Blooms In Aquatic Environments Research Articles

Cyanobacteria mediate the dissemination of bacterial antibiotic resistance through conjugal transfer

Cyanobacterial blooms are expanding world-wide in freshwater and marine environments, and can cause serious ecological and environmental issues, which also contribute to the spread of antibiotic resistance genes (ARGs). However, the mechanistic understanding of cyanobacteria-mediated resistance dynamics is not fully elucidated yet. We selected Microcystis aeruginosa as a model cyanobacteria to illustrate how cyanobacteria mediate the evolution and transfer processes of bacterial antibiotic resistance. The results show that the presence of cyanobacteria significantly decreased the abundance of antibiotic resistant bacteria (ARB) and antibiotic resistant genes (ARGs) by 3% – 99% and 2%-18%, respectively. In addition, it clearly altered bacterial community structure, with the dominant genera evolving from Acinetobacter (27%) and Enterobacter (42%) to Porphyrobacter (59%). The abundance of ARGs positively correlated with Proteobacteria and Firmicutes, rather than Cyanobacteria, and Bacteroidetes. In the presence of cyanobacteria, the transfer events of bacterial resistance genes via conjugation were found to decrease by 10% – 89% (p < 0.05). Surprisingly, we found an extradentary high transfer frequency (about 0.1) for the ARGs via plasmid conjugation from the bacteria into M. aeruginosa population. It confirmed the role of cyanobacterial population as the competent hosts to facilitate ARGs spreading. Our findings provide valuable information on the risk evaluation of ARGs caused by cyanobacterial blooms in aquatic environments, key for the protection and assessment of aquatic environmental quality.

Combinatory effects of microplastics and emerging contaminants on alga Chlamydomonas reinhardtii

In oceans today, there is much concern about the effects of microplastics (MPs) and other emerging contaminants (ECs). Here, the authors investigated the combinatory effects of the MPs poly(vinyl chloride) (PVC) and acrylates/C10–30 alkyl acrylates cross-polymer (AC) (which are commonly found in face wash), together with 2-phenoxyethanol (an EC commonly used in soaps). The model photosynthetic unicellular alga Chlamydomonas reinhardtii was used to study the potential of these pollutants to initiate algal blooms. It was shown that AC alone resulted in a greater decline in algal biomass as compared with PVC in the short term (14 days). While algal cultures exposed to PVC registered the highest increase in concentrations of the chlorophyll a pigment, it was the combinatory effects of each MP and 2-phenoxyethanol that were the most pronounced in terms of the large increase in algal biomass and the formation of extracellular polymeric substances. Proliferative growths of C. reinhardtii after prolonged exposure to AC–EC contaminants show potential for initiating algal blooms in aquatic environments. Hence, AC should be considered for regulation of waste water removal into water bodies, and other combinations of MPs and ECs should also be investigated.

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.

Structural Insights into Common and Host-Specific Receptor-Binding Mechanisms in Algal Picorna-like Viruses.

Marnaviridae viruses are abundant algal viruses that regulate the dynamics of algal blooms in aquatic environments. They employ a narrow host range because they merely lyse their algal host species. This host-specific lysis is thought to correspond to the unique receptor-binding mechanism of the Marnaviridae viruses. Here, we present the atomic structures of the full and empty capsids of Chaetoceros socialis forma radians RNA virus 1 built-in 3.0 Å and 3.1 Å cryo-electron microscopy maps. The empty capsid structure and the structural variability provide insights into its assembly and uncoating intermediates. In conjunction with the previously reported atomic model of the Chaetoceros tenuissimus RNA virus type II capsid, we have identified the common and diverse structural features of the VP1 surface between the Marnaviridae viruses. We have also tested the potential usage of AlphaFold2 for structural prediction of the VP1s and a subsequent structural phylogeny for classifying Marnaviridae viruses by their hosts. These findings will be crucial for inferring the host-specific receptor-binding mechanism in Marnaviridae viruses.

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.

Causal relationship between alkaline phosphatase activities and phosphorus dynamics in a eutrophic coastal lagoon in Lake Michigan

Alkaline phosphatase plays an important role in regulating nutrient dynamics and algal blooms in aquatic environments, but the causal relationship between alkaline phosphatase (AP), nutrient status, and chemical speciation of phosphorus (P) in the water column remains elusive. A year-long time series (weekly to biweekly) sampling was conducted to investigate the causality between alkaline phosphatase dynamics, transformation of P species, and phytoplankton biomass in Veterans Park Lagoon, a closed lagoon with intense seasonal cyanobacterial blooms. As water temperature increased from spring to summer, depletion of dissolved inorganic P (DIP) drove increases in cell-associated AP (APcell, in nmol L−1). The elevated cell-associated alkaline phosphatase activities (APAcell, in nmol L−1 h−1) resulted in the transformation of particulate organic P (POP) into DIP, which enhanced the algal blooms. Not driven by DIP depletion, dissolved AP (APdiss) was spontaneously released during cyanobacterial blooms and the elevated dissolved APA (APAdiss) resulted in increase of DIP during the growing stage. This explains the concurrent high potential APA and high DIP concentrations in the water column observed here and other previous studies. The low-molecular-weight dissolved organic P (LMW-DOP) was found to be independent of both APAcell and APAdiss, consistent with previous results derived from isotope tracers. During the transition stage between fall and winter with lower water temperatures, APAdiss increased as a result of DIP depletion, while DOP was depleted and APAcell increased, and vice versa. The increase in both APAcell and APAdiss further resulted in the increase in concentration of particulate inorganic P through promoting the release of DIP from carbon-phosphate bonds and the adsorption of DIP onto particle surfaces especially under lower water temperature. Our results provide improved understanding of the concurrently high APA and DIP in the water column and provide new insights into the causal relationship between AP and P species in aquatic environments.

Cyanobacteria in an urban lake: hidden diversity revealed by metabarcoding

The study and monitoring of communities within microbiomes is important as some organisms can synthesize toxic substances, such as cyanotoxins synthesized by cyanobacteria. Cyanobacteria is a large portion of the periphyton biomass and is responsible for toxic blooms in aquatic environments. This makes urban environments an interesting environment for observing cyanobacteria diversity, due to the disturbances from anthropic activities. As many classes of cyanobacteria are difficult to identify using traditional morphology methods, the use of molecular tools could complement periphyton community studies. Herein, we use the hypervariable V4 region of 16S rRNA gene to observe cyanobacteria diversity in the periphyton from an urban lake. After DNA extraction and metabarcoding analyses, the reads were classified according to the SILVA database, and the cyanobacteria operational taxonomic units (OTUs) were separated to compare with the GenBank database. Most of the cyanobacteria OTUs obtained in this study do not correspond to cyanobacteria previously found in this environment by traditional methods, and our GenBank comparison generated significantly improved taxonomic assignments. Metabarcoding is a useful tool and has allowed our first step toward understanding the true cyanobacteria diversity in the periphyton community of urban lakes.

Involvement of microcystins, colony size and photosynthetic activity in the benthic recruitment of Microcystis

Cyanobacterial blooms in aquatic environments are a worldwide problem that greatly depend on the recruitment of benthic Microcystis species. In addition to environmental factors, physiological characteristics are also crucial for benthic recruitment of Microcystis, although the exact details remain poorly understood. In the present study, we studied the involvement of physiological characteristics in benthic recruitment from three aspects: photosynthetic activity, colony size and intracellular microcystin (MC) content. After UV irradiation the Microcystis cells were damaged and in poor physiological state. Normal benthic Microcystis (NBM) exhibited higher recruitment than damaged benthic Microcystis (DBM). This might be explained by the difference in photosynthetic activity. Small benthic colonies (20–60 μm) could reinvade the water column from sediments more easily than large colonies. Furthermore, poor physiological state was correlated with lower survival of large colonies (140–220 μm) which might decompose into smaller colonies (40–80 μm). Toxic Microcystis not only survived more easily than non-toxic ones in sediments but also recruited more readily into the water column from sediments. This might be due to the presence of intracellular MCs. During the benthic phase, toxic Microcystis might consume or release intracellular MCs to acclimate to benthic environment. We also found that sediment mixing in the form of passive suspension facilitated recruitment, but physiological characteristics, an active process, played a more decisive role. This knowledge on the physiological characteristics of Microcystis expands our understanding of benthic recruitment.

Monitoring studies should consider temporal variability to reveal relations between cyanobacterial abundance and environmental variables.

One of the main goals of monitoring cyanobacteria blooms in aquatic environments is to reveal the relationship between cyanobacterial abundance and environmental variables. Studies typically correlate data that were simultaneously sampled. However, samplings occur sparsely over time and may not reveal the short-term responses of cyanobacterial abundance to environmental changes. In this study, we tested the hypothesis that stronger cyanobacteria x environment relationships in monitoring are found when the temporal variability of sampling points is incorporated in the statistical analyses. To this end, we investigated relationships between cyanobacteria and seven environmental variables that were sampled twice yearly for three years across 11 reservoirs, and data from an intensive monitoring in one of these reservoirs. Poor correlations were obtained when correlating data simultaneously sampled. In fact, the 'highly recurrent' role of phosphorus in cyanobacteria blooms is not properly observed in all sampling periods. On the other hand, the strongest correlation values for the total phosphorus x cyanobacteria relationship were observed when we used the variation of sampling points. We have also shown that environment variables better explain cyanobacteria when a time lag is considered. We conclude that, in cyanobacteria monitoring, the best approach to reveal determinants of cyanobacteria blooms is to consider environmental variability.

Heat Shock Protein 70 and 90 Genes in the Harmful Dinoflagellate Cochlodinium polykrikoides: Genomic Structures and Transcriptional Responses to Environmental Stresses.

The marine dinoflagellate Cochlodinium polykrikoides is responsible for harmful algal blooms in aquatic environments and has spread into the world's oceans. As a microeukaryote, it seems to have distinct genomic characteristics, like gene structure and regulation. In the present study, we characterized heat shock protein (HSP) 70/90 of C. polykrikoides and evaluated their transcriptional responses to environmental stresses. Both HSPs contained the conserved motif patterns, showing the highest homology with those of other dinoflagellates. Genomic analysis showed that the CpHSP70 had no intron but was encoded by tandem arrangement manner with separation of intergenic spacers. However, CpHSP90 had one intron in the coding genomic regions, and no intergenic region was found. Phylogenetic analyses of separate HSPs showed that CpHSP70 was closely related with the dinoflagellate Crypthecodinium cohnii and CpHSP90 with other Gymnodiniales in dinoflagellates. Gene expression analyses showed that both HSP genes were upregulated by the treatments of separate algicides CuSO4 and NaOCl; however, they displayed downregulation pattern with PCB treatment. The transcription of CpHSP90 and CpHSP70 showed similar expression patterns under the same toxicant treatment, suggesting that both genes might have cooperative functions for the toxicant induced gene regulation in the dinoflagellate.

Neurotoxic action of microcystin-LR is reflected in the transcriptional stress response of Caenorhabditis elegans

Cyanobacterial blooms in aquatic environments are frequently characterized by elevated levels of microcystins, a potent hepatotoxin. Here we exposed the nematode Caenorhabditis elegans with environmentally realistic concentrations of MC-LR to explore its non-hepatic toxicity. Lifespan, reproduction and growth assays confirmed the toxic potential of 100μg/L MC-LR even in this liver-lacking invertebrate. Whole-genome microarray analysis revealed that a neuromodulating action was the dominant response in nematodes challenged with 100μg/L MC-LR. Indeed, most of the 201 differentially expressed genes were associated with neurobehavior, neurogenesis, and signaling associated pathways. In addition, a whole-genome miRNA-microarray highlighted that, in particular, members of the let-7 family were differentially regulated. These miRNAs are involved in the developmental timing of cell fates, including neurons, and are probably also part of the stress response system. To conclude, neurological modulation is the main transcriptional stress response in C. elegans exposed to MC-LR.

UV-induced photochemical heterogeneity of dissolved and attached organic matter associated with cyanobacterial blooms in a eutrophic freshwater lake

Cyanobacterial blooms represent a significant ecological and human health problem worldwide. In aquatic environments, cyanobacterial blooms are actually surrounded by dissolved organic matter (DOM) and attached organic matter (AOM) that bind with algal cells. In this study, DOM and AOM fractionated from blooming cyanobacteria in a eutrophic freshwater lake (Lake Taihu, China) were irradiated with a polychromatic UV lamp, and the photochemical heterogeneity was investigated using fluorescence excitation–emission matrix (EEM)-parallel factor (PARAFAC) analysis and synchronous fluorescence (SF)-two dimensional correlation spectroscopy (2DCOS). It was shown that a 6-day UV irradiation caused more pronounced mineralization for DOM than AOM (59.7% vs. 41.9%). The EEM-PARAFAC analysis identified one tyrosine-, one humic-, and two tryptophan-like components in both DOM and AOM, and high component photodegradation rates were observed for DOM versus AOM (k > 0.554 vs. <0.519). Moreover, SF-2DCOS found that the photodegradation of organic matters followed the sequence of tyrosine-like > humic-like > tryptophan-like substances. Humic-like substances promoted the indirect photochemical reactions, and were responsible for the higher photochemical rate for DOM. The lower photodegradation of AOM benefited the integrality of cells in cyanobacterial blooms against the negative impact of UV irradiation. Therefore, the photochemical behavior of organic matter was related to the adaptation of enhanced-duration cyanobacterial blooms in aquatic environments.

Grazing on Microcystis aeruginosa and degradation of microcystins by the heterotrophic flagellate Diphylleia rotans

Cyanobacterial toxins can cause damage in aquatic ecosystems worldwide, as well as the poisoning of livestock, plants and humans when ingested in large amounts. Although many studies investigated grazing of harmful cyanobacteria by metazoan plankton, grazing of cyanobacteria by hetertophic flagellates is largely unexplored. This laboratory study investigated grazing of toxic Microcystis aeruginosa by the heterotrophic flagellate Diphylleia rotans isolated from a Saudi hypertrophic lake. D. rotans was able to feed on M. aeruginosa with estimated ingestion (10.2 to 16.5 prey flagellate −1d−1) and specific growth rates (0.71 to 0.99d−1) differed with the increase in the initial density of the flagellate. Grazing increased microcystin production within Microcystis cells during first two days of incubation, and afterwards induced the release of these toxins into the medium. The concentrations of releasing microcystin were strongly reduced in grazing-treated cultures compared to controls, indicating the degradation of microcystins by D. rotans growing under axenic conditions. Taken these results, D. rotans can play an important role in the reduction of Microcystis biomass and microcystin toxins, and thus could be used as a safe bioagent for the biocontrol of harmful algal blooms in aquatic environments.

Development and optimization of a method for the determination of Cylindrospermopsin from strains of Aphanizomenon cultures: Intra-laboratory assessment of its accuracy by using validation standards

The occurrence of cyanobacterial blooms in aquatic environments is increasing in many regions of the world due to progressive eutrophication of water bodies. Because of the production of toxins such as Cylindrospermopsin (CYN), contamination of water with cyanobacteria is a serious health problem around the world. Therefore it is necessary to develop and validate analytical methods that allow us to quantify CYN in real samples in order to alert the public of this toxin. In this work, an analytical method has been developed an optimized for the determination of CYN from Aphanizomenon ovalisporum cultures. The analytical procedure is based on solvent extraction followed by a purification step with graphitized cartridges and CYN quantification by LC–MS/MS. The extraction and purification steps were optimized using a two-level full factorial design with replications. A suitable and practical procedure for assessing the trueness and precision of the proposed method has been applied by using validation standards. The method has been suitably validated: the regression equation was calculated from standards prepared in extracts from lyophilized M. aeruginosa PCC7820 (r2≥0.9999) and the linear range covered is from 5 to 500μg CYN/L, equivalent to 0.18–18.00μg CYN/g dry weight lyophilized cells. Limits of detection and quantification were 0.04 and 0.15μg CYN/g, respectively, the recovery range (%) oscillated between 83 and 94% and intermediate precision (RSD %) values from 5.6 to 11.0%. Moreover, the present method showed to be robust for the three factors considered: the batch of the graphitized carbon cartridges, the flow rate of the sample through the cartridge, and the final re-dissolved water volume after SPE treatment, which permits its validation. The validated method has been applied to different lyophilized cultures of A. ovalisporum (LEGE X-001) to evaluate CYN content. This procedure can be used for determining CYN in lyophilized natural blooms samples in environmental studies.

Importance of strain type to predict the toxicological risk associated with Microcystis aeruginosa blooms: comparison of Microtox® analysis and immunoassay

The occurrence of toxic cyanobacterial blooms in aquatic environments, associated with human health problems and animal deaths, has increased the need for rapid, reliable and sensitive methods to determine the toxicity of microcystin produced by cyanobacteria. An in vitro Microtox(®) system and a commercially available microcystin ELISA were used to screen out the potential risk associated with selected Microcystis aeruginosa strains (Ma1D-Ma8D). Results showed the existence of three differentiated groups in the selected M. aeruginosa strains. Strains Ma7D and Ma6D were determined to be very toxic, strains Ma2D, Ma1D and Ma5D as moderately toxic and strains Ma8D, Ma4D and MA3D as non-toxic. These results agreed with the microcystin concentration values obtained by immunoassay. Although the data obtained by other authors clearly show that Microtox(®) is not sensitive to microcystins, our results suggested that this bioluminescence assay may prove useful in the preliminary screening of cyanobacterial blooms for microcystin-based toxicity. Additionally, the combination of immunodetection and toxicity-based Microtox(®) provides a useful addition to the methods already available for detection of cyanobacterial toxins.

Allelopathic Effects of Cyanobacterial Filtrates on Baltic Diatom

Abstract Allelopathy may be one of the factors affecting the formation of massive and harmful algal blooms in aquatic environments. Recent studies indicate that blooms of cyanobacteria in the Baltic Sea has grown significantly in last decades, so it is important to determine the allelopathic interactions between the dominant species of cyanobacteria and microalgae. In this work we investigated the influence of allelopathic compounds on the growth of Skeletonema marinoi by addition of cell-free filtrate of the Baltic cyanobacterium Nodularia spumigena cultures grown under different temperature (15-25°C). Additionally the effects of filtrates of both an exponential and a stationary growing culture of N. spumigena were tested on diatom. These studies indicate that high temperature affected the donor species by increasing its production of allelochemicals. The highest drop of growth of analyzed diatom were observed after the addition of cell-free filtrate obtained from N. spumigena grown at 25°C and constituted 70% of their control. N. spumigena was only allelopathic in exponential growth phase, whereas the cyanobacteria filtrate from stationary phase have any effect on S. marinoi. These findings suggest that N. spumigena may reveal allelopathic activity and that the production of allelopathic substances is influenced by the temperature and growth phase of cyanobacteria.

An opinion on the distribution and behavior of chemicals in response to climate change, with particular reference to the Asia-Pacific region

There is a general lack of knowledge as regards the effects of climate change on pollutant behavior. This is particularly true of the Asia-Pacific Region (APR). This region has major significance in terms of global pollutant emission and also displays a wide variety of environments. This review presents the authors’ opinions on possible implications of climate change for pollutant behavior in the APR. Although differing responses can be expected across the region, there are clear implications as regards the short- and long-term behavior of pollutants. Effects can be predicted through modeling, but further data are required for model calibration. Nevertheless, it can be predicted that climate change will affect processes including global distillation of persistent organic pollutants, airborne transport of heavy metals, half-life of readily degradable pollutants, and eutrophication in water bodies. Particulates are expected to play a central role in mediating the effects of climate change, and successful predictive models will need to be based on particulate-mediated transport and behavior. Climate change also has the potential to cause an increase in the intensity and frequency of harmful algal blooms in aquatic environments throughout the region, with significant implications for supply of both food and drinking water.

Characteristics of a Microcystin-Degrading Bacterium under Alkaline Environmental Conditions

The pH of the water associated with toxic blooms of cyanobacteria is typically in the alkaline range; however, previously only microcystin-degrading bacteria growing in neutral pH conditions have been isolated. Therefore, we sought to isolate and characterize an alkali-tolerant microcystin-degrading bacterium from a water bloom using microcystin-LR. Analysis of the 16S rRNA gene sequence revealed that the isolated bacterium belonged to the genus Sphingopyxis, and the strain was named C-1. Sphingopyxis sp. C-1 can grow; at pH 11.0; however, the optimum pH for growth was pH 7.0. The microcystin degradation activity of the bacterium was the greatest between pH 6.52 and pH 8.45 but was also detected at pH 10.0. The mlrA homolog encoding the microcystin-degrading enzyme in the C-1 strain was conserved. We concluded that alkali-tolerant microcystin-degrading bacterium played a key role in triggering the rapid degradation of microcystin, leading to the disappearance of toxic water blooms in aquatic environments.

Use of a rapid bioluminescence assay for detecting cyanobacterial microcystin toxicity.

The recent rise in the awareness of the occurrence of toxic cyanobacterial blooms in aquatic environments, with associated human health problems and animal deaths, has increased the need for rapid, reliable and sensitive methods of determining cyanobacterial toxicity. A luminescent bacterial toxicity test was assessed as a complement to the established mouse bioassay. Seventeen samples including pure cyanobacterial microcystin-LR hepatotoxin, laboratory isolates and natural blooms of cyanobacteria were tested and toxicity data compared with mouse LD50 values. Microcystin-LR and all five microcystin-containing cyanobacterial samples, hepatotoxic by mouse test gave EC50 values of less than 0.46 mg/ml in bioluminescence-based Microtox assays. Of 11 samples non-toxic by mouse bioassay, only two gave an EC50 of less than 0.98 mg/ml by bioluminescence assay. It is suggested that the Microtox bioluminescence assay may prove useful in the preliminary screening of cyanobacterial blooms for microcystin-based toxicity.