell size measurements (based on dry weight, biovolume, and surface area) were significantly correlated with atrazine uptake (R2 > 0.45, P-value < 0.05). There was a significant correlation between atrazine uptake and species-sensitivity to atrazine (R2 = 0.5413 , P-value = 0.0012). These results indicate that smaller cells with greater surface area to volume ratios will incorporate more atrazine, and in general, will be more sensitive to atrazine exposure. However, I. galbana, with small cell size and relatively high atrazine uptake was the least sensitive species tested. This species and others may have mechanisms to compensate for atrazine stress that make predicting responses of microalgal communities difficult.

Atrazine↗
PubMed2003

Dissecting a cyanobacterial proteolytic system: efficiency in inducing degradation of the D1 protein of photosystem II in cyanobacteria and plants.

A chromatography fraction, prepared from isolated thylakoids of a fatty acid desaturation mutant (Fad6/desA Colon, two colons Km(r)) of the cyanobacterium Synechocystis 6803, could induce an initial cleavage of the D1 protein in Photosystem II (PSII) particles of Synechocystis 6803 mutant and Synechococcus 7002 wild type as well as in supercomplexes of PSII-light harvesting complex II of spinach. Proteolysis was demonstrated both in darkness and in light as a reduction in the amount of full-length D1 protein or as a production of C-terminal initial degradation fragments. In the Synechocystis mutant, the main degradation fragment was a 10-kDa C-terminal one, indicating an initial cleavage occurring in the cytoplasmic DE-loop of the D1 protein. A protein component of 70-90 kDa isolated from the chromatographic fraction was found to be involved in the production of this 10-kDa fragment. In spinach, only traces of the corresponding fragment were detected, whereas a 24-kDa C-terminal fragment accumulated, indicating an initial cleavage in the lumenal AB-loop of the D1 protein. Also in Synechocystis the 24-kDa fragment was detected as a faint band. An antibody raised against the Arabidopsis DegP2 protease recognized a 35-kDa band in the proteolytically active chromatographic fraction, suggesting the existence of a lumenal protease that may be the homologue DegP of Synechocystis. The identity of the other protease cleaving the D1 protein in the DE-loop exposed on the stromal (cytoplasmic) side of the membrane is discussed.

ATP-Dependent Proteases↗
PubMed2006

The nitrate/nitrite ABC transporter of Phormidium laminosum: phosphorylation state of NrtA is not involved in its substrate binding activity.

Most cyanobacteria take up nitrate or nitrite through a multisubunit ABC transporter (ATP-binding cassette) located in the cytoplasmic membrane. Nitrate and nitrite transport activity is instantaneously blocked by the presence of ammonium in the medium. Previous biochemical studies reported the existence of phosphorylation/dephosphorylation events of the nitrate transporter (NRT) related to the presence of ammonium-sensitive kinase/phosphatase activities in plasma membranes of the cyanobacterium Synechococcus elongatus PCC 6301. In this work, we have analyzed the biochemical properties of the periplasmic nitrate/nitrite-binding subunit (NrtA) of NRT from the thermophilic nondiazotrophic cyanobacterium Phormidium laminosum. Our results show that cyanobacterial NrtA is phosphorylated in vivo. However, substrate binding activity in vitro is not affected by the phosphorylation state of the protein, ruling out the possibility that phosphorylation/dephosphorylation of NrtA is involved in the regulation of the nitrate/nitrite uptake by NRT transporter. Moreover, NrtA is present as multiple isoforms showing the same molecular mass but different isoelectric points ranging from pI 5 to 6. Mass spectrometric characterization of NrtA isoforms shows that the protein is phosphorylated at residue Tyr203, and contains several methionine sulphoxide residues which account for the observed isoforms. Both phosphorylated and non-phosphorylated forms of NrtA are active in vitro, showing comparable binding affinity for nitrate and nitrite. Both substrates behave as pure competitive inhibitors with a binding stoichiometry of one molecule of anion per NrtA monomer.

ATP-Binding Cassette Transporters↗
PubMed2005

Direct mediatorless electron transport between the monolayer of photosystem II and poly(mercapto-p-benzoquinone) modified gold electrode--new design of biosensor for herbicide detection.

Photosystem II (PSII) modified gold electrodes have been prepared providing mediatorless electron transport on the basis of electrodeposited conductive layer poly-mercapto-p-benzoquinone (polySBQ). Such electrodes are suitable in construction of biosensors for PSII inhibiting herbicides. PolySBQ layer was synthesized on (i) screen-printed gold electrodes and (ii) gold microelctodes in an array on silicon substrate, by electrochemical-oxidation of sulpho-p-benzoquinone (SBQ) at +650 mV versus Ag/AgCl. The basic properties of polySBQ layer were characterized using linear sweep voltammetry and atomic force microscopy (AFM). The typical redox response for quinones was observed. The optimal length of the polymer providing direct electron transfer (DET) was found to be very close to 30 nm. PSII particles isolated from the thermophilic cyanobacteria Synechococcus bigranulatus were physically adsorbed on the polySBQ covered gold electrodes. The generation of photocurrent was observed at E=+250 mV (versus Ag/AgCl) without addition of any mediator. The basic properties of DET were studied. We concluded that: (i) PSII active in DET is immobilized in form of monolayer; (ii) the charge transport from PSII to gold working electrode (AuWE) is fast and dominated by the rate of the enzymatic reaction; (iii) polySBQ layer drains electrons from the Q(A) pocket of the photosystem since the electrode activity is inhibited by specific inhibitor, i.e. diuron (DCMU); (iv) the stability of the photosystem immobilized on gold electrodes by using polySBQ is comparable to the stability of PSII in solution under the same experimental conditions; (v) the inhibition of the photosystem by herbicide DCMU follows the sigmoid dependence; (vi) I(50) as well as limit of detection (LOD) show an improved sensitivity compared to other published biosensing systems using PSII as bioactive part.

Adsorption↗
PubMed2005

Evaluation of the sensitivity of marine microalgal strains to the heavy metals, Cu, As, Sb, Pb and Cd.

The sensitivity of nine marine microalgal species (consisting of five divisions and seven genera) to the five heavy metals, Cu(II), As(V), Sb(III), Pb(II) and Cd(II) was studied by using a fluorometric growth-inhibition assay with 96-well microplates. The algal strains studied were Cylindrotheca sp. and the LPP group that respectively characterize aggregating and filamentous types, and Chlorococcum littorale, Chlorococcum sp., Isochrysis galbana, Tetraselmis tetrathele, Heterocapsa sp., Synechococcus sp. and Prasinococcus sp. for types that occur as single cells. A good linear relationship was observed between the chlorophyll a concentration and intensity of chlorophyll fluorescence (485-nm excitation filter and 645-nm emission filter) when the chlorophyll a concentration was within the range of 0.10-5.0 microg ml(-1). A starting cell concentration of 0.10 or 0.25 microg Chl a ml(-1) was therefore selected. In accordance with OECD 201 standard procedures, the IC(50) value (concentration of a metal producing 50% growth inhibition relative to the control) was determined 72 h after adding a heavy metal by using the biomass integral. The microplate toxicity test used in this study is considered to be applicable to diverse algae, not only enumerating species but also hardly enumerating ones.

Biological Assay↗
PubMed2005

Ultrastructural stability under high temperature or intensive light stress conferred by a small heat shock protein in cyanobacteria.

The role and sub-cellular localization of the small heat shock protein HspA under stress conditions was investigated comparing the cyanobacterium Synechococcus strain ECT16-1, which constitutively expresses HspA, with the reference strain ECT. The ultrastructure of ECT cells under elevated temperature or intensive light stress exhibited severe damage including aggregation of cytosol and disordered thylakoid membranes, but in ECT16-1 cells these ultrastructural changes were much less conspicuous. Immunocytochemical studies showed that the main localization of HspA in the ECT16-1 cells shifted from the thylakoid area to the cytoplasm, then back to thylakoid area during the heat stress. Expression of HspA stabilized the morphology of nucleoids. The results are discussed, in particular with respect to the unique property of HspA to associate with thylakoid membranes.

Bacterial Proteins↗
PubMed2004

The light-responsive promoter of cyanobacterial ORF76 gene overlaps with the htpG terminator.

A Synechococcus PCC7942 gene, encoding 76 amino acids of an unknown protein (designated ORF76), is located at the same orientation and downstream of the htpG gene. The processed site of ORF76 transcripts is located at position +39 with respect to the true transcription initiation site. The non-E. colisigma70-like basal promoter of ORF76 (-51 to -9) is controlled by three cis-acting elements: positively acting element (-160 to -86), negative regulatory element (-86 to -51) and light-responsive element (-51 to +63) that, together, respond to high light induction at transcriptional level. The ORF76 gene is expressed as monocistronic transcript. The promoter elements of ORF76 gene overlap with the coding sequence and 3' end formation signal of htpG gene.

Amino Acid Sequence↗
PubMed2004

Global carbon/nitrogen control by PII signal transduction in cyanobacteria: from signals to targets.

PII signal transduction plays a pervasive role in microbial nitrogen control. Different phylogenetic lineages have developed various signal transduction schemes around the highly conserved core of the signalling system, which consists of the PII proteins. Among all various bacterial PII signalling systems, the one in cyanobacteria is so far unique: in unicellular strains, the mode of covalent modification is by serine phosphorylation and the interpretation of the cellular nitrogen status occurs by measuring the 2-oxoglutarate levels. Recent advances have been the identification of the phospho-PII phosphatase, the resolution of the crystal structure of PII proteins from Synechococcus and Synechocystis strains and the identification of novel functions of PII regulation in cyanobacteria, which highlight the central role of PII signalling for the acclimation to changing carbon-nitrogen regimes.

Bacterial Proteins↗
PubMed2006

Evolutionary relationship between initial enzymes of tetrapyrrole biosynthesis.

Glutamate-1-semialdehyde 2,1-aminomutase (GSAM) is the second enzyme in the C(5) pathway of tetrapyrrole biosynthesis found in most bacteria, in archaea and in plants. It catalyzes the transamination of glutamate-1-semialdehyde to 5-aminolevulinic acid (ALA) in a pyridoxal 5'-phosphate (PLP)-dependent manner. We present the crystal structure of GSAM from the thermophilic cyanobacterium Thermosynechococcus elongatus (GSAM(Tel)) in its PLP-bound form at 2.85A resolution. GSAM(Tel) is a symmetric homodimer, whereas GSAM from Synechococcus (GSAM(Syn)) has been described as asymmetric. The symmetry of GSAM(Tel) thus challenges the previously proposed negative cooperativity between monomers of this enzyme. Furthermore, GSAM(Tel) reveals an extensive flexible region at the interface of the proposed complex of GSAM with glutamyl-tRNA reductase (GluTR), the preceding enzyme in tetrapyrrole biosynthesis. Compared to GSAM(Syn), the monomers of GSAM(Tel) are rotated away from each other along the dimerization interface by 10 degrees . The associated flexibility of GSAM may be essential for complex formation with GluTR to occur. Unexpectedly, we find that GSAM is structurally related to 5-aminolevulinate synthase (ALAS), the ALA-producing enzyme in the Shemin pathway of alpha-proteobacteria and non-plant eukaryotes. This structural relationship applies also to the corresponding subfamilies of PLP-dependent enzymes. We thus propose that the CoA-subfamily (including ALAS) and the aminotransferase subfamily II (including GSAM) are evolutionarily closely related and that ALAS may thus have evolved from GSAM.

5-Aminolevulinate Synthetase↗