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The accumulation of organic co-solvents in cells is a basic strategy for organisms from various species to increase stress tolerance in extreme environments. Widespread representatives of this class of co-solvents are trimethylamine-N-oxide (TMAO) and betaine; these small molecules are able to stabilize the native conformation of proteins and prevent their aggregation. Despite their importance, detailed experimental studies on the impact of these co-solvents on the energy landscape of proteins have not yet been carried out. We use single-molecule spectroscopy at cryogenic temperatures to examine the influence of these physiological relevant co-solvents on photosystem I (PSI) from Thermosynechococcus elongatus. In contrast to PSI ensemble spectra, which are almost unaffected by the addition of TMAO and betaine, statistical analysis of the fluorescence emission from individual PSI trimers yields insight into the interaction of the co-solvents with PSI. The results show an increased homogeneity upon addition of TMAO or betaine. The number of detectable zero-phonon lines (ZPLs) is reduced, indicating spectral diffusion processes with faster rates. In the framework of energy landscape model these findings indicate that co-solvents lead to reduced barrier heights between energy valleys, and thus efficient screening of protein conformations can take place., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Cyanobacterial blooms have become a serious problem in Lake Taihu during the last 20 years, and Microcystis aeruginosa and Synechococcus sp. are the two dominant species in cyanobacterial blooms of Lake Taihu. A freshwater bacterial strain, Shewanella sp. Lzh-2, with strong algicidal properties against harmful cyanobacteria was isolated from Lake Taihu. Two substances with algicidal activity secreted extracellularly by Shewanella sp. Lzh-2, S-2A and S-2B, were purified from the bacterial culture of strain Lzh-2 using ethyl acetate extraction, column chromatography, and high performance liquid chromatography (HPLC) in turn. The substances S-2A and S-2B were identified as hexahydropyrrolo[1,2-a]pyrazine-1,4-dione and 2, 3-indolinedione (isatin), respectively, based on liquid chromatography-mass spectrometry (LC-MS), gas chromatography-mass spectrometry (GC-MS), and hydrogen-nuclear magnetic resonance (H-NMR) analyses, making this the first report of their algicidal activity toward cyanobacteria. S-2A (hexahydropyrrolo[1,2-a]pyrazine-1,4-dione) had no algicidal effects against Synechococcus sp. BN60, but had a high level of algicidal activity against M. aeruginosa 9110. The LD50 value of S-2A against M. aeruginosa 9110 was 5.7 μg/ml. S-2B (2, 3-indolinedione) showed a potent algicidal effect against both M. aeruginosa 9110 and Synechococcus sp. BN60, and the LD50 value of S-2B against M. aeruginosa 9110 and Synechococcus sp. BN60 was 12.5 and 34.2 μg/ml, respectively. Obvious morphological changes in M. aeruginosa 9110 and Synechococcus sp. BN60 were observed after they were exposed to S-2A (or S-2B) for 24 h. Approximately, the algicidal activity, the concentration of S-2A and S-2B, and the cell density of Lzh-2 were positively related to each other during the cocultivation process. Overall, these findings increase our knowledge about algicidal substances secreted by algicidal bacteria and indicate that strain Lzh-2 and its two algicidal substances have the potential for use as a bio-agent in controlling cyanobacterial blooms in Lake Taihu.

The carbon dioxide (CO2)-concentrating mechanism of cyanobacteria is characterized by the occurrence of Rubisco-containing microcompartments called carboxysomes within cells. The encapsulation of Rubisco allows for high-CO2 concentrations at the site of fixation, providing an advantage in low-CO2 environments. Cyanobacteria with Form-IA Rubisco contain α-carboxysomes, and cyanobacteria with Form-IB Rubisco contain β-carboxysomes. The two carboxysome types have arisen through convergent evolution, and α-cyanobacteria and β-cyanobacteria occupy different ecological niches. Here, we present, to our knowledge, the first direct comparison of the carboxysome function from α-cyanobacteria (Cyanobium spp. PCC7001) and β-cyanobacteria (Synechococcus spp. PCC7942) with similar inorganic carbon (Ci; as CO2 and HCO3-) transporter systems. Despite evolutionary and structural differences between α-carboxysomes and β-carboxysomes, we found that the two strains are remarkably similar in many physiological parameters, particularly the response of photosynthesis to light and external Ci and their modulation of internal ribulose-1,5-bisphosphate, phosphoglycerate, and Ci pools when grown under comparable conditions. In addition, the different Rubisco forms present in each carboxysome had almost identical kinetic parameters. The conclusions indicate that the possession of different carboxysome types does not significantly influence the physiological function of these species and that similar carboxysome function may be possessed by each carboxysome type. Interestingly, both carboxysome types showed a response to cytosolic Ci, which is of higher affinity than predicted by current models, being saturated by 5 to 15 mm Ci. This finding has bearing on the viability of transplanting functional carboxysomes into the C3 chloroplast.

The residues of anti-neoplastic drugs are new and emerging pollutants in aquatic environments. This is not only because of their increasing use, but also because due to their mechanisms of action, they belong to a group of particularly dangerous compounds. However, information on their ecotoxicological properties is very limited. We tested the toxicities of four anti-neoplastic drugs with different mechanisms of action (5-fluorouracil [5-FU], cisplatin [CDDP], etoposide [ET], and imatinib mesylate [IM]), and some of their binary mixtures, against two phytoplankton species: the alga Pseudokirchneriella subcapitata, and the cyanobacterium Synechococcus leopoliensis. These four drugs showed different toxic potential, and the two species examined also showed differences in their susceptibilities towards the tested drugs and their mixtures. With P. subcapitata, the most toxic of these drugs was 5-FU (EC50, 0.13 mg/L), followed by CDDP (EC50, 1.52 mg/L), IM (EC50, 2.29 mg/L), and the least toxic, ET (EC50, 30.43 mg/L). With S. leopoliensis, the most toxic was CDDP (EC50, 0.67 mg/L), followed by 5-FU (EC50, 1.20 mg/L) and IM (EC50, 5.36 mg/L), while ET was not toxic up to 351 mg/L. The toxicities of the binary mixtures tested (5-FU + CDDP, 5-FU + IM, CDDP + ET) were predicted by the concepts of 'concentration addition' and 'independent action', and are compared to the experimentally determined toxicities. The measured toxicity of 5-FU + CDDP with P. subcapitata and S. leopoliensis was higher than that predicted, while the measured toxicity of CDDP + ET with both species was lower than that predicted. The measured toxicity of 5-FU + IM with P. subcapitata was higher, and with S. leopoliensis was lower, than that predicted. These data show that these mixtures can have compound-specific and species-specific synergistic or antagonistic effects, and they suggest that single compound toxicity data are not sufficient for the prediction of the aquatic toxicities of such anticancer drug mixtures., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

In the present paper, the impact of freshwater (ARC21 and LS0519) and marine (PCC8806) Synechococcus cyanobacteria on calcium carbonate (CaCO3) precipitation has been examined in respect of the formation rates and morphology of crystals. Acid-base potentiometric titrations were employed to study surface functional groups, while CaCO3 experiments have been carried out in presence and absence of cells at low to near-equilibrium conditions in respect to CaCO3. During these experiments, the pH values have been monitored, Ca and alkalinity were measured and precipitates have been investigated by Raman spectroscopy and Atomic Force and Scanning Electron microscopy. Our results showed that the Synechococcus strains exhibited different surface reactivity with total concentration of surface functional groups of 0.342 and 0.350 mMg(-1) of dry bact. for freshwater strains, and 0.662 mMg(-1) of dry bact. for the marine strain, which are on the same order of magnitude as that reported for bacterial cell surfaces. The marine strain showed the highest CaCO3 formation rate with Ca(2+) removal of 18 mMg(-1) dry bact. compared to 6-7 mMg(-1) dry bact. for freshwater strains. The morphological diversity in crystals has been linked to presence of specific functional groups. The linking cell surface properties to crystal morphologies and precipitation rates propose that bacterial surfaces may modulate CaCO3 formation. Results of this work should allow better understanding of biominiralization in marine and freshwater systems as they define the precipiatation rates in typical range of pH necessary for estimation of CaCO3 formation by cyanobacterial communities., (Crown Copyright © 2013. Published by Elsevier B.V. All rights reserved.)

The repair of photosystem II (PSII) after photodamage is particularly sensitive to reactive oxygen species-such as H2O2, which is abundantly produced during the photoinhibition of PSII. In the present study, we generated a transformant of the cyanobacterium Synechococcus elongatus PCC 7942 that expressed a highly active catalase, VktA, which is derived from a facultatively psychrophilic bacterium Vibrio rumoiensis, and examined the effect of expression of VktA on the photoinhibition of PSII. The activity of PSII in transformed cells declined much more slowly than in wild-type cells when cells were exposed to strong light in the presence of H2O2. However, the rate of photodamage to PSII, as monitored in the presence of chloramphenicol, was the same in the two lines of cells, suggesting that the repair of PSII was protected by the expression of VktA. The de novo synthesis of the D1 protein, which is required for the repair of PSII, was activated in transformed cells under the same stress conditions. Similar protection of the repair of PSII in transformed cells was also observed under strong light at a relatively low temperature. Thus, the expression of the highly active catalase mitigates photoinhibition of PSII by protecting protein synthesis against damage by H2O2 with subsequent enhancement of the repair of PSII.

Cyanobacteria are valuable organisms for studying the physiology of photosynthesis and carbon fixation, as well as metabolic engineering for the production of fuels and chemicals. This work describes a novel counter selection method for the cyanobacterium Synechococcus sp. PCC 7002 based on organic acid toxicity. The organic acids acrylate, 3-hydroxypropionate, and propionate were shown to be inhibitory towards Synechococcus sp. PCC 7002 and other cyanobacteria at low concentrations. Inhibition was overcome by a loss of function mutation in the gene acsA, which is annotated as an acetyl-CoA ligase. Loss of AcsA function was used as a basis for an acrylate counter selection method. DNA fragments of interest were inserted into the acsA locus and strains harboring the insertion were isolated on selective medium containing acrylate. This methodology was also used to introduce DNA fragments into a pseudogene, glpK. Application of this method will allow for more advanced genetics and engineering studies in Synechococcus sp. PCC 7002 including the construction of markerless gene deletions and insertions. The acrylate counter-selection could be applied to other cyanobacterial species where AcsA activity confers acrylate sensitivity (e.g. Synechocystis sp. PCC 6803).

Among the known functions of the P(II) protein (the glnB gene product) in the cyanobacterium Synechococcus elongatus, negative regulation of the activity of PipX, a transcriptional co-activator of the NtcA regulon, has been thought to be essential for cell viability, because all the P(II)-less mutants thus far constructed carry spontaneous mutations in pipX. PipX is thus deduced to be a toxic protein, but its toxicity has not been clearly defined because of the lack of P(II)-deficient mutants carrying wild-type pipX. In this study, we developed a method to construct a targeted P(II)-less mutant of S. elongatus without the pipX mutation and determined the contribution of PipX to the detrimental effects of P(II) deficiency. Growth defects of the mutant were severe under nitrogen-replete conditions, i.e. in the presence of ammonium, but were also apparent under nitrogen-limited conditions. Genetic analyses indicated that the growth impairment observed under the nitrogen-limited conditions is largely due to the toxicity of PipX. Some of the phenotypes observed under the nitrogen-replete conditions, including reduced pigmentation and death of most of the cells after transfer from nitrogen-limited conditions to nitrogen-replete conditions, were ascribed to the toxicity of PipX, but inactivation of pipX only partially rescued the growth defect observed in the presence of ammonium, indicating the presence of an as yet unknown P(II) function(s) required for normal growth. Effects of ammonium addition on the nitrite uptake activity of the glnB mutant revealed a new function for P(II) in regulation of the activity of the ABC-type cyanate/nitrite transporter.

A series of isobenzofuran-1(3H)-ones (phthalides), analogues of the naturally occurring phytotoxin cryphonectric acid, were designed, synthesized, and fully characterized by NMR, IR, and MS analyses. Their synthesis was achieved via condensation, aromatization, and acetylation reactions. The measurement of the electron transport chain in spinach chloroplasts showed that several derivatives are capable of interfering with the photosynthetic apparatus. Few of them were found to inhibit the basal rate, but a significant inhibition was brought about only at concentrations exceeding 50 μM. Some other analogues acted as uncouplers or energy transfer inhibitors, with a remarkably higher effectiveness. Isobenzofuranone addition to the culture medium inhibited the growth of the cyanobacterium Synechococcus elongatus , with patterns consistent with the effects measured in vitro upon isolated chloroplasts. The most active derivatives, being able to completely suppress algal growth at 20 μM, may represent structures to be exploited for the design of new active ingredients for weed control.

Highly variable regions called genomic islands are found in the genomes of marine picocyanobacteria, and have been predicted to be involved in niche adaptation and the ecological success of these microbes. These picocyanobacteria are typically highly sensitive to copper stress and thus, increased copper tolerance could confer a selective advantage under some conditions seen in the marine environment. Through targeted gene inactivation of genomic island genes that were known to be upregulated in response to copper stress in Synechococcus sp. strain CC9311, we found two genes (sync_1495 and sync_1217) conferred tolerance to both methyl viologen and copper stress in culture. The prevalence of one gene, sync_1495, was then investigated in natural samples, and had a predictable temporal variability in abundance at a coastal monitoring site with higher abundance in winter months. Together, this shows that genomic island genes can confer an adaptive advantage to specific stresses in marine Synechococcus, and may help structure their population diversity.

Two unicellular cyanobacteria Synechocystis sp. PCC 6803 and Synechococcus elongatus PCC 7942 showed contrasting responses to chromate stress with EC50 of 12 ± 2 and 150 ± 15 μM potassium dichromate respectively. There was no depletion of chromate in growth medium in both the cases. Using labeled chromate, very low accumulation (<1 nmol/10(8) cells) was observed in Synechocystis after incubation for 24 h in light. No accumulation of chromate could be observed in Synechococcus under these conditions. Chromate oxyanion is known to enter the cells using sulfate uptake channels. Therefore, inhibition of sulfate uptake caused by chromate was monitored using (35)S labeled sulfate. IC50 values of chromate for (35)sulfate uptake were higher in Synechococcus as compared to Synechocystis. The results suggested that the sulfate transporters in Synechococcus have lower affinity to chromate than those from Synechocystis possibly due to differences in affinity of sulfate receptors for chromate. Bioinformatic analyses revealed presence of sulfate and chromate transporters with considerable similarity; however, minor differences in these may play a role in their differential response to chromate. In both cases the IC50 values decreased when sulfate concentration was reduced in the medium indicating competitive inhibition of sulfate uptake by chromate. Interestingly, Synechococcus showed stimulation of growth at concentrations of chromate less than 100 μM, which affected its cell size without disturbing the ultrastructure and thylakoid organization. In Synechocystis, growth with 12 μM potassium dichromate damaged the ultrastructure and thylakoid organization with slight elongation of the cells. The results suggested that Synechococcus possesses efficient strategies to prevent entry and to remove chromate from the cell as compared to Synechocystis. This is the first time a differential response of Synechococcus 7942 and Synechocystis 6803 to chromate is reported. The contrasting characteristics observed in the two cyanobacteria will be useful in understanding the basis of resistance or susceptibility to chromate.

A custom photobioreactor was designed to enable automatic light adjustments using computerized feedback control. The system consisted of a 7.5-L cylindrical vessel and an aluminum enclosure housing quantum sensors and light-emitting diode arrays, which provide 630 or 680 nm light to preferentially excite the major cyanobacterial pigments, phycocyanin and/or chlorophyll a, respectively. Custom-developed software rapidly measures light transmission and subsequently adjusts the irradiance to maintain a defined light profile to compensate for culture dynamics, biomass accumulation, and pigment adaptations during physiological transitions, thus ensuring appropriate illumination across batch and continuous growth modes. In addition to chemostat cultivation, the photobioreactor may also operate as a turbidostat, continuously adjusting the media dilution to achieve maximal growth at a fixed culture density. The cultivation system doubles as an analytical device, using real-time monitoring to avoid sampling bias (e.g., in-situ light-saturation response), determine conditions for optimal growth, and observe perturbation responses at high time-resolution., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Background Information: Cyanobacteria possess Aquaporin-Z (AqpZ) membrane channels which have been suggested to mediate the water efflux underlying osmostress-inducible gene expression and to be essential for glucose metabolism under photomixotrophic growth. However, preliminary observations suggest that the biophy-sical properties of transport and physiological meaning of AqpZ in such photosynthetic microorganisms are not yet completely assessed., Results: In this study, we used Xenopus laevis oocyte and proteoliposome systems to directly demonstrate the water permeability of the cyanobacterium Synechococcus sp. PCC7942 aquaporin, SsAqpZ. By an in vitro assay of intracellular acidification in yeast cells, SsAqpZ was found to transport also CO2 . Consistent with this result, during the entire exponential phase of growth, Synechococcus SsAqpZ-null-mutant cells grew slower than the corresponding wild-type cells. This phenotype was stronger with higher levels of extracellular CO2 . In line with the conversion of CO2 gas into HCO3(-) ions under alkaline conditions, the impairment in growth of the SsAqpZ-null strain was weaker in more alkaline culture medium., Conclusions: Cyanobacterial SsAqpZ may exert a pleiotropic function in addition to the already reported roles in macronutrient homeostasis and osmotic-stress response as it appears to constitute an important pathway in CO2 uptake, a fundamental step in photosynthesis., (Copyright © 2013 Soçiété Française des Microscopies and Soçiété de Biologie Cellulaire de France.)

The aim of the present study was to investigate the effect of silver nanoparticles (AgNP) of different sizes toward two primary producer aquatic species. Thalassiosira pseudonana and Synechococcus sp. have been selected as representative models for the lower trophic organisms in marine and freshwater habitats, respectively. Time-dependent cellular growth was measured upon exposure to both AgNP and silver nitrate (AgNO(3)). In addition, AgNP behavior in freshwater and marine waters has been followed by CPS disc centrifuge, in the time frame of AgNP exposure studies, and the kinetic release of silver from AgNP of different sizes was measured by dialysis and inductively coupled plasma mass spectrometry (ICP-MS). The combination and interpretation of all these data suggest that a shared effect of AgNP and released silver was responsible for the toxicity in both organisms. Furthermore, the toxic effects induced by AgNP exposure in the present study seem to result from a mixture of parameters including aggregated state, size of the AgNP, stability of the preparation, and speciation of the released silver.

Cyanobacteria are prokaryotic algae found in oceans and freshwaters worldwide. These organisms are important primary producers in aquatic ecosystems because they can provide essential food for grazers and herbivores. In this study, the physiological and biochemical responses of the freshwater cyanobacterium Synechococcus sp. PCC7942 to two organic booster biocides Irgarol 1051 and diuron were compared and evaluated using 96 h growth tests in a batch-culture system. The 96 h median effective concentrations (EC(50)) were 0.019 and 0.097 μmol L(-1) for Irgarol 1051 and diuron, respectively, which indicate that Irgarol 1051 is about 5 times more toxic than diuron to cyanobacteria. Moreover, remarkable physiological and biochemical responses occurred in the Irgarol 1051 and diuron treatments. Irgarol 1051 and diuron stimulated cyanobacterial growth, increased the soluble protein content, and enhanced the catalase (CAT) activity at low concentrations, but inhibited them at high concentrations. However, the malondialdehyde (MDA) and polysaccharide content of the cyanobacteria were only significantly affected by Irgarol 1051. These observations suggest that Irgarol 1051 and diuron are toxic to Synechococcus sp. PCC7942, and their use should be restricted in maritime industries., (Copyright © 2012 Elsevier B.V. All rights reserved.)

The direct conversion of carbon dioxide into biofuels by photosynthetic microorganisms is a promising alternative energy solution. In this study, a model cyanobacterium, Synechococcus elongatus PCC 7942, is engineered to produce free fatty acids (FFA), potential biodiesel precursors, via gene knockout of the FFA-recycling acyl-ACP synthetase and expression of a thioesterase for release of the FFA. Similar to previous efforts, the engineered strains produce and excrete FFA, but the yields are too low for large-scale production. While other efforts have applied additional metabolic engineering strategies in an attempt to boost FFA production, we focus on characterizing the engineered strains to identify the physiological effects that limit cell growth and FFA synthesis. The strains engineered for FFA-production show reduced photosynthetic yields, chlorophyll-a degradation, and changes in the cellular localization of the light-harvesting pigments, phycocyanin and allophycocyanin. Possible causes of these physiological effects are also identified. The addition of exogenous linolenic acid, a polyunsaturated FFA, to cultures of S. elongatus 7942 yielded a physiological response similar to that observed in the FFA-producing strains with only one notable difference. In addition, the lipid constituents of the cell and thylakoid membranes in the FFA-producing strains show changes in both the relative amounts of lipid components and the degree of saturation of the fatty acid side chains. These changes in lipid composition may affect membrane integrity and structure, the binding and diffusion of phycobilisomes, and the activity of membrane-bound enzymes including those involved in photosynthesis. Thus, the toxicity of unsaturated FFA and changes in membrane composition may be responsible for the physiological effects observed in FFA-producing S. elongatus 7942. These issues must be addressed to enable the high yields of FFA synthesis necessary for large-scale biofuel production., (Copyright © 2012 Wiley Periodicals, Inc.)

A new configuration of the fluid dynamic gauging technique for measuring soft layers on surfaces was used to monitor the growth of a cyanobacterium, Synechococcus sp. WH 5701, on stainless steel (SS), glass and an indium tin oxide (ITO) on a polyethylene terephthalate (PET) substratum. The biofilm thickness increased steadily over 4 weeks and exhibited noticeable changes in microstructure and strength. The biofilms all exhibited a two-layer structure, with a compact layer next to the substratum and a loose layer above. Biofilms on ITO or SS exhibited cohesive failure when removed by fluid shear whereas those on glass exhibited adhesive failure. The technique is able to elucidate various aspects of biofilm behaviour, as illustrated by the action of a biocide (NaOCl) on a mature biofilm.

In this article, we describe the modifications in the antioxidant system of Synechococcus elongatus PCC7942 mutant Mu2 capable of growing at five times higher concentration of bentazone than wild type. Nevertheless, in both the strains, bentazone almost identically induced light-dependent H(2)O(2) production and its extracellular release. However unlike the wild type, peroxide produced upon prolong bentazone incubation was immediately degraded in Mu2. Consequently, the lipid peroxidation activity was also kept low. With prolong incubation of bentazone the mutant displayed a steady increase in glutathione peroxidase-reductase enzyme activities and reduced glutathione content, respectively, by 60% and 130%, favoring an efficient detoxification of bentazone-produced H(2)O(2). Catalase-peroxidase and glutathione S-transferase, though present, remained ineffective in rendering bentazone tolerance. In-gel assays of glutathione S-transferase and glutathione reductase revealed presence of between four and five oligomeric states with mobility shifts. One oligomeric form each enzyme in wild-type strain disappeared upon bentazone treatment. Upon two-dimensional electrophoresis and MALDI-TOF/TOF, a bacterioferritin comigratory protein (peroxiredoxin Q) was found to be already highly expressed in Mu2; whereas in wild type, its level increased only upon bentazone exposure. The bcp transcript pool in WT was relatively low but increased with bentazone, whereas Mu2 exhibited high bcp mRNA even without herbicide. Bacterioferritin comigratory protein and glutathione peroxidase-reductase appear to be responsible for detoxification of bentazone-derived peroxide in Mu2.

Resistance to heavy metals is important for the survival of bacteria in contaminated environments. In this study, we show that the unicellular cyanobacterial species Synechococcus sp. IU 625 adapts to growth in the presence of mercuric chloride, recovering from pigmentation and morphological defects. Cells accumulate mercury within 2 h of growth and by 3 days, the total mercury concentration is significantly reduced, with all remaining mercury associated with the cells. This suggests that Synechococcus sp. IU 625 can convert mercury to a volatile form., (Copyright © 2011 Elsevier GmbH. All rights reserved.)

In the present study we investigated the role of the PsbU subunit in the electron transport characteristics and light sensitivity of the Photosystem II complex. The experiments were performed by using an earlier characterized PsbU-less mutant of the cyanobacterium Synechococcus PCC 7942, which has enhanced antioxidant capacity (Balint et al. FEBS Lett. 580 (2006) 2117-2122). Flash induced Chl fluorescence measurements in the presence and absence of the electron transport inhibitor DCMU showed that both the S(2)Q(A)(-) and the S(2)Q(B)(-) recombination is slowed down in the PsbU mutant relative to the WT strain. Thermoluminescence measurements confirmed the increased stability of the S(2)Q(A)(-) and S(2)Q(B)(-) charge pairs by showing an increased peak temperature of Q and B bands, which were measured in the presence and absence of DCMU, respectively. In addition, the intensity of the TL bands is also increased in the PsbU mutant (≈1.7 times for the B band), as compared to the WT. The PsbU mutant shows enhanced loss of Photosystem II activity under exposure to high light intensity both in the absence and presence of the protein synthesis inhibitor lincomycin. It is concluded from the data that the lack of the PsbU subunit in Synechococcus PCC 7942 affects the energetic stability of the S(2)Q(A)(-) and S(2)Q(B)(-) charge pairs by modifying both the PSII donor and acceptor side components. This effect is most likely caused by structural changes in the vicinity of the Mn cluster and in the inner part of the PSII complex, which are induced by the lack of the PsbU subunit from the lumenal part of the complex. The light sensitivity of Photosystem II in Synechococcus 7942 in the absence of the PsbU subunit is likely due to reactive oxygen species, which are produced as a consequence of disturbed donor side structure and/or due to the modified energetic properties of the primary radical pair., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Iron limitation has a strong impact on electron transport reactions of the unicellular fresh water cyanobacterium Synechococcus elongatus PCC 7942 (thereafter referred to as S. elongatus). Among the various adaptational processes on different cellular levels, iron limitation induces a strongly enhanced expression of IdiC (iron-deficiency-induced protein C). In this article, we show that IdiC is loosely attached to the thylakoid and to the cytoplasmic membranes and that its expression is enhanced during conditions of iron starvation and during the late growth phase. The intracellular IdiC level was even more increased when additional iron was replenished in the late growth phase. On the basis of its amino acid sequence and of its absorbance spectrum, IdiC can be classified as a member of the family of thioredoxin (TRX)-like (2Fe-2S) ferredoxins. The presence of an iron cofactor in IdiC was detected by inductive coupled plasma optical emission spectrometry (ICP-OES). Comparative measurements of electron transport activities of S. elongatus wild type (WT) and an IdiC-merodiploid mutant called MuD, which contained a strongly reduced IdiC content under iron-sufficient as well as iron-deficient growth conditions, were performed. The results revealed that MuD had a strongly increased light sensitivity, especially under iron limitation. The measurements of photosystem II (PS II)-mediated electron transport rates in WT and MuD strain showed that PS II activity was significantly lower in MuD than in the WT strain. Moreover, P(700) (+) re-reduction rates provided evidence that the respiratory activities, which were very low in the MuD strain in the presence of iron, significantly increased in iron-starved cells. Thus, an increase in respiration may compensate for the drastic decrease of photosynthetic electron transport activity in MuD grown under iron starvation. Based on the similarity of the S. elongatus IdiC to the NuoE subunit of the NDH-1 complex in Escherichia coli, it is likely that IdiC has a function in the electron transport processes from NAD(P)H to the plastoquinone pool. This is in agreement with the up-regulation of IdiC in the late growth phase as well as under stress conditions when PS II is damaged. As absence or high reduction of the IdiC level would prevent or reduce the formation of functional NDH-1 complexes, under such conditions electron transport routes via alternative substrate dehydrogenases, donating electrons to the plastoquinone pool, can be assumed to be up-regulated.

Marine Synechococcus undergo a wide range of environmental stressors, especially high and variable irradiance, which may induce oxidative stress through the generation of reactive oxygen species (ROS). While light and ROS could act synergistically on the impairment of photosynthesis, inducing photodamage and inhibiting photosystem II repair, acclimation to high irradiance is also thought to confer resistance to other stressors. To identify the respective roles of light and ROS in the photoinhibition process and detect a possible light-driven tolerance to oxidative stress, we compared the photophysiological and transcriptomic responses of Synechococcus sp. WH7803 acclimated to low light (LL) or high light (HL) to oxidative stress, induced by hydrogen peroxide (H₂O₂) or methylviologen. While photosynthetic activity was much more affected in HL than in LL cells, only HL cells were able to recover growth and photosynthesis after the addition of 25 μM H₂O₂. Depending upon light conditions and H₂O₂ concentration, the latter oxidizing agent induced photosystem II inactivation through both direct damage to the reaction centers and inhibition of its repair cycle. Although the global transcriptome response appeared similar in LL and HL cells, some processes were specifically induced in HL cells that seemingly helped them withstand oxidative stress, including enhancement of photoprotection and ROS detoxification, repair of ROS-driven damage, and regulation of redox state. Detection of putative LexA binding sites allowed the identification of the putative LexA regulon, which was down-regulated in HL compared with LL cells but up-regulated by oxidative stress under both growth irradiances.

Chemical arrays were employed to screen ligands for HtpG, the prokaryotic homologue of Hsp (heat-shock protein) 90. We found that colistins and the closely related polymyxin B interact physically with HtpG. They bind to the N-terminal domain of HtpG specifically without affecting its ATPase activity. The interaction caused inhibition of chaperone function of HtpG that suppresses thermal aggregation of substrate proteins. Further studies were performed with one of these cyclic lipopeptide antibiotics, colistin sulfate salt. It inhibited the chaperone function of the N-terminal domain of HtpG. However, it inhibited neither the chaperone function of the middle domain of HtpG nor that of other molecular chaperones such as DnaK, the prokaryotic homologue of Hsp70, and small Hsp. The addition of colistin sulfate salt increased surface hydrophobicity of the N-terminal domain of HtpG and induced oligomerization of HtpG and its N-terminal domain. These structural changes are discussed in relation to the inhibition of the chaperone function.

The aquatic toxicity of sulfaquinoxaline (SQO) and sulfaguanidine (SGD) was evaluated on the following test organisms: Daphnia magna (reproduction test), Pseudokirchneriella subcapitata, Scenedesmus dimorphus, Synecococcus leopoliensis (algal growth inhibition test) and Lemna gibba (duckweed growth inhibition test). Furthermore, the additivity of the two compounds was measured on D. magna (acute immobilisation test) and P. subcapitata (algal growth inhibition test) using the isobologram method. Results show that SQO and SGD are more toxic to green algae and daphnids, respectively, than other veterinary sulfonamides (SAs) and that their mixtures have a less then additive interaction. Taking into account the highest concentrations detected so far in surface waters for SQO (0.112 μg L(-1)) and for SGD (0.145 μg L(-1)) and the lowest NOECs obtained with the five test organisms, divided by an assessment factor of 10, the following PNECs and risk quotients (RQs) were calculated. SQO: PNEC 2 μg L(-1); RQ 0.056. SGD: PNEC 39.5 μg L(-1); RQ 0.004. Consequently, at the concentrations actually detected in the aquatic environment, the two SAs alone should not harm the freshwater organisms. However, it seems advisable, for veterinary mass treatments, the use of other SAs that have a lesser impact on the aquatic environment. Furthermore, considering the high probability of having complex mixtures of different SAs residues in water, each individual contamination should be evaluated by applying to the SAs mixtures the conservative criteria of additivity., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Long range atmospheric transport and deposition is a significant introduction pathway of organic pollutants to remote oceanic regions, leading to their subsequent accumulation in marine organisms. Persistent organic pollutants (POPs) bioconcentrate in planktonic food webs and these exert a biogeochemical control on the regional and global cycling of POPs. Therefore, an important issue is to determine whether the anthropogenic chemical perturbation of the biosphere introduced by the myriad of organic pollutants present in seawater influences phytoplankton abundance and productivity. The results reported here from five sets of experiments performed in the NE Atlantic Ocean show that there is a toxic effect induced by trace levels of complex mixtures of organic pollutants on phytoplankton oceanic communities. The levels of single pollutant, such as phenanthrene and pyrene, at which lethality of phytoplankton is observed are high in comparison to field levels. Complex mixtures of organic pollutants, however, have an important toxic effect on phytoplankton abundances, viability and concentrations of Chlorophyll a at pollutant concentrations 20-40 folds those found in the open ocean. The toxicity of these complex mixtures of organic pollutants exceeds by 10(3) times the toxicity expected for a single pollutant. Therefore, our results point out the need for a systematic investigation of the influence of complex mixtures of organic hydrophobic pollutants to oceanic phytoplankton communities, a perturbation not accounted for on previous assessments of anthropogenic pressures in the marine environment., ((c) 2010 Elsevier Ltd. All rights reserved.)

Synechococcus elongatus PCC 7942 was grown with SO(4) (2-) or S(2)O(3) (2-) sulfur source with varying concentration of SeO(4) (2-). Up to 150 muM, SeO(4) (2-) was growth supportive and above this it was inhibitory. Selenate is believed to induce ROS production, and to counter, the cells produce increasing amounts of ROS quenching enzymes. To investigate the differential growth response of SeO(4) (2-) at the level of ROS production, the activities of antioxidant enzymes viz. glutathione peroxidase, catalase, pyrogallol-peroxidase, superoxide dismutase and glutathione reductase were determined. Regardless of SeO(4) (2-) concentration in the medium, except catalase, the activity of other enzymes increased over SeO(4) (2-)-free controls. To understand the fate of SeO(4) (2-) added at lower concentrations, the activities of key inorganic sulfur metabolizing enzymes, ATP sulfurylase in SO(4) (2-) medium and thiosulfate reductase in S(2)O(3) (2-) medium were measured. This was done with an assumption that these enzymes would consume the SO(4) (2-) analog SeO(4) (2-) as sulfur source. We found enzymatic SeO(4) (2-)/ATP dependent formation of inorganic pyrophosphate in a reaction, analogous to ATP sulfurylase (SO(4) (2-) + ATP --> pyrophosphate) carried out by an enzyme different from ATP sulfurylase, tentatively called ATP:selenate adenylyltransferase. We hypothesize that selenium could act as trace element for S. elongatus PCC 7942., (Copyright 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Standard microalgae toxicity tests should be able to establish responses in real ecosystems. Natural marine picoplankton samples collected during the months of March, June, August, October 2007 and January 2008, where exposed to 72 h copper toxicity tests. Results analysed by flow cytometry distinguished two groups, with different cytometric characteristics that can match with two of Synechococcus populations. EC(50) values for these two populations resulted low, ranging from 0.62 to 26.28 microg L(-1), this converts copper in a very powerful contaminant and Synechococcus in one of the most sensitive groups of phytoplankton. Differences in EC(50) values for a same population can be related to the month of collection including different initial cellular densities and oceanographic parameters that can affect the picoplankton's tolerance and distribution.

Copper appears to be influencing the distribution and abundance of phytoplankton in marine environments, and cyanobacteria are thought to be the most sensitive of the phytoplankton groups to copper toxicity. By using growth assays of phylogenetically divergent clades, we found that coastal strains of marine Synechococcus species were more tolerant to copper shock than open-ocean strains. The global transcriptional response to two levels of copper shock were determined for both a coastal strain and an open-ocean strain of marine Synechococcus species using whole-genome expression microarrays. Both strains showed an osmoregulatory-like response, perhaps as a result of increasing membrane permeability. This could have implications for marine carbon cycling if copper shock leads to dissolved organic carbon leakage in Synechococcus species. The two strains additionally showed a common reduction in levels of photosynthesis-related gene transcripts. Contrastingly, the open-ocean strain showed a general stress response, whereas the coastal strain exhibited a more specifically oxidative or heavy-metal acclimation response that may be conferring tolerance. In addition, the coastal strain activated more regulatory elements and transporters, many of which are not conserved in other marine Synechococcus strains and may have been acquired by horizontal gene transfer. Thus, tolerance to copper shock in some marine Synechococcus strains may in part be a result of a generally increased ability to sense and respond in a more stress-specific manner.

A marine, unicellular cyanobacterium, Synechococcus elongatus strain BDU/75042 was found to sequester uranium from aqueous systems at pH 7.8. The organism could remove 72% (53.5 mg U g(-1) dry weight) of uranium from test solutions containing 100 microM uranyl carbonate within 1h. The equilibrium data fitted well in the Langmuir isotherm thus suggesting a monolayer adsorption of uranium on the cyanobacterial biomass and predicted the maximum adsorption capacity of 124 mg U g(-1) dry weight. Light and scanning electron microscopy coupled with energy dispersive X-ray fluorescence (EDXRF) spectroscopy confirmed the uranyl adsorption by this organism. Most of the bound uranium was found to be associated with the extracellular polysaccharides (EPS) suggesting its interaction with the surface active ligands. Fourier transform infrared (FT-IR) spectroscopy suggested the amide groups and the deprotonated carboxyl groups on the cyanobacterial cell surface were likely to be involved in uranyl adsorption. The cell bound uranium could be released by washing with ethylene diamine tetraacetic acid (EDTA) or 0.1N HCl. The X-ray diffraction (XRD) analyses revealed the identity of uranium deposits associated with the cell biomass as uranyl carbonate hydrate. The study revealed the potential of this cyanobacterium for harvesting uranium from natural aquatic environments.

Small heat-shock proteins are molecular chaperones that bind and prevent aggregation of nonnative proteins. They also associate with membranes. In this study, we show that the small heat-shock protein HspA plays a protective role under oxidative stress in the cyanobacterium Synechococcus elongatus strain ECT16-1, which constitutively expresses HspA. Compared with the reference strain ECT, ECT16-1 showed much better growth and viability in the presence of hydrogen peroxide. Under the peroxide stress, pigments in thylakoid membrane, chlorophyll, carotenoids, and phycocyanins, were continuously reduced in ECT, but in ECT16-1 they decreased only during the first 24 h of stress; thereafter no further reduction was observed. For comparison, we analyzed a wild type and an hspA deletion strain from Synechocystis sp. PCC 6803 and found that lack of hspA significantly affected the viability of the cell and the pigment content in the presence of methyl viologen, suggesting that HspA stabilizes membrane proteins such as the photosystems and phycobilisomes from oxidative damage. In vitro pull down assays showed a direct interaction of HspA with components of phycobilisomes. These results show that HspA and small heat-shock proteins in general play an important role in the acclimation to oxidative stress in cyanobacteria.

Synechococcus elongatus strain PCC 7942 is an alkaliphilic cyanobacterium that tolerates a relatively high salt concentration as a freshwater microorganism. Its genome sequence revealed seven genes, nha1 to nha7 (syn&#95;pcc79420811, syn&#95;pcc79421264, syn&#95;pcc7942359, syn&#95;pcc79420546, syn&#95;pcc79420307, syn&#95;pcc79422394, and syn&#95;pcc79422186), and the deduced amino acid sequences encoded by these genes are similar to those of Na(+)/H(+) antiporters. The present work focused on molecular and functional characterization of these nha genes encoding Na(+)/H(+) antiporters. Our results show that of the nha genes expressed in Escherichia coli, only nha3 complemented the deficient Na(+)/H(+) antiporter activity of the Na(+)-sensitive TO114 recipient strain. Moreover, two of the cyanobacterial strains with separate disruptions in the nha genes (Deltanha1, Deltanha2, Deltanha3, Deltanha4, Deltanha5, and Deltanha7) had a phenotype different from that of the wild type. In particular, DeltanhA3 cells showed a high-salt- and alkaline-pH-sensitive phenotype, while Deltanha2 cells showed low salt and alkaline pH sensitivity. Finally, the transcriptional profile of the nha1 to nha7 genes, monitored using the real-time PCR technique, revealed that the nha6 gene is upregulated and the nha1 gene is downregulated under certain environmental conditions.

The effects of the herbicide Roundup (glyphosate) on natural marine microbial communities were assessed in a 7-day field experiment using microcosms. Bottles were maintained underwater at 6m depth, and 10% of their water content was changed every other day. The comparison of control microcosms and surrounding surface water showed that the microcosm system tested here can be considered as representative of the natural surrounding environment. A temporal temperature gradient gel electrophoresis (TTGE) was run on 16S and 18S rDNA-amplified extracts from the whole microbial community. Cluster analysis of the 16S gel showed differences between control and treatment fingerprints for Roundup at 1 microg L(-1) (ANOSIM, p=0.055; R=0.53), and 10 microg L(-1) (ANOSIM, p=0.086; R=0.40). Flow cytometry analysis revealed a significant increase in the prasinophyte-like population when Roundup concentration was increased to 10 microg L(-1). This study demonstrates that a disturbance was caused to the marine microbial community exposed to 1 microg L(-1) Roundup concentration, a value typical of those reported in coastal waters during a run-off event.

The cmp operon of the cyanobacterium Synechococcus elongatus strain PCC 7942, encoding the subunits of the ABC-type bicarbonate transporter, is activated under CO2-limited growth conditions in a manner dependent on CmpR, a LysR family transcription factor of CbbR subfamily. The 0.7 kb long regulatory region of the operon carried a single promoter, which responded to CO2 limitation. Using the luxAB reporter system, three cis-acting elements involved in the low-CO2 activation of transcription, each consisting of a pair of LysR recognition signatures overlapping at their ends, were identified in the regulatory region. CmpR was shown to bind to the regulatory region, yielding several DNA-protein complexes in gel shift assays. Addition of ribulose-1,5-bisphosphate (> 1 mM) or 2-phosphoglycolate (> 10 microM) enhanced the binding of CmpR in a concentration-dependent manner, promoting formation of large DNA-protein complexes. Given the involvement of O2 in adaptive responses of cyanobacteria to low-CO2 conditions, our results suggest that 2-phosphoglycolate, which is produced by oxygenation by ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) of ribulose-1,5-bisphosphate under CO2-limited conditions, acts as the co-inducer in the activation of the cmp operon by CmpR.

Phthalocyanines and their analogues show great potential as photodynamic agents producing reactive oxygen species (ROS), especially in medicine. However, their biocidal effects may also be employed to inhibit various undesirable organisms. This study explores their potential algicidal effects. The laboratory tests concern the effects of various phthalocyanine derivatives on the green alga Pseudokirchneriella subcapitata and cyanobacterium Synechococcus nidulans. Their effects on one example of the sensitive nontarget aquatic organism-crustacean Daphnia magna were also screened. Among 31 tested compounds, the cationic phthalocyanines substituted with heterocycle exhibited the strongest effects on phytoplankton species, some of them even below the level of 1 mg/L, while effects on crustaceans ranged from 3.6 to more than 50 mg/L. These results show that some phthalocyanine derivatives can act as potent algicides., ((Copyright) 2008 Wiley Periodicals, Inc.)

Three clock proteins--KaiA, KaiB, and KaiC--have been identified as essential components of the circadian oscillator in cyanobacteria, and Kai-based chemical oscillation is thought to be the basic circadian timing mechanism in Synechococcus elongatus PCC 7942. Transcription and translation of kaiBC in cyanobacterial cells was quantitatively studied to elucidate how these processes are coupled to the chemical oscillator using a strain in which circadian oscillation is under the control of IPTG (isopropyl-beta-D-thiogalactopyranoside). The kinetics of repression of kaiBC promoter triggered by IPTG allowed estimation of transient response at 10 h. This response time is suitable for cyanobacterial transcription and/or translation to match with the Kai-based oscillator. Interestingly, kaiBC promoter activity and KaiC phosphorylation showed robust circadian rhythms, whereas trc promoter-driven kaiBC mRNA levels and KaiC accumulation were almost arrhythmic. These results indicate that cyanobacterial circadian rhythms can be generated even if kaiBC expression is constitutive. Moreover, there was a positive correlation between activation of the kaiBC promoter and an increase in the KaiC phosphorylation ratio in three rhythmic conditions. Based on these observations, it is likely that the KaiC phosphorylation ratio is the main factor in the activation of kaiBC promoter. Finally, we quantitatively compared the threshold level of phosphorylated KaiC for the repression or derepression of kaiBC promoter and found that this parameter is an important factor in repressing the kaiBC promoter.

Cyanobacteria dominate the world's oceans where iron is often barely detectable. One manifestation of low iron adaptation in the oligotrophic marine environment is a decrease in levels of iron-rich photosynthetic components, including the reaction center of photosystem I and the cytochrome b6f complex [R.F. Strzepek and P.J. Harrison, Photosynthetic architecture differs in coastal and oceanic diatoms, Nature 431 (2004) 689-692.]. These thylakoid membrane components have well characterised roles in linear and cyclic photosynthetic electron transport and their low abundance creates potential impediments to photosynthetic function. Here we show that the marine cyanobacterium Synechococcus WH8102 exhibits significant alternative electron flow to O2, a potential adaptation to the low iron environment in oligotrophic oceans. This alternative electron flow appears to extract electrons from the intersystem electron transport chain, prior to photosystem I. Inhibitor studies demonstrate that a propyl gallate-sensitive oxidase mediates this flow of electrons to oxygen, which in turn alleviates excessive photosystem II excitation pressure that can often occur even at relatively low irradiance. These findings are also discussed in the context of satisfying the energetic requirements of the cell when photosystem I abundance is low.

Transformation with the bacterial gene codA for choline oxidase allows Synechococcus sp. PCC 7942 cells to accumulate glycinebetaine when choline is supplemented exogenously. First, we observed two types of protective effect of glycinebetaine against heat-induced inactivation of photosystem II (PSII) in darkness; the codA transgene shifted the temperature range of inactivation of the oxygen-evolving complex from 40-52 degrees C (with half inactivation at 46 degrees C) to 46-60 degrees C (with half inactivation at 54 degrees C) and that of the photochemical reaction center from 44-55 degrees C (with half inactivation at 51 degrees C) to 52-63 degrees C (with half inactivation at 58 degrees C). However, in light, PSII was more sensitive to heat stress; when moderate heat stress, such as 40 degrees C, was combined with light stress, PSII was rapidly inactivated, although these stresses, when applied separately, did not inactivate either the oxygen-evolving complex or the photochemical reaction center. Further our studies demonstrated that the moderate heat stress inhibited the repair of PSII during photoinhibition at the site of synthesis de novo of the D1 protein but did not accelerate the photodamage directly. The codA transgene and, thus, the accumulation of glycinebetaine alleviated such an inhibitory effect of moderate heat stress on the repair of PSII by accelerating the synthesis of the D1 protein. We propose a hypothetical scheme for the cyanobacterial photosynthesis that moderate heat stress inhibits the translation machinery and glycinebetaine protects it against the heat-induced inactivation.

Following a N-methyl-N'-nitro-N-nitrosoguanidine-based mutagenesis of Synechococcus elongatus PCC 7942 wild type, we were able to select several mutants with an enhanced tolerance toward the herbicide bentazone (3-isopropyl-1H-2,1,3-benzothiadiazine-4(3H)-one 2,2-dioxide). Mutant Mu1 has in part been previously characterized. In the present paper we report on another mutant, called Mu2, which also has a higher tolerance toward bentazone. Since Mu2 showed a better growth than WT when cultivated with elevated NaCl concentrations in the growth medium and since S. elongatus WT has previously been classified to be low salt tolerant, we were especially interested in the identification of the modifications conferring this higher salt tolerance to mutant Mu2. Immunoblot analyses provided evidence that Mu2 had a constitutively higher expression of PsbO and of IsiA. In addition, in Mu2 a significantly higher concentration of IdiA was detected under salt stress as compared to WT. These three proteins most likely contribute to a better protection and/or stabilization of photosystem II. Moreover, Mu2 had a higher amount of the photosystem I reaction center proteins PsaAB under salt stress than WT. In addition, the amount of the ferredoxin:NADP+ oxidoreductase and also of the ATP synthase was constitutively higher in Mu2 than in WT. In contrast to WT the latter two proteins did not decrease under salt stress in Mu2. Therefore, it can be assumed that Mu2 could maintain a high cyclic electron transport activity around photosystem I under salt stress. It can be assumed that the combination of these modifications of the electron transport chain cause a better protection of photosystem II against oxidative damage and cause an increase of cyclic electron transport activity around photosystem I with ATP synthesis. Thus, the overall cellular energization in Mu2 relative to WT is improved. Together with putative other not yet identified modifications this seems to enable Mu2 to energize its cytoplasmic membrane-localized ion pumps more effectively than WT and, as a consequence, to keep the intracellular NaCl concentration low.

Precipitation of CaCO3 catalyzed by the growth and physiology of cyanobacteria in the genus Synechococcus represents a potential mechanism for sequestration of atmospheric CO2 produced during the burning of coal for power generation. Synechococcus sp. strain PCC 8806 and Synechococcus sp. strain PCC 8807 were tested in microcosm experiments for their ability to calcify when exposed to a fixed calcium concentration of 3.4 mM and dissolved inorganic carbon concentrations of 0.5, 1.25 and 2.5 mM. Synechococcus sp. strain PCC 8806 removed calcium continuously over the duration of the experiment producing approximately 18.6 mg of solid phase calcium. Calcium removal occurred over a two-day time period when Synechococcus sp. strain PCC 8807 was tested and only 8.9 mg of solid phase calcium was produced. Creation of an alkaline growth environment catalyzed by the physiology of the cyanobacteria appeared to be the primary factor responsible for CaCO3 precipitation in these experiments.

Synechococcus elongatus PCC 7942 was able to grow with several S sources. The sulphur metabolizing enzymes viz. ATP sulphurylase, cysteine synthase, thiosulphate reductase and L- and D-cysteine desulphydrases were regulated by sulphur sources, particularly by sulphur amino acids and organic sulphate esters. Sulphur starvation reduced ATP sulphurylase and cysteine synthase whereas reduced glutathione appreciated Cys degradation activity. With partially purified enzymes apparent Km values for sulphate, ATP, D- and L-Cys, thiosulphate, sulphide and O-acetyl serine were in a range of 12-50 microM. p-Nitrophenyl sulphate inhibited ATP sulphurylase competitively. Met was a feedback inhibitor of several key enzymes.

Glycinebetaine (hereafter referred to as betaine) is a compatible solute that accumulates in certain plants and microorganisms in response to various types of stress. We demonstrated previously that when the cyanobacterium Synechococcus sp. PCC 7942 (hereafter Synechococcus) is transformed with the codA gene for choline oxidase, it can synthesize betaine from exogenously supplied choline, exhibiting enhanced tolerance to salt and cold stress. In this study, we examined the effects of salt stress and betaine synthesis on the photoinhibition of photosystem II (PSII). Salt stress due to 220 mm NaCl enhanced photoinhibition of PSII and betaine protected PSII against photoinhibition under these conditions. However, neither salt stress nor betaine synthesis affected photodamage to PSII. By contrast, salt stress inhibited repair of photodamaged PSII and betaine reversed this inhibitory effect of salt stress. Pulse-chase-labeling experiments revealed that salt stress inhibited degradation of D1 protein in photodamaged PSII and de novo synthesis of D1. By contrast, betaine protected the machinery required for degradation and synthesis of D1 under salt stress. Neither salt stress nor betaine affected levels of psbA transcripts. These observations suggest that betaine counteracts the inhibitory effects of salt stress, with resultant accelerated repair of photodamaged PSII.

Biofilm growth on stone surfaces is a significant contributing factor to stone biodeterioration. Current market based biocides are hazardous to the environment and to public health. We have investigated the photo-dynamic effect of methylene blue (MB) in the presence of hydrogen peroxide (H2O2) on the destruction of the cyanobacterium Synechococcus leopoliensis (S. leopoliensis) under irradiation with visible light. Data presented in this paper illustrate that illumination of S. leopoliensis in the presence of a photosensitiser (MB) and H2O2 results in the decomposition of both the cyanobacterium and the photosensitiser. The presence of MB and H2O2 affects the viability of the photosensitiser and the cyanobacterium with the fluorescence of both decreasing by 80% over the irradiation time investigated. The photo-dynamic effect was observed under aerobic and anaerobic conditions indicating that oxygen was not necessary for the process. This novel combination could be effective for the remediation of biofilm colonised stone surfaces.

PsbU is a subunit of the extrinsic complex attached to the core of photosystem II. A PsbU-mutant of Synechococcus PCC 7942 was isolated based on its elevated resistance to externally applied oxidative stress. PsbU-mutant exhibits fast rates of degradation of the photosystem II core protein, D1, under sub-saturating as well as high-light conditions. While forward electron transfer is not affected, back electron flow is severely impaired in the mutant. We suggest that impairment of psbU results in production of reactive-oxygen-species, which trigger antioxidative mechanisms even under standard growth conditions. Accordingly, when challenged with external oxidative stress, these cells are more resistant than wild type cells.

[structure: see text] Nostocarboline and seven derivatives were prepared and displayed minimal inhibitory concentration (MIC) values >or=100 nM against the growth of Microcystis aeruginosa PCC 7806, Synechococcus PCC 6911, and Kirchneriella contorta SAG 11.81, probably via the inhibition of photosynthesis. The natural product hybrid nostocarboline/ciprofloxacin displayed additional antibacterial activity against several Gram-negative bacteria (MICs >or=0.7 microM). Nostocarboline can thus be considered a potent, selective, readily available, natural algicide.

The effects of the energization of cells by light and by exogenous glucose on the salt-induced inactivation of the photosynthetic machinery were investigated in the cyanobacterium Synechococcus sp. PCC 7942. The incubation of the cyanobacterial cells in a medium supplemented with 0.5 M NaCl induced a rapid decline with a subsequent slow decline, in the oxygen-evolving activity of Photosystem (PS) II and in the electron-transport activity of PSI. Light and exogenous glucose each protected PSII and PSI against the second phase of the NaCl-induced inactivation. The protective effects of light and glucose were eliminated by an uncoupler of phosphorylation and by lincomycin, an inhibitor of protein synthesis. Light and glucose had similar effects on the NaCl-induced inactivation of Na(+)/H(+) antiporters. After photosynthetic and Na(+)/H(+)-antiport activities had been eliminated by the exposure of cells to 0.5 M NaCl in the darkness, both activities were partially restored by light or exogenous glucose. This recovery was prevented by lincomycin. These observations suggest that cellular energization by either photosynthesis or respiration, which is necessary for protein synthesis, is important for the recovery of the photosynthetic machinery and Na(+)/H(+) antiporters from inactivation by a high level of NaCl.

Nitrate and phosphate concentrations higher than those found in the natural environment slowed down growth of two strains of non-bloom-forming, phycoerythrin-rich Synechococcus spp. isolated from mesotrophic subalpine lakes. The results make clear why isolation of these picocyanobacteria in standard cultivation media was difficult. At low concentrations, closely related strains exhibited distinct growth characteristics with respect to these two nutrients, possibly explaining differences in their seasonal appearance in the natural environment.