Cylindrospermopsis Raciborskii Research Articles

Removal of algae from ballast water by cationic flocculant-composite titanium xerogel coagulant: Differences in freshwater and seawater

The treatment of ballast water has been garnering increasing attention, with planktonic algae removal being a crucial part. Coagulation has been demonstrated as an effective method for algae removal, albeit few coagulants exhibit excellent coagulation performance in both freshwater and seawater. To address this issue, the cationic flocculant poly dimethyl diallyl ammonium chloride (PDADMAC) was composited with titanium xerogel coagulant (TXC), abbreviated as PT. Using the algae Cyclotella meneghiniana as the research object, the algal removal performance and mechanisms of PT in freshwater and seawater were investigated. Cell integrity, superoxide dismutase (SOD) activity, and malondialdehyde (MDA) content of C. meneghiniana during floc storage were also evaluated. The PT composite coagulant exhibited excellent coagulation performance in both freshwater and seawater. Its algal removal ability was superior to TXC and the commercial coagulants polyaluminum chloride (PAC) and polymerized ferrous sulfate (PFS), with removal rates for C. meneghiniana reaching 98.3 % in freshwater and 98.4 % in seawater at a 80 mg/L dosage. PT also exhibited excellent removal performance over wide dosage and pH ranges. PT acted via distinct coagulation mechanisms in freshwater and seawater, with charge neutralization and bridging played major roles in freshwater and sweeping being important in seawater. The floc storage experiment indicated that the coagulation process did not directly lead to algal cell fragmentation, but PT accelerated and exacerbated oxidative stress and oxidative damage to algal cells during floc storage. Furthermore, PT also showed excellent removal performance for the marine diatom Skeletonema costatum and the freshwater cyanobacteria Cylindrospermopsis raciborskii. This work not only provides a novel approach for algae removal in ballast water, but also enhances our understanding of the coagulation behavior of titanium-based coagulants in different water environments.

Tradeoffs between phage resistance and nitrogen fixation drive the evolution of genes essential for cyanobacterial heterocyst functionality.

Harmful blooms caused by diazotrophic (nitrogen-fixing) Cyanobacteria are becoming increasingly frequent and negatively impact aquatic environments worldwide. Cyanophages (viruses infecting Cyanobacteria) can potentially regulate cyanobacterial blooms, yet Cyanobacteria can rapidly acquire mutations that provide protection against phage infection. Here, we provide novel insights into cyanophage:Cyanobacteria interactions by characterizing the resistance to phages in two species of diazotrophic Cyanobacteria: Nostoc sp. and Cylindrospermopsis raciborskii. Our results demonstrate that phage resistance is associated with a fitness tradeoff by which resistant Cyanobacteria have reduced ability to fix nitrogen and/or to survive nitrogen starvation. Furthermore, we use whole-genome sequence analysis of 58 Nostoc-resistant strains to identify several mutations associated with phage resistance, including in cell surface-related genes and regulatory genes involved in the development and function of heterocysts (cells specialized in nitrogen fixation). Finally, we employ phylogenetic analyses to show that most of these resistance genes are accessory genes whose evolution is impacted by lateral gene transfer events. Together, these results further our understanding of the interplay between diazotrophic Cyanobacteria and their phages and suggest that a tradeoff between phage resistance and nitrogen fixation affects the evolution of cell surface-related genes and of genes involved in heterocyst differentiation and nitrogen fixation.

WATER QUALITY AND PHYTO-ZOOPLANKTONIC BIOINDICTORS IN THE COCÓ RIVER ESTUARY, FORTALEZA/CE

With the aim of analyzing water quality and verify the presence of phyto-zooplanktonic bioindicators in the Cocó River estuary, monthly plankton collections were carried out between April/22 and April/23. In situ the parameters of water temperature and transparency, salinity, pH, dissolved oxygen (DO), and phosphate and ammonia contents were obtained. The phyto-zooplankton was collected with a specific net and, in the laboratory, analyzed using a trinocular microscope with an attached camera. The presence of Escherichia coli was also verified. The results showed water with transparency characteristic of mesotrophic water, while the phosphate and ammonia contents were similar to those of eutrophic waters. 13 phytoplankton species were identified, distributed in the Cyanophyceae, Bacillariophyceae and Chlorophyceae Classes. As bioindicator species of eutrophicated waters were identified: Cylindrospermopsis raciborskii, Nitzschia sp., Chroococcus sp., Oscillatoria spp. and Ulothrix sp. Species diversity and richness were low, with significant evenness. As for the zooplankton, 18 species were identified, distributed in the Classes Eurotatoria, Copepoda, Branchiopoda, Tubulinea and Ostracoda. As bioindicator species: Brachionus calyciflorus, Filinia longiseta, Moina sp., Hexarthra sp. and Polyarthra sp. Diversity was medium, richness was low and evenness was significant. Microbiological analyzes showed the presence of E. coli. Overall, the waters of the Cocó River estuary were classified as Class 3 brackish and eutrophic.

Bacillus cereus strain L7 lyses Cylindrospermopsis raciborskii through intercellular contact

Cylindrospermopsis raciborskii is a new type of toxic filamentous cyanobacteria commonly found in tropical regions but has recently spread to temperate areas. It is considered an invasive species that poses a serious threat to drinking water sources and human health. Bacillus cereus strain L7, previously isolated and identified by our group, was found to have efficient algicidal activity against C. raciborskii FACHB-1503 in this study. The growth period and initial concentration of L7 had a significant impact on algicidal activity, with L7 culture in the decline phase exhibiting the highest algicidal activity (I = 99.62 %). The ideal environmental conditions for the coculture system were 30 °C, pH = 8, and a light-dark cycle (12 h light: 12 h dark). In experiments to confirm the algicidal mode of L7, the pellet resuspension with R2A medium had the highest algicidal efficiency (I = 98.54 %, t = 6 d), even higher than that of the L7 culture. In contrast, sterile filtrate and pellet resuspension with sterile water had no discernible impact on the algal growth, indicating that L7 performed algicidal activity through direct contact with algal cells. Following 6 days of coculture of L7 culture with C. raciborskii solution, the activity of the PSII system and the photosynthetic efficiency of algal cells were both zero. Following SEM and TEM results, it was discovered that the process of L7 lysis of algal cells begins with the disruption of their multicellular filamentous structure, rupture of the cell wall, efflux of the cell contents, and complete disappearance of the algal cell structure. This is the first research to demonstrate that L7 lyses C. raciborskii directly, which serves as an excellent strategic direction for launching innovative freshwater bloom control strategies.

Relating algal-derived extracellular and intracellular dissolved organic nitrogen with nitrogenous disinfection by-product formation

The dissolved organic nitrogen (DON) pool from algal-derived extracellular and intracellular organic matter (EOM and IOM) comprises proteins, peptides, free amino acids and carbohydrates, of which, proteins can contribute up to 100% of the DON. Previous reports of algal-derived DON character have focused on bulk properties including concentration, molecular weight and hydrophobicity. However, these can be similar between algal species and between the EOM and IOM even when the inherent molecular structures vary. A focus on bulk character presents challenges to the research on algal-derived nitrogenous-disinfection by-product (N-DBP) formation as N-DBP formation is sensitive to the changes in molecular structure. Hence, the main aim of this study was to characterize algal EOM and IOM-derived DON, specifically proteinaceous-DON, using a combination of bulk and molecular characterization techniques to enable a more detailed exploration of the relationship between the character of algal-derived proteins and the N-DBP formation potential. DON from the EOM and IOM of four commonly found algae and cyanobacteria in natural waters were evaluated, namely Chlorella vulgaris, Microcystis aeruginosa, Dolichospermum circinale, and Cylindrospermopsis raciborskii. It was observed that 77-96% of total DON in all EOM and IOM samples was of proteinaceous origin. In the proteins, DON concentrations were highest in the high molecular weight fraction of IOM-derived bulk proteins (0.13–0.75 mg N L−1) and low to medium molecular weight fraction of EOM-derived bulk proteins (0.15–0.63 mg N L−1) in all species. Similar observations were also made via sodium dodecyl sulphate polyacrylamide gel electrophoresis and liquid chromatography-high resolution mass spectrometry. Solid-state 15N nuclear magnetic resonance (NMR) spectroscopy of the EOM and IOM revealed the existence of common aliphatic and heterocyclic N-groups in all samples, including a dominant 2° amide peak. Species dependent variability was also observed in the spectra, particularly in the EOM; e.g. nitro signals were found only in the Cylindrospermopsis raciborskii EOM. Dichloroacetonitrile (DCAN) and N-nitrosamine concentrations from the EOM of the species evaluated in this study were lower than the guideline limits set by regulatory agencies. It is proposed that the dominant 2° amide in all samples decreased N-DBP formation upon chlorination. For chloramination, the presence of nitro groups and aliphatic and heterocyclic N-DBP precursors could cause variable N-nitrosamine formation. Compared to non-algal impacted waters, algae-laden waters are characterised by low organic carbon: organic nitrogen ratios of ∼7–14 and elevated DON and protein concentrations. Hence, relying only on bulk characterization increases the perceived risk of N-DBP formation from algae-laden waters.

Enhanced photocatalytic inactivation of Cylindrospermopsis raciborskii by modified TiO2/Ag3PO4: Efficiency and mechanism

To effectively inhibit the emerging harmful algae Cylindrospermopsis raciborskii, modified TiO2/Ag3PO4 (T-P25/A) with oxygen vacancies was successfully synthesized by tea polyphenol (TP) reduction and chemical deposition methods for algae removal under visible light. The creation of oxygen vacancies affected the band structure of P25 and improved the photocatalytic performance of the T-P25/A composite. The photogenerated holes (h+) and superoxide radicals (·O2–) are dominant reactive species in the photocatalytic system of T-P25/A, which yielded a 91.75 % inactivation rate to Cylindrospermopsis raciborskii (cyanobacteria cells) after 5 h of visible light irradiation. This degradation rate was about 1.5 and 1.7 times that of P25/A and Ag3PO4, respectively. Furthermore, the algal inactivation mechanism by T-P25/A under visible light was indicated by changes in morphological characteristics, cellular content degradation, oxidative species accumulation, and enzyme activity. This research provides valuable information about applicational prospects for the inactivation of harmful algal cells in real water bodies.

Identification of Cyanobacteria and Its Potential Toxins in the Joanes I Reservoir, Bahia, Brazil

The Joanes I Reservoir is responsible for 40% of the drinking water supply of the Metropolitan Region of Salvador, Bahia, Brazil. For water sources such as this, there is concern regarding the proliferation of potentially toxin-producing cyanobacteria, which can cause environmental and public health impacts. To evaluate the presence of cyanobacteria and their cyanotoxins in the water of this reservoir, the cyanobacteria were identified by microscopy; the presence of the genes of the cyanotoxin-producing cyanobacteria was detected by molecular methods (polymerase chain reaction (PCR)/sequencing); and the presence of toxins was determined by liquid chromatography with tandem mass spectrometry (LC-MS/MS). The water samples were collected at four sampling points in the Joanes I Reservoir in a monitoring campaign conducted during the occurrence of phytoplankton blooms, and the water quality parameters were also analysed. Ten cyanobacteria species/genera were identified at the monitoring sites, including five potentially cyanotoxin-producing species, such as Cylindrospermopsis raciborskii, Cylindrospermopsis cf. acuminato-crispa, Aphanocapsa sp., Phormidium sp., and Pseudanabaena sp. A positive result for the presence of the cylindrospermopsin toxin was confirmed at two sampling points by LC-MS/MS, which indicated that the populations are actively producing toxins. The analysis of the PCR products using the HEPF/HEPR primer pair for the detection of the microcystin biosynthesis gene mcyE was positive for the analysed samples. The results of this study point to the worrisome condition of this reservoir, from which water is collected for public supply, and indicate the importance of the joint use of different methods for the analysis of cyanobacteria and their toxins in reservoir monitoring.

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.

Succession Pattern and Consequences of the Dominant Species During Cyanobacterial Bloom and Its Influencing Factors

The succession of dominant species always occurs during cyanobacterial blooms because there are certain conditions for cyanobacterial blooms formed by different cyanobacteria; this results in more uncertain and complex effects in cyanobacterial blooms. However, the succession pattern and consequences of dominant species and its driving factors have not received enough attention during cyanobacteria blooms. In this study, the phytoplankton community characteristics and water environment factors of Nanpeng Reservoir, a drinking water source in Chongqing, were monitored and analyzed from April to September 2018. The results showed that:① a total of 108 species of phytoplankton belonging to 59 genera and 8 phyla were identified in Nanpeng Reservoir. Of this, 13 species of 4 phyla were identified as dominant species, among which the dominance index of Cylindrospermopsis raciborskii was the highest, followed by that of Pseudoanabaena sp. ② The most dominant cyanobacteria were Pseudoanabaena and Cylindrospermopsis in May and July, respectively, in which cyanobacteria density peaked, whereas the Shannon-Weiner diversity and Pielou evenness were significantly lower than those in the other months. ③ NMDS results showed that the correlation between Cylindrospermopsis or Pseudoanabaena and the ambient phytoplankton community was 0.58 and 0.48, respectively. Moreover, the VPA results showed that 47.51% of the community variation could be explained by environmental factors, and only 12.04% and 12.74% of variation in community composition could be explained by Cylindrospermopsis and Pseudoanabaena, respectively. ④ The abundance of Cylindrospermopsis was significantly positively affected by WT, pH, and RUEN and negatively affected by SD and RUEP. However, the abundance of Pseudoanabaena was significantly positively affected by permanganate index and negatively affected by EC and DO. These results suggested that both dominating cyanobacteria had significant effects on the surrounding phytoplankton community. Relative to that of Pseudoanabaena, however, Cylindrospermopsis had a more obvious impact on the aquatic ecosystem. Moreover, the synergistic effect of N limitation and warming of the water column may have caused the replacement of Pseudoanabaena with Cylindrospermopsis to form a dominant population.

Bioremoval of Cylindrospermopsis raciborskii cells and cylindrospermopsin toxin in batch culture by the yeast Aureobasidium pullulans.

This study describes the ability of a yeast strain, Aureobasidium pullulans KKUY0701 isolated from eutrophic lake to eliminate Cylindrospermopsis raciborskii and cylindrospermopsin (CYN) toxin. The anti-cyanobacterial activity of this yeast strain was evaluated by growing with living cells and filtrate of C. raciborskii. CYN bioremoval was assayed using living and heat-inactivated yeast cells. Both living cells and filtrate of this yeast strain were able to suppress the growth of C. raciborskii, with total cell death occurring at day 2 and day 3, respectively. Living and inactivated yeast cells, but not yeast filtrate, reduced CYN concentrations released into cyanobacterial cultures, indicating that this toxin might be removed from the culture medium via absorption onto yeast surface rather than enzymatic biodegradation. The adsorption experiments also confirmed the elimination of CYN by living and heat-inactivated yeast. Nevertheless, inactivated yeast exhibited higher capacity (K = 3.3) and intensity (n = 1.4) than living yeast (K = 1.9, n = 1) for CYN adsorption. The study suggests that this yeast strain could be employed for bioremediation of Cylindrospermopsis blooms in freshwaters. Additionally, heat-inactivated yeast biomass could be used in slow sand filters for elimination of CYN in drinking water treatment plants.

Invasive and toxic cyanobacteria regulate allochthonous resource use and community niche width of reservoir zooplankton

Abstract Cyanobacterial dominance or blooms can influence ecosystem structure in reservoirs, yet there are only few studies of its effect on the resource use and trophic structure of zooplankton. We hypothesised that zooplankton traits would exhibit a strong response to the increase of invasive and toxic cyanobacteria. We investigated the effect of an invasive bloom‐forming cyanobacterium Raphidiopsis raciborskii (formerly Cylindrospermopsis raciborskii) on zooplankton functional traits (e.g., growth, reproduction, allochthonous resource use and realised niche) through laboratory experiments and 3‐year field investigations in two subtropical reservoirs. The realised niche (i.e., resource and habitat use) was quantified using stable isotopes (termed isotopic niches). We fed the cladoceran zooplankton Moina sp. with Scenedesmus obliquus (chlorophyte), R. raciborskii, and a mixture of S. obliquus and R. raciborskii in laboratory experiments. A diet of R. raciborskii alone depressed the growth and reproduction of Moina sp. compared to a diet of S. obliquus alone, but a mixture of S. obliquus and R. raciborskii greatly alleviated the inhibition effects caused by cyanobacteria. Under natural field conditions, we did not find a strong inhibition effect of R. raciborskii dominance on the zooplankton, but a high biomass of R. raciborskii was associated with an increase (17%) in the relative allochthonous resource (terrestrially derived organic matter) use by cladocerans (but not for copepods), even though the chlorophyll‐a concentration increased from 17 μg/L in the non‐bloom period to 28 μg/L during periods of R. raciborskii dominance or blooms. Furthermore, a high biomass of R. raciborskii increased the contribution of inter‐taxa variation (taxa sorting) to the expanded isotopic niches of the zooplankton community. Our study helps to clarify cyanobacteria‐zooplankton interactions and highlights the importance of cyanobacterial dominance or blooms in regulating cross‐ecosystem resource use and biogeochemical cycling mediated by zooplankton in aquatic ecosystems.

Spatial and temporal variations of phytoplankton composition and biomass in Lake Bunyonyi, South-Western Uganda.

The purpose of this study was to examine the spatial and temporal variations of phytoplankton species composition and biomass in Lake Bunyonyi, South-Western Uganda. Samples were collected monthly from nine fixed stations in the lake from October 2019 to September 2020. Based on the morphological characterization, 52 different species of phytoplankton were recorded. These were dominated by cyanobacteria (21 species) and chlorophytes (15 species) followed by diatoms (10 species), euglenophytes (4 species), dinoflagellates (2 species), and cryptophytes (1 species). The biomass (Chl-a concentration) ranged from 0.019 ± 0.009mg/L at Heissesero station to 0.045 ± 0.013mg/L obtained at Nyombe station. On a temporal basis, the highest mean Chl-a concentration of 0.044 ± 0.03mg/L was recorded in March 2020while the least concentration of 0.015 ± 0.011mg/L was obtained in September 2020. Significant differences existed in the Chl-a concentration values between stations and across sampling months. Chl-a concentration was significantly positively correlated with dissolved oxygen (DO), turbidity but negatively correlated with temperature. The Shannon-Wiener index and evenness put it clear that the distribution of phytoplankton species in the lake is inequitable. Besides, 94.2% of the phytoplankton species revealed had never been reported by the previous studies in the study area. The dominance of species cyanobacteria (such as Microcystis spp., Cylindrospermopsis raciborskii, Anabaenopsis sp., and Anabaena sp.) presents potential future challenges to water quality management. Therefore, the establishment of a strong and committed committee dubbed "Lake Bunyonyi Water Management Committee" to oversee the activities and avert potential water quality challenges is strongly recommended. The existence of some toxic phytoplankton species calls for regular monitoring and careful use of the lake and its food products.

Isolation and characterization of a novel Lambda-like phage infecting the bloom-forming cyanobacteria Cylindrospermopsis raciborskii.

Summary Cylindrospermopsis raciborskii is a central bloom‐forming cyanobacteria. However, despite its ecological significance, little is known of its interactions with the phages that infect it. Currently, only a single sequenced genome of a Cylindrospermopsis‐infecting phage is publicly available. Here we describe the isolation and characterization of Cr‐LKS3, a second phage infecting Cylindrospermopsis. Cr‐LKS3 is a siphovirus with a higher genome similarity to prophages within heterotrophic bacteria genomes than to any other cyanophage/cyano‐prophage, suggesting that it represents a novel cyanophage group. The function, order and orientation of the 72 genes in the Cr‐LKS3 genome are highly similar to those of Escherichia virus Lambda (hereafter Lambda), despite the very low sequence similarity between these phages, showing high evolutionary convergence despite the substantial difference in host characteristics. Similarly to Lambda, the genome of Cr‐LKS3 contains various genes that are known to be central to lysogeny, suggesting it can enter a lysogenic cycle. Cr‐LKS3 has a unique ability to infect a host with a dramatically different GC content, without carrying any tRNA genes to compensate for this difference. This ability, together with its potential lysogenic lifestyle shed light on the complex interactions between C. raciborskii and its phages.

Biochemical Mapping of Pyrodinium bahamense Unveils Molecular Underpinnings behind Organismal Processes.

Proteins, lipids, and carbohydrates from the harmful algal bloom (HAB)-causing organism Pyrodinium bahamense were characterized to obtain insights into the biochemical processes in this environmentally relevant dinoflagellate. Shotgun proteomics using label-free quantitation followed by proteome mapping using the P. bahamense transcriptome and translated protein databases of Marinovum algicola, Alexandrium sp., Cylindrospermopsis raciborskii, and Symbiodinium kawagutii for annotation enabled the characterization of the proteins in P. bahamense. The highest number of annotated hits were obtained from M. algicola and highlighted the contribution of microorganisms associated with P. bahamense. Proteins involved in dimethylsulfoniopropionate (DMSP) degradation such as propionyl CoA synthethase and acryloyl-CoA reductase were identified, suggesting the DMSP cleavage pathway as the preferred route in this dinoflagellate. Most of the annotated proteins were involved in amino acid biosynthesis and carbohydrate degradation and metabolism, indicating the active roles of these molecules in the vegetative stage of P. bahamense. This characterization provides baseline information on the cellular machinery and the molecular basis of the ecophysiology of P. bahamense.

Tunisian inland water microflora as a source of phycobiliproteins and biological activity with beneficial effects on human health

Abstract Ten monoclonal microalgal cultures were obtained from several Tunisian inland water bodies, and their dichloromethane and methanolic extracts were screened for antibacterial, antileishmanial, and antioxidant properties, as well as phycobiliprotein production capacity. Cylindrospermopsis raciborskii has been shown to synthesize high levels of phycocyanin and may be an effective alternative source to other sources used for commercial production of phycocyanin. Chroococcus sp. and Leptolyngbya sp1. exhibited the strongest radical scavenging activity against DPPH (IC50 = 212.15 and 263.91 μg ml−1, respectively), indicating their promising potential for use as new effective and non-toxic antioxidants. Furthermore, Dunaliella sp. showed an interesting antileishmanial activity against the pathogens Leishmania infantum and Leishmania major (IC50 = 151 and 284 μg ml−1, respectively), thus representing a good candidate for use against cutaneous and visceral leishmaniasis in Tunisia, a country endemic to these diseases where thousands of new cases are registered every year. These results suggest that the strains of microalgae featured in this work have the potential to serve as natural alternative, safe and sustainable sources of high value-added products that could be used to improve the final biomass value.

Nutrient Regulation of Relative Dominance of Cylindrospermopsin-Producing and Non-cylindrospermopsin-Producing Raphidiopsis raciborskii.

Raphidiopsis raciborskii (previously Cylindrospermopsis raciborskii) can produce cylindrospermopsin (CYN) which is of great concern due to its considerable toxicity to human and animals. Its CYN-producing (toxic) and non-CYN-producing (non-toxic) strains co-exist commonly in natural water bodies, while how their relative dominance is regulated has not been addressed. In this study, we combined field investigation with laboratory experiments to assessed the relationship between toxic and non-toxic R. raciborskii abundances under different nutrient levels. The rpoC1- and cyrJ-based qPCR was applied for quantifying total and toxic R. raciborskii abundances, respectively. The field survey showed that toxic R. raciborskii was detected in 97 of 115 reservoirs where its proportion ranged from 0.3% to 39.7% within the R. raciborskii population. Both total and toxic R. raciborskii abundances increased significantly with trophic level of these reservoirs, consistent with our monoculture and co-culture experiments showing in an increase in R. raciborskii growth with increasing nitrogen (N) or phosphorus (P) concentrations. In the monoculture experiments, growth rates of non-toxic and toxic strains from Australia or China were not significantly different under the same culture conditions. On the other hand, in the co-culture experiments, the toxic strains displayed a significantly faster growth than non-toxic strains under nutrient-replete conditions, resulting in an obvious shift toward the dominance by toxic strains from day 3 to the end of the experiments, regardless of the strain originating from Australia or China. The reverse was found under N- or P-limited conditions. Our results indicated that the toxic strains of R. raciborskii have a competitive advantage relative to the non-toxic strains in a more eutrophic world. In parallel to an increase in dominance, both toxic strains grown in the mixed population significantly increased CYN production under nutrient-replete conditions as compared to nutrient-limited conditions, suggesting that CYN may be of significance for ecological advantage of toxic R. raciborskii. These results highlight the importance of nutrient availability in regulating abundances and strain dominance of two genotypes of R. raciborskii. Our findings demonstrated that elevated nutrients would favor the growth of CYN-producing R. raciborskii and CYN production, leading to more blooms with higher toxicity at global scale.

Precision early detection of invasive and toxic cyanobacteria: A case study of Raphidiopsis raciborskii

Blooms of the toxic cyanobacterium, Raphidiopsis raciborskii (basionym Cylindrospermopsis raciborskii), are becoming a major environmental issue in freshwater ecosystems globally. Our precision prevention and early detection of R. raciborskii blooms rely upon the accuracy and speed of the monitoring method. A duplex digital PCR (dPCR) monitoring approach was developed and validated to detect the abundance and toxin-producing potential of R. raciborskii simultaneously in both laboratory spiked and environmental samples. Results of dPCR were strongly correlated with traditional real time quantitative PCR (qPCR) and microscopy for both laboratory and environmental samples. However, discrepancies between methods were observed when measuring R. raciborskii at low abundance (1 − 105 cells L − 1), with dPCR showing a higher precision compared to qPCR at low cell concentration. Furthermore, the dPCR assay had the highest detection rate for over two hundred environmental samples especially under low abundance conditions, followed by microscopy and qPCR. dPCR assay had the advantages of simple operation, time-saving, high sensitivity and excellent reproducibility. Therefore, dPCR would be a fast and precise monitoring method for the early warning of toxic bloom-forming cyanobacterial species and assessment of water quality risks, which can improve prediction and prevention of the impacts of harmful cyanobacterial bloom events in inland waters.

Harvesting of different microalgae through 100-μm-pore-sized screen filtration assisted by cationic polyacrylamide and specific extracellular organic matter

Cationic polyacrylamide (CPAM) can induce efficient harvest of microalgae at low dosages (0.5–2 mg/L), and the large flocs that form as a result are beneficial for later screen filtration. However, flocculation is dependent on the microalgae species, especially their extracellular organic matter (EOM). In this study, harvesting of microalgae with CPAM flocculation and screen filtration (100-μm pore size) was compared, using four cyanobacteria species (Microcystis aeruginosa, M. wesenbergii, Cylindrospermopsis raciborskii, and Phormidium ambiguum) and three green algae species (Chlorella vulgaris, Scenedesmus quadricauda, and Pediastrum duple). The influence of EOM concentration and characteristics (i.e. charge density and molecular weight) was of particular focus in this study. All cyanobacteria were effectively flocculated with 1–2 mg/L CPAM, though the retention of C. raciborskii (78%) was significantly lower than the others (>90%). For green algae, only Ch. vulgaris could be effectively flocculated with retention > 90%, but a higher CPAM dosage (4 mg/L) was required. When mixed with EOM of other microalgae, the retention of S. quadridcauda and P. duple increased to > 78%. Successful retention was highly correlated with high molecular weight (MW) and negative charge density of the EOM. The > 100 kDa EOM fractions were responsible for effective retention of cyanobacteria and 30–100 kDa EOM fractions for Ch. vulgaris, while these fractions were rarely present in the EOM of S. quadricauda and P. duple. Though effective for cyanobacteria, the application of CPAM flocculation and screen filtration for harvesting some green algae is limited due to a lack of high-MW and negatively charged EOM components.

Competitive exclusion of toxic cyanobacterial species by an allelopathic strain of Phormidium

Blooms of freshwater toxic cyanobacteria are a growing environmental health problem, enhanced by anthropogenic eutrophication and climate change. A variety of techniques were tested for their remediation, from physical methods using artificial mixing or flocculation, to chemical methods employing synthetic and natural compounds, as well as constructed wetlands. In this work, we conducted an evaluation at microcosm scale of the usefulness of the allelochemicals produced by a strain of the filamentous cyanobacteria Phormidium sp. for the bioremediation of proliferations of four strains of toxic freshwater cyanobacteria (Cylindrospermopsis raciborskii, Chrysosporum ovalisporum, Anabaena sp. and Nodularia sp.). Allelochemicals produced by this strain of Phormidium sp. belong to the portoamides compounds family. Their effect was tested in bioassays using cell-free filtrate, the results showing that all the four strains were sensitive. In addition, we performed phosphate-limited long-term competition experiments in continuous cultures, in which Phormidium sp. was co-cultured with each of the toxic cyanobacterial strains. The purpose of these later experiments was to demonstrate that allelopathy and not resource competition was responsible for the ecological exclusion of the toxic cyanobacteria strains, and also to employ higher population abundances to test the effectiveness of the allelochemicals. Before that, we needed to estimate the competitive ability of each species to limit the resource that we employed (phosphate). Phormidium sp. were clearly a better competitor for phosphate than Anabaena sp., worse than Nodularia sp., and very similar to C. raciborskii and C. ovalisporum. Only in the case of Nodularia sp. could we demonstrate that the ecological exclusion of the toxic cyanobacteria was caused by allelopathy. However, the rapid exclusion shown in our experiments suggests that allelopathy was the main cause in all cases. An inter-specific competition model including only competition for phosphate and an allelopathic interaction was able to accurately describe the patterns of population dynamics observed in our experiments.

Phenotypic plasticity and developmental noise in hybrid and parental clones of Daphnia longispina complex

According to the “temporal hybrid superiority hypothesis”, seasonal variability in environmental factors in temperate lakes gives hybrid clones within the D. longispina complex a temporary fitness advantage, thus allowing long-term, dynamic coexistence of hybrids and maternal taxa. However, the maintenance of hybrids would not require their superiority under any given set of environmental conditions if their average fitness over longer periods surpassed that of more specialized and less flexible parental clones. Phenotypic plasticity and developmental noise of several hybrid and maternal clones of Daphnia (Daphnia galeata, Daphnia hyalina, their hybrids and backcrosses) were compared in a series of laboratory experiments. Changes in depth selection and body size at first reproduction were scored in Daphnia exposed to predator (planktivorous fish) threat, to the presence of filamentous cyanobacteria (Cylindrospermopsis raciborskii), and to the presence of toxic compounds (PCB52 and PCB153). The hybrid clones were found to exhibit the broadest phenotypic plasticity of the studied traits in response to the different stress factors. Developmental noise in depth selection behaviour was the lowest in Daphnia galeata, the highest in Daphnia hyalina, and intermediate in hybrid and backcross clones. This diversity of reaction norms might permit the coexistence of closely related Daphnia clones in the variable and often unpredictable lake environment.