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PubMed1986

Influence of very low doses of ionizing radiation on Synechococcus lividus metabolism during the initial growth phase.

Previous results from this laboratory have shown that very low chronic doses of gamma radiation can stimulate proliferation of the Cyanobacterium Synechococcus lividus. This modification of cell proliferation occurred during the first doubling. In this paper, we have compared the metabolism of cells cultivated in a normal environment or under chronic irradiation. Incubation of the cells in a new medium induced a high superoxide dismutase (EC 1.15.1.1, SOD) activity at the 18th hour and a degradation of phycocyanin, thus demonstrating that cells were submitted to a photooxidative stress. This increase in superoxide dismutase activity was followed by concomitant peaks of glutathione reductase (EC 1.6.4.2, GR) and glucose-6-phosphate dehydrogenase (EC 1.1.1.49, G6P-DH) at the 24th hour. Irradiated cultures at a dose of 53.5 mGray/year show an earlier and higher peak of SOD, GR, and G6P-DH. In a second stage, cultures showed an earlier onset of photosynthesis under irradiation, as evidenced by an increase in pigment content and an enhancement of glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.13, GAP-DH). These results show that the radiostimulation is related to the activation of enzymes protecting against peroxides that were induced under oxidative circumstances and to the activation of a glucose catabolism via the oxidative pentose phosphate pathway.

Chlorophyll↗

PubMed1975

CO2 fixation and its regulation in Anacystis nidulans (Synechococcus).

Anacystis nidulans (Synechococcus) had a minimal doubling time of 5 hrs at 30 degrees C at saturating light intensity and carbon dioxide concentration. Half maximal growth rates in saturating CO2 occured at a light intensity of 0.54 mW per cm2, and there was an apparent threshold intensity of 0.13 mW per cm2 below which no growth occurred. Growth rate in saturating light was dependent on the concentration of CO2+H2CO3 in the medium, rather than on total dissolved CO2; half maximal rates were estimated at 0.1 mM CO2+H2CO3. Under saturating conditions of light and CO2, 14CO2 was fixed primarily into 3-PGA, and subsequently moved into sugar phosphates and amino acids. Incorporation into aspartate was relatively slow. CO2 fixation was strictly light-dependent. The changes in adenylate and pyridine nucleotide pools were followed in light/dark and dark/light transitions. Whereas adenylates relaxed slowly over 15-20 min to the concentrations characteristic of illuminated cells following the abrupt changes induced by darkening, the sharp drop in intracellular NADPH showed little dark recovery although rapid restoration occurred on reillumination. Other pyridine nucleotides showed no changes during these transitions. The nucleotide specificity and Km of partially purfied GAP dehydrogenase suggest a role for this enzyme in the regulation of CO2 fixation.

Adenosine Monophosphate↗

PubMed1975

Phosphate utilization and alkaline phosphatase activity in Anacystis nidulans (Synechococcus).

Anacystis nidulans (Synechococcus) was maintained in a medium of low phosphate concentration (0.1 mM) and grew with a normal doubling time of 5 hrs at 30 degrees C. Such cultures had a normal pigment composition and alkaline phosphatase was detectable at low specific activities only. The onset of phosphate-limited growth occurred when the phosphate concentration in the medium fell to a value below 4 muM (the limit of accurate determination by the assay method used ) and resulted in increases in alkaline phosphatase activity, reaching a final 10 to 15 fold increase in specific activity after a period of several hours. Marked changes in the overall pigment composition occurred in this period of growth restriction. The addition of phosphate to such cultures resulted in a halt in synthesis of the enzyme and the restoration of normal pigmentation before growth resumed at the normal rate. Several oraganic phosphate esters could replace inorganic phosphate for growth and were also hydrolyzed by the partially purified enzyme, but growth rates were characteristically lower and the specific activity only 3 to 4 fold higher than in cultures grown in phosphate excess. Studies with the partially purified enzyme suggested that it differed in some of its properties from other alkaline phosphatases described in the literature.

Alkaline Phosphatase↗

PubMed1994

Purification and some properties of glyceraldehyde 3-phosphate dehydrogenase from Synechococcus sp.

Glyceraldehyde 3-phosphate dehydrogenase (EC 1.2.1.13) was purified 386 fold to apparent homogeneity from the thermophilic cyanobacterium Synechococcus sp. grown at optimum light intensities in batch cultures. The molecular mass of the tetrameric form of the enzyme was 160 kDa as determined by gel filtration and sucrose gradient centrifugation in a phosphate buffer containing DTT. The pH optimum for the oxidation of NADPH was broad (6-8) and the enzyme had a pI of 4.5. The turnover number was 36,000 min-1 at 40 degrees C. The activation energy was 12.4 Kcal for t > 29 degrees C and 20.6 Kcal for t < 29 degrees C. The specific absorption coefficient, A 1% 1cm 280 mm of the pure enzyme in phosphate buffer at pH 6.8 was 15.2. By SDS gel electrophoresis molecular masses of 78 kDa and 39 kDa were found, indicating that the purified enzyme is a tetramer, probably a homotetramer. When Tris was used as buffer in the homogenization and phosphate and DTT were omitted, a high molecular form with a molecular mass above 500 kDa was found. This form was less active than the purified tetrameric form. Acetone and other organic solvents stimulated the native enzyme several fold.

Cyanobacteria↗

PubMed1994

A conditional expression vector for the cyanobacteria Synechocystis sp. strains PCC6803 and PCC6714 or Synechococcus sp. strains PCC7942 and PCC6301.

An expression vector, pFC1, has been constructed based on the promiscuous plasmid RSF1010, which provides autonomous replication in several cyanobacteria of the genera Synechocystis and Synechococcus [Mermet-Bouvier et al., Curr Microbiol 26:323-327]. pFC1 harbors the lambda cI857 repressor-encoding gene and pR promoter, followed by the lambda cro ribosome-binding site and ATG translation initiation codon. The latter is located within the unique NdeI restriction site (CATATG) of pFC1 and can be exposed after cleavage with this enzyme for in-frame fusion with the protein-coding sequence to be expressed. The Escherichia coli lacZ reporter gene cloned in pFC1 appeared to be highly expressed in heat-induced E. coli or cyanobacterial cells. In every case, beta-galactosidase amounted to at least 10% of soluble proteins.

Base Sequence↗

PubMedDate not supplied

Phylogeny of the 5S ribosomal RNA from Synechococcus lividus II: the cyanobacterial/chloroplast 5S RNAs form a common structural class.

The complete nucleotide sequence of the 5S ribosomal RNA from the cyanobacterium Synechococcus lividus II has been determined. The sequence is (sequence in text) This 5S RNA has the cyanobacterial- and chloroplast-specific nucleotide insertion between positions 30 and 31 (using the numbering system of the generalized eubacterial 5S RNA) and the chloroplast-specific nucleotide-deletion signature between positions 34 and 39. The 5S RNA of S. lividus II has 27 base differences compared with the 5S RNA of the related strain S. lividus III. This large difference may reflect an ancient divergence between these two organisms. The electrophoretic mobilities on nondenaturing polyacrylamide gels of renatured 5S RNAs from S. lividus II, S. lividus III, and spinach chloroplasts are identical, but differ considerably from that of Escherichia coli 5S RNA. This most likely reflects differences in higher-order structure between the 5S RNA of E. coli and these cyanobacterial and chloroplast 5S RNAs.

Base Sequence↗

PubMed1989

Purification and partial amino acid sequence of the glutamate 1-semialdehyde aminotransferase of barley and synechococcus.

Glutamate-1-semialdehyde aminotransferase (E.C. 5.4.3.8) was purified from barley and the cyanobacteria Synechococcus PCC 6301. The purification procedure involved serial affinity chromatography and preparative polyacrylamide gel electrophoresis under non-denaturing conditions. The aminotransferase of these two organisms showed different mobilities in non-denaturing gels. In SDS-PAGE the enzyme from both organisms migrated as a single protein with an apparent molecular weight of 46.000 Da. An antibody against the barley enzyme cross-reacted with the cyanobacterial aminotransferase. This antibody also recognized a 17 kDa peptide cleaved from the barley protein with cyanogen bromide. Amino acid sequences of the NH2-termini revealed significant homology between the eucaryotic and cyanobacterial enzyme.

Amino Acid Sequence↗

PubMed2002

Effects of nitrogen availability on pigmentation and carbon assimilation in the cyanobacterium Synechococcus sp. strain SH-94-5.

Because pigments of phototrophs can be involved either in photosynthesis or photoprotection, pigmentation changes in response to nutrient availability can affect how cells interact with their solar environment. We investigated the impact of nitrogen availability both on pigmentation of the cyanobacterium Synechococcus sp. strain SH-94-5 and on carbon assimilation by this strain in the presence or absence of UV radiation. Pigmentation changes in strain SH-94-5 due to ammonium exhaustion included phycobiliprotein degradation, an exponential decline in chlorophyll a content, and a net increase in beta-carotene. Following its replenishment, ammonium stimulated non-photosynthetic carbon assimilation for several hours prior to the resumption of photosynthesis and growth. Carbon fixation during this lag phase was concurrent with the metabolism of glycogen reserves, and it is likely that inorganic carbon was incorporated into glycogen-derived carbon skeletons primarily for amino acid synthesis. In contrast, carbon fixation was almost exclusively photosynthetic during exponential growth. UV-A radiation (320-400 nm) inhibited photosynthetic but not non-photosynthetic carbon assimilation. Only growing cells were inhibited, and the disappearance of inhibition following nitrogen depletion appeared to result from the reduction of cellular photosensitizing targets below a threshold level rather than from the inactivation of photosynthesis.

Carbon↗

PubMed2002

Expression of the iron-responsive irpA gene from the cyanobacterium Synechococcus sp strain PCC 7942.

Expression of the iron-stress-induced irpA gene of Synechococcus sp. strain PCC 7942 was investigated by constructing luminescent p irpA::luxAB promoter fusions. Growth of Fe-replete and Fe-limited cultures yielded high levels of luminescence only under conditions of iron deficiency. Promoter fusion deletions revealed that low Fe irpA transcription is dependent on a 25-nucleotide sequence that includes a region of dyad symmetry centered 19 nucleotides from the transcription start. Assaying luminescence at defined iron concentrations in trace-metal-buffered media showed that irpA transcription is activated at concentrations below 100 nm Fe. Overall, the expression pattern and promoter structure of irpAsuggests a novel form of metal-dependent regulation in this species.

Bacterial Outer Membrane Proteins↗

PubMedDate not supplied

Growth phase and metal-dependent regulation of the dpsA gene in Synechococcus sp. strain PCC 7942, USA.

The Synechococcus sp. strain PCC 7942 dpsA gene encodes a stress-inducible DNA-binding protein whose transcription increases in the stationary phase. Such transcription is likely under the control of an alternative sigma factor. Our current work indicated that dpsA transcription is also important under metal-ion limitation, because dpsA mRNA levels increased 12-fold under low-iron conditions, and that dpsA function is essential for growth under iron-limiting conditions. Promoter activity of the dpsA-promoter-lacZ reporter gene constructs implied that a region of dyad symmetry centered 28 nucleotides from the transcription start is required for metal-dependent repression, as judged by the level of lacZ induction following treatment of cultures with the chelator 2,2'-dipyridyl. This potential operator sequence is distinct from the site recognized by the cyanobacterial Fur repressor homologue. No other nutrient stresses (nitrogen, sulfur, phosphorus) yielded the high level of induction seen following chelator treatment. These studies suggest that there may be more than one class of metal-dependent repressor in cyanobacteria.

Bacterial Proteins↗

PubMed1998

Alteration of low-temperature susceptibility of the cyanobacterium Synechococcus sp. PCC 7002 by genetic manipulation of membrane lipid unsaturation.

Cyanobacteria acclimate to low temperature by desaturating their membrane lipids. Mutant strains of Synechococcus sp. PCC 7002 containing insertionally inactivated desA (Delta12 acyl-lipid desaturase) and desB (omega3 acyl-lipid desaturase) genes were produced, and their low-temperature susceptibility was characterized. The desA mutant synthesized no linoleic acid or alpha-linolenic acid, and the desB mutant did not produce alpha-linolenic acid. The desA mutant grew more slowly than the wild-type at 22 degrees C and could not grow at 15 degrees C. The desB mutant could not continuously grow at 15 degrees C, although no observable phenotype appeared at higher temperatures. It has been shown that expression of the desA gene occurs at 38 degrees C and is up-regulated at 22 degrees C, and that the desB gene is only expressed at 22 degrees C. These results indicate that the expression of the desA and desB genes occurs at higher temperatures than those at which a significant decline in physiological activities is caused by the absence of their products. The temperature dependency of photosynthesis was not affected by these mutations. Since chlorosis and inability to grow at 15 degrees C with nitrate was suppressed by the substitution of urea as a nitrogen source, it is very likely that the chilling susceptibility of the desaturase mutants is attributable to nutrient limitation.

Adaptation, Physiological↗

PubMed1998

Characterization of the alternative sigma-factors SigD and SigE in Synechococcus sp. strain PCC 7002. SigE is implicated in transcription of post-exponential-phase-specific genes.

The sigD and sigE genes, which encode two alternative sigma-factors from the unicellular marine cyanobacterium Synechococcus sp. PCC 7002, were cloned and characterized. Strains in which the sigD and sigE genes were insertionally inactivated were viable under standard laboratory conditions, indicating that SigD and SigE are group 2 sigma-factors. When stationary-phase cells were diluted into fresh growth medium, it was observed that the sigE mutant strain required longer times to re-establish exponential growth than the wild-type strain. By monitoring the growth rates in such dilution experiments, it was observed that the lag times for the mutant strain became progressively longer as the original cultures progressed towards stationary phase. Transcripts for the sigE gene initially increased and subsequently decreased as cells grew further into stationary phase. It was determined that a functional SigE protein is required for the expression of the starvation-induced protein DpsA/PexB. The results suggest that SigE is involved in the transcription of genes specifically expressed in the post-exponential phase.

Amino Acid Sequence↗

PubMed1999

Nitrogen starvation in synechococcus PCC 7942: involvement of glutamine synthetase and NtcA in phycobiliprotein degradation and survival

The nondiazotrophic cyanobacterium Synechococcus sp. strain PCC 7942 responds to nitrogen deprivation by differentiating into nonpigmented resting cells able to survive prolonged periods of starvation. The degradation of photosynthetic pigments, termed chlorosis, proceeds in an ordered manner in which the light-harvesting phycobiliproteins are degraded prior to chlorophyll. Here, we show that the function of the global transcription activator of nitrogen-regulated genes, NtcA, is required for the sequential pigment degradation and cell survival. The P(II) protein, known to signal the nitrogen status of the cells, is most probably not involved in the perception of the nitrogen-starvation-specific signal since in a mutant lacking P(II), chlorosis proceeded in the same manner as in the wild type. Inhibition of glutamine synthetase with l-methionine sulfoximine led to a rapid decrease of apc mRNA and to an increase of nblA mRNA levels, which is characteristic for nitrogen deprivation, suggesting that nitrogen starvation is sensed by a metabolic signal connected to glutamine synthetase activity. However, l-methionine sulfoximine treatment did not induce phycobiliprotein degradation, but led to an immediate cessation of this proteolytic process after its induction by nitrogen deprivation. This suggests that the proteolytic activity elicited by the expression of nblA has to be supported by glutamine synthetase activity.

Journal Article↗

PubMed2004

Atrazine-induced chlorosis in Synechococcus elongatus cells.

The effects of a widely used herbicide, atrazine, on the freshwater cyanobacterium Synechococcus elongatus were studied. The cyanobacteria were exposed to varying concentrations of atrazine (0.025, 0.05, 0.1, 0.25, and 0.75 microM) for 96 h. Different parameters such as growth, autofluorescence of chlorophyll a, pigment content, volume, and internal granularity of the cells were determined daily. Differences were detected between cultures with and cultures without atrazine for the parameters analyzed. Atrazine exposure induced the process of chlorosis in cyanobacterial cells, given that this herbicide has an effect on photosynthesis, chlorotic subpopulations having low values of chlorophyll a autofluorescence. More unpigmented subpopulations (chlorotic) appeared as the atrazine concentration increased and better growth rates resulted. Atrazine also induced changes in cell volume and internal granularity, these being most apparent after 48 h of exposure and in cultures with higher atrazine concentrations (0.25 and 0.75 microM).

Atrazine↗

PubMed1998

Characterization of two pore-forming proteins isolated from the outer membrane of Synechococcus PCC 6301.

Two major proteins, A and B, were isolated and purified from outer membranes of the unicellular cyanobacterium Synechococcus PCC 6301 by gel filtration, anion-exchange chromatography, and preparative SDS-PAGE. Protein A revealed a single-channel conductance of 0.4 nanoSiemens (nS) in 1 M KCl, whereas preparations containing both proteins showed two different conductance maxima of 0.4 and 0.9 nS, suggesting that B also forms pores. The apparent molecular mass of the two closely migrating proteins was determined as 52 kDa, whereas native porin extracts revealed a relative molecular mass of ca. 140 kDa, indicating trimeric pore-forming units. Partial sequences of both proteins were obtained by N-terminal sequencing of tryptic peptides, and the C-terminal amino acid sequences were derived from the complete proteins. These sequences were aligned to protein sequences available in the databases. The results are discussed.

Amino Acid Sequence↗

PubMed2000

A novel nucleic acid-binding protein in the cyanobacterium Synechococcus sp. PCC6301: a soluble 33-kDa polypeptide with high sequence similarity to ribosomal protein S1.

Cyanobacteria are prokaryotes that carry out plant-type photosynthesis and contain several eukaryotic-type RNA-binding proteins. Using a single-stranded DNA column, a 33-kDa protein was isolated and characterized from Synechococcus sp. PCC6301. This protein of 293 amino acids is similar in overall structure to the ribosomal protein S1 found in the same species, and contains three repeated units that are highly similar to the S1 motif originally found in the ribosomal protein S1 of Escherichia coli. However, the 33-kDa protein was found not to be associated with ribosomes and its nucleic acid binding specificity is distinct from that of the ribosomal protein S1. As this protein has high affinity for both single- and double-stranded DNA, as well as for poly(G) and poly(A), we tentatively named it nucleic acid-binding protein 1 (Nbp1).

Amino Acid Sequence↗

PubMed2004

Characterization of the heme-histidine cross-link in cyanobacterial hemoglobins from Synechocystis sp. PCC 6803 and Synechococcus sp. PCC 7002.

The recombinant product of the hemoglobin gene of the cyanobacterium Synechocystis sp. PCC 6803 forms spontaneously a covalent bond linking one of the heme vinyl groups to a histidine located in the C-terminal helix (His117, or H16). The present report describes the (1)H, (15)N, and (13)C NMR spectroscopy experiments demonstrating that the recombinant hemoglobin from the cyanobacterium Synechococcus sp. PCC 7002, a protein sharing 59% identity with Synechocystis hemoglobin, undergoes the same facile heme adduct formation. The observation that the extraordinary linkage is not unique to Synechocystis hemoglobin suggests that it constitutes a noteworthy feature of hemoglobin in non-N(2)-fixing cyanobacteria, along with the previously documented bis-histidine coordination of the heme iron. A qualitative analysis of the hyperfine chemical shifts of the ferric proteins indicated that the cross-link had modest repercussions on axial histidine ligation and heme electronic structure. In Synechocystis hemoglobin, the unreacted His117 imidazole had a normal p K(a) whereas the protonation of the modified residue took place at lower pH. Optical experiments revealed that the cross-link stabilized the protein with respect to thermal and acid denaturation. Replacement of His117 with an alanine yielded a species inert to adduct formation, but inspection of the heme chemical shifts and ligand binding properties of the variant identified position 117 as important in seating the cofactor in its site and modifying the dynamic properties of the protein. A role for bis-histidine coordination and covalent adduct formation in heme retention is proposed.

Acids↗

PubMed2000

Production of eicosapentaenoic acid by a recombinant marine cyanobacterium, Synechococcus sp.

The eicosapentaenoic acid (EPA) synthesis gene cluster from an EPA-producing bacterium, Shewanella sp. SCRC-2738, was cloned into a broad-host range vector, pJRD215, and then introduced into a marine cyanobacterium, Synechococcus sp. NKBG15041c, by conjugation. The transconjugant cyanobacteria produced 3.7 +/- 0.2% (2.24 +/- 0.13 mg/L) EPA (n-3) and 2.5 +/- 0.2% (1.49 +/- 0.06 mg/L) eicosatetraenoic acid (n-3) of the total fatty acids when the cells were cultured at 23 degrees C at a light intensity of 1,000-1,500 Lux. The EPA and eico-satetraenoic acid contents of the cells were increased to 4.6 +/- 0.6% (3.86 +/- 1.11 mg/L) and 4.7 +/- 0.3% (3.86 +/- 0.82 mg/L), and 7.5 +/- 0.3% (1.76 +/- 0.10 mg/L) and 5.1 +/- 0.2% (1.19 +/- 0.06 mg/L) when they were cultured at low temperature (18 degrees C) and at lower light intensity (40 Lux), respectively.

Alteromonas↗