Ecology of toxic cyanobacteria

Eutrophication of waters bodies, as a consequence of human activities, results in the loss of biodiversity followed by massive appearance of cyanobacteria. In freshwater ecosystems, the blooms are mostly formed by the genera Microcystis, Planktothrix, Anabaena and Cylindrospermopsis; in brackish and marine waters Nodularia spumigena, Aphanizomenon flos-aquae and Trichodesmium can thrive under favorable conditions. Species belonging to the order Nostocales and Oscillatoriales live in filaments. The vegetative cells of Nostocales may differentiate into heterocytes and akinets. The order Chroococcales aggregates in colonies of different shape and size; they rarely produce akinets. Cyanobacteria have developed a wide range of adaptation mechanisms which enable them to inhabit different niches of aquatic ecosystems and out-compete other phytoplankton organisms. Due to N2 fixation, the filamentous and heterocytes forming species can grow in nitrogen depleted waters; gas vesicles are used to regulate buoyancy and adjust to optimal light intensity, while accessory pigments (phycocyanin, phycorytrin) enable them to absorb light in most efficient way. Growth of cyanobacteria is determined by a number of environmental factors, including water temperature, light intensity, ratio between nitrogen and phosphorus concentrations as well as the dynamics of water masses. Some species produce secondary metabolites harmful to humans and animals. The compounds show hepatotoxic, neurotoxic, cytotoxic and dermatotoxic activities. Cyclic oligopeptides, termed microcystins, are the most commonly occurring cyanobacterial toxins. Like other non-ribosomal peptides, they are synthesized by thiotemplate mechanism. From one water bloom both microcystin-producing and non-microcystin-producing strains can be isolated. In some studies relationship between microcystin production and the morphology of Microcystis has been revealed. It was also proved that microcystin concentration in bloom material mostly depends on the contribution of toxic genotype; it is also affected by environmental factors, but to a lesser extent. Exposure of aquatic animals to toxin-producing cyanobacteria leads to contamination of their tissues and organs. Microcystins and nodularin may accumulate in the organisms via ingestion, transdermal rout or by taking up directly from water in dissolved form. The toxins were detected in zooplankton, mussels, snails, fish and birds from freshwater and marine environments. In liver and viscera the concentration of the compounds was highest; they were also found in muscles, gonads, kidney, gills and in feather of birds. As polar compounds, cyanobacterial hepatotoxins are probably not biomagnified in aquatic food web. Some authors suggested that detoxication of aquatic organisms proceeds through formation of glutathion conjugates. The process is probably not complete, as microcystin and nodularin were detected in the animal tissues several months after the bloom of toxic cyanobacteria. Sediments are regarded to be a secondary source of contamination of filter-feeders with the toxins. As many other compounds, microcystin and nodularin are sorbed on sediment particles, especially those with fine-grained structure. Toxic cyanobacteria blooms pose a serious threat to humans and animals. A variety of methods and techniques, characterized by different sensitivity and selectivity, are used to assess the risk for people exposed to cyanobacterial bloom or dissolved toxin in water. Additionally, some national and international regulations were issued to protect users of drinking and recreational waters. The World Health Organization derived and recommended a provisional guideline value for drinking water of 1 µg dm-3. In the Directive of European Union (2006/7/EC) the importance of cyanobacterial risk in bathing sites has been addressed. With the view of the fact that cyanotoxins accumulate in edible aquatic organisms, this source of intoxication should not be overlooked

Morphologic, Phylogenetic and Chemical Characterization of a Brackish Colonial Picocyanobacterium (Coelosphaeriaceae) with Bioactive Properties

Despite their cosmopolitan distribution, knowledge on cyanobacteria in the family Coelosphaeriaceae is limited. In this study, a single species culture of a coelosphaeran cyanobacterium isolated from a brackish rock pool in the Baltic Sea was established. The strain was characterized by morphological features, partial 16S rRNA sequence and nonribosomal oligopeptide profile. The bioactivity of fractionated extracts against several serine proteases, as well as protein-serine/threonine phosphatases was studied. Phylogenetic analyses of the strain suggested a close relationship with Snowella litoralis, but its morphology resembled Woronichinia compacta. The controversial morphologic and phylogenetic results demonstrated remaining uncertainties regarding species division in this cyanobacteria family. Chemical analyses of the strain indicated production of nonribosomal oligopeptides. In fractionated extracts, masses and ion fragmentation spectra of seven possible anabaenopeptins were identified. Additionally, fragmentation spectra of cyanopeptolin-like peptides were collected in several of the fractions. The nonribosomal oligopeptide profile adds another potential identification criterion in future inter- and intraspecies comparisons of coelosphaeran cyanobacteria. The fractionated extracts showed significant activity against carboxypeptidase A and trypsin. Inhibition of these important metabolic enzymes might have impacts at the ecosystem level in aquatic habitats with high cyanobacteria densities

Specific Chemical and Genetic Markers Revealed a Thousands-Year Presence of Toxic Nodularia spumigena in the Baltic Sea

In the Baltic Sea, diazotrophic cyanobacteria have been present for thousands of years, over the whole brackish water phase of the ecosystem. However, our knowledge about the species composition of the cyanobacterial community is limited to the last several decades. In the current study, the presence of species-specific chemical and genetic markers in deep sediments were analyzed to increase the existing knowledge on the history of toxic Nodularia spumigena blooms in the Baltic Sea. As chemical markers, three cyclic nonribosomal peptides were applied: the hepatotoxic nodularin, which in the sea was detected solely in N. spumigena, and two anabaenopeptins (AP827 and AP883a) characteristic of two different chemotypes of this species. From the same sediment samples, DNA was isolated and the gene involved in biosynthesis of nodularin, as well as the phycocyanin intergenic spacer region (PC-IGS), were amplified. The results of chemical and genetic analyses proved for the first time the thousands-year presence of toxic N. spumigena in the Baltic Sea. They also indicated that through all this time, the same two sub-populations of the species co-existed

Chemical and Genetic Diversity of Nodularia spumigena from the Baltic Sea

Nodularia spumigena is a toxic, filamentous cyanobacterium occurring in brackish waters worldwide, yet forms extensive recurrent blooms in the Baltic Sea. N. spumigena produces several classes of non-ribosomal peptides (NRPs) that are active against several key metabolic enzymes. Previously, strains from geographically distant regions showed distinct NRP metabolic profiles. In this work, conspecific diversity in N. spumigena was studied using chemical and genetic approaches. NRP profiles were determined in 25 N. spumigena strains isolated in different years and from different locations in the Baltic Sea using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Genetic diversity was assessed by targeting the phycocyanin intergenic spacer and flanking regions (cpcBA-IGS). Overall, 14 spumigins, 5 aeruginosins, 2 pseudaeruginosins, 2 nodularins, 36 anabaenopeptins, and one new cyanopeptolin-like peptide were identified among the strains. Seven anabaenopeptins were new structures; one cyanopeptolin-like peptide was discovered in N. spumigena for the first time. Based on NRP profiles and cpcBA-IGS sequences, the strains were grouped into two main clusters without apparent influence of year and location, indicating persistent presence of these two subpopulations in the Baltic Sea. This study is a major step in using chemical profiling to explore conspecific diversity with a higher resolution than with a sole genetic approach

Linking environmental heterogeneity and chemo-diversity in cyanobacteria: A culture-dependent profile based analysis

Cyanobacteria are ecologically versatile microorganisms that inhabit most environments, ranging from marine systems to arid deserts. Given their ability to survive under harsh and extreme conditions, we hypothesize that cyanobacteria could produce a wide variety of compounds in specific niches. In this context, we sampled a number of different environments, from freshwater and brackish ecosystems to terrestrial and anchialine caves, spanning from the Canary Islands and Iceland to Estonia and Greece. Forty-four (44) cyanobacteria strains were analyzed with de novo peptide fragmentation in order to detect their metabolome profile; further, their antimicrobial, cytotoxic, and enzyme inhibitory activity was investigated. Both freshwater/planktic and rock-dwelling/benthic strains exhibited different types of inhibitory activities. However, cyanopeptides were only detected in freshwater strains; microcystins, anabaenopeptins, and aeruginosins congeners from Microcystis spp., Thrichormus variabilis, and Calothrix epiphytica strains. Therefore, our results indicate a high degree of unknown chemo-diversity, as we could not link the presence/absence of any known cyanopeptides and inhibitory activities from strains derived from other habitats, in contrast with freshwater cyanobacteria strains. In this work we discuss the correlation between the cyanobacteria chemo- and lifestyle diversity providing a missing study material for profile-based analysis on cyanobacteria from under-explored environments

Blooms of toxic cyanobacterium Nodularia spumigena in Norwegian fjords during Holocene warm periods

In paleoecological studies, molecular markers are being used increasingly often to reconstruct community structures, environmental conditions and ecosystem changes. In this work, nodularin, anabaenopeptins and selected DNA sequences were applied as Nodularia spumigena markers to reconstruct the history of the cyanobacterium in the Norwegian fjords. For the purpose of this study, three sediment cores collected in Oslofjorden, Trondheimsfjorden and Balsfjorden were analyzed. The lack of nodularin in most recent sediments is consistent with the fact that only one report on the sporadic occurrence and low amounts of the cyanobacterium in Norwegian Fjords in 1976 has been published. However, analyses of species-specific chemical markers in deep sediments showed that thousands of years ago, N. spumigena constituted an important component of the phytoplankton community. The content of the markers in the cores indicated that the biomass of the cyanobacterium increased during the warmer Holocene periods. The analyses of genetic markers were less conclusive; they showed the occurrence of microcystin/nodularin producing cyanobacteria of Nostocales order, but they did not allow for the identification of the organisms at a species level

Characterization and diversity of microcystins produced by cyanobacteria from the Curonian Lagoon (SE Baltic Sea)

Microcystins (MCs) are the most widely distributed and structurally diverse cyanotoxins that can have significant health impacts on living organisms, including humans. The identification of MC variants and their quantification is very important for toxicological assessment. Within this study, we explored the diversity of MCs and their potential producers from the Curonian Lagoon. MC profiles were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) method, while the potential producers were detected based on the presence of genus-specific mcyE gene sequences. Among the numerous MCs detected, one new potential MC variant with m/z 1057 was partially characterized. Moreover, two other MCs with m/z 1075 and m/z 1068 might belong to new variants with serine (Ser), rarely detected in position one of the peptides. They might also represent MC-Y(OMe)R and MC-WR, respectively. However, the application of a low-resolution MS/MS system made the unambiguous identification of the MCs impossible. Based on this example, the problems of peptide structure identification are discussed in the work. Genetic analysis revealed that potential MCs producers include Dolichospermum/Anabaena, Microcystis spp., and Planktothrix agardhii. The diversity and temporal variations in MC profiles may indicate the presence of several chemotypes of cyanobacteria in the Curonian Lagoon

Phytoplankton of the Curonian Lagoon as a new interesting source for bioactive natural products. Special impact on cyanobacterial metabolites

The bioprospecting of marine and brackish water systems has increased during the last decades. In this respect, microalgae, including cyanobacteria, and their metabolites are one of the most widely explored resources. Most of the bioactive compounds are isolated from ex situ cultures of microorganisms; however, analysis of field samples could also supply valuable information about the metabolic and biotechnological potential of microalgae communities. In this work, the activity of phytoplankton samples from the Curonian Lagoon was studied. The samples were active against antibiotic resistant clinical and environmental bacterial strains as well as against serine proteases and T47D human breast adenocarcinoma cells. No significant effect was found on Daphnia magna. In addition, using LC-MS/MS, we documented the diversity of metabolites present in field samples. A list of 117 detected cyanopeptides was presented. Cyanopeptolins constituted the largest class of cyanopeptides. As complex bloom samples were analyzed, no link between the observed activity and a specific sample component can be established. However, the results of the study showed a biotechnological potential of natural products from the Curonian Lagoon

Effect of Increased Temperature on Native and Alien Nuisance Cyanobacteria from Temperate Lakes: An Experimental Approach

In response to global warming, an increase in cyanobacterial blooms is expected. In this work, the response of two native species of Planktothrix agardhii and Aphanizomenon gracile, as well as the response of two species alien to Europe—Chrysosporum bergii and Sphaerospermopsis aphanizomenoides—to gradual temperature increase was tested. The northernmost point of alien species distribution in the European continent was recorded. The tested strains of native species were favoured at 20⁻28 °C. Alien species acted differently along temperature gradient and their growth rate was higher than native species. Temperature range of optimal growth rate for S. aphanizomenoides was similar to native species, while C. bergii was favoured at 26⁻30 °C but sensitive at 18⁻20 °C. Under all tested temperatures, non-toxic strains of the native cyanobacteria species prevailed over the toxic ones. In P. agardhii, the decrease in concentration of microcystins and other oligopeptides with the increasing temperature was related to higher growth rate. However, changes in saxitoxin concentration in A. gracile under different temperatures were not detected. Accommodating climate change perspectives, the current work showed a high necessity of further studies of temperature effect on distribution and toxicity of both native and alien cyanobacterial species