Temperature Effects Explain Continental Scale Distribution of Cyanobacterial Toxins

Insight into how environmental change determines the production and distribution of cyanobacterial toxins is necessary for risk assessment. Management guidelines currently focus on hepatotoxins (microcystins). Increasing attention is given to other classes, such as neurotoxins (e.g., anatoxin-a) and cytotoxins (e.g., cylindrospermopsin) due to their potency. Most studies examine the relationship between individual toxin variants and environmental factors, such as nutrients, temperature and light. In summer 2015, we collected samples across Europe to investigate the effect of nutrient and temperature gradients on the variability of toxin production at a continental scale. Direct and indirect effects of temperature were the main drivers of the spatial distribution in the toxins produced by the cyanobacterial community, the toxin concentrations and toxin quota. Generalized linear models showed that a Toxin Diversity Index (TDI) increased with latitude, while it decreased with water stability. Increases in TDI were explained through a significant increase in toxin variants such as MC-YR, anatoxin and cylindrospermopsin, accompanied by a decreasing presence of MC-LR. While global warming continues, the direct and indirect effects of increased lake temperatures will drive changes in the distribution of cyanobacterial toxins in Europe, potentially promoting selection of a few highly toxic species or strains.Peer reviewe

The Effects of Cyanobacterial Bloom Extracts on the Biomass, Chl-a, MC and Other Oligopeptides Contents in a Natural Planktothrix agardhii Population

Blooms of the cyanobacterium Planktothrix agardhii are common in shallow, eutrophic freshwaters. P. agardhii may produce hepatotoxic microcystins (MCs) and many other bioactive secondary metabolites belonging mostly to non-ribosomal oligopeptides. The aim of this work was to study the effects of two extracts (Pa-A and Pa-B) of P. agardhii-predominated bloom samples with different oligopeptide profiles and high concentration of biogenic compounds on another natural P. agardhii population. We hypothesised that the P. agardhii biomass and content of oligopeptides in P. agardhii is shaped in a different manner by diverse mixtures of metabolites of different P. agardhii-dominated cyanobacterial assemblages. For this purpose, the biomass, chlorophyll a and oligopeptides content in the treated P. agardhii were measured. Seven-day microcosm experiments with four concentrations of the extracts Pa-A and Pa-B were carried out. Generally, aeruginosins (AERs), cyanopeptolins (CPs) and anabaenopeptins (APs) were the most numerous peptides; however, only 16% of them were common for both extracts. The addition of the extracts resulted in similar effects on P. agardhii: an increase in biomass, Chl-a and MC content in the exposed P. agardhii as well as changes in its oligopeptide profile were observed. MCs present in the extracts did not inhibit accumulation of P. agardhii biomass, and did not have any negative effect on MC and Chl-a content. No evidence for bioaccumulation of dissolved peptides in the P. agardhii exposed was found. As the two tested extracts differed considerably in oligopeptide composition, but contained similar high concentrations of nutrients, it seems that biogenic compounds, not oligopeptides themselves, positively influenced the mixed natural P. agardhii population

Degradation of Three Microcystin Variants in the Presence of the Macrophyte Spirodela polyrhiza and the Associated Microbial Communities

Cyanobacteria, which form water blooms all over the world, can produce a wide range of cyanotoxins such as hepatotoxic microcystins (MCs) and other biologically active metabolites harmful to living organisms, including humans. Microcystin biodegradation, particularly caused by bacteria, has been broadly documented; however, studies in this field focus mainly on strains isolated from natural aquatic environments. In this paper, the biodegradation of microcystin-RR (MC-RR), microcystin-LR (MC-LR), and microcystin-LF (MC-LF) after incubation with Spirodela polyrhiza and the associated microorganisms (which were cultured under laboratory conditions) is shown. The strongest MC biodegradation rate after nine days of incubation was observed for MC-RR, followed by MC-LR. No statistically significant decrease in the concentration of MC-LF was noted. Products of MC decomposition were detected via the HPLC method, and their highest number was found for MC-RR (six products with the retention time between 5.6 and 16.2 min), followed by MC-LR (two products with the retention time between 19.3 and 20.2 min). Although the decrease in MC-LF concentration was not significant, four MC-LF degradation products were detected with the retention time between 28.9 and 33.0 min. The results showed that MC-LF was the most stable and resistant MC variant under experimental conditions. No accumulation of MCs or their biodegradation products in S. polyrhiza was found. The findings suggest that the microorganisms (bacteria and algae) associated with S. polyrhiza could be responsible for the MC biodegradation observed. Therefore, there is a need to broaden the research on the biodegradation products detected and potential MC-degraders associated with plants

Role of Hydrology in Cyanobacterial Blooms in the Floodplain Lakes

River floodplains are sites of extremely high environmental and ecological value due to high biodiversity. Floodplain lakes (FPLs) are essential parts of complex floodplain ecosystems’ biological and hydro-chemical processes. Clear seasonal cycles, determined by the regime of the parent river and closely linked to climatic conditions, are observed in these lakes. Both the quantity and the quality of water are determined by the functional phases of a floodplain lake; limnophase, when the lake is isolated from the river, and potamophase (inundation), when the floodplain lake is overflowed by the river waters. These phases highly modify lake bathymetry, water balance, chemistry, and biology. Human pressure, mostly dam construction and land use changes, alter the frequency, duration, and intensity of natural cycles of inundation. The majority of large rivers in the Northern Hemisphere have been impacted by human activity. Floodplain lakes are also affected by continuous climate change, due to the alterations of the hydrological regimes. Cyanobacterial blooms in floodplain lakes are often characterized by high qualitative and quantitative annual and long-term variability. The main forces driving cyanobacterial blooms can be found in the flooding dynamics and intensity influencing hydraulic residence time and the concentration of biogenic compounds in lake water. Cyanotoxin production and seasonal dynamics in floodplain lakes have been rarely studied, particularly in connection with the hydrological regime. Moreover, the effects of cyanobacterial blooms and their toxicity to organisms inhabiting floodplain lakes, connected rivers, and floodplains are poorly understood. Therefore, knowledge of the processes controlling floodplain lakes’ ecological conditions is crucial to implementing water management and restoration practices, protecting those fragile and precious ecosystems from degradation and possible extension

Effects of Extracts Containing Metabolites of Different Cyanobacteria from an Ambient Spring (Central Europe) on Zooplankters Daphnia magna and Duckweed Spirodela polyrhiza

Toxic cyanobacterial blooms are a well-known problem in eutrophic water bodies, but cyanobacterial toxicity in ambient springs is unexplored. Therefore, we studied the toxin content and effects of two extracts obtained from epilithic and benthic microbial mats containing different algae and filamentous cyanobacteria, Phormidium breve and Oscillatoria limosa, respectively, on fresh biomass, number of roots, and pigment content in duckweed Spirodela polyrhiza and on survivorship of Daphnia magna (Cladocera). Mat samples, used to prepare extracts for bioassays, were collected in the anthropogenically transformed limnocrenic Górecko spring, located (50°31′08″ N and 22°57′10″ E) in the Roztocze region (Eastern Poland). It drains an abundant aquifer built with Cretaceous sediments. Neither anatoxin-a (ANTX) nor microcystins (MCs) were detected in the extracts using HPLC techniques; however, negative effects of the extracts on tested organisms were observed. The Phormidium extract contained concentrations of cyanobacterial metabolites a few times higher than the Oscillatoria extract. In general, both extracts affected plants in a dose-dependent manner; however, the Oscillatoria extract influenced pigment production without a clear trend. The highest concentrations of Phormidium extract (p < 0.05) significantly decreased the number of roots and the content of chlorophylls and carotenoids in S. polyrhiza. The Oscillatoria extract caused a statistically significant (p < 0.05) decrease in biomass and number of roots; however, it generally positively influenced the production of pigments. The extract containing O. limosa metabolites was more toxic to D. magna than the extract containing higher amounts of metabolites of P. breve. Cyanobacteria inhabiting temperate springs may negatively affect hydrobionts by producing secondary metabolites other than ANTX and MCs; however, the contribution of algae cannot be excluded. Extensive research on cyanobacteria in springs, their metabolites, and their effects on living organisms should be conducted

The role of abiotic and biotic environmental factors in shaping epiphyton on common reed in shallow, hydrologically transformed, temperate lakes

Epiphytic algae are an important group of organisms involved in primary productivity, nutrient cycling, and energy transfer in littoral food webs. However, multifactorial studies conducted on epiphyton on the same substrate across a spectrum of environmental parameters are very limited. Here, we present first complex field study on the role of abiotic and biotic factors in shaping the species richness, diversity, abundance, and biomass composition of epiphyton on common reed in four shallow lakes with different trophic status, water and fish management, and the abundance and structure of potential algal grazers: littoral crustaceans and fish. The obtained results revealed that the algal taxa richness was the lowest in the hypertrophic lake and the highest in the meso-eutrophic lake. Epiphyton abundance (predominated by pennate diatoms) and biomass were found to be the highest in eutrophic water bodies. Biomass consisted primarily of diatoms, but we found the seasonal predominance of filamentous Chlorophyta (in the eutrophic lakes) and Chlorophyceae (in the meso-eutrophic lake). Redundancy analysis (RDA) showed that the frequency of water level fluctuations was the most significant variable in the composition of epiphyton. RDA also revealed the importance of grazing pressure of fish. Thus, in hydrologically transformed lakes, man-made factors may be of great relevance in the development of epiphytic algae

Toxic oligopeptides in the cyanobacterium

Cyanobacterial toxins are a global threat to aquatic organisms; however, they represent only one group of bioactive cyanobacterial metabolites. Very little is known about the effects of other cyanobacterial products (e.g., non-ribosomal oligopeptides) on freshwater macrophytes. Our experimental study revealed that the development of young duckweed Spirodela polyrhiza was inhibited by two aquatic extracts of cyanobacterial bloom samples predominated by Planktothrix agardhii and pure microcystin-LR (MC-LR). The extracts differed considerably in the content of MCs and other oligopeptides; they contained three or four MC variants and several other oligopeptides such as anabaenopeptins, aeruginosins, and planktocyclin. Their toxic effects on young plants (first frond area, root number, fresh biomass, and chlorophyll a content) were different. The more phytotoxic extract obtained from a higher cyanobacterial biomass contained a lower total MC concentration and different anabaenopeptin variants (e.g., anabaenopeptin H, G, HU892, and E/F) as well as planktocyclin, which were not present in another extract with a higher MC concentration. The obtained results suggested that P. agardhii oligopeptides other than MCs are harmful to young duckweeds and may exert even stronger toxic effects than MC-LR. The production of various variants of MCs together with other oligopeptides, and their toxicity to aquatic plants varied over seasons depending on the taxonomic composition of the cyanobacterial bloom. Germinated turions of S. polyrhiza can be used as a sensitive bioindicator of the cyanobacterial threat in aquatic ecosystems

The role of abiotic and biotic environmental factors in shaping epiphyton on common reed in shallow, hydrologically transformed, temperate lakes

Epiphytic algae are an important group of organisms involved in primary productivity, nutrient cycling, and energy transfer in littoral food webs. However, multifactorial studies conducted on epiphyton on the same substrate across a spectrum of environmental parameters are very limited. Here, we present first complex field study on the role of abiotic and biotic factors in shaping the species richness, diversity, abundance, and biomass composition of epiphyton on common reed in four shallow lakes with different trophic status, water and fish management, and the abundance and structure of potential algal grazers: littoral crustaceans and fish. The obtained results revealed that the algal taxa richness was the lowest in the hypertrophic lake and the highest in the meso-eutrophic lake. Epiphyton abundance (predominated by pennate diatoms) and biomass were found to be the highest in eutrophic water bodies. Biomass consisted primarily of diatoms, but we found the seasonal predominance of filamentous Chlorophyta (in the eutrophic lakes) and Chlorophyceae (in the meso-eutrophic lake). Redundancy analysis (RDA) showed that the frequency of water level fluctuations was the most significant variable in the composition of epiphyton. RDA also revealed the importance of grazing pressure of fish. Thus, in hydrologically transformed lakes, man-made factors may be of great relevance in the development of epiphytic algae

Toxic oligopeptides in the cyanobacterium Planktothrix agardhii-dominated blooms and their effects on duckweed (Lemnaceae) development

Cyanobacterial toxins are a global threat to aquatic organisms; however, they represent only one group of bioactive cyanobacterial metabolites. Very little is known about the effects of other cyanobacterial products (e.g., non-ribosomal oligopeptides) on freshwater macrophytes. Our experimental study revealed that the development of young duckweed Spirodela polyrhiza was inhibited by two aquatic extracts of cyanobacterial bloom samples predominated by Planktothrix agardhii and pure microcystin-LR (MC-LR). The extracts differed considerably in the content of MCs and other oligopeptides; they contained three or four MC variants and several other oligopeptides such as anabaenopeptins, aeruginosins, and planktocyclin. Their toxic effects on young plants (first frond area, root number, fresh biomass, and chlorophyll a content) were different. The more phytotoxic extract obtained from a higher cyanobacterial biomass contained a lower total MC concentration and different anabaenopeptin variants (e.g., anabaenopeptin H, G, HU892, and E/F) as well as planktocyclin, which were not present in another extract with a higher MC concentration. The obtained results suggested that P. agardhii oligopeptides other than MCs are harmful to young duckweeds and may exert even stronger toxic effects than MC-LR. The production of various variants of MCs together with other oligopeptides, and their toxicity to aquatic plants varied over seasons depending on the taxonomic composition of the cyanobacterial bloom. Germinated turions of S. polyrhiza can be used as a sensitive bioindicator of the cyanobacterial threat in aquatic ecosystems

An experimental study on the influence of the bloom-forming alga Gonyostomum semen (Raphidophyceae) on cladoceran species Daphnia magna

The effect of the unicellular, bloom-forming alga Gonyostomum semen (Raphidiophyceae) on the survival rate and body size of Daphnia magna was tested under experimental laboratory conditions. Using samples from four humic lakes with a long history of Gonyostomum blooms, we exposed D. magna for 72 h to various Gonyostomum treatments which included homogenized biomass (frozen and fresh), live cell populations as well as lake water separated from the concentrated biomass of live cells. Filtered lake water and the chlorophycean alga Stichococcus bacillaris population (homogenized biomass or live cells) we used as controls. Our study revealed that (1) frozen homogenized G. semen biomass in the concentrations typical for blooms was not harmful for Daphnia and appeared to have a nutritive effect because it supported its growth; however, Daphnia mortality occurred after exposure to fresh and highly concentrated cell homogenate containing high amount of mucilage; (2) it is unlikely that living Gonyostomum cells excrete extracellular substances harmful for Daphnia; however, dense live Gonyostomum population that formed mucilaginous aggregates immobilized Daphnia and increased its mortality. The results suggest that various interactions between G. semen and D. magna take place and may play an essential role in natural freshwater ecosystems