Synechococcus Cells Research Articles

Diel rhythmicity in amino acid uptake by Prochlorococcus

The marine cyanobacterium Prochlorococcus, the most abundant phototrophic organism on Earth, numerically dominates the phytoplankton in nitrogen (N)-depleted oceanic gyres. Alongside inorganic N sources such as nitrite and ammonium, natural populations of this genus also acquire organic N, specifically amino acids. Here, we investigated using isotopic tracer and flow cytometric cell sorting techniques whether amino acid uptake by Prochlorococcus is subject to a diel rhythmicity, and if so, whether this was linked to a specific cell cycle stage. We observed, in contrast to diurnally similar methionine uptake rates by Synechococcus cells, obvious diurnal rhythms in methionine uptake by Prochlorococcus cells in the tropical Atlantic. These rhythms were confirmed using reproducible cyclostat experiments with a light-synchronized axenic Prochlorococcus (PCC9511 strain) culture and (35)S-methionine and (3)H-leucine tracers. Cells acquired the tracers at lower rates around dawn and higher rates around dusk despite >10(4) times higher concentration of ammonium in the medium, presumably because amino acids can be directly incorporated into protein. Leucine uptake rates by cells in the S+G(2) cell cycle stage were consistently 2.2 times higher than those of cells at the G(1) stage. Furthermore, S+G(2) cells upregulated amino acid uptake 3.5 times from dawn to dusk to boost protein synthesis prior to cell division. Because Prochlorococcus populations can account from 13% at midday to 42% at dusk of total microbial uptake of methionine and probably of other amino acids in N-depleted oceanic waters, this genus exerts diurnally variable, strong competitive pressure on other bacterioplankton populations.

Changes in the abundance and composition of picophytoplankton in relation to the occurrence of a Kyucho and a bottom intrusion in the Bungo Channel, Japan

The Bungo Channel in southwestern Japan receives both warm, called Kyucho, and cold deep-water intrusions (bottom intrusion) from the Pacific Ocean. Abundances of Prochlorococcus, Synechococcus, and eukaryotic picophytoplankton were monitored from 18 July to 17 August 2001 to clarify whether advected picophytoplankton from the Pacific Ocean can grow in the channel or not. Synechococcus cells were further discriminated into low- and high-PUB types according to their fluorescence property in flow cytometry. From 18 to 25 July, the water temperature decreased by 3 °C at a 5-m depth at all stations, indicating the occurrence of a bottom intrusion. From 25 July to 4 August, a Kyucho occurred and the water temperature rapidly increased. From 4 to 17 August, a bottom intrusion and a Kyucho both occurred twice, although the intensities were smaller than those occurring until 4 August. From 18 to 30 July, the abundance of both Prochlorococcus and a high-PUB type of Synechococcus drastically decreased because of a bottom intrusion; however, the abundances rapidly increased due to the advection by a Kyucho. These advected cells increased from 4 to 17 August in the channel and Kitanada Bay. Changes in the abundance of low-PUB type of Synechococcus and eukaryotic picophytoplankton were less noticeable than those in the abundance of Prochlorococcus and high-PUB type. The present study demonstrated that oceanic picophytoplankton advected by the Kyucho could grow in the channel. However, abundances of low-PUB type and eukaryotic picophytoplankton increased higher than those of Prochlorococcus and high-PUB type did. Thus, these oceanic phytoplankters will be excluded when Kyucho does not occur for a long time. The co-occurrence of various types of picophytoplankton found in the channel is probably achieved by both Kyucho event and their growth capability in the channel.

Modelling the vertical distribution of Prochlorococcus and Synechococcus in the North Pacific Subtropical Ocean

A simple model was developed to examine the vertical distribution of Prochlorococcus and Synechococcus ecotypes in the water column, based on their adaptation to light intensity. Model simulations were compared with a 14-year time series of Prochlorococcus and Synechococcus cell abundances at Station ALOHA in the North Pacific Subtropical Gyre. Data were analysed to examine spatial and temporal patterns in abundances and their ranges of variability in the euphotic zone, the surface mixed layer and the layer in the euphotic zone but below the base of the mixed layer. Model simulations show that the apparent occupation of the whole euphotic zone by a genus can be the result of a co-occurrence of different ecotypes that segregate vertically. The segregation of ecotypes can result simply from differences in light response. A sensitivity analysis of the model, performed on the parameter alpha (initial slope of the light-response curve) and the DIN concentration in the upper water column, demonstrates that the model successfully reproduces the observed range of vertical distributions. Results support the idea that intermittent mixing events may have important ecological and geochemical impacts on the phytoplankton community at Station ALOHA.

Phytoplankton dynamics during an in situ iron enrichment experiment (EisenEx) in the Southern Ocean: a comparative study of field and bottle incubation measurements

Composition, physiology and growth response of 5 size classes of phytoplankton, rang- ing from 0.7 to 20 µm, was studied in an in situ iron enrichment experiment (EisenEx) and in bottle incubations in the Southern Ocean during austral spring 2000. In the field, iron enrichment resulted in only minor changes in numerical abundance, cell carbon content, photosynthetic efficiency (Fv:Fm) and the percentage of live cells of Synechococcus spp. and pico-eukaryotes (<2 µm). In these 2 groups, only cellular chlorophyll a (chl a) content increased (by 20 and 100%, respectively). The physiological conditions of the 2 to 20 µm cells improved significantly, but a statistically significant (3- fold higher) biomass was observed only in the largest size fraction (8 to 20 µm). Bottle experiment results were comparable with in situ results, except that the responses occurred earlier. In addition, the total increase in biomass was much larger than that in the field (100- and 25-fold increase for cell carbon and chl a content, respectively). In this respect the control and the iron-enriched bottles showed a comparable trend, suggesting that, next to iron, light was probably a factor of great impor- tance. In the field, phytoplankton cells experience rapidly changing light conditions due to wind- induced turbulence that causes mixing of the water column. In addition to iron-limitation, this results in a generally poor physiological condition of algae in the field. This light-stressor mainly affected the smallest algal size classes (<8 µm). In larger cells, iron enrichment partly compensated for this nega- tive light effect, resulting in a final dominance of larger phytoplankton.

Expression of psbA Genes is Regulated at Multiple Levels in the Cyanobacterium Synechococcus sp. PCC 7942

In cyanobacterium Synechococcus sp. PCC 7942 the photosystem II reaction-center protein D1 is encoded by three psbA genes. The psbAI gene encodes D1:1 protein, the form used for acclimated growth, and psbAII and psbAIII genes encode the stress-induced form, D1:2 protein. Strong light and low temperature have been shown to induce the expression of psbAII/III genes and down-regulate the expression of psbAI gene. Recently, we reported the involvement of reduced thiols in the up-regulation of psbAII/III genes. In this study, we have analyzed the regulation of psbA gene expression in Synechococcus further, at both the transcriptional and post-transcriptional levels. We show that the inhibitors of the photosynthetic electron-transfer chain, which have different effects on the redox state of the plastoquinone (PQ) pool, have similar effect on the transcription of psbA genes. The inhibitors 3-(3,4 dichlorophenyl)-1,1-dimethylurea (DCMU) and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB) do not cause any changes in psbA gene expression when added under low-light conditions, but dramatically reduce the high-light induction of psbAII/III genes when added upon a high-light shift. Moreover, when the thiol reductant, dithiothreitol, is added to Synechococcus cells together with DCMU concomitant with the high-light shift, no inhibition of psbAII/III gene up-regulation takes place, indicating that the thiol redox state rather than the redox state of the PQ pool regulates psbA gene transcription. We also provide evidence for post-transcriptional regulation of psbA gene expression, particularly, inhibition of translation of psbAI transcripts at high light, and demonstrate that the D1 protein synthesis and degradation processes are coregulated in Synechococcus.

Biosorption mechanism of Cr (VI) onto cells of Synechococcus sp.

The biosorption mechanism of Cr (VI) ions on Synechococcus sp. biosorbent was studied by analyzing the biosorption kinetics as well as speciation change and bond formation during the biosorption process. The kinetics study shows that the adsorption process of Cr (VI) consists of a very fast stage in the first several minutes, in which more than half of the saturation adsorption is attained, and a slower stage that approximately follows the first order kinetic model, basically Freundlich isotherm models were observed. Comparative studies of FT-IR spectra of K2Cr2O7, free cells of Synechococcus sp., and Cr-bound cells of Synechococcus sp. show that the speciation of chromium that binds to the cells of Synechococcus sp. is Cr (III), instead of Cr (VI), and the carboxylic, alcoholic, amido and amino groups may be involved in the binding of Cr (III). Integrative analyses of the surface electric potential, the effect of pH value on adsorption behavior of Cr (VI), and the results of FT-IR show that the biosorption of Cr (VI) follows two subsequent steps, biosorption of Cr2O72− by electrostatical force at the protonated active sites and reduction of Cr2O72− to Cr3+ by the reductive groups on the surface of the biosorbents.

Fluorescence induction in the phycobilisome-containing cyanobacterium Synechococcus sp PCC 7942: Analysis of the slow fluorescence transient

At room temperature, the chlorophyll (Chl) a fluorescence induction (FI) kinetics of plants, algae and cyanobacteria go through two maxima, P at ∼ 0.2–1 and M at ∼ 100–500 s, with a minimum S at ∼ 2–10 s in between. Thus, the whole FI kinetic pattern comprises a fast OPS transient (with O denoting origin) and a slower SMT transient (with T denoting terminal state). Here, we examined the phenomenology and the etiology of the SMT transient of the phycobilisome (PBS)-containing cyanobacterium Synechococcus sp PCC 7942 by modifying PBS → Photosystem (PS) II excitation transfer indirectly, either by blocking or by maximizing the PBS → PS I excitation transfer. Blocking the PBS → PS I excitation transfer route with N-ethyl-maleimide [NEM; A. N. Glazer, Y. Gindt, C. F. Chan, and K.Sauer, Photosynth. Research 40 (1994) 167–173] increases both the PBS excitation share of PS II and Chl a fluorescence. Maximizing it, on the other hand, by suspending cyanobactrial cells in hyper-osmotic media [G. C. Papageorgiou, A. Alygizaki-Zorba, Biochim. Biophys. Acta 1335 (1997) 1–4] diminishes both the PBS excitation share of PS II and Chl a fluorescence. Here, we show for the first time that, in either case, the slow SMT transient of FI disappears and is replaced by continuous P → T fluorescence decay, reminiscent of the typical P → T fluorescence decay of higher plants and algae. A similar P → T decay was also displayed by DCMU-treated Synechococcus cells at 2 °C. To interpret this phenomenology, we assume that after dark adaptation cyanobacteria exist in a low fluorescence state (state 2) and transit to a high fluorescence state (state 1) when, upon light acclimation, PS I is forced to run faster than PS II. In these organisms, a state 2 → 1 fluorescence increase plus electron transport-dependent dequenching processes dominate the SM rise and maximal fluorescence output is at M which lies above the P maximum of the fast FI transient. In contrast, dark-adapted plants and algae exist in state 1 and upon illumination they display an extended P → T decay that sometimes is interrupted by a shallow SMT transient, with M below P. This decay is dominated by a state 1 → 2 fluorescence lowering, as well as by electron transport-dependent quenching processes. When the regulation of the PBS → PS I electronic excitation transfer is eliminated (as for example in hyper-osmotic suspensions, after NEM treatment and at low temperature), the FI pattern of Synechococcus becomes plant-like.

Distribution of prokaryotic picophytoplankton from Seto Inland Sea to the Kuroshio region, with special reference to ‘Kyucho’ events

A 'Kyucho' (an intrusion of warm surface water) occurs in the Bungo Channel, located in southwestern Japan. The abundances of Prochlorococcus and Synechococcus during a Kyucho, together with physical and chemical environmental factors, were investigated from the Kuroshio region to the Seto Inland Sea, via Bungo Channel, from 26 November to 5 December 2003. With the occurrence of the Kyucho, oceanic water intruded from the Kuroshio region into the middle of the Bungo Channel. The abundance of Prochlorococcus was the highest in the Kuroshio region and the southern part of the Bungo Channel (>25 x 10 3 cells ml -1) , low in the northern part of the Bungo Channel ( 15 x 10 3 cells ml -1 ) was detected in the Kuroshio region and in the southern part of the Bungo Channel, but the abundance ( 90%); at this location, most of the available light in the deeper layer (>25 m depth) was in the 450 to 500 nm range, corresponding to the peak absorbance of PUB. In contrast, the abundance of low-PUB-type cells accounted for > 75 % of the total in the northern part of the Bungo Channel and in the Seto Inland Sea, where most of the available light in the deeper layer (>10 m depth) was in the 480 to 560 nm range, including the peak absorbance of both PUB and phycoerythrobilin (PEB). These results indicate that Synechococcus cells of high-PUB type, which have a higher Ex 495:545 (>1.5; ratio of orange fluorescence intensity excited at 495 nm to that at 545 nm), as well as Prochlorococcus cells were advected to the Bungo Channel by the Kyucho. The co-occurrence of the 2 pigment types of Synechococcus in coastal waters is highly affected by a physical process, such as the Kyucho.

A New Class of Signal Transducer in His-Asp Phosphorelay Systems

Nitrate transport activity of the LtnT permease of the cyanobacterium Synechococcus elongatus is activated when LtnA, a response regulator without an effector domain, is phosphorylated by LtnB, a hybrid histidine kinase. We identified a protein (LtnC) that is required for activation of LtnT. LtnC consists of an N-terminal histidine-containing phosphoacceptor (HisKA) domain, a receiver domain, and a unique C-terminal domain found in some cyanobacterial proteins. Because LtnC lacks an ATP-binding kinase domain of a histidine kinase, it is incapable of autophosphorylation, but LtnC is phosphorylated by LtnA. The histidine residue in the HisKA domain but not the aspartate residue in the receiver domain is essential for phosphorylation of LtnC and activation of LtnT. LtnC phosphorylation leads to oligomerization of the protein. Fusion of the C-terminal domain of LtnC to glutathione S-transferase, which forms oligomers, also activates LtnT, suggesting that oligomerization of the LtnC C-terminal domain causes LtnT activation. These results indicate that the C-terminal domain of LtnC acts as an effector domain that directs the output of the signal from the phosphorelay system. The two-step (His-Asp-His) phosphorelay system, composed of the LtnB, LtnA, and LtnC proteins, is distinct from the known phosphorelay systems, namely, the typical two-component system (His-Asp) and the multistep phosphorelay system (His-Asp-His-Asp), because the HisKA domain of LtnC is the terminal phosphoacceptor that determines the signal output. LtnC is a new class of signal transducer in His-Asp phosphorelay systems that contains a HisKA domain and an effector domain.

Translation Initiation of Cyanobacterial rbcS mRNAs Requires the 38-kDa Ribosomal Protein S1 but Not the Shine-Dalgarno Sequence

Little is known about the biochemical mechanism of translation in cyanobacteria though substantial studies have been made on photosynthesis, nitrogen fixation, circadian rhythm, and genome structure. To analyze the mechanism of cyanobacterial translation, we have developed an in vitro translation system from Synechococcus cells using a psbAI-lacZ fusion mRNA as a model template. This in vitro system supports accurate translation from the authentic initiation site of a variety of Synechococcus mRNAs. In Synechococcus cells, rbcL and rbcS encoding the large and small subunits, respectively, of ribulose-1,5-bisphosphate carboxylase/oxygenase are co-transcribed as a dicistronic mRNA, and the downstream rbcS mRNA possesses two possible initiation codons separated by three nucleotides. Using this in vitro system and mutated mRNAs, we demonstrated that translation starts exclusively from the upstream AUG codon. Although there are Shine-Dalgarno-like sequences in positions similar to those of the functional Shine-Dalgarno elements in Escherichia coli, mutation analysis indicated that these sequences are not required for translation. Assays with deletions within the 5'-untranslated region showed that a pyrimidine-rich sequence in the -46 to -15 region is necessary for efficient translation. Synechococcus cells contain two ribosomal protein S1 homologues of 38 and 33 kDa in size. UV cross-linking and immunoprecipitation experiments suggested that the 38-kDa S1 is involved in efficient translation via associating with the pyrimidine-rich sequence. The present in vitro translation system will be a powerful tool to analyze the basic mechanism of translation in cyanobacteria.

Prevalence and Evolution of Core Photosystem II Genes in Marine Cyanobacterial Viruses and Their Hosts

Cyanophages (cyanobacterial viruses) are important agents of horizontal gene transfer among marine cyanobacteria, the numerically dominant photosynthetic organisms in the oceans. Some cyanophage genomes carry and express host-like photosynthesis genes, presumably to augment the host photosynthetic machinery during infection. To study the prevalence and evolutionary dynamics of this phenomenon, 33 cultured cyanophages of known family and host range and viral DNA from field samples were screened for the presence of two core photosystem reaction center genes, psbA and psbD. Combining this expanded dataset with published data for nine other cyanophages, we found that 88% of the phage genomes contain psbA, and 50% contain both psbA and psbD. The psbA gene was found in all myoviruses and Prochlorococcus podoviruses, but could not be amplified from Prochlorococcus siphoviruses or Synechococcus podoviruses. Nearly all of the phages that encoded both psbA and psbD had broad host ranges. We speculate that the presence or absence of psbA in a phage genome may be determined by the length of the latent period of infection. Whether it also carries psbD may reflect constraints on coupling of viral- and host-encoded PsbA–PsbD in the photosynthetic reaction center across divergent hosts. Phylogenetic clustering patterns of these genes from cultured phages suggest that whole genes have been transferred from host to phage in a discrete number of events over the course of evolution (four for psbA, and two for psbD), followed by horizontal and vertical transfer between cyanophages. Clustering patterns of psbA and psbD from Synechococcus cells were inconsistent with other molecular phylogenetic markers, suggesting genetic exchanges involving Synechococcus lineages. Signatures of intragenic recombination, detected within the cyanophage gene pool as well as between hosts and phages in both directions, support this hypothesis. The analysis of cyanophage psbA and psbD genes from field populations revealed significant sequence diversity, much of which is represented in our cultured isolates. Collectively, these findings show that photosynthesis genes are common in cyanophages and that significant genetic exchanges occur from host to phage, phage to host, and within the phage gene pool. This generates genetic diversity among the phage, which serves as a reservoir for their hosts, and in turn influences photosystem evolution.

Influence of H+ and Calcium Ions on Surface Functional Groups of Synechococcus PCC 7942 Cells

The chemistry of the surface functional groups of picocyanobacteria Synechococcus PCC 7942 cells was examined as a function of H+ and calcium concentrations. Titration experiments, infrared spectroscopy, biosorption experiments, and chemical modeling were used to gain insight into the mechanisms of biosorption. The pKa and concentration of active sites on the cell wall were clarified with the aid of potentiometric titration. Modeling calculations and infrared spectra are consistent with pKa's values of 4.3, 5.2, 6.9, 9.1, and 10.0 and a total concentration of 7.8 x 10(-4) mol g(-1). Spectral analysis of an aqueous cellular suspension revealed a presence of carboxyl, amide, phosphate, hydroxyl, and carbohydrate moieties. Correspondence between spectral data and potentiometric titration curves supported the hypothesis that carboxylate groups and phosphodiester groups mediate calcium adsorption to bacterial cells. This process is strongly pH dependent. In the second part of the experimental work, Synechococcus cells were suspended in the presence of different calcium concentrations. Mechanistic modeling demonstrated that the calcium adsorption phenomenon can be described taking into account only two mechanisms: ion exchange and complexation.

Growth rates of Synechococcus types with different phycoerythrin composition estimated by dual-laser flow cytometry in relationship to the light environment in the Uwa Sea

In the Uwa Sea, Synechococcus types with low- and high-phycourobilin (PUB) to phycoerythrobilin (PEB) ratio co-occurred throughout a year. To clarify the effects of light quality and quantity on the two types of Synechococcus, we measured the growth rates of two pigment types of Synechococcus cells with in situ incubation experiments. Incubations were conducted at 2, 10, and 20 m depth between May and October 2002. Synechococcus were divided into high- and low-PUB types using a dual-laser flow cytometer. Two indexes were used to evaluate the light environment: one was the relative light intensity (RLI) to that at the surface, and the other was the ratio of the light intensities of blue (490–500 nm) to green (540–550 nm). At 2 m depth, where the relative light intensities were above 20%, the growth rates of the low-PUB type were generally slightly higher than those of the high-PUB type. In contrast, at 10 and 20 m depth, the type that grew faster did not depend on the combination of light intensity and quality. Available light in the deeper layer of the Uwa Sea ranged from 490 to 550 nm. The range covers absorbance maxima of both PUB (ca. 495 nm) and PEB (545 nm). For this reason, light quality may not have caused one type to grow faster. These results explain the co-occurrence of two pigment types of Synechococcus in coastal waters.

Dimethylsulfoniopropionate (DMSP) assimilation by Synechococcus in the Gulf of Mexico and northwest Atlantic Ocean

A variety of bacterial phylogenetic groups assimilate dimethylsulfoniopropionate (DMSP), an organic sulfur compound that can satisfy most of the sulfur (S) demand of bacteria in the surface waters of the ocean. Marine Synechococcus are capable of utilizing some forms of dissolved organic matter, but it is unknown if Synechococcus also assimilate DMSP. To better understand the role of Synechococcus in the flux of DMSP, we used microautoradiography to follow the assimilation of 35S-DMSP and 35S-methanethiol, an intermediate in DMSP assimilation, by Synechococcus in the surface waters of the Gulf of Mexico and the northwest Atlantic Ocean. About 85% of Synechococcus cells assimilated S from DMSP and methanethiol in these environments, and Synechococcus assimilated more DMSP per cell than other bacteria. On average, Synechococcus accounted for roughly 20% of prokaryotic DMSP assimilation in the northwest Atlantic and the Gulf of Mexico. Tests with axenic cultures of Synechococcus revealed that two phycoerythrin-containing strains (WH8102 and WH7803) were capable of DMSP transport, although these strains did not produce dimethylsulfide (DMS). These data indicate that DMSP could provide a significant amount of S to Synechococcus and that Synechococcus are important consumers of DMSP in the ocean.

Time series observation based InfraRed Epifluorescence Microscopic (TIREM) approach for accurate enumeration of bacteriochlorophyll-containing microbes in marine environments

Bacteriochlorophyll a Containing Microbes (BCM) are a unique group of microorganisms in the marine environment. Accurate determination of their abundance is critical for understanding their role in energy flow and carbon cycle in the ecosystem. The InfraRed Epifluorescence Microscopy (IREM) method, using infrared fluorescence as the diagnostic signal of BCM, is the most convenient means to date for enumeration of BCM in seawater, but IREM methodology suffers from serious errors introduced by cyanobacteria, which also can emit infrared fluorescence and whose abundance is of the same order of magnitude as BCM. In the present study, an advanced “Time-series observation based cyanobacteria-calibrated InfraRed Epifluorescence Microscopy (TIREM)” approach is established for accurate enumeration of BCM in marine environments. The protocol is distinguished by its use of time series observation, auto-imaging and digital analysis. In principle, the correct count of BCM can be obtained by subtracting the cyanobacterial count from the total infrared positive count. The challenge, however, is that Prochlorococcus, the most abundant cyanobacterium in the sea, is readily visible in infrared images but not visible in the initial cyanobacterial images obtained by epifluorescence microscopy because its emission signals are masked by brighter fluorescence from larger cells like Synechococcus coexisting in seawater samples. Prochlorococcus cells become gradually visible when the fluorescence from Synechococcus cells declines after a period of exposure to excitation light. Therefore the plateau (maximum) count of the cyanobacterial cells in time series images rather than in the initial ones, as previously believed, represents the correct count for the total number of cyanobacteria ( Synechococcus plus Prochlorococcus cells). Thus, the accurate estimation of BCM abundance can only be calculated from the formula: [BCM cells] = [plateau count of infrared positive cells] − [plateau count of cyanobacterial cells]. The conceptual advance of the TIREM protocol is that in classical epifluorescence microscopy or in IREM protocols, quick observation is recommended to avoid quenching the fluorescence, but in the TIREM protocol, instead, time series observation is the key for obtaining reliable data. The TIREM protocol is validated by studies using BCM and cyanobacterial pure cultures as well as by examination of samples from various marine environments.

Polycistronic strategy for cyanobacterial expression vector construction: Co-transcription of a human gene and a selective marker gene

Abstract A polycistronic expression vector, pKGA-NTF1, was constructed for the cyanobacterium. Within this vector, the spectinomycin/streptomycin resistance gene (aadA) facilitated the selection of transformants when co-transcribed with favorite genes. A natural glnA gene was selected as the platform to introduce the plasmid into a neutral site of the Synechococcus sp. PCC 7002 chromosome. Function of the vector was demonstrated by the insertion of a modified human Trefoil factor 3 gene (NTF1) to upstream of th aadA gene and by the analyses of the transformed strains. Antibiotics resistance assays showed that the dicistronic expression cassette conferred high spectinomucin resistance to both the E. coli cells and the Synechococcus cells. PCR analysis and Western-blot analysis were carried out to confirm the integration and expression of the NTF1 gene, respectively. Through simple molecular manipulations, the artificial polycistronic structure described here can be conveniently used to express other favourable genes or operons in cyanobacteria, and to study the cyanobacterial gene expression as well.

FesM, a membrane iron-sulfur protein, is required for cyclic electron flow around photosystem I and photoheterotrophic growth of the cyanobacterium Synechococcus sp. PCC 7002.

While it is known that cyclic electron flow around photosystem I is an important pathway of photosynthetic electron transfer for converting light energy to chemical energy, some components of cyclic electron flow remain to be revealed. Here, we show that fesM, encoding a novel membrane iron-sulfur protein, is essential to cyclic electron flow in the cyanobacterium Synechococcus sp. PCC 7002. The FesM protein is predicted to have a cAMP-binding domain, an NtrC-like domain, a redox sensor motif, and an iron-sulfur (4Fe-4S) motif. Deletion of fesM (fesM-D) led to an inability for Synechococcus cells to grow in the presences of glycerol and 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Photoheterotrophic growth was restored by a complete fesM gene present on a replicable plasmid. A mutant fesM gene encoding a truncated FesM protein lacking the cAMP domain failed to restore the phenotype, suggesting this domain is important to the function of FesM. Measurements of reduction of P700(+) and the redox state of interphotosystem electron carriers showed that cells had a slower rate of respiratory electron donation to the interphotosystem electron transport chain, and cyclic electron flow around photosystem I in fesM-D was impaired, suggesting that FesM is a critical protein for respiratory and cyclic electron flow. Phosphatase fusion analysis showed that FesM contains nine membrane-spanning helices, and all functional domains of FesM are located on the cytoplasmic face of the thylakoid membranes.

Feeding by red-tide dinoflagellates on the cyanobacterium Synechococcus

We investigated the feeding by 18 red-tide dinoflagellate species on the cyanobacterium Synechococcus sp. We also calculated grazing coefficients by combining the field data on abundances of the dinoflagellates Prorocentrum donghaiense and P. micans and co-occurring Synechococcus spp. with laboratory data on ingestion rates obtained in the present study. All 17 cultured red-tide dinoflagellates tested (Akashiwo sanguinea, Alexandrium catenella, A. minutum, A. tamarense, Cochlodinium polykrikoides, Gonyaulax polygramma, G. spinifera, Gymnodinium catenatum, G. impudicum, Heterocapsa rotundata, H. triquetra, Karenia brews, Lingulodinium polyedrum, Prorocentrum donghaiense, P. minimum, P. micans, and Scrippsiella trochoidea) were able to ingest Synechococcus. Also, Synechococcus cells were observed inside the protoplasms of P. triestinum cells collected from the coastal waters off Shiwha, western Korea, during red tides dominated by the dinoflagellate in July 2005. When prey concentrations were 1.1 to 2.3 x 10 6 cells ml -1 , the ingestion rates of these cultured red-tide dinoflagellates on Synechococcus sp. (1.0 to 64.2 cells dinoflagellate -1 h -1 ) generally increased with increasing size of the dinoflagellate predators (equivalent spherical diameters = 5.2 to 38.2 μm). The ingestion rates of P. donghaiense and P. micans on Synechococcus sp. increased with increasing mean prey concentration, with saturation occurring at a mean prey concentration of approximately 1.1 to 1.4 × 10 6 cells ml -1 . The maximum ingestion and clearance rates of P. micans on Synechococcus sp. (38.2 cells dinoflagellates -1 h -1 and 4.3 μl dinoflagellate -1 h -1 ) were much higher than those of P. donghaiense on the same prey species (7.7 cells dinoflagellate -1 h -1 and 2.6 μl dinoflagellates -1 h -1 ). The ingestion rates of red-tide dinoflagellates on Synechococcus sp. were comparable to those of the heterotrophic nanoflagellates and ciliates on Synechococcus spp., so far reported in the literature. The calculated grazing coefficients attributable to small Prorocentrum spp. (P. donghaiense + P. minimum) and P. micans on co-occurring Synechococcus spp. were up to 3.6 and 0.15 h -1 , respectively. The results of the present study suggest that red-tide dinoflagellates potentially have a considerable grazing impact on populations of Synechococcus.

Ecology of a novel Synechococcus clade occurring in dense populations in saline Antarctic lakes

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 291:65-80 (2005) - doi:10.3354/meps291065 Ecology of a novel Synechococcus clade occurring in dense populations in saline Antarctic lakes L. M. Powell1, J. P. Bowman1,*, J. H. Skerratt2, P. D. Franzmann3, H. R. Burton4 1Australian Food Safety Centre for Excellence, School of Agricultural Science, University of Tasmania, Private Bag 54, Hobart, Tasmania 7001, Australia2CSIRO Marine Research Division, Castray Esplanade, Hobart, Tasmania 7001, Australia3CSIRO Land and Water Division, Underwood Avenue, Floreat Park, Perth, Western Australia 6014, Australia4Australian Antarctic Division, Channel Highway, Kingston, Tasmania 7050, Australia *Corresponding author. Email: john.bowman@utas.edu.au ABSTRACT: The seasonal distribution and abundance of Synechococcus-like morphotypes was investigated in meromictic lakes and coastal areas of the Vestfold Hills, Antarctica. Populations were monitored by flow cytometry utilising phycoerythrin content and small cell size to distinguish the cells from other phytoplankton. In Ace Lake, the Synechococcus bloom commenced in September at the water temperature minimum and peaked in late November. Populations (up to 8 × 106 cells ml–1) were maximally stratified at a depth of 11 m, corresponding to waters which were supersaturated with oxygen, high in phosphate and which received >5 µmol photons m–2 s–1 of light. At this depth, salinity (30 g kg–1) was constant throughout the year and temperature ranged from 4.5°C in October to 10.5°C in February. In late November, high numbers of Synechococcus cells also occurred in the moderate salinity water bodies Lake Abraxas and Pendant Lake (salinity 16.5 to 31.0 g kg–1), with populations highly stratified in Lake Abraxas (up to 1.5 × 107 cells ml–1, temperature 8.0°C, salinity 20.3 g kg–1) but less so in the colder waters of Pendant Lake (max. 1.5 × 107 cells ml–1, temperature 0.1 to 1.1°C, salinity 31.0 g kg–1). Synechococcus populations did not occur in brackish, coastal marine or hypersaline water bodies in the Vestfold Hills. Populations appear to be controlled primarily by temperature and to a lesser extent by light availability and grazing. Characterization of non-axenic cultures indicated that the Antarctic lake Synechococcus populations were similar to other polar picocyanobacteria in terms of cardinal growth temperatures (minimum, optimum, maximum: Tmin –17.0°C, Topt 19.8°C, Tmax 29.5°C) and slow growth. Related only peripherally to Synechococcus sp. Cluster 5.2 (Marine Cluster B), the Antarctic strains represent a unique and highly adapted clade in the stable water columns of some saline Antarctic lakes. KEY WORDS: Synechococcus · Antarctica · Meromictic lakes · Marine ecosystems Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 291. Online publication date: April 28, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Production of cobalt binding ligands in a Synechococcus feature at the Costa Rica upwelling dome

The Costa Rica upwelling dome (CRD; ;8.678N and 90.68W) was characterized chemically for cobalt and nickel abundances and speciation and biologically using cyanobacterial abundances and phylogeny. Total dissolved cobalt was 93 pmol L 21 at 90 m depth and decreased in surface waters to 45 pmol L 21 at 10 m. Cobalt was 40% labile at 90 m but was completely complexed by strong ligands at 10 m. A surface transect out of the dome showed decreasing total dissolved cobalt from 57 pmol L 21 to 12 pmol L 21 . Detection window studies showed that natural cobalt-ligand complexes have conditional stability constants greater than 10 16.8 and that competition with nickel did not release cobalt bound to organic complexes, consistent with natural cobalt ligands being Co(III) complexes. Synechococcus cell densities at the CRD are among the highest reported in nature, varying between 1.2 3 10 6 and 3.7 3 10 6 cells ml 21 . Phylogenetic analysis using the 16S‐23S rDNA internally transcribed spacer showed the majority of clones were related to Synechococcus strain MIT S9220, while the remaining subset form a novel group within the marine Synechococcus lineage. In a bottle incubation experiment chlorophyll increased with cobalt and iron additions relative to each element alone and the unamended control treatment. Cobalt speciation analysis of incubation experiments revealed large quantities of strong cobalt-ligand complexes in the cobalt addition treatments (401 pmol L 21 ), whereas cobalt added to a 0.2-mm filtered control remained predominantly labile (387 pmol L 21 ), demonstrating that the Synechococcus-dominated community is a source of strong cobalt ligands.