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PubMed2006

Effect of temperature and light on growth of and photosynthesis by Synechococcus isolates typical of those predominating in the octopus spring microbial mat community of Yellowstone National Park.

Previous molecular analysis of the Octopus Spring cyanobacterial mat revealed numerous genetically distinct 16S rRNA sequences from predominant Synechococcus populations distantly related to the readily cultivated unicellular cyanobacterium Synechococcus lividus. Patterns in genotype distribution relative to temperature and light conditions suggested that the organisms contributing these 16S rRNA sequences may fill distinct ecological niches. To test this hypothesis, Synechococcus isolates were cultivated using a dilution and filtration approach and then shown to be genetically relevant to natural mat populations by comparisons of similarities of 16S rRNA genes and 16S-23S internal transcribed spacer (ITS) regions. Most isolates were identical or nearly identical at both loci to predominant mat genotypes; others showed 1- to 2-nucleotide differences at the 16S rRNA locus and even greater difference in ITS sequences. Isolates with predominant mat genotypes had distinct temperature ranges and optima for growth that were consistent with their distributions in the mat. Isolates with genotypes not previously detected or known to be predominant in the mat exhibited temperature ranges and optima that were not representative of predominant mat populations and also grew more slowly. Temperature effects on photosynthesis did not reflect temperature relations for growth. However, the isolate with the highest temperature optimum and upper limit was capable of performing photosynthesis at a higher temperature than other isolates. Growth rate and photosynthetic responses provided evidence for light acclimation but evidence of, at best, only subtle light adaptation.

DNA, Bacterial↗

PubMed2006

A suppression subtractive hybridization approach reveals niche-specific genes that may be involved in predator avoidance in marine Synechococcus isolates.

Picocyanobacteria of the genus Synechococcus are important contributors to marine primary production and are ubiquitous in the world's oceans. This genus is genetically diverse, and at least 10 discrete lineages or clades have been identified phylogenetically. However, little if anything is known about the genetic attributes which characterize particular lineages or are unique to specific strains. Here, we used a suppression subtractive hybridization (SSH) approach to identify strain- and clade-specific genes in two well-characterized laboratory strains, Synechococcus sp. strain WH8103 (clade III) and Synechococcus sp. strain WH7803 (clade V). Among the genes that were identified as potentially unique to each strain were genes encoding proteins that may be involved in specific predator avoidance, including a glycosyltransferase in strain WH8103 and a permease component of an ABC-type polysaccharide/polyol phosphate export system in WH7803. During this work the genome of one of these strains, WH7803, became available. This allowed assessment of the number of false-positive sequences (i.e., sequences present in the tester genome) present among the SSH-enriched sequences. We found that approximately 9% of the WH8103 sequences were potential false-positive sequences, which demonstrated that caution should be used when this technology is used to assess genomic differences in genetically similar bacterial strains.

Bacterial Proteins↗

PubMed2006

Biochemical bases of type IV chromatic adaptation in marine Synechococcus spp.

Chromatic adaptation (CA) in cyanobacteria has provided a model system for the study of the environmental control of photophysiology for several decades. All forms of CA that have been examined so far (types II and III) involve changes in the relative contents of phycoerythrin (PE) and/or phycocyanin when cells are shifted from red to green light and vice versa. However, the chromophore compositions of these polypeptides are not altered. Some marine Synechococcus species strains, which possess two PE forms (PEI and PEII), carry out another type of CA (type IV), occurring during shifts from blue to green or white light. Two chromatically adapting strains of marine Synechococcus recently isolated from the Gulf of Mexico were utilized to elucidate the mechanism of type IV CA. During this process, no change in the relative contents of PEI and PEII was observed. Instead, the ratio of the two chromophores bound to PEII, phycourobilin and phycoerythrobilin, is high under blue light and low under white light. Mass spectroscopy analyses of isolated PEII alpha- and beta-subunits show that there is a single PEII protein type under all light climates. The CA process seems to specifically affect the chromophorylation of the PEII (and possibly PEI) alpha chain. We propose a likely process for type IV CA, which involves the enzymatic activity of one or several phycobilin lyases and/or lyase-isomerases differentially controlled by the ambient light quality. Phylogenetic analyses based on the 16S rRNA gene confirm that type IV CA is not limited to a single clade of marine Synechococcus.

Adaptation, Physiological↗

PubMedDate not supplied

[The first protein map of Synechococcus sp. strain PCC 7942].

The first protein map was developed of Synechococcus sp. strain PCC 7942, a model organism for studies of photosynthesis, prokaryotic circadian rhythms, cell division, carbon-concentrating mechanisms, and adaptive responses to a variety of stresses. The proteome was analyzed by two-dimensional gel electrophoresis with subsequent MALDI-TOF mass spectroscopy and database analysis. Of the 140 analyzed protein spots, 110 were successfully identified as 62 different proteins, many of which occurred as multiple spots on the gel. The identified proteins participate in the major metabolic and cellular processes in cyanobacterial cells during the exponential growth phase. In addition, 14 proteins which were previously either unknown or considered to be hypothetical were shown to be true gene products in Synechococcus sp. strain PCC 7942. These results may be helpful for the annotation of the recently sequenced genome of this cyanobacterium, as well as for biochemical and physiological studies of Synechococcus.

Bacterial Proteins↗

PubMed2004

Physiological and biochemical analyses of microcystin-RR toxicity to the cyanobacterium Synechococcus elongatus.

Freshwater Microcystis may form dense blooms in eutrophic lakes. It is known to produce a family of related cyclic hepatopeptides (microcystins, MC) that constitute a threat to aquatic ecosystems. Most toxicological studies of microcystins have focused on aquatic animals and plants, with few examining the possible effects of microcystins on phytoplankton. In this study we chose the unicellular Synechococcus elongatus (one of the most studied and geographically most widely distributed cyanobacteria in the picoplankton) as the test material and investigated the biological parameters: growth, pigment (chlorophyll-a, phycocyanin), photosynthetic activity, nitrate reductase activity, and protein and carbohydrate content. The results revealed that microcystin-RR concentrations above 100 microg x L(-1) significantly inhibited the growth of Synechococcus elongatus. In addition, a change in color of the toxin-treated algae (chlorosis) was observed in the experiments. Furthermore, MC-RR markedly inhibited the synthesis of the pigments chlorophyll-a and phycocyanin. A drastic reduction in photochemical efficiency of PSII (F(v)/F(m)) was found after a 96-h incubation. Changes in protein and carbohydrate concentrations and in nitrate reductase activity also were observed during the exposure period. This study aimed to evaluate the mechanisms of microcystin toxicity on a cyanobacterium, according to the physiological and biochemical responses of Synechococcus elongatus to different doses of microcystin-RR. The ecological role of microcystins as an allelopathic substance also is discussed in the article.

Chlorophyll↗

PubMed1996

Molecular characterization and resistance to hydrogen peroxide of two fructose-1,6-bisphosphatases from Synechococcus PCC 7942.

In Synechococcus PCC 7942 cells, two catalytic fructose-1,6-bisphosphatase isoenzymes, designated F-I and F-II, have been resolved by chromatography on a HiLoad 26/10 Q Sepharose column at 0.24 and 0.34 M of NaCl, respectively; the former represented the major part of the total extractable enzyme activity. F-I has been purified to electrophoretic homogeneity from the cells. F-I and F-II had respective molecular masses of 160 and 150 kDa and each enzyme was composed of four identical subunits. F-I hydrolyzed both fructose 1,6-bisphosphate and sedoheptulose 1,7-bisphosphate, whereas F-II hydrolyzed only fructose 1,6-bisphosphate. The apparent Km values of F-I and F-II for fructose 1,6-bisphosphate were 52 +/- 4.5 and 25 +/- 1.5 microM, respectively. F-I was inhibited by AMP with a Ki value of 0.26 mM, but F-II was not affected by AMP. The F-I failed to cross-react by Western blotting with the antibody raised against F-II; similarly, the F-II did not react with the F-I antibody. The genes encoding F-I and F-II were cloned from the chromosomal DNA of Synechococcus PCC 7942. A 1068-bp open reading frame, encoding F-I of 356 amino acid residues (approx molecular mass of 38.3 kDa) was observed. The nucleotide sequence of the F-II gene showed an open reading frame of 1017 bp that encodes a protein of 339 amino acid residues (approx molecular mass of 37.2 kDa). The recombinant enzymes expressed in Escherichia coli as well as the native enzymes of F-I and F-II from Synechococcus PCC 7942 cells were resistant to 1 mM hydrogen peroxide unlike the light-activated higher plant chloroplast enzymes.

Amino Acid Sequence↗

PubMed1993

Nitrite reductase gene from Synechococcus sp. PCC 7942: homology between cyanobacterial and higher-plant nitrite reductases.

The gene encoding nitrite reductase (nir) from the cyanobacterium Synechococcus sp. PCC 7942 has been identified and sequenced. This gene comprises 1536 nucleotides and would encode a polypeptide of 56,506 Da that shows similarity to nitrite reductase from higher plants and to the sulfite reductase hemoprotein from enteric bacteria. Identities found at positions corresponding to those amino acids which in the above-mentioned proteins hold the Fe4S4-siroheme active center suggest that nitrite reductase from Synechococcus bears an active site much alike that present in those reductases. The fact that the Synechococcus and higher-plant nitrite reductases are homologous proteins gives support to the endosymbiont theory for the origin of chloroplasts.

Amino Acid Sequence↗

PubMed1996

Effect of heat shock on DNA-dependent RNA polymerase from the cyanobacterium Synechococcus sp.

Purification of DNA-dependent RNA polymerase from exponentially growing cells of the cyanobacterium Synechococcus sp. is described in cultures grown at normal temperature (39 degrees C) and after heat shock (HS) (47 degrees C). Polyethyleneimine precipitation followed by chromatography and gel filtration steps results in a 39% yield. The enzyme has a component of molar mass of 43 kDa, designated sigma, in addition to the typical procaryotic beta' beta alpha 2 and gamma. The results suggest that Synechococcus RNA polymerase is similar to that of cyanobacterial and E. coli RNA polymerases. Electrophoresis of the HS preparation showed that the enzyme has a component of 18 kDa. This suggests the existence of a functional relationship between this protein and the HS response of Synechococcus RNA polymerase, probably in salvaging denatured RNA polymerase or helping to regain its native structure.

Cyanobacteria↗

PubMed1999

Detection of seven major evolutionary lineages in cyanobacteria based on the 16S rRNA gene sequence analysis with new sequences of five marine Synechococcus strains.

Although molecular phylogenetic studies of cyanobacteria on the basis of the 16S rRNA gene sequence have been reported, the topologies were unstable, especially in the inner branchings. Our analysis of 16S rRNA gene phylogeny by the maximum-likelihood and neighbor-joining methods combined with rate homogeneous and heterogeneous models revealed seven major evolutionary lineages of the cyanobacteria, including prochlorophycean organisms. These seven lineages are always stable on any combination of these methods and models, fundamentally corresponding to phylogenetic relationships based on other genes, e.g., psbA, rbcL, rnpB, rpoC, and tufA. Moreover, although known genotypic and phenotypic characters sometimes appear paralleled in independent lineages, many characters are not contradictory within each group. Therefore we propose seven evolutionary groups as a working hypothesis for successive taxonomic reconstruction. New 16S rRNA sequences of five unicellular cyanobacterial strains, PCC 7001, PCC 7003, PCC 73109, PCC 7117, and PCC 7335 of Synechococcus sp., were determined in this study. Although all these strains have been assigned to "marine clusters B and C," they were separated into three lineages. This suggests that the organisms classified in the genus Synechococcus evolved diversely and should be reclassified in several independent taxonomic units. Moreover, Synechococcus strains and filamentous cyanobacteria make a monophyletic group supported by a comparatively high statistical confidence value (80 to 100%) in each of the two independent lineages; therefore, these monophylies probably reflect the convergent evolution of a multicellular organization.

Biological Evolution↗

PubMed1999

Isolation and characterization of Synechococcus PCC7942 promoters: tRNApro gene functions as a promoter.

Promoter-active fragments of Synechococcus PCC7942 were isolated by transcriptional gene fusion to the promoterless beta-glucuronidase (GUS) gene of E. coli, which was used as a reporter gene. Several of the isolated promoter-active fragments expressed GUS activity in Synechococcus comparable to that of the lambdaPR promoter. Only 10% of the isolated promoter-active fragments also functioned in E. coli. The transcription initiation sites of the two promoter-active fragments, D13 and E3, were identified. The major transcription initiation sites of D13 and E3 in Synechococcus were located within the nucleotides TTTG and TTG respectively, which were identical to those corresponding to E. coli. The inferred -10 and -35 regions of D13 were TAAACT and TTGTAG respectively, which conformed to the E. coli sigma70 promoter. Immediately upstream of the E3 transcription initiation sites was the tRNApro (GGG) gene, which contained two regions exhibiting strong homology to the major promoter elements in eukaryotic tRNA genes, but did not contain the E. coli promoter element. Thus, the tRNApro gene can act as a promoter.

Amino Acid Sequence↗

PubMed2006

Roles for heme-copper oxidases in extreme high-light and oxidative stress response in the cyanobacterium Synechococcus sp. PCC 7002.

The ctaCIDIEI and ctaCIIDIIEII gene clusters that encode heme-copper cytochrome oxidases have been characterized in the marine cyanobacterium Synechococcus sp. PCC 7002 and the inactivation of ctaDI was shown to affect high-light adaptation. In this study, Synechococcus sp. PCC 7002 wild-type, ctaDI, ctaDII, and ctaDI-ctaDII double mutants were grown under extreme high-light and oxidative stress to further assess the roles of cytochrome oxidases in cyanobacteria. Cells of the ctaDI mutant strain barely grew under extreme high-light illumination of 4.5 mE m(-2) s(-1), suggesting that CtaDI is required for high-light acclimation in Synechococcus sp. PCC 7002. The ctaDI-ctaDII double mutant cells unexpectedly tolerated extreme high-light intensity, indicating that the disruption of ctaDII gene suppresses the high-light sensitivity phenotype of the ctaDI single mutant. The ctaDII mutant cells also exhibited higher tolerance to the oxidative stress compound, methyl viologen, in the growth media. The ctaDII mutant and the ctaDI-ctaDII double mutant cells had approximately twofold higher levels of superoxide dismutase (SOD) activity, indicating that the disruption of ctaDII gene increased the capacity to decompose active oxygen species. These results suggest that the CtaII cytochrome oxidase may be involved with the oxidative stress response, including the control of SOD expression.

Bacterial Proteins↗

PubMed1996

Identification of two classes of transcriptional regulator genes in the cyanobacterium Synechococcus sp. strain PCC 7942.

We designed a strategy to isolate and characterize response regulator genes from the cyanobacterium Synechococcus sp. strain PCC 7942 based on the premise that cyanobacterial response regulators would bear strong similarity to their counterparts from other eubacteria. Two response regulator genes, srrA and srrB, were isolated from Synechococcus and found to encode proteins similar to the OmpR subclass of response regulators. Disruption of either gene by insertional mutagenesis did not produce an obvious phenotype and did not affect the accumulation of psbAII mRNA under high-light conditions, indicating that these gene products are not involved in mediating the well characterized standard- to high-light transition response of photosystem II genes in this cyanobacterium. Analysis of the chromosomal region adjacent to srrA revealed the presence of another presumptive transcriptional activator gene. This gene, named lrrA, belongs to the lysR family. Attempts to disrupt lrrA or an adjacent ORF (orfG) were not successful, suggesting that these genes are important for the growth of Synechococcus.

Amino Acid Sequence↗

PubMed1999

Expression of a higher-plant chloroplast psbD promoter in a cyanobacterium (Synechococcus sp. strain PCC7942) reveals a conserved cis-element, designated PGT, that differentially interacts with sequence-specific binding factors during leaf development.

The chloroplast psbD gene, which encodes the D2 subunit of photosystem II, is regulated by a blue light-responsive promoter (BLRP). We tested the ability of different regions of the barley (Hordeum vulagare) BLRP to drive transcription of the lacZ reporter gene in genomic transformants of Synechococcus sp. strain PCC7942. The barley BLRP was transcribed in Synechococcus from the same initiation sites that are used in plant chloroplasts in vivo. A region of the BLRP, residing between -83 and -112 bp upstream from the transcription initiation sites, functioned as a negative element in Synechococcus. Nucleotide sequences within this region are conserved among the psbD genes of several monocots and dicots, and with the nuclear negative regulatory element GT. Thus this new cis-element was designated Plastid GT, PGT. Proteins from chloroplasts of barley and Arabidopsis thaliana interacted with PGT in a sequence-specific and developmental-dependent manner. The DNA-protein complexes from Arabidopsis chloroplasts are composed of 60- and 38-kDa polypeptides. We postulate that GT and PGT have evolved in the nucleus and chloroplast, respectively, from a common ancestral regulatory element.

Arabidopsis↗

PubMed1999

Priority of light/dark entrainment over temperature in setting the circadian rhythms of the prokaryote Synechococcus RF-1.

Light/dark (L/D) and temperature are two major factors in the entrainment of circadian rhythms. The input pathways of these two environmental factors for the entrainment of circadian rhythms in Synechococcus RF-1 are different since the overt rhythms in mutant CR-1, one of the circadian-rhythm mutants of Synechococcus RF-1, could be established by temperature cycles but not by L/D. Therefore, it was of interest to investigate the phases of Synechococcus RF-1 cells entrained simultaneously by L/D and temperature. The circadian rhythms of nitrogenase activity and protein synthesis in RF-1 cells entrained by L/D, and by lowered or raised temperatures differed in their peaks of activity. Comparison of the phases of RF-1 cells entrained by L/D and temperature independently, and by L/D and temperature simultaneously indicated that L/D entrainment has priority over the temperature effect.

Journal Article↗

PubMed2004

Salicylhydroxamic acid (SHAM) inhibits O(2) photoreduction which protects nitrogenase activity in the cyanobacterium Synechococcus sp. RF-1.

Synechococcus sp. RF-1, a unicellular N(2)-fixing cyanobacterium, can grow photosynthetically and diazotrophically in continuous light. How the organism protects its nitrogenase from damage by oxygen is unclear. In cyanobacerial cells, electron transport carriers associated with photosynthesis and respiration are all on the thylakoid membranes and share some common components, including plastoquinone pool and cytochrome b (6) f complex, and the pathways are interacting with each other. In this work, a pulse amplitude modulation (PAM) fluorometer (PAM-101) and an O(2) electrode are used simultaneously to study the chlorophyll a fluorescence and to monitor O(2) exchanges in Synechococcus sp. RF-1 cells. At the CO(2) compensation point, the photochemical quenching activity remained high unless the O(2) was exhausted by the glucose oxidase system (GOS). It indicates that in addition to CO(2), O(2) can also act as electron acceptor to receive electrons derived from Q(A). Studies with various inhibitors of the electron transport chain demonstrated that 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB) and salicylhydroxamic acid (SHAM) inhibited the photoreduction of O(2), while glycolaldehyde, disalicylidenepropanediamine (DSPD), methyl viologen (MV) and KCN did not. These results imply that a KCN-resistant and SHAM-sensitive oxidase transfers electrons generated from Photosystem II to O(2) between cytochrome b (6) f complex and ferredoxin. When SHAM blocked this alternative electron transport pathway, the dinitrogen-fixing activity decreased significantly. The results indicate that a novel oxidase may function as an intracellular O(2)-scavenger in Synechococcus sp. RF-1 cells.

Journal Article↗

PubMed1992

Cloning and characterization of the secY gene from the cyanobacterium Synechococcus PCC7942.

The secY gene product is an essential component of the Escherichia coli cytoplasmic membrane, which mediates the protein translocation across the membrane. We found a gene homologous to secY in the genome of the cyanobacterium Synechococcus PCC7942. The deduced amino acid sequence, 439 amino acids long, shows 43% homology with that of the E. coli secY. The hydrophobic profile suggests that the Synechococcus SecY protein is an integral membrane protein containing ten membrane-spanning segments, which are closely related to the E. coli counterpart. The SecY protein may participate in the protein translocation across the cytoplasmic or thylakoid membrane in Synechococcus PCC7942.

Amino Acid Sequence↗

PubMed1995

Partial amino acid sequence of an L-amino acid oxidase from the cyanobacterium Synechococcus PCC6301, cloning and DNA sequence analysis of the aoxA gene.

A novel type of L-amino acid oxidase from Synechococcus PCC6301 was purified and subjected to amino acid sequence analysis. Since the N-terminus of the L-amino acid oxidase protein was not accessible for Edman degradation, the protein was partially hydrolysed and a contiguous sequence of 17 amino acid residues was obtained from an endogenous peptide fragment. Based on the partial peptide sequence two oligonucleotides were designed, which were used as probes in Southern hybridization experiments in order to identify the corresponding aoxA gene. The aoxA gene was isolated from a size-fractionated genomic library of Synechococcus PCC6301 and subsequently sequenced. From the nucleotide sequence (data base accession number Z48565) it can be deduced that the L-amino acid protein consists of 355 amino acid residues resulting in a molar mass of 39.2 kDa. The calculated isoelectric point of the protein is 9.81. The L-amino acid oxidase from Synechococcus PCC6301 shows low homologies to other flavin oxidases/dehydrogenases, especially amine oxidases, but no homologies to other so far sequenced L- or D-amino acid oxidases.

Amino Acid Oxidoreductases↗

PubMed1984

Length of foreign DNA in chimeric plasmids determines the efficiency of its integration into the chromosome of the cyanobacterium Synechococcus R2.

The photosynthetic cyanobacterium Synechococcus R2 is efficiently transformed by DNA molecules that contain antibiotic genes from Escherichia coli linked to a segment of Synechococcus R2 chromosomal DNA. Antibiotic-resistant transformants result from integration of donor DNA into the cyanobacterial chromosome by homologous recombination. Foreign DNA interrupting the cyanobacterial sequence in the donor molecule integrates by replacement of homologous recipient DNA with donor DNA containing the foreign insert. Foreign DNA linked to the ends of the cyanobacterial fragment in a circular donor molecule integrates by a reciprocal cross-over between donor and recipient sequences. Using donor molecules that contain different lengths of foreign DNA in both of the above positions, we have determined that the probability of integration decreases by half for each increase of 2 to 3 kb in length of a foreign segment, regardless of its position in the donor molecule. The length of one of the two foreign segments has no effect on the integration of the other. Foreign DNA 20 kb in length is completely stable when it has integrated by the replacement mechanism. The ability to stably introduce large pieces of foreign DNA makes Synechococcus R2 an attractive organism in which to study and modify both native and heterologous genes involved in oxygenic photosynthesis.

Cyanobacteria↗