Baltic Sea Cyanobacteria Research Articles

Structures and Activity of New Anabaenopeptins Produced by Baltic Sea Cyanobacteria.

Anabaenopeptins, bioactive cyclic hexapeptides, were isolated by preparative reversed-phase high performance liquid chromatography from an extract of Baltic Sea cyanobacterial bloom material composed of Nodularia spumigena (50%), Aphanizomenon flos-aquae (40%) and Dolichospermum spp. (10%). Five new anabaenopeptins and nine previously known anabaenopeptins were isolated, and their putative structures were determined by tandem mass spectrometry. The activity of the peptides against carboxypeptidase A and protein phosphatase 1 as well as chymotrypsin, trypsin and thrombin was tested. All anabaenopeptins inhibited carboxypeptidase A (apart from one anabaenopeptin variant) and protein phosphatase 1 with varying potency, but no inhibition against chymotrypsin, trypsin and thrombin was observed.

Selective inhibition of cancer cells' proliferation by compounds included in extracts from Baltic Sea cyanobacteria

Cyanobacteria are a rich source of biologically active compounds used in pharmacology and biotechnology. Due to their high capacity of adaptation, which is reflected in the production of diverse metabolites, including toxins, these microorganisms are able to inhabit very different environments. In this work, water and ethanol extracts from 11 cyanobacterial strains derived from the Baltic Sea (Microcystis, Synechocystis, Leptolyngbya, Pseudanabaena, Lyngbya, Phormidium, Nodularia and Anabaena genera) were screened for anticancer activity. MCF-7 human breast cancer and HeLa cervical cancer cell lines, as well as HDFa normal human fibroblasts, were used. Three extracts derived from Pseudanabaena sp., Pseudanabaena cf. galeata and Microcystis aeruginosa revealed potent and selective antiproliferative activities against cancer cells. The mechanism of the anticancer activity was explored in MCF-7 cells, and was found to rely on the inhibition of the pro-survival Akt kinase and induction of cell death. The peptide profiles of selected cyanobacterial extracts were determined using LC-MS/MS, and classes of bioactive compounds that might be potentially responsible for the observed anticancer activities are presented.

Modeling the Role of pH on Baltic Sea Cyanobacteria.

We simulate pH-dependent growth of cyanobacteria with an ecosystem model for the central Baltic Sea. Four model components—a life cycle model of cyanobacteria, a biogeochemical model, a carbonate chemistry model and a water column model—are coupled via the framework for aquatic biogeochemical models. The coupled model is forced by the output of a regional climate model, based on the A1B emission scenario. With this coupled model, we perform simulations for the period 1968–2098. Our simulation experiments suggest that in the future, cyanobacteria growth is hardly affected by the projected pH decrease. However, in the simulation phase prior to 1980, cyanobacteria growth and N-fixation are limited by the relatively high pH. The observed absence of cyanobacteria before the 1960s may thus be explained not only by lower eutrophication levels, but also by a higher alkalinity.

Trace metals and nutrients in Baltic Sea cyanobacteria: Internal and external fractions and potential use in nitrogen fixation

Even though the availability of trace metals influences nitrogen fixation and growth of cyanobacteria, field data on their cellular metal composition are scarce. In this study, contents of Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Mo, Cd, and the major elements C, N, P and Si were studied in filamentous, nitrogen-fixing cyanobacteria sampled over the growth season March–October at two locations in the Baltic proper (years 2004 and 2007) and one location in the Bothnian Sea (2006). The Al and Ti contents indicated that lithogenic Fe was an important Fe fraction associated with Nodularia spumigena, but not with Aphanizomenon sp. Treatment with an oxalate–EDTA solution indicated that less than 5% of total Fe was adsorbed as oxides, but relatively high adsorbed fractions were found for Mn and Cu. Despite the large variation in biomass and dissolved Fe concentrations, the Fe:C ratio of Aphanizomenon was highly consistent within years and across sampling stations (76±13μmolmol−1 C, average ±1SD), indicating growth controls other than Fe. Species-mixed samples corrected for lithogenic metals indicate similar Fe content in Nodularia as in Aphanizomenon. Calculations based on the use efficiency of Mo for N2 fixation indicate that most Mo in Nodularia and at least a third of the Mo in Aphanizomenon are used in nitrogenase, corresponding to 5–24% of the Fe content. The high Ni content suggests excess storage or extensive use in enzymes such as Ni superoxide dismutase or in Fe-dependent Ni-hydrogenases. The trace metal composition of the investigated Baltic cyanobacteria was similar to that reported for the oceanic genus Trichodesmium, suggesting common physiological requirements of these filamentous nitrogen-fixing cyanobacteria.

Projected climate change impact on Baltic Sea cyanobacteria

Compared to other phytoplankton groups, nitrogen-fixing cyanobacteria generally prefer high water temperatures for growth and are therefore expected to benefit from global warming. We use a coupled biological-physical model with an advanced cyanobacteria life cycle model to compare the abundance of cyanobacteria in the Baltic Sea during two different time periods (1969–1998; 2069–2098). For the latter, we find prolonged growth and a more than twofold increase in the climatologically (30 years) averaged cyanobacteria biomass and nitrogen fixation. Additional sensitivity experiments indicate that the biological-physical feedback mechanism through light absorption becomes more important with global warming. In general, we find a nonlinear response of cyanobacteria to changes in the atmospheric forcing fields as a result of life-cycle related feedback mechanisms. Overall, the sensitivity of the cyanobacteria-driven system suggests that biological-physical and life-cycle related feedback mechanisms are important and must therefore be included in future projection studies.

Phosphorus-limited growth dynamics in two Baltic Sea cyanobacteria, Nodularia sp. and Aphanizomenon sp.

Rates of carbon (C) specific growth and nitrogen (N2) fixation were monitored in cultures of Baltic Sea Nodularia and Aphanizomenon exposed to gradual limitation by inorganic phosphorus (P). Both cyanobacteria responded by decreased cellular P content followed by lowered rates of growth and N2 fixation. C-specific growth and cellular N content changed faster in Aphanizomenon both when inorganic P was lowered as well as during reintroduction of P. Aphanizomenon also showed a more rapid increase in N-specific N2 fixation associated with increased C-specific growth. When ambient concentrations of inorganic P declined, both cyanobacteria displayed higher rates of alkaline phosphatase (APase) activity. Lower substrate half-saturation constants (KM) and higher Vmax : KM ratio of the APase enzyme associated with Nodularia suggest a higher affinity for dissolved organic P (DOP) substrate than Aphanizomenon. Aphanizomenon, which appears more sensitive to changes in ambient dissolved inorganic P, may be adapted to environments with elevated concentrations of P or repeated intrusions of nutrient-rich water. Nodularia on the other hand, with its higher tolerance to increased P starvation may have an ecological advantage in stratified surface waters of the Baltic Sea during periods of low P availability.

BASIC: Baltic Sea cyanobacteria. An investigation of the structure and dynamics of water blooms of cyanobacteria in the Baltic Sea—responses to a changing environment

The blooms of cyanobacteria that develop each summer in the Baltic Sea are composed of two functional groups, namely the small-sized picocyanobacteria ( Synechococcus sp.) and the larger, colony-forming, filamentous N 2-fixing cyanobacteria. The former encompassed both red (phycoerythrin-rich) and blue-green (phycocyanin-rich) species. The majority of the picocyanobacteria measured less than 1 μm and this size fraction comprised as much as 80% of the total cyanobacterial biomass and contributed as much as 50% of the total primary production of a cyanobacterial bloom. The picocyanobacteria are incapable of fixing N 2, do not possess gas vesicles and are not toxic. However, a small filamentous Pseudanabaena sp. that could potentially fix N 2 was isolated from the picocyanobacteria fraction. The larger cyanobacteria may form surface scums because they possess gas vesicles that make them buoyant. Although their biomass was less than the picocyanobacteria, they therefore form the more conspicuous and nuisance-forming part of the bloom. The larger cyanobacteria were composed mainly of three different species: Nodularia spumigena, Aphanizomenon flos-aquae and Anabaena sp. These all belong to the heterocystous, N 2-fixing cyanobacteria. N. spumigena and A. flos-aquae were the dominant species; only N. spumigena was toxic. Although individual Nodularia filaments showed a range of different phenotypes, they all belong to one species as judged from 16S rDNA sequencing. Through determination of the genotypes of many individual Nodularia filaments, it was shown that this population was not clonal and that horizontal exchange of genetic information occurs. N. spumigena and A. flos-aquae were different with respect to their photosynthetic and N 2-fixing potentials. Depending on prevailing environmental conditions, these differences would promote the proliferation of one species over the other and hence would determine overall the toxicity of a bloom. Daily integrals of photon irradiance rather than temperature determined the onset of bloom formation. During a bloom, the diazotrophic cyanobacteria fixed N 2 at a rate that was 10–20% in excess of their own demand for N. Picocyanobacteria assimilated most of this excess N as shown by 15N incorporation. During bloom conditions, the diazotrophic cyanobacteria met about 50% of the N demand of the total cyanobacterial community. The picocyanobacteria were predominantly N-limited while the diazotrophic cyanobacteria were probably iron limited. These findings allow us to understand the formation of toxic cyanobacterial blooms and also to develop tools to predict bloom formation.

Localization of Fe‐containing superoxide dismutase in cyanobacteria from the Baltic Sea: depth and light dependency

The abundance and cellular location of Fe‐containing superoxide dismutase (Fe‐SOD) in trichomes of Nodularia, Aphanizomenon and Anabaena collected from various depths in the Baltic Sea, and in trichomes of a cultured Nodularia strain, BC Nod‐9427, isolated from the Baltic Sea, was examined by immunogold labelling. For trichomes collected from natural populations the areal concentration of Fe‐SOD labelling decreased with depth: trichomes collected from surface accumulations had between 8 and 11 gold particles μm−2 whereas trichomes collected from a depth of 18 m were unlabelled. When trichomes collected from a depth of 10 m (mean areal labelling density 0·5 gold particles μm−2) were exposed to the higher irradiances present at 1 m, the areal concentration of Fe‐SOD increased to 3·5–4 gold particles μm−2 within 4 h. When cultures of Nodularia strain BC Nod‐9427, adapted to low light (10 μmol m−2 s−1), were transferred to an incident irradiance of 1350 μmol m−2 s−1, a doubling of the areal concentration of Fe‐SOD gold label was observed within 1 h. Addition of 3‐(3,4‐dichlorophenyl)‐1,1′‐dimethylurea (DCMU) to cultures immediately before their transfer to increased illumination resulted in a decrease in areal Fe‐SOD concentrations whereas addition of CdCl2 caused an increase over and above that induced by the elevated irradiance. These results suggest that Baltic Sea cyanobacteria are able to modulate their Fe‐SOD content but that this might be in response to oxidative stress rather than to light per se.

Growth, nitrogen fixation, and nodularin production by two baltic sea cyanobacteria

In late summer, nitrogen-fixing cyanobacteria Nodularia spumigena and Aphanizomenon flos-aquae form blooms in the open Baltic Sea. N. spumigena has caused several animal poisonings, but Baltic A. flos-aquae is not known to be toxic. In this laboratory study, performed with batch cultures, the influences of environmental conditions on the biomass and nitrogen fixation rate of N. spumigena and A. flos-aquae were compared and the toxin (nodularin) concentration produced by N. spumigena was measured. Several differences in the biomasses and nitrogen fixation rates of N. spumigena and A. flos-aquae were observed. A. flos-aquae preferred lower irradiances, salinities, and temperatures than N. spumigena. The biomass of both species increased with high phosphate concentrations and with accompanying bacteria and decreased with unnaturally high inorganic nitrogen concentrations. Nodularin concentrations in cells and growth media, as well as nitrogen fixation rates, were generally highest under the conditions that promoted growth. Intracellular nodularin concentrations increased with high temperature, high irradiance, and high phosphate concentration and decreased with low and high salinities and high inorganic nitrogen concentrations. Nodularin concentrations in growth media increased with incubation time, indicating that intracellular nodularin was released when cells lysed. The different responses of A. flos-aquae and N. spumigena to changes in salinity, irradiance, and temperature may explain the different spatial and temporal distribution of these species in the Baltic Sea. According to the results, toxic N. spumigena blooms may be expected in late summer in areas of the Baltic Sea with high phosphorus concentrations and moderate salinity.

Comparison of 15N2 and acetylene reduction methods for the measurement of nitrogen fixation by Baltic Sea cyanobacteria

The aim of this study was to compare nitrogen fixation rates by cyanobacteria measured by acetylene reduction and 15N2, fixation. The effect of environmental stress on the theoretical conversion factor 4 (mol C2H2 per mol N2 reduced) between the methods was studied experimentally in cultures and in field samples from the open Baltic Sea. Axenic and non-axenic laboratory cultures of Nodularia spumigena Mertens (strain BY1). Nodularia sphaerocarpa Bornet et Flahault (strain HKVV) and Aphanizomenon cf. flos-aquae Ralfs ex Bornet et Flahault (strain TR183) isolated from the Baltic Sea were used to test the effect of salinity and NH4+ concentration. The conversion factor was 0.6–4.8 for Nodularia spumigena. 2.6–11.0 for Nodulorio sphaerocarpa and 1.0–15.5 for Aphanizomenon. Changes in salinity and NH4+ concentrations did not affect the conversion factors. but the conversion factor varied among cyanobacterial strains and growth phases.The effect of sample concentration and light level on the conversion factor was tested during a field study of 11 days at the entrance to the Gulf of Finland. A decrease in nitrogenase activity from 0.08 to 0.01 nmol N2 (μg particulate organic nitrogen) 1 h−1 (unconcentrated sample) (15N2 method) occurred when the heterocyst frequency of Nodularia spumigena and Aphanizomenon cf. flos-aquae decreased. indicating that the bloom was decaying. The conversion factor between methods was 1.0–31.8 during the field study, and there was an increase in the factor during the study period. A higher conversion factor in nature than in culture samples may be due to methodological problems during nitrogen fixation measurements. to variation in the conversion factor. or to both.