Cyanobacterial Bloom Formation Research Articles

Cyanobacterial Bloom Formation by Enhanced Ecological Adaptability and Competitive Advantage of Microcystis-Non-Negligible Role of Quorum Sensing.

Microcystis-dominated cyanobacterial blooms (MCBs) frequently occur in freshwaters worldwide due to massive Microcystis colony formation and severely threaten human and ecosystem health. Quorum sensing (QS) is a direct cause of Microcystis colony formation that drives MCBs outbreak by regulating Microcystis population characteristics and behaviors. Many novel findings regarding the fundamental knowledge of the Microcystis QS phenomenon and the signaling molecules have been documented. However, little effort has been devoted to comprehensively summarizing and discussing the research progress and exploration directions of QS signaling molecules-mediated QS system in Microcystis. This review summarizes the action process of N-acyl homoserine lactones (AHLs) as major signaling molecules in Microcystis and discusses the detailed roles of AHL-mediated QS system in cellular morphology, physiological adaptability, and cell aggregation for colony formation to strengthen ecological adaptability and competitive advantage of Microcystis. The research progress on QS mechanisms in Microcystis are also summarized. Compared to other QS systems, the LuxI/LuxR-type QS system is more likely to be found in Microcystis. Also, we introduce quorum quenching (QQ), a QS-blocking process in Microcystis, to emphasize its potential as QS inhibitors in MCBs control. Finally, in response to the research deficiencies and gaps in Microcystis QS, we propose several future research directions in this field. This review deepens the understanding on Microcystis QS knowledge and provide theoretical guidance in developing strategies to monitor, control, and harness MCBs.

Bacteria-based Sodium Alginate Formulation to Control Toxic Microcystis Blooms

Cyanobacterial bloom formation in freshwaters is a major socio-economic and health concern across the globe. Presently used chemical and physical control strategies are inefficient in complete removal of blooms and chemical application often lead to secondary pollution in water. Hence, the current study aimed to develop a bacteria-based formulation to control toxic bloom-forming Microcystis aeruginosa in freshwaters. Two bacterial strains, Exiguobacterium acetylicum and Pseudomonas previously isolated from Sri Lankan freshwaters and characterized for M. aeruginosa cell lysis and their microcystin (MC) toxin degradation were used in the study. Initially, suitability of bacterial strains to develop into solid formulations was evaluated through biofilm formation, antibiotic sensitivity and strain compatibility. Both strains formed biofilms on the surface of microtiter plates indicating their ability to attach and colonize on solid surfaces. The multiple antibiotic resistance indices for both strains were below the threshold risk level (0.2) against the seven tested classes of antibiotics. This result indicates that there is a low risk in introducing these bacterial strains to the natural environment. Further, plate assay showed that the two strains were compatible to stay together showing no antagonistic effect on the growth of each other. Having fulfilled all three criteria tested, the two strains were immobilized into beads (~5 mm) prepared from sodium alginate at 1:1 ratio of 1×108 cells/mL bacterial inoculum. Different weights (1.0, 2.0, 3.0 g) of bacteria-immobilized beads were enclosed in sachets made with Cambrella synthetic fabric. They were introduced to M. aeruginosa grown in BG-11 medium (OD=0.2, 730 nm) and kept at 26 °C. During incubation, growth stimulation of M. aeruginosa was visually observed in 1.0 and 2.0 g beads-containing cultures, whereas, gradual discoloration of colonies was observed with 3.0 g of beads. Microscopic observations also proved complete disintegration of M. aeruginosa colonies and lysis of cells in discolored cultures. After 15 days, M. aeruginosa cell lysis was estimated as a measure of chlorophyll degradation. The highest (8.4%) cell lysis was observed in cultures containing 3.0 g of beads. This indicates that bacteria cell lysis activity depends on the load of bacteria-immobilized beads. Degradation of MC toxin was estimated by enzyme-linked immunosorbent assay. The highest (57.6%) MC degradation was observed in cultures with 3.0 g of beads after 15 days of incubation. The efficiency of bacteria release from beads was tested by placing sachets in sterilized water. At 15 days, bacterial count in water was x107 CFU/mL, with all loadings of immobilized-bacteria indicating highly efficient bacteria release from the formulation. In conclusion, this study highlights that bacteria-based sodium alginate formulations can be made as a source of inoculum to control M. aeruginosa growth and MC degradation. 
 Keywords: Bacteria-based formulations, Cell lysis, Microcystis blooms, Microcystin

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

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

Selection of photosynthetic traits by turbulent mixing governs formation of cyanobacterial blooms in shallow eutrophic lakes.

Abstract Prediction of the complex cyanobacteria-environment interactions is vital for understanding harmful bloom formation. Most previous studies on these interactions considered specific properties of cyanobacterial cells as representative for the entire population (e.g. growth rate, mortality, and photosynthetic capacity (Pmax)), and assumed that they remained spatiotemporally unchanged. Although, at the population level, the alteration of such traits can be driven by intraspecific competition, little is known about how traits and their plasticity change in response to environmental conditions and affect the bloom formation. Here we test the hypothesis that intraspecific variations in Pmax of cyanobacteria (Microcystis spp.) play an important role in its population dynamics. We coupled a one-dimensional hydrodynamic model with a trait-based phytoplankton model to simulate the effects of physical drivers (turbulence and turbidity) on the Pmax of Microcystis populations for a range of dynamic conditions typical for shallow eutrophic lakes. Our results revealed that turbulence acts as a directional selective driver for changes in Pmax. Depending on the intensity of daily-periodic turbulence, representing wind-driven mixing, a shift in population-averaged phenotypes occurred toward either low Pmax, allowing the population to capture additional light in the upper layers, or high Pmax, enhancing the efficiency of light utilization. Moreover, we observed that a high intraspecific diversity in Pmax accelerated the formation of surface scum by up to more than four times compared to a lower diversity. This study offers insights into mechanisms by which cyanobacteria populations respond to turbulence and underscores the significance of intraspecific variations in cyanobacterial bloom formation. Highlights

Phytoplankton interspecific interactions modified by symbiotic fungi and bacterial metabolites under environmentally relevant hydrogen peroxide concentrations stress

Hydrogen peroxide (H2O2), which accumulates in water and triggers oxidative stress for aquatic microbes, has been shown to have profound impacts on planktonic microbial community dynamics including cyanobacterial bloom formation. Yet, potential effects of H2O2 on interspecific relationships of phytoplankton-microbe symbiotic interactions remain unclear. Here, we investigated effects of environmentally relevant H2O2 concentrations on interspecific microbial relationships in algae-microbe symbiosis. Microbes play a crucial role in the competition between M. aeruginosa and Chlorella vulgaris at low H2O2 concentrations (∼400 nM), in which fungi and bacteria protect Microcystis aeruginosa from oxidative stress. Moreover, H2O2 stimulated the synthesis and release of extracellular microcystin-LR from Microcystis aeruginosa, while intracellular microcystin-LR concentrations remained at a relatively constant level. In the presence of H2O2, loss of organoheterocyclic compounds, organic acids and ketones contributed to the growth of M. aeruginosa, but the reduction of vitamins inhibited it. Regulation of interspecific relationships by H2O2 is achieved by its action on fungal species and bacterial secretory metabolites. This study explored the response of phytoplankton interspecific relationships in symbiotic phytoplankton-microbe interactions to environmentally relevant H2O2 concentrations stress, providing a theoretical basis for understanding the formation of harmful-algae blooming and impact of photochemical properties of water on aquatic ecological safety and stability.

Influence of Denitrification on Cyanobacterial Blooms Trends in Lake Taihu, China

Denitrification is a major process in aquatic ecosystems, and it competes with cyanobacterial growth for nitrogen. However, the effect of denitrification on cyanobacterial blooms under the background of climate change remains unclear. This study explored the interaction between lake denitrification and formation of cyanobacterial blooms, using the historical water quality monitoring data of North Lake Taihu over five years from 2017 to 2021 and via incubation experiments of cyanobacteria and sediment denitrification. The monitoring data showed that algal biomass (Chla as a proxy) primarily peaked during summer and autumn. The seasonal variations in total N concentration showed a completely opposite trend than that of algal biomass, which peaked in winter and spring. Nitrate was the major component of dissolved inorganic nitrogen, and the nitrate concentration was approximately zero in summer and autumn. The total phosphorus concentration varied in the same way as the Chla concentration. The experimental results showed that Cyanobacteria did not grow when the temperature was below 20℃. In comparison, denitrification showed a significant linear relationship with temperatures between 10-25℃ (R2=0.99) and reached the maximum value of (62.98±21.36) μmol·(kg·h)-1 in Lake Taihu at 25℃. Additionally, the nitrate concentration threshold at the maximum denitrification rate was 4 mg·L-1. Cyanobacteria assimilate nitrate for growth, thereby reducing the concentration of nitrate required for denitrification. This study indicated that the advance in lake temperature warming due to climate change may result in earlier growth of cyanobacteria, thereby leading to large amounts of N being assimilated by algae before denitrification, further affecting the dynamics of cyanobacterial blooms. The present results are scientifically important for explaining the mechanism of cyanobacterial bloom rebound in Lake Taihu under the background of recent climate changes.

Bioavailable iron concentrations regulate phytoplankton growth and bloom formation in low-nutrient lakes

The growth of phytoplankton in lakes is thought to be primarily controlled by macronutrient concentrations, but the availability of trace metal micronutrients, such as iron (Fe), are increasingly recognised as important regulators of lake primary production. This study evaluates the role of Fe in regulating phytoplankton growth in lakes of different nutrient status in New Zealand. The results of this unique year-long study, combining highly sensitive trace metal concentration analysis of waters and particulates with advanced trace metal bioavailability and speciation modelling, constrains thresholds for bioavailable Fe and colloidal Fe of 0.8 nmol·L−1 and 30 nmol·L−1, respectively, below which phytoplankton growth-limitation occurs. These thresholds specifically control diatom bloom formation and termination in lakes, thereby exerting a strong influence on freshwater carbon sequestration, given the dominance of diatoms in lake bloom assemblages. Importantly, potentially toxic cyanobacteria thrived only after events of bottom water anoxia, when additional dissolved Fe in concentrations ≥4 nmol·L−1 was released into the water column. These new thresholds for bioavailable and colloidal Fe offer the potential to manage micronutrient levels in lakes for the purpose of regulating algal bloom formation and carbon sequestration, while at the same time, suppressing the formation of harmful cyanobacterial blooms.

Promoting effect and mechanism of residual feed organic matter on the formation of cyanobacterial blooms in aquaculture waters

Cyanobacterial blooms and eutrophication often occur in aquaculture waters where feeds are used. We hypothesize that residual feed organic matter (RFOM) can contribute to increased dissolved reactive phosphorus (SRP) concentrations in the water column by altering sediment phosphorus release characteristics (PRCS), including phosphorus fractions (i.e., Fe–P) and phosphorus adsorption (i.e., Qmax, EPC0), which is ultimately conducive to the formation of cyanobacteria blooms. Three types of aquaculture waters that were never feeding (NF), long-term feeding (LF), and stopped feeding (SF) for several years were studied to verify the above hypothesis. The results showed that the concentrations of SRP and chlorophyll-a in LF were significantly higher than those in SF and NF (P < 0.05). RFOM significantly affects PRCS with a power function relationship with EPC0 and a linear relationship with Qmax. Similarly, SRP in the water column was positively correlated with PRCS (i.e., Fe–P, EPC0), cyanobacterial biomass, and trophic state index (P < 0.01). This suggested that SRP may be an essential link between sediment and algal community structure. Simulation experiments further confirmed the above hypothesis, With the increase in RFOM (94.36 g/kg), PRCS (i.e., Fe–P, EPC0, and Qmax) increased significantly, which were 6.60, 282.36, and 2.47 times that of the control group, respectively. The sediment bacterial community and the partial least squares path model indicated that RFOM could regulate the SRP concentration in the water body and promote the formation of cyanobacterial blooms through PRCS, in which Firmicutes played an important role. This study revealed the driving process and mechanism of feeding behavior on the formation of cyanobacterial blooms and eutrophication in aquaculture waters, which provided a basis for the health management and cleaning strategy of aquaculture waters.

Label-Free Cyanobacteria Quantification Using a Microflow Cytometry Platform for Early Warning Detection and Characterization of Hazardous Cyanobacteria Blooms.

The eutrophication of aquatic ecosystems caused by rapid human urbanization has led to an increased production of potentially hazardous bacterial populations, known as blooms. One of the most notorious forms of these aquatic blooms are cyanobacteria, which in sufficiently large quantities can pose a hazard to human health through ingestion or prolonged exposure. Currently, one of the greatest difficulties in regulating and monitoring these potential hazards is the early detection of cyanobacterial blooms, in real time. Therefore, this paper presents an integrated microflow cytometry platform for label-free phycocyanin fluorescence detection, which can be used for the rapid quantification of low-level cyanobacteria and provide early warning alerts for potential harmful cyanobacterial blooms. An automated cyanobacterial concentration and recovery system (ACCRS) was developed and optimized to reduce the assay volume, from 1000 mL to 1 mL, to act as a pre-concentrator and subsequently enhance the detection limit. The microflow cytometry platform utilizes an on-chip laser-facilitated detection to measure the in vivo fluorescence emitted from each individual cyanobacterial cell, as opposed to measuring overall fluorescence of the whole sample, potentially decreasing the detection limit. By applying transit time and amplitude thresholds, the proposed cyanobacteria detection method was verified by the traditional cell counting technique using a hemocytometer with an R2 value of 0.993. It was shown that the limit of quantification of this microflow cytometry platform can be as low as 5 cells/mL for Microcystis aeruginosa, 400-fold lower than the Alert Level 1 (2000 cells/mL) set by the World Health Organization (WHO). Furthermore, the decreased detection limit may facilitate the future characterization of cyanobacterial bloom formation to better provide authorities with ample time to take the appropriate actions to mitigate human risk from these potentially hazardous blooms.

Long‐term cyanobacterial dynamics from lake sediment DNA in relation to experimental eutrophication, acidification and climate change

Abstract Cyanobacterial blooms in aquatic environments have impacted ecosystem health, altered food webs and contributed to substantial regional economic losses. The relative impacts of climate change, eutrophication and other environmental stressors on the formation of cyanobacterial blooms remain unclear as a consequence of the lack of long‐term data. The analysis of lake sediment archives can help address such questions. The abundance of target cyanobacterial genes was quantified using droplet digital PCR from two experimental and two reference lakes at the IISD ‐ Experimental Lakes Area, Northwestern Ontario, Canada where various anthropogenic drivers have been manipulated and phytoplankton biomass and taxonomy (via microscopy) tracked over the past 50 years. Based on sediment DNA (sedDNA) records, Lake 227 has seen more than two full orders of magnitude rise in cyanobacterial abundance in response to experimental nutrient (nitrogen and phosphorus) loading since 1969. Lake 223 also experienced a small increase in cyanobacterial abundance during a period of experimental acidification. The sedDNA archives also identified an increase in abundance of mcyE, a gene involved in microcystin synthesis, in Lake 227 after 1990 when experimental nitrogen loading ceased and only phosphorus loading continued. Sequencing of the cyanobacterial 16S rRNA gene from sedDNA revealed a shift towards Nostocales dominance in response to eutrophication in Lake 227; this was also seen in the more recent sediments of the other lakes but to a much lesser extent. When comparing the sedDNA data with historical phytoplankton records of the past ~50 years, moderate‐to‐strong correlations were found between the two. This research validated the use of sedDNA for the analysis of long‐term trends in lakes and the results revealed additional changes that were not recorded from the surface‐water records. Experimental nutrient loading had the greatest influence on the cyanobacterial community in Lake 227. However, climate change, via declines in heating degree days, was also significant in explaining variation in the cyanobacterial communities in the experimental lakes as well as the reference lakes.

Sulfolipid substitution ratios of Microcystis aeruginosa and planktonic communities as an indicator of phosphorus limitation in Lake Erie

AbstractPhosphorus (P) availability frequently limits primary production in lakes, influences the physiology of phytoplankton, shapes community structure, and can stimulate or constrain the formation of cyanobacterial blooms. Given the importance of P, numerous methods are available to assess P stress in phytoplankton communities. Marine phytoplankton are known to substitute sulfolipids for phospholipids in response to P limitation. We asked whether sulfolipid substitution might serve as an additional indicator of P stress in freshwater phytoplankton communities. The question was addressed using cultures of Microcystis aeruginosa, Lake Erie microcosms, and surveys of lipid profiles in Lake Erie during a Microcystis spp. bloom. Peak area response ratios of the intact polar lipids sulfoquinovosyldiacylglycerol (SQDG) to phosphatidylglycerol (PG) were used as the metric of lipid substitution. In cultures of M. aeruginosa NIES‐843, the SQDG : PG ratio increased from ~ 0.9 to ~ 3.3 with decreasing P concentration. In P‐limited communities, the SQDG : PG ratio increased from ~ 6 to ~ 11 after 48 h in microcosm controls, while P amendments reduced the ratio to ~ 3. In Lake Erie surveys, the SQDG : PG ratio ranged from ~ 0.4 to ~ 7.4 and was negatively correlated (Pearson r = −0.62) with total dissolved P. The SQDG : PG ratio was not correlated with concentrations of chlorophyll a, soluble reactive P, or N : P molar ratios. These results demonstrated that M. aeruginosa and Microcystis‐dominated communities remodel lipid profiles in response to P scarcity, providing a potential short‐term, time‐integrated biomarker of nutrient history and P stress in fresh waters.

Sequencing the genomes of LPP-1, the first isolated cyanophage, and its relative LPP-2 reveal different integration mechanisms in closely related phages

In the early 1960s, the first cyanophage was isolated. The description of this phage, named LPP-1, led to the extensive investigation of various cyanophages and to the study of their interactions with their cyanobacterial hosts towards controlling blooms. Here, the genomes of LPP-1 and its putative relative, LPP-2 were sequenced. Sequencing these genomes revealed that LPP-1 and LPP-2 are members of a group of short-tailed cyanophages, which are distantly related to the T7-like cyanophages. Most of the phages in this group have the ability to lysogenize their hosts. Their ability to switch between lytic and lysogenic infection may explain the formation of cyanobacterial blooms despite the persistence of their phages. This lysogenic capacity of the LPP-1-like phages occurs despite the lack of an obvious integrase gene within their genomes. Interestingly, we show that LPP-2 integrates into the host genome through an integration site in high proximity to a recombination endonuclease that may have integrase activity. Further understanding of cyanobacterial-phage relationships may provide insight into their population dynamics and suggest novel approaches for control of destructive cyanobacterial blooms.

Blooms and flows: Effects of variable hydrology and management on reservoir water quality

AbstractFlow management has the potential to significantly affect ecosystem condition. Shallow lakes in arid regions are especially susceptible to flow management changes, which can have important implications for the formation of cyanobacterial blooms. Here, we reveal water quality shifts associated with changing source water inflow management. Using in situ monitoring data, we studied a seven‐year time span during which inflows to a shallow, eutrophic drinking water reservoir transitioned from primarily natural landscape runoff (2014–2015) to managed flows from a larger upstream reservoir (Lake Diefenbaker; 2016–2020) and identified significant changes in cyanobacteria (as phycocyanin) using generalized additive models to classify cyanobacterial bloom formation. We then connected changes in water source with shifts in chemistry and the occurrence of cyanobacterial blooms using principal components analysis. Phycocyanin was greater in years with managed reservoir inflow from a mesotrophic upstream reservoir (2016–2020), but dissolved organic matter (DOM) and specific conductivity, important determinants of drinking water quality, were greatest in years when landscape runoff dominated lake water source (2014–2015). Most notably, despite changing rapidly, it took multiple years for lake water to return to a consistent and reduced level of DOM after managed inflows from the upstream reservoir were resumed, an observation that underscores how resilience may be hindered by weak resistance to change and slow recovery. Environmental flows for water quality are rarely defined, yet we show that trade‐offs exist between poor water quality via elevated conductivity and DOM and higher bloom risk, depending on water source. Our work highlights the importance of source water quality, not just quantity, to water security, and our findings have important implications for water managers who must protect ecosystem services while adapting to projected hydroclimatic change.

Shift of calcium-induced Microcystis aeruginosa colony formation mechanism: From cell adhesion to cell division

Colony formation is an essential stage of cyanobacterial blooms. High calcium concentration can promote Microcystis aeruginosa aggregation behavior, but the mechanism of colony formation caused by calcium has rarely been reported. In this study, high calcium-induced colony formation was identified as a shift from cell adhesion to cell division, rather than only cell adhesion as previously thought. Algae responded to this calcium-induced environmental pressure by aggregating and forming colonies. Algal cells initially secreted large quantities of extracellular polysaccharides (EPS) and rapidly aggregated by cell adhesion. The highest aggregation proportion was up to 68.93%. However, high calcium concentrations cannot completely inhibit algal cell growth, but only delay the algae into the rapid growth phase. With adaption to calcium and existing high EPS content, the daughter cells reduced EPS synthesis and the aggregation proportion decreased. The increasing growth rate was also responsible for the decreased xylose content in EPS. The mechanism of colony formation changed to cell division. The downregulation of genes related to EPS secretion also supported this hypothesis. Overall, these results can benefit for our understanding of cyanobacterial bloom formation.

Cyanobacteria, water quality and public health implications: a systematic scoping review

ABSTRACT Cyanobacteria pose a significant threat to human health. Knowledge of the most prominent physical parameters related with cyanobacterial growth not only aids water monitoring but public health risk management, to enable rapid local responses to changing water quality conditions. This paper is a systematic scoping review of Australian environmental studies that examined a link between cyanobacterial growth and one or more specific physical water quality parameters. The 34 included articles showed a consistent correlation between water quality parameters and cyanobacterial growth. Temperature and light exposure were positively correlated with cyanobacteria in all studies. Salinity, flow, wind speed and turbidity were negatively correlated with cyanobacteria in all studies. Geographically, majority of the studies focussed on the Murray-Darling Basin. The consistency across studies indicates a potential for broader environmental monitoring criteria to aid in both water quality management and public health response to cyanobacterial bloom formation.

Transcriptome Analysis Reveals the Algicidal Mechanism of Brevibacillus laterosporus against Microcystis aeruginosa through Multiple Metabolic Pathways.

It is widely accepted that eutrophication has played an important role in the formation of harmful cyanobacterial blooms in recent decades, which impacts water quality and ecological environment and causes huge economic losses. Algicidal bacteria have a promising application prospect in controlling cyanobacterial blooms in aquaculture water. Here, the process of the algicidal bacterium Brevibacillus laterosporus strain Bl-zj acting on Microcystis aeruginosa was explored using transcriptome analysis to elucidate the algicidal mechanism. The results of the co-culture of bacterium and alga showed a strong alga-lysing effect of B. laterosporus against M. aeruginosa with an extreme morphology deformation of the algal cells. A total of 2744 differentially expressed genes of B. laterosporus were identified, which were mainly involved in the metabolism of amino acid, carbohydrate, and lipid. In the co-cultured group, the expression of genes mainly enriched in valine, leucine and isoleucine degradation, and fatty acid degradation were significantly increased. However, the expression of the genes related to ribosome were mainly inhibited. Transcriptome analysis showed that B. laterosporus obtained ATP and energy by the degradation of valine, leucine, isoleucine, and fatty acids, and destroyed algal cells by efflux pump transporters, secretion of hydrolytic enzymes, antibiotics, proteases, and other secondary metabolites, resulting in algal death and achieving the algicidal effect.

Effects of Weather Extremes on the Nutrient Dynamics of a Shallow Eutrophic Lake as Observed during a Three-Year Monitoring Study

The formation of algal and cyanobacterial blooms caused by the eutrophication of water bodies is a growing global concern. To examine the impact of extreme weather events on blooms, eutrophication-related parameters (e.g., water temperature, nitrate, ammonium, nitrite, and soluble reactive phosphate (SRP)) were quantitatively assessed monthly over three years (2017–2019) at Lake Seeburg (Central Germany), a shallow eutrophic lake with regular cyanobacterial blooms. In addition, SRP concentrations in sediment pore water were assessed monthly for one year (2018). The monitoring period included a three-day extremely heavy rain event in 2017 as well as a severe drought in summer 2018. No such extreme weather conditions occurred in 2019. After the heavy rain event in 2017, anoxic water containing high levels of ammonium and SRP entered the lake from flooded upstream wetlands. This external nutrient spike resulted in a heavy but short (3 weeks) and monospecific cyanobacterial bloom. A different situation occurred during the exceptionally hot and dry summer of 2018. Especially favored by high water temperatures, SRP concentrations in sediment pore waters gradually increased to extreme levels (34.4 mg/L). This resulted in a strong and sustained internal SRP delivery into the water column (69 mg/m2·d−1), which supported the longest-lasting cyanobacterial bloom (3 months) within the three-year monitoring period. Subsequent biomass decay led to oxygen-depleted conditions in the bottom waters, elevated ammonium, and, later, nitrate concentrations. Our observations demonstrate the particular effects of extreme weather events on nutrient dynamics and the phytoplankton composition in the lake. As the frequency and intensity of such events will likely increase due to climate change, their impacts need to be increasingly considered, e.g., in future remediation strategies.

Towards the Selection of Single‐Stranded DNA Molecular Recognition Element Against Cyanotoxin L‐BMAA

Global warming, anthropogenic pressure and eutrophication contribute to the formation and persistence of cyanobacterial blooms in aquatic environments. Cyanotoxins produced during these blooms represent a threat to ecosystems, commercial industries and human health. B‐N‐methylamino‐L‐alanine (L‐BMAA) is a neurotoxic amino acid that has been linked to neurodegenerative diseases such as Amyotrophic Lateral Sclerosis/Parkinsonism Dementia Complex (ALS/PDC), Alzheimer’s disease (AD) and Amyotrophic Lateral Sclerosis (ALS). Research has shown that L‐BMAA can act as a glutamate receptor antagonist and can incorporate into proteins occasioning protein misfolding that leads to detrimental processes in brain tissues. Currently, the detection of L‐BMAA is costly, time‐consuming and labor‐intensive. Many research groups around the world are working towards the development of bioanalytical methods to improve the detection of these toxins, including the development of molecular biorecognition elements (MREs) that can provide analyte specificity in biosensing applications. Among MREs, aptamers are well‐known to possess an extraordinary target recognition due to the formation of unique three‐dimensional structures capable of binding specifically to their respective targets.We aim to perform an in vitro selection of a single‐stranded DNA (ssDNA) aptamer that can act as an MRE against L‐BMAA, using the systematic evolution of ligands by exponential enrichment (SELEX) technique. We have worked on the optimization of incubation conditions, PCR amplification parameters and the generation of ssDNA using two different ssDNA libraries, with randomized regions of varying lengths. To facilitate the separation of bound and unbound ssDNA after incubation with the target, we modified L‐BMAA with a biotinylated linker to immobilize it in streptavidin‐coated magnetic beads. For each library, we have identified the appropriate annealing temperature, primer concentrations and number of cycles to favor the amplification of the main product while minimizing by‐product formation. The most challenging step of the SELEX procedure has been the generation and purification of ssDNA in sufficient amounts to continue to the next round of selection. To achieve this, we have tried four main methods: exonuclease digestion, size separation derived from uneven primers, asymmetric PCR and alkaline denaturation using sodium hydroxide. Hitherto, we have completed the first round of selection with both libraries, by performing large‐scale PCR reactions and alkaline denaturation followed by ethanol precipitation to generate the ssDNA. We are working in the first round of negative selection to discard those sequences with affinity to the immobilization linker and enrich only those that bind exclusively to L‐BMAA. Given that our target is a small molecule, our goal is to conduct a stringent SELEX process to obtain a highly specific MRE that can be incorporated into an environmental sensing device.

Community succession during the preventive control of cyanobacterial bloom by hydrogen peroxide in an aquatic microcosm

Hydrogen peroxide (H2O2) is an environmentally friendly algaecide with good prospects for cyanobacterial bloom control. In this study, 0.2–1.5 mg L−1 of H2O2 was applied to an aquatic microcosm containing cyanobacteria, bacteria, and eukaryotic phytoplankton at the early cyanobacterial growth stage·H2O2 generated hormesis in cyanobacteria at 0.2 mg L−1; significantly (p < 0.05) inhibited cyanobacterial growth, cyanobacterial photosynthesis, and microcystin production at 0.5–1.5 mg L−1; and effectively prevented the formation of cyanobacterial bloom without generating adverse effects on eukaryotic phytoplankton at 1.0 and 1.5 mg L−1. Application of 0.5–1.5 mg L−1 H2O2 directly inhibited the abundance of five typical bloom-forming cyanobacterial genera (Microcystis, Anabeana, Synechococcus, Nostoc, and Oscillatoria), which were negatively correlated with four bacterial genera (Actinotalea, Flavobacterium, Fluviicola, and Exiguobacterium) and five eukaryotic phytoplankton genera (Cyclotella, Desmodesmus, Dinobryon, Fragilaria, and Mychonastes) and positively correlated with six proteobacterial genera (Brevundimonas, Devosia, Limnohabitans, Porphyrobacter, Pseudomonas, and Rhodobacter). After application of 1.0 and 1.5 mg L−1 H2O2 for 15 days, H2O2-treated groups showed significantly (p < 0.05) different prokaryotic community structures from that of the control group at the bloom stage (15th day), while eukaryotic community structures in H2O2-treated groups remained stable and showed high similarity with that of the control group at a non-bloom stage (5th day). Application of low-dose H2O2 during the early cyanobacterial growth stage could effectively prevent the formation of cyanobacterial blooms without disrupting non-target organisms.

Optimal Band Selection for Airborne Hyperspectral Imagery to Retrieve a Wide Range of Cyanobacterial Pigment Concentration Using a Data-Driven Approach

Understanding the concentration and distribution of cyanobacteria blooms is an important aspect of managing water quality problems and protecting aquatic ecosystems. Airborne hyperspectral imagery (HSI)—which has high temporal, spatial, and spectral resolutions—is widely used to remotely sense cyanobacteria bloom, and it provides the distribution of the bloom over a wide area. In this study, we determined the input spectral bands that were relevant in effectively estimating the main two pigments (PC, Phycocyanin; Chl-a, Chlorophyll-a) of cyanobacteria by applying data-driven algorithms to HSI and then evaluating the change in the spatio-temporal distribution of cyanobacteria. The input variables for the algorithms consisted of reflectance band ratios associated with the optical properties of PC and Chl-a, which were calculated by the selected hyperspectral bands using a feature selection method. The selected input variable was composed of six reflectance bands (465.7–589.6, 603.6–631.8, 641.2–655.35, 664.8–679.0, 698.0–712.3, and 731.4–784.1 nm). The artificial neural network showed the best results for the estimation of the two pigments with average coefficients of determination 0.80 and 0.74. This study proposes relevant input spectral information and an algorithm that can effectively detect the occurrence of cyanobacteria in the weir pool along the Geum river, South Korea. The algorithm is expected to help establish a preemptive response to the formation of cyanobacterial blooms, and to contribute to the preparation of suitable water quality management plans for freshwater environments.