Cyanobacterium Planktothrix Agardhii Research Articles

Widely used herbicide metolachlor can promote harmful bloom formation by stimulating cyanobacterial growth and driving detrimental effects on their chytrid parasites

Metolachlor (MET) is a widely used herbicide that can adversely affect phytoplanktonic non-target organisms, such as cyanobacteria. Chytrids are zoosporic fungi ubiquitous in aquatic environments that parasitize cyanobacteria and can keep their proliferation in check. However, the influence of organic pollutants on the interaction between species, including parasitism, and the associated ecological processes remain poorly understood. Using the host-parasite system consisting of the toxigenic cyanobacterium Planktothrix agardhii and its chytrid parasite Rhizophydium megarrhizum, we investigated the effects of environmentally relevant concentrations of MET on host-parasite interactions under i) continuous exposure of chytrids and cyanobacteria, and ii) pre-exposure of chytrids. During a continuous exposure, the infection prevalence and intensity were not affected, but chytrid reproductive structures were smaller at the highest tested MET concentration. In the parasite's absence, MET promoted cyanobacteria growth possibly due to a hormesis effect. In the pre-exposure assay, MET caused multi- and transgenerational detrimental effects on parasite fitness. Chytrids pre-exposed to MET showed reduced infectivity, intensity, and prevalence of the infection, and their sporangia size was reduced. Thus, pre-exposure of the parasite to MET resulted in a delayed decline of the cyanobacterial cultures upon infection. After several parasite generations without MET exposure, the parasite recovered its initial fitness, indicating that detrimental effects are transient. This study demonstrates that widely used herbicides, such as MET, could favor cyanobacterial bloom formation both directly, by promoting cyanobacteria growth, and indirectly, by inhibiting their chytrid parasites, which are known to play a key role as top-down regulators of cyanobacteria. In addition, we evidence the relevance of addressing multi-organism systems, such as host-parasite interactions, in toxicity assays. This approach offers a more comprehensive understanding of the effects of pollutants on aquatic ecosystems.

Fate of hepatotoxin microcystin during infection of cyanobacteria by fungal chytrid parasites

Chytrid parasites are increasingly recognized as ubiquitous and potent control agents of phytoplankton, including bloom-forming toxigenic cyanobacteria. In order to explore the fate of the cyanobacterial toxin microcystins (MCs) and assess potential upregulation of their production under parasite attack, a laboratory experiment was conducted to evaluate short- and long-term variation in extracellular and intracellular MC in the cyanobacteria Planktothrix agardhii and P. rubescens, both under chytrid infection and in the presence of lysates of previously infected cyanobacteria. MCs release under parasite infection was limited and not different to uninfected cyanobacteria, with extracellular toxin shares never exceeding 10%, substantially below those caused by mechanical lysis induced by a cold-shock. Intracellular MC contents in P. rubescens under infection were not significantly different from uninfected controls, whereas infected P. agardhii showed a 1.5-fold increase in intracellular MC concentrations, but this was detected within the first 48 hours after parasite inoculation and not later, indicating no substantial MC upregulation in cells being infected. The presence of lysates of previously infected cyanobacteria did not elicit higher intracellular MC contents in exposed cyanobacteria, speaking against a putative upregulation of toxin production induced via quorum sensing in response to parasite attack. These results indicate that chytrid epidemics can constitute a bloom decay mechanism that is not accompanied by massive release of toxins into the medium.

Functional Analysis of the Endopeptidase and Holin From Planktothrix agardhii Cyanophage PaV-LD.

A cyanophage PaV-LD, previously isolated from harmful filamentous cyanobacterium Planktothrix agardhii, was sequenced, and co-expression of its two ORFs in tandem, ORF123 and ORF124, inhibited growth on the model cyanobacterium Synechocystis sp. PCC6803 cells. However, the mechanism of action of ORF123 and ORF124 alone remains to be elucidated. In this study, we aimed to study the individual function of ORF123 or ORF124 from PaV-LD. Our data showed that the ORF123 encoded an endopeptidase, which harbored an M23 family peptidase domain and a transmembrane region. The expression of the endopeptidase in Escherichia coli alone revealed that the protein exhibited remarkable bacteriostatic activity, as evidenced by observation of growth inhibition, membrane damage, and leakage of the intracellular enzyme. Similarly, the holin, a membrane-associated protein encoded by the ORF124, showed weak bacteriostatic activity on E. coli. Moreover, deletion mutations indicated that the transmembrane domains of endopeptidase and holin were indispensable for their bacteriostatic activity. Meanwhile, the bacteriostatic functions of endopeptidase and holin on cyanobacteria cells were confirmed by expressing them in the cyanobacterium Synechocystis sp. PCC6803. Collectively, our study revealed the individual role of endopeptidase or holin and their synergistic bacteriolytic effect, which would contribute to a better understanding of the lytic mechanism of cyanophage PaV-LD.

Detection of morphological changes caused by chemical stress in the cyanobacterium Planktothrix agardhii using convolutional neural networks

The presence of harmful algal bloom in many reservoirs around the world, alongside the lack of sanitation law/ordinance regarding cyanotoxin monitoring (particularly in developing countries), create a scenario in which the local population could potentially chronically consume cyanotoxin-contaminated waters. Therefore, it is crucial to develop low cost tools to detect possible systems failures and consequent toxin release inferred by morphological changes of cyanobacteria in the raw water. This paper aimed to look for the best combination of convolutional neural network (CNN), optimizer and image segmentation technique to differentiate P. agardhii trichomes before and after chemical stress caused by the addition of hydrogen peroxide. This method takes a step towards accurate monitoring of cyanobacteria in the field without the need for a mobile lab. After testing three different network architectures (AlexNet, 3ConvLayer and 2ConvLayer), four different optimizers (Adam, Adagrad, RMSProp and SDG) and five different image segmentations methods (Canny Edge Detection, Morphological Filter, HP filter, GrabCut and Watershed), the combination 2ConvLayer with Adam optimizer and GrabCut segmentation, provided the highest median accuracy (93.33%) for identifying H2O2-induced morphological changes in P. agardhii. Our results emphasize the fact that the trichome classification problem can be adequately tackled with a limited number of learned features due to the lack of complexity in micrographs from before and after chemical stress. To the authors' knowledge, this is the first time that CNNs were applied to detect morphological changes in cyanobacteria caused by chemical stress. Thus, it is a significant step forward in developing low cost tools based on image recognition, to shield water consumers, especially in the poorest regions, against cyanotoxin-contaminated water.

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.

Sorption and Biodegradation of Octyl- and Nonylphenols by the Cyanobacterium Planktothrix agardhii (Gomont) Anagn. & Komárek

The removal of endocrine-disrupting xenobiotics, technical nonylphenol (NP) and 4-tert-octylphenol (OP), from aquatic environment by the cyanobacterium Planktothrix agardhii has been studied. It is shown that nonyl- and octylphenols are removed from aqueous medium in the presence of the cyanobacterium P. agardhii mainly via abiotic pathways—photolysis and hydrolysis—and biodegradation by cyanobacterial cells rather than by adsorption and accumulation in the cells. P. agardhii has a higher destructive and sorption ability for nonylphenol compared to octylphenol. The results indicate the possibility of self-purification of water bodies contaminated with alkylphenols with the participation of the mass species of cyanobacteria Planktothrix agardhii.

Molecular Mechanisms of the Response to 4-tert-Octylphenol-Induced Stress in a Cyanobacterium Planktothrix agardhii

The molecular mechanisms of stress response of Planktothrix agardhii, one of the dominant cya-nobacteria in the basins of the Northwestern Russia and other regions during “blooming,” on the effect of 4-tert-octylphenol (OP), a hormone-like xenobiotic of anthropogenic origin, were studied. In the presence of OP, an increase in the permeability of P. agardhii cell membranes occurred, one of the reasons for which was the oxidation of membrane lipids under conditions of oxidative stress caused by generation of reactive oxygen species. A dose-dependent increase of the activities of enzymatic and non-enzymatic antioxidants in P. agardhii was registered in response to octylphenol-induced oxidative stress, indicating OP action as an activator of expression of stress regulons genes. Due to the structural similarity of 4-tert-octylphenol and alkylresorcinols (AR), the natural microbial regulators controlling development of microbial populations, OP released into the environment may imitate the functions of AR, interfering with the communication process of microbial cells in the population, which may adversely affect the succession and stability of functioning of microbial communities.

The Potency of Toxic Cyanobacteria Planktothrix agardhii isolated from A Retention Pond in Palembang to Cyprinus carpio L: A Preliminary Study

Potential toxic filamentous cyanobacterium Planktothrix agardhii was detected to be dominated in one of the retention ponds located in Palembang city. It showed persistent domination in the location during observations. This species is known to produce a toxin that potentially causes environmental health problems. Hepatotoxin, microcystin (the cyanotoxin most commonly detected in the freshwater environment) are known types of toxin that is produced by this species. Its potential produced a toxin that is in concern. A preliminary study was conducted to study its potential toxic effect to fish (Cyprinus carpio L.); in this study, four different concentrations of Planktothrix agardhii biomass were used to study its effects to Cyprinus carpio L. gills. The results showed the higher the biomass concentrations (5,4086 x 107 cells/ml), the shorter the length of time for the fishes to be dead (± 2-2 hours 15 minutes). The fishes also showed swimming behavior changes such as swimming direction and excessive mucus excretion. Histopathological changes of the fishes’ gills that exposed to Planktothrix agardhii., compared to the un-treated fishes (control) were observed such as edema, lamela gill hyperplasia, and necrosis.

Impact of lake‐catchment processes on phytoplankton community structure in temperate shallow lakes

AbstractResearch on lake‐catchment and biological processes is still innovative. Few reports on this topic exist in the scientific literature. This paper presents species richness, diversity, biomass composition of phytoplankton, and occurrence of cyanobacterial blooms in relation to complex lake‐catchment processes in four shallow lakes. The results revealed that phytoplankton species richness increased with increasing lake trophic state, whereas the opposite relationship was observed for phytoplankton biodiversity. In less eutrophic and deeper lakes, the majority of dominant taxa were representatives of mixed, meso to eutrophic small‐ and medium‐sized lakes. In highly eutrophic lakes, the dominant taxa were common representatives of shallow, very rich in nutrients, turbid, mix layers, and eu‐hypertrophic environments. Redundancy analysis showed that lake depth, flushing time, and conductivity were the most significant factors for phytoplankton development and composition. The hypertrophic, polimictic, and flow‐through Lake Syczyńskie was the most dynamic ecosystem among the lakes. Water mixing and high concentrations of P‐PO4 were beneficial for heavy blooms of the cyanobacterium Planktothrix agardhii observed in Lake Syczyńskie despite the high rate of water exchange. Contrary to the findings of some previous studies, P. agardhii seems to be resistant to flushing at very high loads and concentrations of nutrients (mostly of P‐PO4 and N‐NO3). Phytoplankton assemblages reflected the lakes' habitats, trophic status, and lake‐catchment processes and revealed complex factors that influenced the lakes' functioning. The use of phytoplankton as an indicator of lake‐catchment processes may help understand ecosystem dynamics, essential for the proper selection of management practices protecting aquatic systems against eutrophication.

Cellular responses and bioremoval of nonylphenol by the bloom-forming cyanobacterium Planktothrix agardhii 1113

Abstract Nonylphenol (NP) is extensively used in agricultural, industrial and household applications. Moreover, NP is the major breakdown product of the nonionic surfactants, nonylphenol ethoxylates (NPEOs), the most widely used group of surfactants. Nonylphenol is persistent in the environment, highly toxic to aquatic organisms and is a potential endocrine disruptor. NP and NPEOs have been identified as priority hazardous substances under the Environmental Quality Standards Directive 2013/39/EU and are referred to in the list of substances of particular risk to the Baltic Sea. The toxicity of NP to the bloom-forming cyanobacterium Planktothrix agardhii 1113 isolated from the eastern Gulf of Finland, Baltic Sea and the bioremoval of NP by P . agardhii were studied. NP in concentrations > 0.4 mg L − 1 suppressed cyanobacterial growth. The median effective concentration of NP for P . agardhii after 4 days of treatment (EC 50 ) was 1.5 mg L − 1 . The removal of NP from the culture medium was primarily due to abiotic processes and biodegradation by the cyanobacterium rather than sorption by the cells. NP significantly increased the photosynthetic pigments, extracellular proteins and soluble exopolysaccharides content. The cyanobacterial growth inhibition was accompanied by the increased synthesis of microcystin dm-RR and of the odorous metabolites, geosmin and 2-methylisoborneol (MIB), by P . agardhii 1113. NP also notably increased the microcystin released into the environment. Increased levels of extracellular proteins, soluble exopolysaccharides, microcystins and odorous metabolites may affect the microbial loop in aquatic ecosystems. An increased level of malondialdehyde (MDA) was indicative of the formation of free radicals in P . agardhii under NP stress, whereas increased levels of superoxide dismutase (SOD), catalase (CAT), reduced glutathione (GSH) and proline indicated the occurrence of a scavenging mechanism.

The past and future of phytoplankton in the UK's largest lake, Lough Neagh

Lough Neagh is the largest lake in the UK and has been extensively monitored since 1974. It has suffered from considerable eutrophication and toxic algal blooms. The lake continues to endure many of the symptoms of nutrient enrichment despite improvements in nutrient management throughout the catchment, in particular a permanently dominant crop of the cyanobacterium Planktothrix agardhii. This study examines the historical changes in the Lough, and uses the PROTECH lake model to predict how the phytoplankton community may adapt in response to potential future changes in air temperature and nutrient load. PROTECH was calibrated against 2008 observations, with a restriction on the maximum simulated mixed depth to reflect the shallow nature of the lake and the addition of sediment released phosphorus throughout the mixed water column between 1 May and 1 October (with an equivalent in-lake concentration of 2.0mgm−3). The historical analysis showed that phytoplankton biomass (total chlorophyll a) experienced a steady decline since the mid-1990s. During the same period the key nutrients for phytoplankton growth in the lake have shown contrasting trends, with increases in phosphorus concentrations and declines in nitrate concentrations. The modelled future scenarios which simulated a temperature increase of up to 3°C showed a continuation of those trends, i.e. total chlorophyll a and nitrate concentrations declined in the surface water, while phosphorus concentrations increased and P. agardhii dominated. However, scenarios which simulated a 4°C increase in air temperature showed a switch in dominance to the cyanobacteria, Dolichospermum spp. (formerly Anabaena spp.). This change was caused by a temperature related increase in growth driving nutrient consumption to a point where nitrate was limiting, allowing the nitrogen-fixing Dolichospermum spp. to gain sufficient advantage. These results suggest that in the long term, one nuisance cyanobacteria bloom may only be replaced by another unless the in-lake phosphorus concentration can be greatly reduced.

Effect of Octyl- and Nonylphenols on Growth Photosynthetic Activity and Toxins' Forming of Cyanobacteria Planktothrix Agardhii

Effect of Octyl- and Nonylphenols on Growth Photosynthetic Activity and Toxins' Forming of Cyanobacteria Planktothrix Agardhii

Application of hydrogen peroxide to the control of eutrophic lake systems in laboratory assays.

We exposed water samples from a recreational lake dominated by the cyanobacterium Planktothrix agardhii to different concentrations of hydrogen peroxide (H2O2). An addition of 0.33 mg·L−1 of H2O2 was the lowest effective dose for the decay of chlorophyll-a concentration to half of the original in 14 h with light and 17 h in experiments without light. With 3.33 mg·L−1 of H2O2, the values of the chemical oxygen demand (COD) decreased to half at 36 and 126 h in experiments performed with and without light, respectively. With increasing H2O2, there is a decrease in the total and faecal coliform, and this effect was made more pronounced by light. Total and faecal coliform were inhibited completely 48 h after addition of 3.33 mg·L−1 H2O2. Although the densities of cyanobacterial cells exposed to H2O2 did not decrease, transmission electron microscope observation of the trichomes showed several stages of degeneration, and the cells were collapsed after 48 h of 3.33 mg·L−1 of H2O2 addition in the presence of light. Our results demonstrate that H2O2 could be potentially used in hypertrophic systems because it not only collapses cyanobacterial cells and coliform bacteria but may also reduce chlorophyll-a content and chemical oxygen demand.

Vertical distribution of cyanobacteria biomass and cyanotoxin production in the polymictic Siemianówka Dam Reservoir (eastern Poland)

Abstract The summer-autumn dominance of the toxic cyanobacterium Planktothrix agardhii was described in the lowland polymictic Siemianowka Dam Reservoir (SDR) in 2010 and 2011. The study was conducted at a station located in the deepest part of the reservoir. The species composition of phytoplankton was very similar at the four depths analyzed. Microcystins were continually present in the cyanobacterial biomass. Demethylated microcystin-RR (dmMC-RR) and microcystin-RR (MC-RR) were identified as the major microcystin variants in most samples, while demethylated microcystin-LR (dmMC-LR) and microcystin-LR (MC-LR) were each recorded only once. The concentration of microcystin-RR correlated strongly with the biomass of P. agardhii. The effect of environmental factors on cyanobacterial biomass the production of microcystins by cyanobacteria was minor, but increased water temperatures and pH favored the production of microcystins. Phytoplankton biomass was also influenced by how water outflow from the reservoir was regulated; the biomas increased with depth when the upper flaps were opened, but it was very similar throughout the water column when they were closed. According to the Polish phytoplankton-based index (IFPL), the ecological potential of the reservoir was determined to be poor.

The role of a cascade of reservoirs and seasonal variation in the phytoplankton structure in a tropical river

This study aims to analyse the influence of a cascade of reservoirs on the density, richness and functional groups of phytoplankton in the Contas River, a tropical river of Brazil. This river has two dams along its course, forming the Pedra and Funil reservoirs. Samples were collected over three consecutive years (Dec., 2007 to Dec., 2010) at 28 sampling stations along the river. We identified 198 species and the stretches downstream from the reservoirs showed greater richness. Chlorophyceae, followed by Bacillariophyceae and Cyanophyceae were the dominant groups and highest density was recorded during the rainy season. Overall, a longitudinal pattern in algal densities was found for both seasons, with the lowest values recorded in sections of the Pedra and Funil reservoirs and the highest densities in the downstream sections. Nine functional groups were identified (C, F, J, MP, S1, Sn, Td, Y, Ws); of these, F and J grouped the species with the highest relative abundance during the dry season, while the S1 group, represented by the cyanobacterium Planktothrix agardhii, was dominant in the rainy season. The present study showed a high longitudinal variation in the phytoplankton richness and density, attributed to the hydrological change between the lotic and lentic stretches. Furthermore, the effects of the cascade of reservoirs on phytoplankton, such as reduced density, increased richness and changes in algal associations, were strongly influenced by habitat heterogeneity found in this environment, as well as the rainfall in the region.

Ciliate Nassula sp. grazing on a microcystin-producing cyanobacterium (Planktothrix agardhii): impact on cell growth and in the microcystin fractions

The proliferation of microcystins (MCs)-producing cyanobacteria (MCs) can have detrimental effects on the food chain in aquatic environments. Until recently, few studies had focused on the fate of MCs in exposed organisms, such as primary consumers of cyanobacteria. In this study, we investigate the impact of an MC-producing strain of the cyanobacterium Planktothrix agardhii on the growth and physiology of a Nassula sp. ciliate isolated from a non-toxic cyanobacterial bloom. We show that this Nassula sp. strain was able to consume and grow while feeding exclusively on an MC-producing cyanobacterium over a prolonged period of time (8 months). In short-term exposure experiments (8 days), ciliates consuming an MC-producing cyanobacterial strain displayed slower growth rate and higher levels of antioxidant enzymes than ciliates feeding on two non-MC-producing strains. Three high-performance methods (LC/MS, LC/MS–MS and ELISA) were used to quantify the free and bound MCs in the culture medium and in the cells. We show that ciliate grazing led to a marked decrease in free MCs (methanol extractable) in cells, the MCs were therefore no longer found in the surrounding culture medium. These findings suggest that MCs may have undergone redistribution (free vs bound MCs) or chemical degradation within the ciliates.

What drives the distribution of the bloom-forming cyanobacteria Planktothrix agardhii and Cylindrospermopsis raciborskii?

The cyanobacteria Planktothrix agardhii and Cylindrospermopsis raciborskii are bloom-forming species common in eutrophic freshwaters. These filamentous species share certain physiological traits which imply that they might flourish under similar environmental conditions. We compared the distribution of the two species in a large database (940 samples) covering different climatic regions and the Northern and Southern hemispheres, and carried out laboratory experiments to compare their morphological and physiological responses. The environmental ranges of the two species overlapped with respect to temperature, light and total phosphorus (TP); however, they responded differently to environmental gradients; C.raciborskii biovolume changed gradually while P. agardhii shifted sharply from being highly dominated to a rare component of the phytoplankton. As expected, P.agardhii dominates the phytoplankton with high TP and low light availability conditions. Contrary to predictions, C.raciborskii succeeded in all climates and at temperatures as low as 11°C. Cylindrospermopsis raciborskii had higher phenotypic plasticity than P.agardhii in terms of pigments, individual size and growth rates. We conclude that the phenotypic plasticity of C.raciborskii could explain its ongoing expansion to temperate latitudes and suggest its future predominance under predicted climate-change scenarios.

Selective suppression of harmful cyanobacteria in an entire lake with hydrogen peroxide

Although harmful cyanobacteria form a major threat to water quality, few methods exist for the rapid suppression of cyanobacterial blooms. Since laboratory studies indicated that cyanobacteria are more sensitive to hydrogen peroxide (H2O2) than eukaryotic phytoplankton, we tested the application of H2O2 in natural waters. First, we exposed water samples from a recreational lake dominated by the toxic cyanobacterium Planktothrix agardhii to dilute H2O2. This reduced the photosynthetic vitality by more than 70% within a few hours. Next, we installed experimental enclosures in the lake, which revealed that H2O2 selectively killed the cyanobacteria without major impacts on eukaryotic phytoplankton, zooplankton, or macrofauna. Based on these tests, we introduced 2 mg L−1 (60 μM) of H2O2 homogeneously into the entire water volume of the lake with a special dispersal device, called the water harrow. The cyanobacterial population as well as the microcystin concentration collapsed by 99% within a few days. Eukaryotic phytoplankton (including green algae, cryptophytes, chrysophytes and diatoms), zooplankton and macrofauna remained largely unaffected. Following the treatment, cyanobacterial abundances remained low for 7 weeks. Based on these results, we propose the use of dilute H2O2 for the selective elimination of harmful cyanobacteria from recreational lakes and drinking water reservoirs, especially when immediate action is urgent and/or cyanobacterial control by reduction of eutrophication is currently not feasible. A key advantage of this method is that the added H2O2 degrades to water and oxygen within a few days, and thus leaves no long-term chemical traces in the environment.

Structure and spatial distribution of winter phytoplankton of the Curonian Lagoon (Baltic Sea)

The winter phytoplankton of the Russian part of the hyper-trophic Curonian Lagoon (Baltic Sea) was studied in 2010. Diatoms, cyanobacteria and cryptomonads prevailed in phytoplankton. Diatom Aulacoseira islandica was dominant and especially prevailing in the southern area of the lagoon, i. e. the area influenced by the Deyma River. Cyanobacteria Planktothrix agardhii was also a dominant species. The composition of the complex of dominant species and vertical distribution of phytoplankton differed compared to the results obtained 30 years ago in the same area. The study revealed the increase of the abundance of winter phytoplankton compared to the formerly recorded data.

Perennial toxigenic Planktothrix agardhii bloom in selected lakes of Western Poland

The presence of toxigenic blooms dominated by filamentous cyanobacterium Planktothrix agardhii with estimation of microcystins (MCs) concentration and toxicity was measured in two lakes: Bytynskie and Lubosinskie situated in Western Poland. Investigations were carried out in summer, autumn, and winter of 2007/2008 and early spring of 2008. In both lakes, a domination of P. agardhii in relation to the total cyanobacterial biomass oscillated, throughout the year, almost on the same level between 75 and 99%. The PCR analysis of mcyE gene indicated a presence of toxigenic strains in all collected samples. In addition, the result of semiquantification of mcyE gene band showed that both lakes seem to have variable, throughout the seasons, toxigenic potential with the highest density of mcyE gene in spring. Two separate methods were used: protein phosphatase inhibition assay for estimation of MCs toxicity (biological activity) and high-performance liquid chromatography for determination of MCs concentration (quantity). The highest seasonal MCs toxicity (15.8 μg/L Bytynskie and 21.9 μg/L Lubosinskie) and concentration (34.6 μg/L Bytynskie and 52.2 μg/L Lubosinskie) were determined in autumn and indicated on a Second Alert Level, according to WHO guidelines for bathing water. The results showed the ability of toxigenic strains of cyanobacteria dominated by P. agardhii to remain and produce MCs during the whole year. This was confirmed by significant correlations between P. agardhii biomass and MCs concentrations in both lakes (r = 0.84, Bninskie and r = 0.79, Lubosinskie; P < 0.05).