Toxic Cyanobacteria: A Growing Threat to Water and Air Quality

3D Impedimetric Biosensor for Cyanobacteria Detection in Natural Water Sources

The excessive growth of cyanobacteria in freshwater sources produces the development of toxic blooms mainly due to the production of cyanotoxins. Here, a novel impedimetric biosensor based on a three-dimensional interdigitated electrode array (3D-IDEA) for detection of cyanobacteria cells is reported. The 3D-IDEA sensor surface biofunctionalization was performed by means of the layer-by-layer method using polyethyleneimine (PEI) as the anchoring layer and concanavalin A (Con A) as the bioreceptor to lipopolysaccharides of cyanobacteria cells. The developed PEI-Con A 3D-IDEA sensors show a linear response (R2 = 0.992) of the impedance changes (RS) versus the logarithm of cyanobacteria concentrations in the range of 102–105 cells·mL−1 with the detection limit of 100 cells·mL−1. Moreover, to prevent the interference from components that may be present in real water samples and minimize a possible sample matrix effect, a filtration methodology to recover cyanobacterial cells was developed. The proposed methodology allows 91.2% bacteria recovery, permitting to obtain results similar to controlled assays. The developed system can be used in aquatic environments to detect cyanobacteria and consequently to prevent the formation of blooms and the production of cyanotoxins. Con A can bind to most polysaccharides and so react with other types of bacteria. However, currently, on the market, it is not possible to find specific biorecognition elements for cyanobacteria. Taking into consideration the specificity of samples to be analyzed (natural water resources), it is difficult to expect high concentration of other bacteria. In this sense, the developed methodology may be used as an alarm system to select samples for more thorough and precise laboratory analysis.

Fabrication of H2O2 slow-releasing composites for simultaneous Microcystis mitigation and phosphate immobilization

Hydrogen peroxide (H₂O₂) is a widely accepted algicide in controlling cyanobacterial blooms. However, this method includes two disadvantages: 1) a low H₂O₂ concentration (<5 mg L^-1) is required; 2) H₂O₂-induced cell lysis causes phosphorus (P) contamination. To overcome the drawbacks, a H₂O₂ slow-releasing composite (HSRC) based on calcium peroxide (CaO₂) was fabricated to substitute liquid H₂O₂. According to the results, a higher CaO₂ dose increased H₂O₂ yield and releasing rate. H₂O₂ yield of 160 mg L^-1 CaO₂ in HSRC reached 32.9 mg L^-1 and its releasing rate was 0.407 h^-1. In addition, a higher temperature decreased H₂O₂ yield and increased H₂O₂-releasing rate. Besides, HSRC endowed with a remarkable ability to immobilize P. Higher CaO₂ dose, pH value, and temperature increased the rate of P immobilization. The highest rate was 0.185 h^-1, which occurred with 160 mg L^-1 CaO₂ in HSRC at 25 °C and pH 8.0. Toxicity assays showed that HSRC exerted sustaining oxidative stress on Microcystis aeruginosa. Accumulation of intracellular reactive oxygen species resulted in the disruption of enzymatic systems and inactivation of photosystem. Tracking the variations of cell growth and H₂O₂ concentration during HSRC treatments, it suggested that the lethal effect on Microcystis aeruginosa was achieved with a super-low H₂O₂ concentration (<0.3 mg L^-1). In addition, cell lysis did not cause a sudden rise in P concentration due to the P immobilization by HSRC. Therefore, HSRC successfully offsets the drawbacks of liquid H₂O₂ in mitigating cyanobacterial blooms. It may be a novel and promising algicide that not only kills cyanobacteria but also reduces eutrophication momentarily.

New insights into toxicity of microcystins produced by cyanobacteria using in silico ADMET prediction

In silico methodologies can be used in the discovery of new drugs for measuring toxicity, predicting effects of substances not yet analyzed by in vivo methodologies. The ADMET Predictor® software (absorption, distribution, metabolism, elimination, and toxicity [ADMET]) was used in this work to predict toxic effects of microcystin variants MC-LR, MC-YR, MC-RR, and MC-HarHar. In the case of rodents, predictive results for all analyzed variants indicated carcinogenic potential. The predictive model of respiratory sensitivity in this group differentiated microcystins into 2 categories: sensitizer (MC-LR and -YR) and non-sensitizer (MC-HarHar and -RR). Predictive results for humans indicated that MC-LR and -RR are phospholipidosis inducers; on the other hand, MC-LR showed the highest predictive value of permeability in rabbit cornea and probability of crossing lipoprotein barriers (MC-LR>-YR>-HarHar>-RR). Considering bioavailable fractions, microcystins are more likely to cause biological effects in rats than humans, showing significant differences between models. The results of ADMET predictions add valuable information on microcystin toxicity, especially in the case of variants not yet studied experimentally.

Regulation of Photosynthesis in Bloom-Forming Cyanobacteria with the Simplest β-Diketone

Selective inhibition of photosynthesis is a fundamental strategy to solve the global challenge caused by harmful cyanobacterial blooms. However, there is a lack of specificity of the currently used cyanocides, because most of them act on cyanobacteria by generating nontargeted oxidative stress. Here, for the first time, we find that the simplest β-diketone, acetylacetone, is a promising specific cyanocide, which acts on Microcystis aeruginosa through targeted binding on bound iron species in the photosynthetic electron transport chain, rather than by oxidizing the components of the photosynthetic apparatus. The targeted binding approach outperforms the general oxidation mechanism in terms of specificity and eco-safety. Given the essential role of photosynthesis in both natural and artificial systems, this finding not only provides a unique solution for the selective control of cyanobacteria but also sheds new light on the ways to modulate photosynthesis.

Algal blooms modulate organic matter remineralization in freshwater sediments: A new insight on priming effect

This study provides a novel insight into the degradation of sediment organic matter (SOM) regulated by algae-derived organic matter (AOM) based on priming effect. We tracked the dynamics of SOM mineralization products and pathways, together with priming effects (PE) using the compound-specific stable isotope (δ¹³C) technique following addition of low- and high-density algal debris in sediments. We found that algal debris increased the total carbon oxidation rate, and resulted in denitrification and methanogenesis-dominated SOM mineralization. While iron reduction and sulphate reduction played important roles in the early period of algal accumulation. Total carbon oxidation rate and anaerobic rates (R_anaerobic) were higher in the amended treatments compared with that in the control. Analysis indicated that algal debris had a positive PE on SOM mineralization, which caused an intensified mineralization in the initial phase with over 80% of dissolved inorganic carbon deriving from SOM degradation. Total carbon oxidation rate of SOM deduced from priming effect (R_TCOR-PE) was similar to R_anaerobic, further indicating SOM mineralization was a critical source of the end products. These findings deviate the causal focus from the decomposition of AOM, and confirm the accumulation of AOM as the facilitator of SOM mineralization. Our study offers empirical evidences to advance the traditional view on the effect of AOM on SOM mineralization.

Cyanobacteria, Cyanotoxins, and Neurodegenerative Diseases: Dangerous Liaisons

The prevalence of neurodegenerative disease (ND) is increasing, partly owing to extensions in lifespan, with a larger percentage of members living to an older age, but the ND aetiology and pathogenesis are not fully understood, and effective treatments are still lacking. Neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis are generally thought to progress as a consequence of genetic susceptibility and environmental influences. Up to now, several environmental triggers have been associated with NDs, and recent studies suggest that some cyanotoxins, produced by cyanobacteria and acting through a variety of molecular mechanisms, are highly neurotoxic, although their roles in neuropathy and particularly in NDs are still controversial. In this review, we summarize the most relevant and recent evidence that points at cyanotoxins as environmental triggers in NDs development.

Florida’s Harmful Algal Bloom (HAB) Problem: Escalating Risks to Human, Environmental and Economic Health With Climate Change

Harmful Algal Blooms (HABs) pose unique risks to the citizens, stakeholders, visitors, environment and economy of the state of Florida. Florida has been historically subjected to reoccurring blooms of the toxic marine dinoflagellate Karenia brevis (C. C. Davis) G. Hansen &amp; Moestrup since at least first contact with explorers in the 1500’s. However, ongoing immigration of more than 100,000 people year–1 into the state, elevated population densities in coastal areas with attendant rapid, often unregulated development, coastal eutrophication, and climate change impacts (e.g., increasing hurricane severity, increases in water temperature, ocean acidification and sea level rise) has likely increased the occurrence of other HABs, both freshwater and marine, within the state as well as the number of people impacted by these blooms. Currently, over 75 freshwater, estuarine, coastal and marine HAB species are routinely monitored by state agencies. While only blooms of K. brevis, the dinoflagellate Pyrodinium bahamense (Böhm) Steidinger, Tester, and Taylor and the diatom Pseudo-nitzschia spp. have resulted in closure of commercial shellfish beds, other HAB species, including freshwater and marine cyanobacteria, pose either imminent or unknown risks to human, environmental and economic health. HAB related human health risks can be classified into those related to consumption of contaminated shellfish and finfish, consumption of or contact with bloom or toxin contaminated water or exposure to aerosolized HAB toxins. While acute human illnesses resulting from consumption of brevetoxin-, saxitoxin-, and domoic acid-contaminated commercial shellfish have been minimized by effective monitoring and regulation, illnesses due to unregulated toxin exposures, e.g., ciguatoxins and cyanotoxins, are not well documented or understood. Aerosolized HAB toxins potentially impact the largest number of people within Florida. While short-term (days to weeks) impacts of aerosolized brevetoxin exposure are well documented (e.g., decreased respiratory function for at-risk subgroups such as asthmatics), little is known of longer term (&gt;1 month) impacts of exposure or the risks posed by aerosolized cyanotoxin [e.g., microcystin, β-N-methylamino-L-alanine (BMAA)] exposure. Environmental risks of K. brevis blooms are the best studied of Florida HABs and include acute exposure impacts such as significant dies-offs of fish, marine mammals, seabirds and turtles, as well as negative impacts on larval and juvenile stages of many biota. When K. brevis blooms are present, brevetoxins can be found throughout the water column and are widespread in both pelagic and benthic biota. The presence of brevetoxins in living tissue of both fish and marine mammals suggests that food web transfer of these toxins is occurring, resulting in toxin transport beyond the spatial and temporal range of the bloom such that impacts of these toxins may occur in areas not regularly subjected to blooms. Climate change impacts, including temperature effects on cell metabolism, shifting ocean circulation patterns and changes in HAB species range and bloom duration, may exacerbate these dynamics. Secondary HAB related environmental impacts are also possible due to hypoxia and anoxia resulting from elevated bloom biomass and/or the decomposition of HAB related mortalities. Economic risks related to HABs in Florida are diverse and impact multiple stakeholder groups. Direct costs related to human health impacts (e.g., increased hospital visits) as well as recreational and commercial fisheries can be significant, especially with wide-spread sustained HABs. Recreational and tourism-based industries which sustain a significant portion of Florida’s economy are especially vulnerable to both direct (e.g., declines in coastal hotel occupancy rates and restaurant and recreational users) and indirect (e.g., negative publicity impacts, associated job losses) impacts from HABs. While risks related to K. brevis blooms are established, Florida also remains susceptible to future HABs due to large scale freshwater management practices, degrading water quality, potential transport of HABs between freshwater and marine systems and the state’s vulnerability to climate change impacts.

Selective removal of common cyanotoxins: a review

The development of cyanobacterial blooms can have adverse effects on water bodies and may produce cyanotoxins. Several physical and chemical methods have been applied to remove cyanotoxins, but they have been significantly challenged due to extensive energy footprint and over-used chemicals, which limits practical application on a large scale. Selective removal has been regarded as the most promising approach recently for the elimination of prevalent and major bloom-forming cyanotoxins (e.g., microcystins and cylindrospermopsin) as natural organic matters and radical scavengers are ineluctably present in real scenarios. This paper reviews current advancements in research on selective oxidation and adsorption of cyanotoxins. Its goal is to provide comprehensive information on the treatment mechanism and the process feasibility involved in the cyanotoxin removal from real-world waters. Moreover, perspectives of cyanotoxin control and in situ selective elimination approaches are also reviewed. It is expected that the information gathered and discussed in this review can provide a useful and novel reference and direction for future pilot-scale applications.

Increasing Freshwater Salinity Impacts Aerosolized Bacteria

Increases in the salt concentration of freshwater result in detrimental impacts on water quality and ecosystem biodiversity. Biodiversity effects include freshwater microbiota, as increasing salinity can induce shifts in the structure of native freshwater bacterial communities, which could disturb their role in mediating basal ecosystem services. Moreover, salinity affects the wave breaking and bubble-bursting mechanisms via which water-to-air dispersal of bacteria occurs. Given this dual effect of freshwater salinity on waterborne bacterial communities and their aerosolization mechanism, further effects on aerosolized bacterial diversity and abundance are anticipated. Cumulative salt additions in the freshwater-euhaline continuum (0-35 g/kg) were administered to a freshwater sample aerosolized inside a breaking wave analogue tank. Waterborne and corresponding airborne bacteria were sampled at each salinity treatment and later analyzed for diversity and abundance. Results demonstrated that the airborne bacterial community was significantly different (PERMANOVA; F_1,22 = 155.1, r² = 0.38, p < 0.001) from the waterborne community. The relative aerosolization factor (r-AF), defined as the air-to-water relative abundance ratio, revealed that different bacterial families exhibited either an enhanced (r-AF ≫ 1), neutral (r-AF ∼ 1), or diminished (r-AF ≪ 1) transfer to the aerosol phase throughout the salinization gradient. Going from freshwater to euhaline conditions, aerosolized bacterial abundance exhibited a nonmonotonic response with a maximum peak at lower oligohaline conditions (0.5-1 g/kg), a decline at higher oligohaline conditions (5 g/kg), and a moderate increase at polyhaline-euhaline conditions (15-35 g/kg). Our results demonstrate that increases in freshwater salinity are likely to influence the abundance and diversity of aerosolized bacteria. These shifts in aerosolized bacterial communities might have broader implications on public health by increasing exposure to airborne pathogens via inhalation. Impacts on regional climate, related to changes in biological ice-nucleating particles (INPs) emission from freshwater, are also expected.

Does the Kis-Balaton Water Protection System (KBWPS) Effectively Safeguard Lake Balaton from Toxic Cyanobacterial Blooms?

Lake Balaton is the largest shallow lake in Central Europe. Its water quality is affected by its biggest inflow, the Zala River. During late 20th century, a wetland area named the Kis-Balaton Water Protection System (KBWPS) was constructed in the hopes that it would act as a filter zone and thus ameliorate the water quality of Lake Balaton. The aim of the present study was to test whether the KBWPS effectively safeguards Lake Balaton against toxic cyanobacterial blooms. During April, May, July and September 2018, severe cyanobacterial blooming was observed in the KBWPS with numbers reaching up to 13 million cells/mL at the peak of the bloom (July 2018). MC- and STX-coding genes were detected in the cyanobacterial biomass. Five out of nine tested microcystin congeners were detected at the peak of the bloom with the concentrations of MC-LR reaching 1.29 µg/L; however, accumulation of MCs was not detected in fish tissues. Histopathological analyses displayed severe hepatopancreas, kidney and gill alterations in fish obtained throughout the investigated period. In Lake Balaton, on the other hand, cyanobacterial numbers were much lower; more than 400-fold fewer cells/mL were detected during June 2018 and cyanotoxins were not detected in the water. Hepatic, kidney and gill tissue displayed few alterations and resembled the structure of control fish. We can conclude that the KBWPS acts as a significant buffering zone, thus protecting the water quality of Lake Balaton. However, as MC- and STX-coding genes in the cyanobacterial biomass were detected at both sites, regular monitoring of this valuable ecosystem for the presence of cyanobacteria and cyanotoxins is of paramount importance.

Roles of Nutrient Limitation on Western Lake Erie CyanoHAB Toxin Production

Cyanobacterial harmful algal bloom (CyanoHAB) proliferation is a global problem impacting ecosystem and human health. Western Lake Erie (WLE) typically endures two highly toxic CyanoHABs during summer: a Microcystis spp. bloom in Maumee Bay that extends throughout the western basin, and a Planktothrix spp. bloom in Sandusky Bay. Recently, the USA and Canada agreed to a 40% phosphorus (P) load reduction to lessen the severity of the WLE blooms. To investigate phosphorus and nitrogen (N) limitation of biomass and toxin production in WLE CyanoHABs, we conducted in situ nutrient addition and 40% dilution microcosm bioassays in June and August 2019. During the June Sandusky Bay bloom, biomass production as well as hepatotoxic microcystin and neurotoxic anatoxin production were N and P co-limited with microcystin production becoming nutrient deplete under 40% dilution. During August, the Maumee Bay bloom produced microcystin under nutrient repletion with slight induced P limitation under 40% dilution, and the Sandusky Bay bloom produced anatoxin under N limitation in both dilution treatments. The results demonstrate the importance of nutrient limitation effects on microcystin and anatoxin production. To properly combat cyanotoxin and cyanobacterial biomass production in WLE, both N and P reduction efforts should be implemented in its watershed.