Planktothrix Agardhii Research Articles

Isolation, Identification and Characterization of the Algicidal Micromycete Penicillium chrysogenum SR–1.3

A novel strain SR–1.3 with algicidal properties and the ability to remove microcystin-LR was isolated from the water of Lake Sestroretskij Razliv during the active cyanobacteria vegetation. Based on the morphological and cultural characteristics and the results of sequencing of the ITS DNA region strain SR–1.3 was identified as Penicillium chrysogenum. The SR–1.3 strain exhibited algicidal activity against cyanobacteria and green algae. A dose-dependent and species-specific nature of the algicidal action of the P. chrysogenum SR–1.3 strain has been established. Cyanobacteria showed the highest sensitivity to strain SR–1.3. The complete lysis (100%) of cyanobacteria cells was observed when 10% (vol.) of the culture liquid or the micromycete filtrate were added to the medium. The algicidal effect of strain SR–1.3 on green algae was 30–70%, depending on the culture. According to the level of sensitivity to the algicidal effect SR–1.3, the test cultures can be arranged in the series Planktothrix agardhii Microcystis aeruginosa Aphanizomenon flos-aquae = Anabaena cylindrica Scenedesmus quadricauda Oocystis parva. The inhibitory effect of the strain SR-1.3 mycelium on the cyanobacteria and green algae growth did not exceed 3–6%. Based on the obtained results a conclusion was made about the indirect mechanism of the algicidal action of P. chrysogenum SR–1.3 by excretion into the medium of metabolites that inhibit and/or lyse cells of cyanobacteria and green algae. When toxigenic strains of M. aeruginosa and P. agardhii were cultivated on a medium containing exometabolites of strain SR–1.3, the concentrations of microcystins in the medium decreased by 3.3 and 1.8 times, respectively, compared with control variants. The ability of P. chrysogenum SR–1.3 to remove highly toxic microcystin-LR from the cultivation medium was revealed. The MC-LR content was found to decrease from 1.2 μg/ml to 0.79 μg/ml over 48 hours during the cultivation of strain SR–1.3 on medium with microcystin.

Распространение токсигенных цианобактерий в водных объектах на территории Восточно-Европейской равнины

We analyze the distribution of potentially toxigenic cyanobacteria in water bodies and rivers of the East European (Russian) Plain on the basis of relevant literature and the results of our studies. Special attention is paid to cyanotoxins: microcystins, which are hepatotoxins, cylindrospermopsin, which is hepatotoxin and cytotoxin, and anatoxins and saxi-toxins, which are neurotoxins. Microcystis and Dolichospermum are the most represented genera of potentially toxigenic cyanobacteria, as well as Aphanizomenon flos-aquae Ralfs ex Bornet & Flahault and Planktothrix agardhii (Gomont) Anagnostidis & Komárek species. The above are the most commonly found in water bodies of the study area. The presence of potentially toxigenic cyanobacteria in water bodies was confirmed by the results of phytoplankton studies using molecular genetic methods. The quantitative content of the dissolved in water and intracellular cyanotoxins was determined using enzyme immunoassay methods, high-performance liquid chromatography, and mass spectrometry. It was noted that microcystin- and anatoxin-a-producing cyanobacteria are the most common in most of the studied water bodies and streams, while saxitoxin- and cylindrospermopsin-producing cyanobacteria are less common. The total content of the dissolved microcystins in different water bodies varies from trace amounts up to 1670 μg/L with SanPiN 1.2.3685-21 standard for microcystin-LR 1 μg/L. The maximum recorded anatoxin-a content was 0.600 μg/L. The preparation of this review made it possible to supplement and summarize information on the distribution of toxigenic cyanobacteria and cyanotoxins in rivers, lakes and reservoirs of temperate latitudes, as well as on the quantitative content of cyanotoxins in water.

Cyanobacteria respond to trophic status in shallow aquatic ecosystems

Small and shallow water bodies are particularly sensitive to adverse conditions connected with anthropogenic eutrophication. As model systems, ponds are a good object for ecological research and monitoring of global environmental changes. We examined cyanobacteria along with other groups of algae versus zooplankton and abiotic characteristics of water in 51 aquatic ecosystems exposed to anthropogenic pressure (from natural forest to highly disturbed field ponds) with 3 distinct trophic groups: meso-, eu- and hypertrophic. This study aimed to define how different levels of trophy affect pond-specific cyanobacteria assemblages and to identify species responding to particular trophic states. We demonstrated that trophic type determined the occurrence of certain cyanobacteria species. From among 78 identified taxa, shade- and turbid mixed adapted were the most numerous. Eutrophic ponds had the highest cyanobacteria species and diversity and abundance of zooplankon. Dominating species such as Chroococcus minimus, Anagnostidinema amphibium, Phormidium granulatum or Komvophoron minutum preferred mesotrophic, while e.g. Jaaginema subtilissimum, Limnolyngbya circumcreta, Limnothrix vacuolifera or Romeria leopolienis eutrophic waters and these were not grazed by filtrators. Only 3 species (Aphanizomenon flos-aquae, Dolichospermum circinale, Planktothrix agardhii) were associated with hypertrophic ponds. Therefore, we assume that cyanobacteria taxa have a high indicative potential to distinguish between trophic type of ponds. Reynolds Functional Groups also exhibit responses to changes in water quality. It was partucularly evident in the case of cyanobacteria representatives of codon M which was attributed to eutrophic ponds. Advancing our understanding about trophic preferences of cyanobacteria is crucial, especially in the era of global warming and the persistent issue of water eutrophication, when problems with harmful cyanobacterial blooms are intensifying. The research findings have ecological significance and management implications, highlighting the often-overlooked importance of pond ecosystems in maintaining overall water quality.

The recent disappearance of a persistent Planktothrix bloom: Characterization of a regime shift in the phytoplankton of Sandusky Bay (USA)

Sandusky Bay is the drowned mouth of the Sandusky River in the southwestern portion of Lake Erie. The bay is a popular recreation location and a regional source for drinking water. Like the western basin of Lake Erie, Sandusky Bay is known for being host to summer cyanobacterial harmful algal blooms (cHABs) year after year, fueled by runoff from the predominantly agricultural watershed and internal loading of legacy nutrients (primarily phosphorus). Since at least 2003, Sandusky Bay has harbored a microcystin-producing bloom of Planktothrix agardhii, a species of filamentous cyanobacteria that thrives in low light conditions. Long-term sampling (2003–2018) of Sandusky Bay revealed regular Planktothrix-dominated blooms during the summer months, but in recent years (2019–2022), 16S rRNA gene community profiling revealed that Planktothrix has largely disappeared. From 2017–2022, microcystin decreased well below the World Health Organization (WHO) guidelines. Spring TN:TP ratios increased in years following dam removal, yet there were no statistically significant shifts in other physicochemical variables, such as water temperature and water clarity. With the exception of the high bloom of Planktothrix in 2018, there was no statistical difference in chlorophyll during all other years. Concurrent with the disappearance of Planktothrix, Cyanobium spp. have become the dominant cyanobacterial group. The appearance of other potential toxigenic genera (i.e., Aphanizomenon, Dolichospermum, Cylindrospermopsis) may motivate monitoring of new toxins of concern in Sandusky Bay. Here, we document the regime shift in the cyanobacterial community and propose evidence supporting the hypothesis that the decline in the Planktothrix bloom was linked to the removal of an upstream dam on the Sandusky River.

Harmful blooms across a longitudinal gradient in central Europe during heatwave: Cyanobacteria biomass, cyanotoxins, and nutrients

Climate change has increased the frequency, duration and intensity of heatwaves in Europe. These extreme events result in alterations of physical, chemical, and biological properties of lakes that may synergistically promote cyanobacterial dominance. In our study we focused on cyanobacterial blooms in lakes distributed over a longitudinal gradient in Central Europe during one of the “top ten European heat waves” in summer 2015. 92 lakes were included in the study, located across three climatic subregions: cool northern lakes, situated in Lithuania, temperate northern lakes in Poland, and warm northern lakes in Croatia. The objective of the study was to determine if cyanobacterial biomass, predominant species, and cyanotoxin concentration differed, across the south-north gradient, as a function of water temperature, total phosphorus, and total nitrogen. Statistical significance of observed patterns was tested using the Kruskal-Wallis rank sum test and the generalized linear model. We found the lowest average epilimnion temperature, but the highest average cyanobacterial biomass in the northern, ‘cool’ lakes while the highest average temperature with the lowest average cyanobacterial biomass in the southern, ‘warm’ lakes. The concentration of cyanotoxins was also the highest in the ‘cool’ lakes. Total phosphorus and total nitrogen correlated significantly with cyanobacterial biomass, cyanotoxins concentration and biomass of some cyanobacterial species (mainly Planktothrix agardhii), regardless of the latitude. Only in the ‘cool’ lakes concentration of cyanotoxins (microcystins and anatoxin-a) correlated significantly with cyanobacterial biomass and the biomass of some dominant cyanobacterial species (P. agardhii). Our results emphasized the differences of heat weaves impact on lakes of various latitudes, with the strongest increase in toxic cyanobacterial blooms in northern ‘cool’ lakes, situated in high latitudes. On the other hand, nutrients directly enhanced blooms across all the studied latitudes of Central Europe. The cyanobacteria species dominating in blooms might be recognized as ecological indicators of climate change, especially in the north-eastern part of Europe.

Shifts in phytoplankton and zooplankton communities in three cyanobacteria-dominated lakes after treatment with hydrogen peroxide

Cyanobacteria can reach high densities in eutrophic lakes, which may cause problems due to their potential toxin production. Several methods are in use to prevent, control or mitigate harmful cyanobacterial blooms. Treatment of blooms with low concentrations of hydrogen peroxide (H2O2) is a promising emergency method. However, effects of H2O2 on cyanobacteria, eukaryotic phytoplankton and zooplankton have mainly been studied in controlled cultures and mesocosm experiments, while much less is known about the effectiveness and potential side effects of H2O2 treatments on entire lake ecosystems. In this study, we report on three different lakes in the Netherlands that were treated with average H2O2 concentrations ranging from 2 to 5 mg L−1 to suppress cyanobacterial blooms. Effects on phytoplankton and zooplankton communities, on cyanotoxin concentrations, and on nutrient availability in the lakes were assessed. After every H2O2 treatment, cyanobacteria drastically declined, sometimes by more than 99%, although blooms of Dolichospermum sp., Aphanizomenon sp., and Planktothrix rubescens were more strongly suppressed than a Planktothrix agardhii bloom. Eukaryotic phytoplankton were not significantly affected by the H2O2 additions and had an initial advantage over cyanobacteria after the treatment, when ample nutrients and light were available. In all three lakes, a new cyanobacterial bloom developed within several weeks after the first H2O2 treatment, and in two lakes a second H2O2 treatment was therefore applied to again suppress the cyanobacterial population. Rotifers strongly declined after most H2O2 treatments except when the H2O2 concentration was ≤ 2 mg L−1, whereas cladocerans were only mildly affected and copepods were least impacted by the added H2O2. In response to the treatments, the cyanotoxins microcystins and anabaenopeptins were released from the cells into the water column, but disappeared after a few days. We conclude that lake treatments with low concentrations of H2O2 can be a successful tool to suppress harmful cyanobacterial blooms, but may negatively affect some of the zooplankton taxa in lakes. We advise pre-tests prior to the treatment of lakes to define optimal treatment concentrations that kill the majority of the cyanobacteria and to minimize potential side effects on non-target organisms. In some cases, the pre-tests may discourage treatment of the lake.

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.

Diversity of planktonic pro- and microeukaryotes in water bodies of the Volga-Don basin during the period of cyanobacterial bloom according to metabarcoding data

The first data on the phylogenetic diversity of planktonic communities of pro- and microeukaryotes in different types of water bodies of the Volga-Don basin during the period of cyanobacterial bloom are presented. Aphanizomenon flos-aquae/Dolichospermum flos-aquae blooms were found mainly in the Kuibyshev Reservoir; Planktothrix agardhii bloom was observed in floodplain lakes of the majority of investigated rivers. Bloom of Raphidiopsis raciborskii was found in a lake on the Volga River terrace, and in a pond in the floodplain of the Samara River Anabaenopsis dominated anong Cyanobacteria. Among heterotrophic prokaryotes, Proteobacteria, Bacteroidota, Verrucomicrobiota, Planctomycetota and Actinobacteriota predominate in the number of sequences, and among protists - Ciliophora, Gyrista (mainly Chrysophyceae), Cryptista and Myzozoa. During the period of cyanobacterial bloom, the contributions of Proteobacteria (especially, Burkholderiales and Pseudomonadales) and Actinobacteriota slightly decrease, while Myzozoa, on the contrary, increase. Monodominant blooms of various species of cyanobacteria significantly change the composition and structure of microbial communities, both at the OTUs and higher taxa levels. The plankton of the pond with Anabaenopsis bloom is most peculiar. Communities with blooms of P. agardhii, R. raciborskii and A. flos-aquae/D. flos-aquae are more similar to each other.

Stringent Response of Cyanobacteria and Other Bacterioplankton during Different Stages of a Harmful Cyanobacterial Bloom.

We conducted a field study to investigate the role of stringent response in cyanobacteria and coexisting bacterioplankton during nutrient-deprived periods at various stages of bloom in a freshwater lake (Utah Lake) for the first time. Using metagenomics and metatranscriptomics analyses, we examined the cyanobacterial ecology and expression of important functional genes related to stringent response, N and P metabolism, and regulation. Our findings mark a significant advancement in understanding the mechanisms by which toxic cyanobacteria survive and proliferate during nitrogen (N) and phosphorus (P) limitations. We successfully identified and analyzed the metagenome-assembled genomes (MAGs) of the dominant bloom-forming cyanobacteria, namely, Dolichospermum circinale, Aphanizomenon flos-aquae UKL13-PB, Planktothrix agardhii, and Microcystis aeruginosa. By mapping RNA-seq data to the coding sequences of the MAGs, we observed that these four prevalent cyanobacteria species activated multiple functions to adapt to the depletion of inorganic nutrients. During and after the blooms, the four dominant cyanobacteria species expressed high levels of transcripts related to toxin production, such as microcystins (mcy), anatoxins (ana), and cylindrospermopsins (cyr). Additionally, genes associated with polyphosphate (poly-P) storage and the stringent response alarmone (p)ppGpp synthesis/hydrolysis, including ppk, relA, and spoT, were highly activated in both cyanobacteria and bacterioplankton. Under N deficiency, the main N pathways shifted from denitrification and dissimilatory nitrate reduction in bacterioplankton toward N2-fixing and assimilatory nitrate reduction in certain cyanobacteria with a corresponding shift in the community composition. P deprivation triggered a stringent response mediated by spoT-dependent (p)ppGpp accumulation and activation of the Pho regulon in both cyanobacteria and bacterioplankton, facilitating inorganic and organic P uptake. The dominant cyanobacterial MAGs exhibited the presence of multiple alkaline phosphatase (APase) transcripts (e.g., phoA in Dolichospermum, phoX in Planktothrix, and Microcystis), suggesting their ability to synthesize and release APase enzymes to convert ambient organic P into bioavailable forms. Conversely, transcripts associated with bacterioplankton-dominated pathways like denitrification were low and did not align with the occurrence of intense cyanoHABs. The strong correlations observed among N, P, stringent response metabolisms and the succession of blooms caused by dominant cyanobacterial species provide evidence that the stringent response, induced by nutrient limitation, may activate unique N and P functions in toxin-producing cyanobacteria, thereby sustaining cyanoHABs.

Study of the Antimicrobial Potential of the Arthrospira platensis, Planktothrix agardhii, Leptolyngbya cf. ectocarpi, Roholtiella mixta nov., Tetraselmis viridis, and Nanofrustulum shiloi against Gram-Positive, Gram-Negative Bacteria, and Mycobacteria.

The incidence of diseases brought on by resistant strains of micro-organisms, including tuberculosis, is rising globally as a result of the rapid rise in pathogenic micro-organism resistance to antimicrobial treatments. Secondary metabolites with potential for antibacterial activity are produced by cyanobacteria and microalgae. In this study, gram-positive (S. aureus, E. faecalis) and gram-negative (K. pneumoniae, A. baumannii, P. aeruginosa) bacteria were isolated from pulmonary tuberculosis patients receiving long-term antituberculosis therapy. The antimicrobial potential of extracts from the cyanobacteria Leptolyngbya cf. ectocarpi, Planktothrix agardhii, Arthrospira platensis, Rohotiella mixta sp. nov., Nanofrustulum shiloi, and Tetraselmis (Platymonas) viridis Rouchijajnen was evaluated. On mouse splenocytes and peritoneal macrophages, extracts of cyanobacteria and microalgae had inhibitory effects. In vitro studies have shown that cyanobacteria and microalgae extracts suppress the growth of bacteria and mycobacteria. At the same time, it has been demonstrated that cyanobacterial and microalgal extracts can encourage bacterial growth in a test tube. Additionally, the enhanced fucoxanthin fraction significantly reduced the development of bacteria in vitro. In a mouse experiment to simulate tuberculosis, the mycobacterial load in internal organs was considerably decreased by fucoxanthin. According to the information gathered, cyanobacteria and microalgae are potential sources of antibacterial compounds that can be used in the manufacturing of pharmaceutical raw materials.

Algal Blooms and their Importance in Xochimilco and San Gregorio Atlapulco, Mexico

Algal blooms refer to the massive development of photosynthetic microorganisms in aquatic environments. Microalgae are an important source of food for the primary consumers of these ecosystems, purify water, capture atmospheric CO2 and from them a large number of products for industrial use are obtained; however, in Mexico its study is still incipient, especially with regard to blooms of freshwater species. This paper presents the results obtained from the most abundant and important algal blooms of the Ejidos de Xochimilco and San Gregorio Atlapulco Protected Natural Area. 12 samplings were carried out between the years 2012 to 2022. The samples were collected with 54 μm mesh aperture trawl and van Dorn bottle and were fixed with 4% final formalin and 1% lugol, respectively. 17 algal blooms were recorded, among the Cyanoprokaryotes are: Anabaenopsis circularis, Limnospira maxima, Microcystis aeruginosa, Planktothrix agardhii; among the Chlorophytes Monoraphidium convolutum, Ankistrodesmus falcatus, Closterium acutum, Lemmermannia tetrapedia; among the Euglenophytes Euglena viridis y Phacus pleuronectes and between the Diatoms Cocconeis placentula var. placentula, Stephanocyclus meneghinianus, Epithemia turgida var. turgida, Gomphonema olivaceum, Gomphonema parvulum var. capitata, Hantzschia amphioxys y Craticula cuspidata. Of these species, Limnospira maxima has very high nutritional value, Anabaenopsis circularis, Microcystis aeruginosa y Planktothrix agardhii are potentially toxic or carcinogenic. It should be noted that all the registered species presented great spatiotemporal variations, for the above and given their great importance, it is necessary to expand their knowledge and carry out constant monitoring, as a tool for their understanding, use and management.

A microcystin synthesis mcyE/ndaF gene assay enables early detection of microcystin production in a tropical wastewater pond

Cyanobacteria can dominate the algal community in wastewater ponds, which can lead to the production of cyanotoxins and their release into the environment. We applied traditional and molecular techniques to identify cyanotoxin hazards and high-risk periods in a tropical wastewater treatment system. Potentially toxic cyanobacteria were identified by microscopy and amplicon sequencing over the course of a year. Toxin gene levels were monitored and compared to toxin production to identify likely toxin producing species and high-risk periods. Cyanobacteria were persistent in the effluent year-round, with Planktothrix and Microcystis the most abundant genera; Microcystis could not be resolved beyond genus using amplicon sequencing, but M. flos-aquae was identified as a dominant species by microscopy. Microcystin toxin was detected for the first time in treated effluent at the beginning of the wet season (December 2018), which correlated with an increase in Microcystis amplicon sequence abundance and elevated microcystin toxin gene (mcyE/ndaF) levels. Concomitantly, microscopy data showed an increase in M. flos-aquae but not M. aeruginosa. These data informed a refined sampling campaign in 2019 and results showed a strong correlation between mcyE/ndaF gene abundance, microcystin toxin levels and Microcystis amplicon sequence abundance. Microscopy data showed that in addition to M. flos-aquae, M. aeruginosa was also abundant in February and March 2019, with highest levels coinciding with toxin detection and toxin gene levels. M. aeruginosa was the most abundant Microcystis species detected in selected treated effluent samples by metagenomics analysis, and elevated levels coincided with toxin production. All microcystin genes in the biosynthesis pathway were detected, but microcystin genes from Planktothrix agardhii were not detected.Gene toxin assays were successfully used to predict microcystin production in this wastewater system. Changes in amplicon sequence relative abundance were a useful indicator of changes in the cyanobacterial community. We found that metagenomics was useful not just for identifying the most abundant Microcystis species, but the detection of microcystin biosynthesis genes helped confirm this genus as the most likely toxin producer in this system. We recommend toxin gene testing for the early detection of potential toxin producing cyanobacteria to manage the risk of toxicity and allow the implementation of risk management strategies.

Multi-year molecular quantification and 'omics analysis of Planktothrix-specific cyanophage sequences from Sandusky Bay, Lake Erie.

Planktothrix agardhii is a microcystin-producing cyanobacterium found in Sandusky Bay, a shallow and turbid embayment of Lake Erie. Previous work in other systems has indicated that cyanophages are an important natural control factor of harmful algal blooms. Currently, there are few cyanophages that are known to infect P. agardhii, with the best-known being PaV-LD, a tail-less cyanophage isolated from Lake Donghu, China. Presented here is a molecular characterization of Planktothrix specific cyanophages in Sandusky Bay. Putative Planktothrix-specific viral sequences from metagenomic data from the bay in 2013, 2018, and 2019 were identified by two approaches: homology to known phage PaV-LD, or through matching CRISPR spacer sequences with Planktothrix host genomes. Several contigs were identified as having viral signatures, either related to PaV-LD or potentially novel sequences. Transcriptomic data from 2015, 2018, and 2019 were also employed for the further identification of cyanophages, as well as gene expression of select viral sequences. Finally, viral quantification was tested using qPCR in 2015-2019 for PaV-LD like cyanophages to identify the relationship between presence and gene expression of these cyanophages. Notably, while PaV-LD like cyanophages were in high abundance over the course of multiple years (qPCR), transcriptomic analysis revealed only low levels of viral gene expression. This work aims to provide a broader understanding of Planktothrix cyanophage diversity with the goals of teasing apart the role of cyanophages in the control and regulation of harmful algal blooms and designing monitoring methodology for potential toxin-releasing lysis events.

Effects of water movement and temperature on Rhizophydium infection of Planktothrix in a shallow hypereutrophic lake.

Grand Lake St. Marys (GLSM) is a popular recreational lake located in western Ohio, United States, generating nearly $150 million in annual revenue. However, recurring algal blooms dominated by Planktothrix agardhii, which can produce harmful microcystin toxins, have raised concerns about water safety and negatively impacted the local economy. Planktothrix agardhii is host to a number of parasites and pathogens, including an obligate fungal parasite in the Chytridiomycota (chytrids). In this study, we investigated the potential of these chytrid (Rhizophydium sp.) to infect P. agardhii blooms in the environment by modifying certain environmental conditions thought to limit infection prevalence in the wild. With a focus on temperature and water mixing, mesocosms were designed to either increase or decrease water flow compared to the control (water outside the mesocosm). In the control and water circulation mesocosms, infections were found infrequently and were found on less than 0.75% of the Planktothrix population. On the other hand, by decreasing the water flow to stagnation, chytrid infections were more frequent (found in nearly 3x as many samples) and more prevalent, reaching a maximum infection rate of 4.12%. In addition, qPCR coupled with 16S-18S sequencing was utilized to confirm the genetic presence of both host and parasite, as well as to better understand the effect of water circulation on the community composition. Statistical analysis of the data confirmed that chytrid infection was dependent on water temperature, with infections predominantly occurring between 19°C and 23°C. Additionally, water turbulence can significantly reduce the infectivity of chytrids, as infections were mostly found in stagnant mesocosms. Further, decreasing the water circulation promoted the growth of the cyanobacterial population, while increasing water agitation promoted the growth of green algae (Chlorophyta). This study starts to explore the environmental factors that affect chytrid pathogenesis which can provide valuable insights into controlling measures to reduce the prevalence of harmful algal blooms and improve water quality in GLSM and similarly affected waterbodies.

Interactions between chytrids cause variable infection strategies on harmful algal bloom forming species

Cyanobacteria have a great diversity of natural enemies, such as herbivores and pathogens, including fungal pathogens within the Chytridiomycota (chytrids). While these pathogens have been previously described on a select number of cyanobacterial hosts and are suspected to play a significant ecological role, little is understood about species interactions and how competition between parasites can affect epidemic development and bloom formation. Here, three Planktothrix agardhii isolates from Sandusky Bay, Lake Erie (OH, USA) were challenged in monoculture and polyculture against infection by three isolates (C1, C2, C10) of their obligate chytrid fungal pathogen, Rhizophydiales sp. The chytrid isolates were inoculated as single isolates or a mixture of up to three different isolates. In monoculture, host isolates were characterized as highly susceptible (P. agardhii 1030), moderately susceptible (P. agardhii 1808) or mostly resistant (P. agardhii 1801). Co-infection of chytrid isolates on the highly susceptible host isolate had an additive effect on chytrid prevalence, leading to a culture crash where 2 or 3 chytrid isolates were present. Co-infection of chytrid isolates on the moderately susceptible and mostly resistant isolates had no effect on chytrid infection outcome or prevalence compared to infection with a single isolate. In polyculture, the effect on host growth was most significant in the single chytrid isolate treatment, which was attenuated with the addition of mixed chytrid treatments. Genetic analysis of the resulting population after the experimental period showed a tendency for the chytrid isolate C1 and P. agardhii 1801 to dominate in mixed population samples. Two different interspecific interactions seem to be in play; varied parasite infection strategies allow for the amplification of infection prevalence due to mixed chytrids in a susceptible monoculture, or competition allows for the dominance of a single chytrid isolate in monoculture and the reduction of infection prevalence in a host polyculture. This work thus highlights how interactions between chytrid infections can change the course of epidemic development and harmful algal bloom formation.

Artificial intelligence to explain the variables that favor the cyanobacteria steady-state in tropical ecosystems: A Bayeasian network approach.

The steady-state is a situation of little variability of species dominance and total biomass over time. Maintenance of cyanobacteria are often observed in tropical and eutrophic ecosystems and can cause imbalances in aquatic ecosystem. Bayeasian networks allow the construction of simpls models that summarizes a large amount of variables and can predict the probability of occurrence of a given event. Studies considering Bayeasian networks built from environmental data to predict the occurrence of steady-state in aquatic ecosystems are scarce. This study aims to propose a Bayeasian network model to assess the occurrence, composition and duration of cyanobacteria steady-state in a tropical and eutrophic ecosystem. It was hypothesized long lasting steady-state events, composed by filamentous cyanobacteria species and directly influenced by eutrophication and drought. Our model showed steady-state lasting between 3 and 17 weeks with the monodominance or co-dominance of filamentous species, mainly Raphidiopsis raciborskii and Planktothrix agardhii. These evens occurred frequently under drought and high turbidity, however higher nutrients concentrations did not increase the probability steady-state occurrence or longer duration. The proposed model appears as a tool to assess the effects of future warming on steady-state occurrence and it can be a useful to more traditional process-based models for reservoirs.

Broad screening of toxic and bioactive metabolites in cyanobacterial and harmful algal blooms in Lake of the Woods (Canada and USA), 2016–2019

Cyanobacteria produce toxic/bioactive metabolites that affect human and ecosystem health via inhibition of proteases, carboxypeptidases, or phosphatases. From surface water samples collected between 2016 and 2019 inclusive (n = 78), we report intracellular concentrations of more than 30 such compounds in Lake of the Woods (LOW), a large lake system of multinational importance. Although most surface biomass blooms were dominated by the cyanobacteria Dolichospermum (max. ∼50 mg/L) and Aphanizomenon (max. ∼60 mg/L), there was also significant biomass of other cyanobacteria (Gloeotrichia echinulate along shoreline, max. ∼40,000 mg/L; Woronichinia naegeliana max. ∼100 mg/L; Lyngbya max. ∼10 mg/L; Planktothrix agardhii max. ∼6 mg/L) and phytoplankton (Stephanodiscus niagarae max. ∼6 mg/L). Microcystins (MCs) were present in ∼80 % of samples, peaking at ∼33 µg/L (MC variant-LR). Approximately 50 % of samples contained MC concentrations below 0.1 µg/L. Alkaloid metabolites detected included neurotoxin anatoxin-a (∼60 % < 0.1 µg/L) and cytotoxic cylindrospermopsins (∼30 % < 0.1 µg/L). Anabaenopeptins A/B/F were prevalent (>96 %) and exceeded MCs by >100 fold (max. >4,000 µg/L). Aeruginosamide B was present in ∼75 % of samples (max. ∼10 µg/L). Cyanopeptolin 1040 MB, microginin 690 methyl ester, and oscillaginin A were not detected however, traces of micropeptin 1106 were detected. Microcystin and anabaenopeptin genes were also detected in the majority of samples (78 % and 79 %, respectively), while saxitoxin, cylindrospermopsin, and anatoxin genes occurred at lower frequencies with 59 %, 36 %, and 38 % detection, respectively. These results will aid assessment of risk from cyanobacterial blooms in LOW and inform ongoing binational lake management and policy development.

Genetic Diversity of Microcystin Producers (Cyanobacteria) and Microcystin Congeners in Aquatic Resources across Africa: A Review Paper.

Microcystins are produced by multifaceted organisms called cyanobacteria, which are integral to Africa's freshwater environments. The excessive proliferation of cyanobacteria caused by rising temperature and eutrophication leads to the production and release of copious amounts of microcystins, requiring critical management and control approaches to prevent the adverse environmental and public health problems associated with these bioactive metabolites. Despite hypotheses reported to explain the phylogeography and mechanisms responsible for cyanobacterial blooms in aquatic water bodies, many aspects are scarcely understood in Africa due to the paucity of investigations and lack of uniformity of experimental methods. Due to a lack of information and large-scale studies, cyanobacteria occurrence and genetic diversity are seldom reported in African aquatic ecosystems. This review covers the diversity and geographical distribution of potential microcystin-producing and non-microcystin-producing cyanobacterial taxa in Africa. Molecular analyses using housekeeping genes (e.g., 16S rRNA, ITS, rpoC1, etc.) revealed significant sequence divergence across several cyanobacterial strains from East, North, West, and South Africa, but the lack of uniformity in molecular markers employed made continent-wise phylogenetic comparisons impossible. Planktothrix agardhii, Microcystis aeruginosa, and Cylindrospermopsis raciborskii (presently known as Raphidiopsis raciborskii) were the most commonly reported genera. Potential microcystin (MCs)-producing cyanobacteria were detected using mcy genes, and several microcystin congeners were recorded. Studying cyanobacteria species from the African continent is urgent to effectively safeguard public and environmental health because more than 80% of the continent has no data on these important microorganisms and their bioactive secondary metabolites.

Characterizing a subtropical hypereutrophic lake: From physicochemical variables to shotgun metagenomic data.

Lake Cajititlán is a subtropical and endorheic lake, which is heavily impacted by nutrient pollution. Agricultural runoff and poorly treated wastewater have entered this reservoir at alarming rates during past rainy seasons, causing the cultural eutrophication of this body of water and resulting in several massive fish kill events. In this study, shotgun metagenomic sequencing was used to examine the taxonomic and functional structure of microbial communities in Lake Cajititlán during the rainy season. Several water quality features and their interactions with microbial communities were also assessed to identify the major factors affecting the water quality and biota, specifically fish species. According to current water quality regulations, most of the physicochemical variables analyzed (dissolved oxygen, pH, Secchi disk, NH4 +, NO3 -, blue-green algae, total phosphorus, and chlorophyll-a) were outside of the permissible limits. Planktothrix agardhii and Microcystis aeruginosa were the most abundant phytoplankton species, and the dominant bacterial genera were Pseudomonas, Streptomyces, and Flavobacterium, with Pseudomonas fluorescens, Stenotrophomonas maltophilia, and Aeromonas veronii representing the most abundant bacterial species. All of these microorganisms have been reported to be potentially harmful to fish, and the latter three (P. fluorescens, S. maltophilia, A. veronii) also contain genes associated with pathogenicity in fish mortality (fur, luxS, aer, act, aha, exu, lip, ser). Genetic evidence from the microbial communities analyzed herein reveals that anthropogenic sources of nutrients in the lake altered genes involved in nitrogen, phosphorus, sulfur, and carbon metabolism, mainly at the beginning of the rainy season. These findings suggest that abiotic factors influence the structure of the microbial communities, along with the major biogeochemical cycles of Lake Cajititlán, resulting in temporal variations and an excess of microorganisms that can thrive in high-nutrient and low-oxygen environments. After reviewing the literature, this appears to be the first study that focuses on characterizing the water quality of a subtropical hypereutrophic lake through associations between physicochemical variables and shotgun metagenomic data. In addition, there are few studies that have coupled the metabolism of aquatic ecosystems with nutrient cycles.

Cyanobacteria and Their Metabolites in Mono- and Polidominant Shallow Eutrophic Temperate Lakes.

Monodominant (one species dominates) or polidominant (multiple species dominate) cyanobacterial blooms are pronounced in productive freshwater ecosystems and pose a potential threat to the biota due to the synthesis of toxins. Seasonal changes in cyanobacteria species and cyanometabolites composition were studied in two shallow temperate eutrophic lakes. Data on cyanobacteria biomass and diversity of dominant species in the lakes were combined with chemical and molecular analyses of fifteen potentially toxin-producing cyanobacteria species (248 isolates from the lakes). Anatoxin-a, saxitoxin, microcystins and other non-ribosomal peptides formed the diverse profiles in monodominant (Planktothrix agardhii) and polidominant (Aphanizomenon gracile, Limnothrix spp. and Planktolyngbya limnetica) lakes. However, the harmfulness of the blooms depended on the ability of the dominant species to synthesize cyanometabolites. It was confirmed that P. agardhii produced a greater amount and diverse range of MCs and other NRPs. In the polidominant lake, isolates of the co-dominant A. gracile, L. planctonica and P. limnetica synthesized no or only small amounts of cyanometabolites. In general, the profile of cyanometabolites was greater in cyanobacteria isolates than in environmental samples, indicating a high potential for toxic cyanobacteria bloom.