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PubMed1987

Carbonic Anhydrase and the Uptake of Inorganic Carbon by Synechococcus sp. (UTEX-2380).

We report the changes in the concentrations and (18)O contents of extracellular CO(2) and HCO(3) (-) in suspensions of Synechococcus sp. (UTEX 2380) using membrane inlet mass spectrometry. This marine cyanobacterium is known to have an active uptake mechanism for inorganic carbon. Measuring (18)O exchange between CO(2) and water, we have found the intracellular carbonic anhydrase activity to be equivalent to 20 times the uncatalyzed CO(2) hydration rate in different samples of cells that were grown on bubbled air (low-CO(2) conditions). This activity was only weakly inhibited by ethoxzolamide with an I(50) near 7 to 10 micromolar in lysed cell suspensions. We have shown that even with CO(2)-starved cells there is considerable generation of CO(2) from intracellular stores, a factor that can cause errors in measurement of net CO(2) uptake unless accounted for. It was demonstrated that use of (13)C-labeled inorganic carbon outside the cell can correct for such errors in mass spectrometric measurement. Oxygen-18 depletion experiments show that in the light, CO(2) readily passes across the cell membrane to the sites of intracellular carbonic anhydrase. Although HCO(3) (-) was readily taken up by the cells, these experiments shown that there is no significant efflux of HCO(3) (-) from Synechococcus.

Journal Article↗

PubMed1989

Ethoxyzolamide Inhibition of CO(2)-Dependent Photosynthesis in the Cyanobacterium Synechococcus PCC7942.

Cells of the cyanobacterium, Synechococcus PCC7942, grown under high inorganic carbon (C(i)) conditions (1% CO(2); pH 8) were found to be photosynthetically dependent on exogenous CO(2). This was judged by the fact that they had a similar photosynthetic affinity for CO(2) (K(0.5)[CO(2)] of 3.4-5.4 micromolar) over the pH range 7 to 9 and that the low photosynthetic affinity for C(i) measured in dense cell suspensions was improved by the addition of exogenous carbonic anhydrase (CA). The CA inhibitor, ethoxyzolamide (EZ), was shown to reduce photosynthetic affinity for CO(2) in high C(i) cells. The addition of 200 micromolar EZ to high C(i) cells increased K(0.5)(CO(2)) from 4.6 micromolar to more than 155 micromolar at pH 8.0, whereas low C(i) cells (grown at 30 microliters CO(2) per liter of air) were less sensitive to EZ. EZ inhibition in high and low C(i) cells was largely relieved by increasing exogenous C(i) up to 100 millimolar. Lipid soluble CA inhibitors such as EZ and chlorazolamide were shown to be the most effective inhibitors of CO(2) usage, whereas water soluble CA inhibitors such as methazolamide and acetazolamide had little or no effect. EZ was found to cause a small drop in photosystem II activity, but this level of inhibition was not sufficient to explain the large effect that EZ had on CO(2) usage. High C(i) cells of Anabaena variabilis M3 and Synechocystis PCC6803 were also found to be sensitive to 200 micromolar EZ. We discuss the possibility that the inhibitory effect of EZ on CO(2) usage in high C(i) cells of Synechococcus PCC7942 may be due to inhibition of a ;CA-like' function associated with the CO(2) utilizing C(i) pump or due to inhibition of an internal CA activity, thus affecting CO(2) supply to ribulose bisphosphate carboxylase-oxygenase.

Journal Article↗

PubMed1990

Circadian Rhythm of the Prokaryote Synechococcus sp. RF-1.

The prokaryotic Synechococcus sp. RF-1 exhibited a nitrogen fixation circadian rhythm with characteristics remarkably similar to the circadian rhythm of eukaryotes. The rhythm had a free-running period of about 24 hours when the length of the preen-trained cycle did not differ too much from 24 hours, and it was insensitive to changes in temperature from 22 degrees C to 33 degrees C. Because the endogenous rhythm of nitrogen fixation was not affected by a phase-shift of its previous cycles, the circadian rhythm in Synechococcus sp. RF-1 was not considered to be controlled simply by a feedback mechanism.

Journal Article↗

PubMed1990

Cytochrome c-553 is not required for photosynthetic activity in the cyanobacterium Synechococcus.

In cyanobacteria, the water-soluble cytochrome c-553 functions as a mobile carrier of electrons between the membrane-bound cytochrome b6-f complex and P-700 reaction centers of Photosystem I. The structural gene for cytochrome c-553 (designated cytA) of the cyanobacterium Synechococcus sp. PCC 7942 was cloned, and the deduced amino acid sequence was shown to be similar to known cyanobacterial cytochrome c-553 proteins. A deletion mutant was constructed that had no detectable cytochrome c-553 based on spectral analyses and tetramethylbenzidine-hydrogen peroxide staining of proteins resolved by polyacrylamide gel electrophoresis. The mutant strain was not impaired in overall photosynthetic activity. However, this mutant exhibited a decreased efficiency of cytochrome f oxidation. These results indicate that cytochrome c-553 is not an absolute requirement for reducing Photosystem I reaction centers in Synechococcus sp. PCC 7942.

Amino Acid Sequence↗

PubMed1993

Deletion within the metallothionein locus of cadmium-tolerant Synechococcus PCC 6301 involving a highly iterated palindrome (HIP1).

Genomic rearrangements involving amplification of metallothionein (MT) genes have been reported in metal-tolerant eukaryotes. Similarly, we have recently observed amplification and rearrangement of a prokaryotic MT locus, smt, in cells of Synechococcus PCC 6301 selected for Cd tolerance. Following the characterization of this locus, the altered smt region has now been isolated from a Cd-tolerant cell line, C3.2, and its nucleotide sequence determined. This has identified a deletion within smtB, which encodes a trans-acting repressor of smt transcription. Two identical palindromic octanucleotides (5'-GCGATC-GC-3') traverse both borders of the excised element. This palindromic sequence is highly represented in the smt locus (7 occurrences in 1326 nucleotides) and analysis of the GenBank/EMBL/DDBJ DNA Nucleotide Sequence Data Libraries reveals that this is a highly iterated palindrome (HIP1) in other known sequences from Synechococcus strains (estimated to occur at an average frequency of once every c. 664 bp). HIP1 is also abundant in the genomes of other cyanobacteria. The functional significance of smtB deletion and the possible role of HIP1 in genome plasticity and adaptation in cyanobacteria are discussed.

Amino Acid Sequence↗

PubMed1994

A copper-transporting P-type ATPase found in the thylakoid membrane of the cyanobacterium Synechococcus species PCC7942.

P-type ATPases constitute a large family of cation pumps that play crucial physiological roles in many organisms, including bacteria, plants and mammals. They are postulated to play important roles in a variety of environmental adaptation systems. Recently, we cloned two distinct putative P-type ATPase genes (pacS and pacL) from a photosynthetic cyanobacterium, Synechococcus species PCC7942. In this study, one of the gene products (named PacS) was found to possess a putative metal-binding motif (Gly-Met-X-Cys-X-X-Cys) in its N-terminal portion. Thus we supposed that this ATPase may function as a metal pump. Indeed, the results of Northern blotting analysis showed that pacS-mRNA specifically increases upon addition of copper or silver to the growth medium. The results of Western blotting analysis confirmed the view that PacS accumulates in copper-treated Synechococcus cells. Thus we concluded that the expression of PacS ATPase is regulated in response to the change in concentration of external metals, namely copper and silver. Consistent with this, an insertional inactivation mutant of pacS exhibited hypersensitivity in terms of growth to these potentially toxic metals. It was also revealed that PacS was mainly located in the thylakoid membrane, in which the photosynthetic reactions take place. This P-type ATPase in the thylakoid membrane is implicated as a copper-transporting system that may be involved in copper-homeostasis crucial to the photosynthetic thylakoid function.

Adenosine Triphosphatases↗

PubMed1996

Circadian expression of genes involved in the purine biosynthetic pathway of the cyanobacterium Synechococcus sp. strain PCC 7942.

Extensive circadian (daily) control over gene expression in the cyanobacterium Synechococcus sp. strain PCC 7942 is programmed into at least two differentially phased groups. The transcriptional activity of the smaller group of genes is maximal at about dawn and minimal at about dusk. We identified one of the genes belonging to this latter group as purF, which encodes the key regulatory enzyme in the de novo purine synthetic pathway, glutamine PRPP amidotransferase (also known as amidophosphoribosyltransferase). Its expression pattern as a function of circadian time was confirmed by both luminescence from a purF::luxAB reporter strain and the abundance of purF mRNA. By fusing sequences upstream of the purF coding region to promoterless luxAB genes, we identified a limited upstream region, which potentially regulates purF circadian expression patterns in vivo. We also identified the purL gene immediately upstream of purF. The purL gene encodes FGAM synthetase, the fourth enzyme in the purine nucleotide biosynthesis pathway. Although these genes are expressed as part of a larger operon in other bacteria, reporter gene fusions revealed that purF and purL are transcribed independently in Synechococcus and that they are expressed at different phases of the circadian cycle. This differential expression pattern may be related to the oxygen sensitivity of amidophosphoribosyltransferase.

Amino Acid Sequence↗

PubMed1996

Identification of iron superoxide dismutase and a copper/zinc superoxide dismutase enzyme activity within the marine cyanobacterium Synechococcus sp. WH 7803.

Three constitutive forms of superoxide dismutase activity have been demonstrated in the cyanobacterial marine picoplankter Synechococcus sp. WH 7803 using polyacrylamide gel activity staining techniques. A protein which gave a positive non-haem iron stain on native polyacrylamide gels exhibited N-terminal similarity to both the iron superoxide dismutase and the manganese superoxide dismutase of Escherichia coli. The metal prosthetic group of each of the three activity bands was characterised by analysing their differential sensitivities to 5 mM H2O2, 2 mM cyanide and 2 mM of the copper chelator diethyldithiocarbamate. Three distinct superoxide dismutase activities were observed, an iron superoxide dismutase, a copper/zinc superoxide dismutase and a third form which has not been identified. Growth of Synechococcus cells in ASW medium containing no added iron resulted in no alteration in the activity of the iron superoxide dismutase. Growth of cultures in the absence of copper or zinc resulted in differential changes in the activities of the copper/zinc superoxide dismutase and the unidentified superoxide dismutase.

Amino Acid Sequence↗

PubMed1989

Effect of light on the cell cycle of a marine synechococcus strain.

Light-dependent regulation of cell cycle progression in the marine cyanobacterium Synechococcus strain WH-8101 was demonstrated through the use of flow cytometry. Our results show that, similar to eucaryotic cells, marine Synechococcus spp. display two gaps in DNA synthesis, at the beginning and at the end of the cell cycle. Progression through each of these gaps requires light, and their durations lengthen under light limitation.

Journal Article↗

PubMed1996

A genetic manipulation system for oceanic cyanobacteria of the genus Synechococcus.

Unicellular cyanobacteria of the genus Synechococcus are among the most abundant members of the picoplankton in the open ocean, and their contribution to primary production is considerable. While several isolates have been used for physiological, biochemical, and molecular studies of their unique adaptations to the marine environment, it has become necessary to develop molecular genetic methods for one or more model open-ocean cyanobacteria in order for studies of these organisms and their unique properties to progress. A number of molecular tools for the genetic manipulation of Synechococcus sp. strains WH7803, WH8102, and WH8103 have been developed. These include a plating technique for obtaining isolated colonies at high efficiencies and a conjugation method for introducing both a replicative vector and a suicide vector. In addition, a method for the generation of random, tagged chromosomal insertions (N. Dolganov and A. R. Grossman, J. Bacteriol. 175:7644-7651, 1993; N. F. Tsinoremas, A. K. Kutach, C. A. Strayer, and S. S. Golden, J. Bacteriol. 176:6764-6768, 1994) has been applied to these organisms.

Cyanobacteria↗

PubMed1997

Synechococcus diversity in the California current as seen by RNA polymerase (rpoC1) gene sequences of isolated strains.

Because they are ubiquitous in a range of aquatic environments and culture methods are relatively advanced, cyanobacteria may be useful models for understanding the extent of evolutionary adaptation of prokaryotes in general to environmental gradients. The roles of environmental variables such as light and nutrients in influencing cyanobacterial genetic diversity are still poorly characterized, however. In this study, a total of 15 Synechococcus strains were isolated from the oligotrophic edge of the California Current from two depths (5 and 95 m) with large differences in light intensity, light quality, and nutrient concentrations. RNA polymerase gene (rpoC1) fragment sequences of the strains revealed two major genetic lineages, distinct from other marine or freshwater cyanobacterial isolates or groups seen in shotgun-cloned sequences from the oligotrophic Atlantic Ocean. The California Current low-phycourobilin (CCLPUB) group represented by six isolates in a single lineage was less diverse than the California Current high-phycourobilin (CCHPUB) group with nine isolates in three relatively divergent lineages. The former was found to be the closest known genetic group to Prochlorococcus spp., a chlorophyll b-containing cyanobacterial group. Having an isolate from this group will be valuable for looking at the molecular changes necessary for the transition from the use of phycobiliproteins to chlorophyll b as light-harvesting pigments. Both of the CCHPUB and CCLPUB groups included strains obtained from surface (5 m) and deep (95 m) samples. Thus, contrary to expectations, there was no clear correlation between sampling depth and isolation of genetic groups, despite the large environmental gradients present. To our knowledge, this is the first demonstration with isolates that genetically divergent Synechococcus groups coexist in the same seawater sample.

Base Sequence↗

PubMed1997

Light-induced motility of thermophilic Synechococcus isolates from Octopus Spring, Yellowstone National Park.

This study demonstrates light-induced motility of two thermophilic Synechococcus isolates that are morphologically similar but that belong to different cyanobacterial lineages. Both isolates migrated away from densely inoculated streaks to form fingerlike projections extending toward or away from the light source, depending on the light intensity. However, the two isolates seemed to prefer widely different light conditions. The behavior of each isolate was controlled by several factors, including temperature, preacclimation of inocula, acclimation during the experiment, and strain-specific genetic preferences for different light conditions (adaptation). Time-lapse microscopy confirmed that these projections were formed by actively gliding cells and were not simply the outcome of directional cell division. The observed motility rates of individual cells of 0.1 to 0.3 micrometers s-1 agreed well with the distance traversed by the projections, 0.3 to 0.5 mm h-1, suggesting that most cells in each projection are travelling in the same direction. The finding of motility among two phylogenetically unaffiliated unicellular cyanobacteria suggests that this trait may be widespread among this group. If so, this would have important implications for experiments on colonization, succession, diel positioning, and photosynthetic activity in hot spring mats dominated by Synechococcus-like cyanobacteria.

Cyanobacteria↗

PubMed1998

Effects of visible light and UV radiation on photosynthesis in a population of a hot spring cyanobacterium, a synechococcus sp., subjected to high-temperature stress

Assays of photosynthesis were conducted with a biofilm population of a cyanobacterium, a Synechococcus sp., growing at approximately 70 degreesC in a Yellowstone National Park hot spring to test whether cells growing near the upper temperature limit of photosynthetic life are optimally adapted to their mean environmental temperature. Cell suspensions were assayed at 70, 65, and 55 degreesC while being simultaneously exposed to modified solar environments, including reduction of total irradiance and exclusion of UV radiation. Carbon fixation was greatest at 65 degreesC, while 70 and 55 degreesC were always supraoptimal and suboptimal for photosynthesis, respectively. The degree of temperature stress was dependent upon light intensity, and this light-dependent temperature effect may involve both reduced quantum efficiency at subsaturating irradiances and a lower saturating irradiance at both supraoptimal and suboptimal temperatures. The Synechococcus sp. was also more susceptible to UV inhibition of photosynthesis at nonoptimal temperatures. These results suggest that this population is persisting at a nearly lethal temperature and is consequently subject to greater damage by both visible and UV radiation, but it is speculated that these cells may be avoiding competition with other photoautotrophs under these nonoptimal conditions. In separate experiments monitoring diurnal patterns of photosynthesis, cells exhibited peak productivity during the morning, followed by an afternoon decline. No recovery of photosynthesis was observed during the remaining daytime, and carbon fixation was always UV inhibited under conditions of photosynthetically saturating light.

Journal Article↗

PubMed1999

Expression of the ggpS gene, involved in osmolyte synthesis in the marine cyanobacterium Synechococcus sp. Strain PCC 7002, revealed regulatory differences between this strain and the freshwater strain Synechocystis sp. Strain PCC 6803.

Synthesis of the osmolyte glucosylglycerol (GG) in the marine cyanobacterium Synechococcus sp. strain PCC 7002 was characterized. The ggpS gene, which encodes the key enzyme (GG-phosphate synthase [GgpS]) in GG biosynthesis, was cloned by using PCR. A 2,030-bp DNA sequence which contained one open reading frame (ORF) was obtained. The protein deduced from this ORF exhibited 85% similarity to the GgpS of the freshwater cyanobacterium Synechocystis sp. strain PCC 6803. The function of the protein was confirmed by generating a ggpS null mutant, which was not able to synthesize GG and thus exhibited a salt-sensitive phenotype. Expression of the ggpS gene was analyzed in salt-shocked cells by performing Northern blot and immunoblot experiments. While almost no expression was detected in cells grown in low-salt medium, immediately after a salt shock the amounts of ggpS mRNA and GgpS protein increased up to 100-fold. The finding that salt-induced expression occurred was confirmed by measuring enzyme activities, which were negligible in control cells but clearly higher in salt-treated Synechococcus sp. cells. The salt-induced increase in GgpS activity could be inhibited by adding chloramphenicol, while in protein extracts of the freshwater cyanobacterium Synechocystis sp. strain PCC 6803 a constitutive, high level of enzyme activity that was not affected by chloramphenicol was found. A comparison of GG accumulation in the two cyanobacteria revealed that in the marine strain osmolyte synthesis seemed to be regulated mainly by transcriptional control, whereas in the freshwater strain control seemed to be predominantly posttranslational.

Amino Acid Sequence↗

PubMed1999

Diel rhythms in ribulose-1,5-bisphosphate carboxylase/oxygenase and glutamine synthetase gene expression in a natural population of marine picoplanktonic cyanobacteria (Synechococcus spp.).

Diel periodicity in the expression of key genes involved in carbon and nitrogen assimilation in marine Synechococcus spp. was investigated in a natural population growing in the surface waters of a cyclonic eddy in the northeast Atlantic Ocean. Synechococcus sp. cell concentrations within the upper mixed layer showed a net increase of three- to fourfold during the course of the experiment (13 to 22 July 1991), the population undergoing approximately one synchronous division per day. Consistent with the observed temporal pattern of phycoerythrin (CpeBA) biosynthesis, comparatively little variation was found in cpeBA mRNA abundance during either of the diel cycles investigated. In marked contrast, the relative abundance of transcripts originating from the genes encoding the large subunit of ribulose bisphosphate carboxylase/oxygenase (rbcL) and glutamine synthetase (glnA) showed considerable systematic temporal variation and oscillated during the course of each diel cycle in a reciprocal rhythm. Whereas activation of rbcL transcription was clearly not light dependent, expression of glnA appeared sensitive to endogenous changes in the physiological demands for nitrogen that arise as a natural consequence of temporal periodicity in photosynthetic carbon assimilation. The data presented support the hypothesis that a degree of temporal separation may exist between the most active periods of carbon and nitrogen assimilation in natural populations of marine Synecoccoccus spp.

Cyanobacteria↗

PubMed2000

In situ hybridization of Prochlorococcus and Synechococcus (marine cyanobacteria) spp. with RRNA-targeted peptide nucleic acid probes.

A simple method for whole-cell hybridization using fluorescently labeled rRNA-targeted peptide nucleic acid (PNA) probes was developed for use in marine cyanobacterial picoplankton. In contrast to established protocols, this method is capable of detecting rRNA in Prochlorococcus, the most abundant unicellular marine cyanobacterium. Because the method avoids the use of alcohol fixation, the chlorophyll content of Prochlorococcus cells is preserved, facilitating the identification of these cells in natural samples. PNA probe-conferred fluorescence was measured flow cytometrically and was always significantly higher than that of the negative control probe, with positive/negative ratio varying between 4 and 10, depending on strain and culture growth conditions. Prochlorococcus cells from open ocean samples were detectable with this method. RNase treatment reduced probe-conferred fluorescence to background levels, demonstrating that this signal was in fact related to the presence of rRNA. In another marine cyanobacterium, Synechococcus, in which both PNA and oligonucleotide probes can be used in whole-cell hybridizations, the magnitude of fluorescence from the former was fivefold higher than that from the latter, although the positive/negative ratio was comparable for both probes. In Synechococcus cells growing at a range of growth rates (and thus having different rRNA concentrations per cell), the PNA- and oligonucleotide-derived signals were highly correlated (r = 0.99). The chemical nature of PNA, the sensitivity of PNA-RNA binding to single-base-pair mismatches, and the preservation of cellular integrity by this method suggest that it may be useful for phylogenetic probing of whole cells in the natural environment.

Cyanobacteria↗

PubMed2001

Iron stress in open-ocean cyanobacteria (Synechococcus, Trichodesmium, and Crocosphaera spp.): identification of the IdiA protein.

Cyanobacteria are prominent constituents of the marine biosphere that account for a significant percentage of oceanic primary productivity. In an effort to resolve how open-ocean cyanobacteria persist in regions where the Fe concentration is thought to be limiting their productivity, we performed a number of Fe stress experiments on axenic cultures of marine Synechococcus spp., Crocosphaera sp., and Trichodesmium sp. Through this work, we determined that all of these marine cyanobacteria mount adaptive responses to Fe stress, which resulted in the induction and/or repression of several proteins. We have identified one of the Fe stress-induced proteins as an IdiA homologue. Genomic observations and laboratory data presented herein from open-ocean Synechococcus spp. are consistent with IdiA having a role in cellular Fe scavenging. Our data indicate that IdiA may make an excellent marker for Fe stress in open-ocean cyanobacterial field populations. By determining how these microorganisms respond to Fe stress, we will gain insight into how and when this important trace element can limit their growth in situ. This knowledge will greatly increase our understanding of how marine Fe cycling impacts oceanic processes, such as carbon and nitrogen fixation.

Bacterial Proteins↗

PubMed2001

Chromatic adaptation in marine Synechococcus strains.

Characterization of two genetically distinct groups of marine Synechococcus sp. strains shows that one, but not the other, increases its phycourobilin/phycoerythrobilin chromophore ratio when growing in blue light. This ability of at least some marine Synechococcus strains to chromatically adapt may help explain their greater abundance in particular ocean environments than cyanobacteria of the genus Prochlorococcus.

Adaptation, Physiological↗