Raphidiopsis Raciborskii Research Articles

Bloom-forming cyanobacteria and dinoflagellates in five Argentinian reservoirs: Multi-year sampling

Harmful algal blooms are important threats to reservoir condition. Over a 15-year period, we sampled five Argentinian reservoirs to identify the responsible species for harmful algal blooms and determine the water quality factors driving their occurrence. These reservoirs exhibit diverse morphological and hydrological characteristics and are distributed across varying climatic zones. Cyanobacterial blooms included an array of species, including toxin producers such as Raphidiopsis raciborskii, Aphanizomenon gracile, and Microcystis aeruginosa. In contrast, dinoflagellate blooms were predominantly characterized by Ceratium. The cyanobacterial blooms primarily occurred in the shallower reservoirs located in warmer regions, whereas dinoflagellate blooms occurred where temperatures were lower. The most intense blooms occurred during the summer, and although cyanobacterial and chlorophyte blooms co-occurred, they never coexisted with dinoflagellate blooms. We identified cyanotoxins in the reservoirs over the past three years, a phenomenon previously unreported in the region. Given that these reservoirs are drinking water sources for human populations, ongoing and systematic monitoring is needed to protect public health. Controlling the proliferation of algae and cyanobacteria in reservoirs requires resource management at the watershed level, and in the case of the Itiyuro and El Limón, requires binational management with Bolivia.

Chlorella pyrenoidosa mitigated the negative effect of cylindrospermopsin-producing and non-cylindrospermopsin-producing Raphidiopsis raciborskii on Daphnia magna as a dietary supplement.

Feeding effects are crucial for evaluating the capacity of zooplankton to regulate phytoplankton populations within freshwater ecosystems. To examine the impact of the bloom-forming cyanobacteria Raphidiopsis raciborskii, which occurs in tropical and subtropical freshwaters, on the growth of zooplankton Daphnia in relation to toxins, filament length and fatty acid content, we fed D. magna with R. raciborskii only (cylindrospermopsin (CYN)-producing and non-CYN-producing, as the negative controls), Chlorella pyrenoidosa only (as the positive control) and a mixed diet containing R. raciborskii (CYN-producing and non-CYN-producing) and C. pyrenoidosa. Consequently, our findings revealed that the toxic effect of CYN-producing R. raciborskii strains on Daphnia was mitigated by the coexistence of C. pyrenoidosa containing stearidonic acid (SDA, C18:4 ω3) in mixed diets. This was evident in the elevated survival rate compared that from diets containing only R. raciborskii and a significantly higher reproduction and population intrinsic increase rate compared to diets consisting of only R. raciborskii or C. pyrenoidos. Additionally, a strong positive correlation was observed between arachidonic acid (ARA, 20:4ω6) and the population intrinsic increase rate of Daphnia; notably, R. raciborskii strains were found to be rich in the ω6 polyunsaturated fatty acid ARA. These outcomes reinforce the crucial role of polyunsaturated fatty acids in predicting the population increase of crustacean zooplankton, which has long been neglected. Furthermore, our results underscore the potential effectiveness of zooplankton, particularly in temperate lakes, in controlling CYN-producing R. raciborskii populations.

An empty stomach is not a good adviser: avoiding toxic Cyanobacteria can compromise tadpole antipredator defenses

Abstract Eutrophication events resulting from increased primary production are becoming common under changing environmental conditions that include habitat degradation and disturbance of food webs. They cause several detrimental ecological consequences including the intoxication of animals that ingest toxic Cyanobacteria. We tested whether the tadpole of an anthropophilic frog (Scinax longilineus) would avoid feeding on a potentially toxic Cyanobacteria using Raphidiopsis raciborskii as a model. We maintained tadpoles in water collected from a natural monospecific growth of R. raciborskii at the original concentration (100%) and concentrations of 0, 25, 50 and 75% of the original sample diluted in rested tap water. We evaluated the amount of R. raciborskii ingested by the tadpoles and conducted behavioral tests by exposing tadpoles to an aversive stimulus and quantifying their escape response. Tadpoles ate the least R. raciborskii the highest the concentration of this Cyanobacteria was in the water. Tadpoles exposed to 50 and 75% of the original concentration of the R. raciborskii sample had a reduction of time spent escaping, what is likely to compromise their ability to escape a real predator attack. Tadpoles at the highest concentration (100%) did not show significant changes in their escape performance, however they practically stopped feeding, what would not be a solution in the long term (i.e., duration of a real bloom). We conclude that tadpoles of S. longilineus can recognize the presence of R. raciborskii and avoid its ingestion, with potential sub-lethal effects represented by a reduced ability to escape predators.

An overview of the distribution and ecology of the alien cyanobacteria species Raphidiopsis raciborskii, Sphaerospermopsis aphanizomenoides and Chrysosporum bergii in Europe

Cyanobacteria can form blooms and pose a threat to the functioning of freshwater ecosystems. Cyanobacterial invasions are expected to increase due to climate change. Alien species cause a decline in biodiversity by displacing native species, lead to extinctions, affect food webs, and produce cyanotoxins which potentially impact the environment and human health. Three species, Raphidiopsis raciborskii, Sphaerospermospis aphanizomenoides and Chrysosporum bergii, are considered non-native to European waters. Recently, they have expanded their native habitats and become established in temperate lakes. In this article, we provide a detailed overview of the countries where they are distributed and the occurrence of the blooms in Europe. We discuss the biotic and abiotic environmental factors that influence their establishment, as well as the characteristics of the species that make them so adaptable in non-native habitats. Understanding the interplay of these factors will allow us to better recognise patterns of invasiveness and predict their future threats to ecosystems.

Use of decomposition products of Pontederia crassipes Mart., Solms (water yacinth) for inhibition of cyanobacteria growth: A full-scale study

Eutrophication exacerbates the growth of primary producers that may reduce water quality, such as macrophytes and cyanobacteria. The floating macrophyte Pontederia crassipes and the cyanobacterium Raphidiopsis raciborskii occur worldwide in eutrophic environments, but data on the inhibition of R. raciborskii by floating macrophytes are scarce. We aimed to test the inhibitory activity of P. crassipes on cyanobacterial growth, especially R. raciborskii. First, we tested the effect of live P. crassipes exudates and decomposing macrophyte extracts on a R. raciborskii strain under culture conditions. Cyanobacterial growth was not affected by the exudate from the live macrophyte. In contrast, exposure to decaying macrophyte extracts containing 4.0 and 6.0 mg L−1 total phenols completely inhibited cyanobacterial growth after five days and decreased photosynthetic activity. Mass spectrometry FT-IRC analysis led to the identification of some molecules in P. crassipes extracts, but no association with the inhibitory effect of the was identified. We then tested the inhibitory effect of P. crassipes in mesocosms containing a natural cyanobacterial bloom. The slow release of chemicals from the dry biomass over 12 days decreased chlorophyll concentrations. Finally, in a field experiment, we applied tons of P. crassipes dry biomass to large areas (900 m3) of a reservoir to test the release of chemicals into the water during one month. At the final time, the phenol concentration in the backwater region was close to the inhibitory value found for cyanobacterial growth and an inverse correlation was observed between chlorophyll and phenol concentrations. Thus, under natural conditions, the release of phenolic compounds and other allelochemicals from the decomposing material of macrophyte mats inhibits cyanobacterial growth. Macrophyte biomass, which is usually considered waste, might be used to mitigate cyanobacterial blooms and may be a promising new and sustainable biotechnological tool to improve water quality.

Saxitoxin-Producing Raphidiopsis raciborskii (Cyanobacteria) Constrains Daphnia Fitness and Feeding Rate despite High Nutritious Food Availability.

Changes in food quality can dramatically impair zooplankton fitness, especially in eutrophic water bodies where cyanobacteria are usually predominant. Cyanobacteria are considered a food with low nutritional value, and some species can produce bioactive secondary metabolites reported as toxic to zooplankton. Considering that cyanobacteria can limit the survival, growth and reproduction of zooplankton, we hypothesized that the dietary exposure of neotropical Daphnia species (D. laevis and D. gessneri) to saxitoxin-producing cyanobacteria impairs Daphnia feeding rates and fitness regardless of a high availability of nutritious algae. Life table and grazing assays were conducted with different diets: (1) without nutritional restriction, where neonates were fed with diets at a constant green algae biomass (as a nutritious food source), and an increasing cyanobacterial concentration (toxic and poor food source), and (2) with diets consisting of different proportions of green algae (nutritious) and cyanobacteria (poor food) at a total biomass 1.0 mg C L-1. In general, the presence of high proportions of cyanobacteria promoted a decrease in Daphnia somatic growth, reproduction and the intrinsic rate of population increase (r) in both diets with more pronounced effects in the nutritionally restricted diet (90% R. raciborskii). A two-way ANOVA revealed the significant effects of species/clone and treatments in both assays, with significant interaction between those factors only in the second assay. Regarding the grazing assay, only D. laevis was negatively affected by increased cyanobacterial proportions in the diet. In the life table assay with constant nutritious food, a reduction in the reproduction and the intrinsic rate of the population increase (r) of all species were observed. In conclusion, we found adverse effects of the toxic cyanobacterial strain R. raciborskii on Daphnia fitness, regardless of the constant amount of nutritious food available, proving the toxic effect of R. raciborskii and that the nutritional quality of the food has a greater influence on the fitness of these animals.

Phosphorus storage and utilization strategies of two bloom-forming freshwater cyanobacteria.

The inter-relationships between cellular phosphorus (P) storage, dissolved inorganic P (DIP) uptake affinity, alkaline phosphatase activity (APA) and dissolved inorganic nitrogen (DIN) concentrations were studied in two ubiquitous diazotrophic freshwater cyanobacteria, Raphidiopsis raciborskii (six strains) and Chrysosporum ovalisporum (two strains). DIP uptake kinetics were measured using rates of incorporation of the radio-isotope, 33P and APA as a proxy for DOP-ester utilization. The study showed that DIP uptake of individual strains followed Michaelis-Menten kinetics (modified in our study to incorporate cellular P quotas), but differed with DIN and P availability, and between growth stages. High-affinity DIP uptake and APA were activated below a P quota threshold of approximately 0.01 µg P µg-1 C across the species and strains. C. ovalisporum had significantly higher APA and P quotas (per unit C and cell) but lower uptake affinity than R. raciborskii. Demand for DIP by C. ovalisporum increased when N fixation occurred, but typically not for R. raciborskii. Our results indicate that cyanobacterial species and strains differ in their strategies to P limiting conditions, and highlight the interplay between N and P. Physiological adaptations like APA and diazotrophy of cyanobacteria adapting to low DIP and/or DIN conditions may occur simultaneously and drive species dominance in oligotrophic environments.

Phytoremediation of a mixture of toxic cyanobacteria. Does phytoplankton composition affect the amount of toxins removed?

Phytoremediation is an environmentally friendly method for removing harmful cyanotoxins from water. The main objective of the study was to test whether the presence of several cyanobacteria at the same time in the medium together with a macrophyte would affect its ability to phytoremediate cyanotoxins. Analyses using high-performance liquid chromatography indicated that the presence of the plant in all cases caused a significant reduction in the intracellular pool of toxins and cyanobacterial biomass. The addition of the plant to the cyanobacterial mixture after 14 days resulted in a 0.99–1.59-fold reduction in the intracellular pool of anatoxin-a (ATX-a). At the same time, the concentration of the toxin in the medium decreased 0.23 times during the co-cultivation of Dolichospermum flos-aquae/Micorcystis aeruginosa and increased from 0.10 to 1.30-fold in the presence of Raphidiopsis raciborskii. During the experiments, the plant showed the ability to take up ATX-a from the medium (from 40% to 70% of the total pool). The plant reduced the intracellular cylindrospermopsin content from 0.54 to 0.92-fold, while increasing the release of the toxin into the medium from 0.39 to 4.23-fold. The plant was equally effective in reducing the amount of intracellular microcystin-LR by 1.00–1.37 times, while leading to the release of the toxin into the medium. The increase in the amount of toxin in the medium ranged from 0.94 to 28.86 times. Based on the obtained results, it can be concluded that the plants' efficiency of cyanotoxins phytoremediation varies significantly depending on the cyanobacteria composition in mixed culture.

Preliminary Study on the Inhibitory Effect and Mechanism of Eichhornia crassipes on Co-Cultured Raphidiopsis raciborskii

Raphidiopsis raciborskii, which harms water supply and ecological security, may expand its range with climate warming. To explore the ecological management method of R. raciborskii blooms, the co-culture system of Eichhornia crassipes and R. raciborskii was established to study the inhibitory effect and inhibition mechanism of E. crassipes on R. raciborskii compared with the shaded culture of R. raciborskii alone. It was found that after co-cultured with E. crassipes (fresh weight, 5.10 ± 0.60 g·L−1) for seven days under initial high nutrient concentration, the algal cell density of co-culture groups with an initial cell density of 1.57 × 108 cells·L−1 and 1.57 × 109 cells·L−1 decreased by 63.19% and 14.87%, respectively. Meanwhile, the algal cell density in the co-culture group was significantly lower than that in the control group (p < 0.01). The algal cell density change showed that the growth of R. raciborskii was inhibited by co-cultured E. crassipes. In addition, E. crassipes could significantly reduce the nitrogen and phosphorus content in the water, but the growth state and photosynthesis of E. crassipes were not inhibited by R. raciborskii. These results suggested that E. crassipes has the potential to control R. raciborskii blooms. The study also found that when co-cultured, there was no significant difference in algal cell density between the groups supplemented with a certain amount of nutrients and the group without additional nutrients. Meanwhile, the inhibition rates of the co-culture groups were over 99% on day 4. These results showed that nutrient factors had no significant effect on the inhibitory effect of E. crassipes in the range of nutrients regulated by the experiment, and other factors played a leading role. In other words, under experimental conditions, nutrient competition was not the primary inhibitory mechanism of E. crassipes. This study also confirmed that E. crassipes had inhibitory allelopathy on R. raciborskii. The contribution and significance of allelopathy and other mechanisms could be studied in the future.

Paramecium jenningsi effectively grazes on toxic Raphidiopsis raciborskii and degrades cylindrospermopsin: Implications for control harmful cyanobacterial blooms

Harmful cyanobacterial blooms (HCB) represent a serious threat to aquatic ecosystems due to their production for potent toxins that have negative effects on plant, animal and human health. Although grazing process can be exploited to reduce harmful cyanobacteria in eutrophic waters, the feeding capacity and detoxification capability of the grazer should be considered as key traits of a safe biocontrol agent. In this study, laboratory experiments were conducted to investigate the grazing rate of the ciliate Paramecium jenningsi on toxic Raphidiopsis raciborskii and potential cylindrospermopsin (CYN) degradation during feeding process. P. jenningsi efficiently ingested R. raciborskii cells with high growth (0.1- 0.26 d−1) and grazing rates (0.1-1.4 × 104 cyanobacterial cells ciliate −1 d−1), varying with the initial ciliate density. CYN concentrations within Raphidiopsis cells displayed an elevation under grazing conditions (5.3-7.2 pg cell−1) compared to control cultures (4.4 pg cell−1). CYN concentrations within the ciliate cells showed a reduction (degradation rate =121-276 pg ciliate−1 d−1) and became undetectable after all Raphidiopsis cells were grazed out, indicating that this ciliate could not accumulate CYN within its body during feeding process. Therefore, P. jenningsi could be used as a safe bioagent for the biocontrol of HCBs in water sources. However, a further in situ study is needed for a possible application of Paramecium species for mitigation of toxic cyanobacteria and their cyanotoxins in the natural environment.

Sedimentary DNA and pigments show increasing abundance and toxicity of cyanoHABs during the Anthropocene

Abstract Cyanobacterial harmful algal blooms (cyanoHABs) are assumed to be increasing in abundance and toxicity, but comprehensive analysis of change through time is limited, in part, because some key taxa (e.g., Microcystis) leave ambiguous evidence of historical abundance and toxicity. Sedimentary DNA (sedDNA) can allow the reconstruction of the cyanobacteria community as well as the frequency of genes specific to cyanotoxin production, enabling us to determine which taxa are present and their potential for toxin‐production. Using a combination of droplet digital polymerase chain reaction (ddPCR) and high‐throughput sequencing (HTS), we quantified the abundance of cyanobacterial genes of known function and changes in cyanobacteria taxa from sedDNA over the last century in nine lakes along a gradient of lake size, depth and trophic state in Minnesota, U.S.A. Using ddPCR, we quantified genes associated with microcystin toxin‐producing potential (mcyE), total cyanobacteria (CYA, 16S rRNA) and the genus Microcystis (MICR, 16S rRNA). Using HTS on a subset of lakes, we investigated how the abundance of this toxin‐producing gene covaried with the cyanobacteria community composition. We also compared ddPCR and HTS data to fossil pigments, a well‐established palaeolimnological method used to track changes in primary producers over time. Our results showed a significant correlation between MICR and the quantity of mcyE gene and cyanobacterial taxa with known toxin‐production potential. The abundance of both genes likewise increased concomitantly through time. Community analyses of HTS data showed significant change in cyanobacterial communities commencing c. 1950 when major land‐use change in this region led to increased lake productivity, and c. 1990 when Dolichospermum and Microcystis genera increased in abundance, and the subtropical exotic cyanobacteria Raphidiopsis raciborskii and Sphaerospermopsis aphanizomenoides became abundant. Cyanobacteria pigment data reflected these changes only in deeper lakes, suggesting issues related to benthic production or biomarker preservation in shallower systems. This study provides evidence for historical development of increasingly toxic cyanoHABs across a diverse set of lakes and illustrates how sedDNA may help link changes in the cyanobacteria community to the expression of potentially toxic genes.

Ecological Implications in a Human-Impacted Lake-A Case Study of Cyanobacterial Blooms in a Recreationally Used Water Body.

This study was aimed primarily at describing the planktonic assemblages with special attention to invasive and toxin-producing cyanobacterial species in the context of ecological and health threats. The second aim was to analyze the aspect of recreational pressure, which may enhance the cyanobacterial blooms, and, as a consequence, the negative changes and loss of planktonic biodiversity. This study was carried out in recreationally used Lake Sztynorckie throughout the whole growing season of 2020 and included an assessment of the abundance and biomass of phytoplankton (cyanobacteria and algae) in relation to environmental variables. The total biomass was in the range of 28-70 mg L-1, which is typical for strong blooms. The dominant filamentous cyanobacteria were Pseudanabaena limnetica, Limnothrix redekei, Planktolyngbya limnetica, and Planktothrix agarhii, and three invasive nostocalean species Sphaerospermopsis aphanizomenoides, Cuspidothrix issatschenkoi, and Raphidiopsis raciborskii. They can pose a serious threat not only to the ecosystem but also to humans because of the possibility of cyanobacteria producing cyanotoxins, such as microcystins, saxitoxins, anatoxin-a, and cylindrospermopsins, having hepatotoxic, cytotoxic, neurotoxic, and dermatoxic effects. The water quality was assessed as water bodies had bad ecological status (based on phytoplankton), were highly meso-eutrophic (based on zooplankton), and had very low trophic efficiency and low biodiversity.

Does temperature favour the spread of Raphidiopsis raciborskii, an invasive bloom-forming cyanobacterium, by altering cellular trade-offs?

As a tropical filamentous cyanobacterium, Raphidiopsis raciborskii has attracted much attention due to its expansion and toxin production. However, the mechanisms of its expansion to temperate regions have not been studied in detail. To address the potential strategies, the physiological and metabolomic profiles of R. raciborskii FACHB 1096 isolated from a temperate lake in China were determined and measured at different temperatures (10 °C, 15 °C, 20 °C, 25 °C, and 32 °C). The results demonstrated that temperature significantly changed cell viability, chlorophyll a content, specific growth rate, Chl a fluorescence, and filamentous shape of R. raciborskii. Low temperature decreased cell viability, specific growth rate, and photosynthetic efficiency, while the proportion of akinete and carbon fixation per unit cell were significantly increased compared with high temperature (32 °C). A constructed unimodal model indicated that filament length, cell volume, and cell length/width of R. raciborskii were significantly reduced in both high and low temperature environments. Under low-temperature conditions, R. raciborskii suffered different degrees of oxidative damage and produced corresponding antioxidant substances to resist oxidative stress, suggesting that low temperature changes the metabolic level of the cells, causing the cells to gradually switch from development to defense. Metabolomic data further confirmed that temperature change induced shifts in metabolic pathways in R. raciborskii, including starch and sucrose metabolic pathways, glutathione metabolic pathways, and the pentose phosphate pathways (PPP), as well as metabolic pathways related to the tricarboxylic acid (TCA) cycle. Our results indicated that the trade-offs of R. raciborskii cells among the growth, cell size, and metabolites can be significantly regulated by temperature, with broad implications for its global expansion in temperate waterbodies.

Recent Advances in the Ecology of Bloom-Forming Raphidiopsis (Cylindrospermopsis) raciborskii: Expansion in China, Intraspecific Heterogeneity and Critical Factors for Invasion.

Water blooms caused by the invasive cyanobacterium Raphidiopsis raciborskii occur in many reservoirs in the tropical and subtropical regions of China. In recent decades, this species has spread rapidly to temperate regions. Phenotypic plasticity and climate warming are thought to promote the worldwide dispersion of R. raciborskii. However, investigations into the genetic and phenotypic diversities of this species have revealed significant intraspecific heterogeneity. In particular, competition between R. raciborskii and Microcystis aeruginosa was highly strain dependent. Although the concept of an ecotype was proposed to explain the heterogeneity of R. raciborskii strains with different geographic origins, microevolution is more reasonable for understanding the coexistence of different phenotypes and genotypes in the same environment. It has been suggested that intraspecific heterogeneity derived from microevolution is a strong driving force for the expansion of R. raciborskii. Additionally, temperature, nutrient fluctuations, and grazer disturbance are critical environmental factors that affect the population establishment of R. raciborskii in new environments. The present review provides new insights into the ecological mechanisms underlying the invasion of R. raciborskii in Chinese freshwater ecosystems.

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.

Species composition of Cyanoprokaryota in the summer phytoplankton of 55 lakes and reservoirs, sampled in Bulgaria in the years 2018, 2019, 2021 and 2023

The paper presents detailed results on cyanoprokaryote diversity in the summer phytoplankton of 55 lakes, small and large reservoirs sampled in Bulgaria in the frame of three joined projects related to algal blooms threat to human health and national security. The phytoplankton of twenty from these selected waterbodies was sampled for first time. In total, 185 species and one variety from 55 genera have been identified, 54 of which (29%) were novel for the country. The average contribution of cyanophytes to the phytoplankton per site was 8 species (or 44% of the total biodiversity), reaching in some sites 80%. According to the morphology, the recorded algae were distributed as follows: 83 coccal, 52 non-heterocytous filamentous and 51 heterocytous filamentous cyanoprokaryotes. Their average contribution to the phytoplankton diversity was estimated as 4 coccal, 2 non-heterocytous and 2 heterocytous species per site. Most of the cyanoprokaryote species (94, or 51%) were recorded only once, even in the case of wetlands and sites which have been repeatedly visited during all sampling campaigns. These 96 species embrace 39 coccal, 23 non-heteroctous and 32 heterocytous forms. No species was found in all studied waterbodies. The most widely spread species were Microcystis aeruginosa (19 records), Planktolyngbya limnetica (17 records), Aphanizomenon klebahnii (16 records), Microcystis wesenbergii (16 records), Aphanocapsa delicatissima (13 records), Cuspidothrix issatschenkoi (12 records), Coelomoron pusillum (11 records), Pseudanabaena limnetica (11 records), Anagnostidinema amphibium (10 records), Raphidiopsis raciborskii (10 records), Limnococcus limneticus (10 records), and separate cells of Microcystis as well (15 records). The record of the chytrid parasite Rhizosiphon anabaenae on separate trichomes of Sphaerospermopsis aphanizomenoides is described.

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.

Interaction between Raphidiopsis raciborskii and rare bacterial species revealed by dilution-to-extinction experiments

Interactions between heterotrophic bacteria and cyanobacteria regulate the structure and function of aquatic ecosystems and are thus crucial for the prediction and management of cyanobacterial blooms in relation to water security. Currently, abundant bacterial species are of primary concern, while the role of more diverse and copious rare species remains largely unknown. Using a dilution-to-extinction approach, rare bacterial species from reservoir water were co-cultured with the bloom-forming cyanobacterium Raphidiopsis raciborskii in the lab to explore their interactions by using Phyto-PAM and 16S rRNA gene high-throughput sequencing. We found that a ≤1000-fold bacterial dilution led to bacteria control of the growth and photosynthesis of R. raciborskii. Moreover, the bacterial community compositions in the low-dilution groups were clearly diverged from the high-dilution groups. Importantly, rare species changed dramatically in the low-dilution groups, resulting in lower phylogenetic diversity and narrower niche width. The network complexity and compositional stability of bacterial communities decreased in the low-dilution groups. Collectively, our results suggest that rare bacterial species inhibit R. raciborskii growth and photosynthesis through microbial interactions mediated by species coexistence and interaction mechanisms. Our study provides new knowledge of the ecological role of rare bacteria and offers new perspectives for understanding the outbreak and regression of R. raciborskii blooms.

Rapid detection methods and modelling simulations provide new insights into cyanobacteria detection and bloom management in a tropical reservoir

The increasing occurrence of cyanobacteria blooms is of global concern, and is often associated with environmental and socio-economic problems, such as degenerated ecosystems and aquaculture impairment. The diazotrophic cyanobacterium Raphidiopsis raciborskii (R. raciborskii) grows rapidly in the tropics, and produces the toxin, cylindrospermopsin (CYN), which has harmful effects on aquatic organisms. Thus, to protect water quality and ecosystem, it is essential to have rapid and reliable methods for cyanobacteria and R. raciborskii detection and prediction so that early warning can be provided for management. Molecular assays, such as PCR, real-time quantitative PCR (qPCR), two-step PCR assays are accurate and widely used, but still require several hours from sample preparation to data analysis. In this study, insulated isothermal PCR (iiPCR) assays in conjunction with fast DNA extraction method, were developed and verified as a rapid detection assay in detecting cyanobacteria and R. raciborskii within 50 min, and also with high detection accuracy (98.8%) and the overall high agreement level (98.8%, k = 97.5%)) comparing to conventional qPCR assay. However, the limitation of the iiPCR assay is that it only generates qualitative results. Therefore, the quantified iiPCR assay, named as A-iiPCR, by coupling iiPCR device with fluorescence signal catching and interpretation instrument (Andor spectrometer with Solis spectroscopy software) was developed and verified with in situ environmental samples. The fluorescence intensity decreased accordingly with the drop of DNA concentration until reaching 1.32 ng/μL. Also, Delft 3D modelling was established to simulate R. raciborskii change in predicting spatial and temporal variabilities for reservoir management, as the simulated R. raciborskii concentration was the highest at sampling site 1, as well as temporally highest in April and October, posing as the most high-risk location and time periods for R. raciborskii bloom-forming requiring corresponding governance measures.

Simulating oligotrophication in a eutrophic shallow lake to assess the effect of periphyton bioreactor on phytoplankton and epipelon.

We evaluated the effects of a periphyton bioreactor on phytoplankton by experimentally simulating oligotrophication in a shallow eutrophic system. The experiment had two 50% diluted treatments with and without a periphyton bioreactor. Sampling was performed on days 6, 9, 12, 15, and 20 of the experimental period. The periphyton bioreactor accumulated biomass (chlorophyll-a, AFDM) and TP during the experimental period. Despite the biomass and TP loss due to periphyton detachment from the substrate after community reaching the algal biomass peak, the gains exceeded the losses, and the net rate was positive for all attributes in the bioreactor. Based on the average, our findings suggest that periphyton bioreactors negatively affected the phytoplankton total biovolume. Cyanobacteria were the most abundant phytoplankton group. However, the periphyton bioreactor caused the biomass loss of the Raphidiopsis raciborskii in phytoplankton. Our results suggest that bioreactor influenced the phytoplankton structure, reducing cyanobacterial biomass, especially Raphidiopsis raciborskii. However, the bioreactor did not reflect a significant increase in the epipelon biomass during the experimental period. We conclude that the periphyton bioreactor has the potential to assist in the maintenance of restored shallow lakes and reservoirs, especially in controlling phytoplankton growth.