Detection of potentially producing cylindrospermopsin and microcystin strains in mixed populations of cyanobacteria by simultaneous amplification of cylindrospermopsin and microcystin gene regions

Cyanotoxins, biosynthetic gene clusters, and factors modulating cyanotoxin biosynthesis

Cyanobacterial harmful algal blooms (CHABs) are a global environmental concern that encompasses public health issues, water availability, and water quality owing to the production of various secondary metabolites (SMs), including cyanotoxins in freshwater, brackish water, and marine ecosystems. The frequency, extent, magnitude, and duration of CHABs are increasing globally. Cyanobacterial species traits and changing environmental conditions, including anthropogenic pressure, eutrophication, and global climate change, together allow cyanobacteria to thrive. The cyanotoxins include a diverse range of low molecular weight compounds with varying biochemical properties and modes of action. With the application of modern molecular biology techniques, many important aspects of cyanobacteria are being elucidated, including aspects of their diversity, gene-environment interactions, and genes that express cyanotoxins. The toxicological, environmental, and economic impacts of CHABs strongly advocate the need for continuing, extensive efforts to monitor cyanobacterial growth and to understand the mechanisms regulating species composition and cyanotoxin biosynthesis. In this review, we critically examined the genomic organization of some cyanobacterial species that lead to the production of cyanotoxins and their characteristic properties discovered to date.

Molecular detection of some toxogenic cyanobacteria in Tigris River in Baghdad-Iraq

Cyanobacteria and their pollution are being increasingly commonly reported worldwide that cause a serious hazard to environmental and human health. Cyanotoxin was the most algal toxin reported to be produced by several orders of cyanobacteria. This study aimed to provide a technique to detect cylindrosprmopsin and saxitoxin biosynthesis genes in the river. In November, December 2019, and January 2020. Cyanobacteria were isolated from freshwater of Tigris River and identified by compound microscope also conventional PCR. Five isolates of cyanobacteria that successfully amplified a gene fragment from the phycocyanin were found in all cyanobacteria (Microcystis flosaquae, Microcystis sp, anabaena circinalis, nostoc commune and westiellopsis prolifica) and all isolates successfully amplified aoaC gene to detecting the cylidrospemopsin and the saxitoxin. Our results concluded that PCR assay can be used for early detection of cylidrospemopsin and the saxitoxin producing cyanobacteria in river water that useful to stations responsible for the preparation of drinking water to public.

Overview of toxic cyanobacteria and cyanotoxins in Ibero-American freshwaters: Challenges for risk management and opportunities for removal by advanced technologies

The increasing occurrence of cyanobacterial blooms worldwide represents an important threat for both the environment and public health. In this context, the development of risk analysis and management tools as well as sustainable and cost-effective treatment processes is essential. The research project TALGENTOX, funded by the Ibero-American Science and Technology Program for Development (CYTED-2019), aims to address this ambitious challenge in countries with different environmental and social conditions within the Ibero-American context. It is based on a multidisciplinary approach that combines ecology, water management and technology fields, and includes research groups from Chile, Colombia, Mexico, Peru and Spain. In this review, the occurrence of toxic cyanobacteria and cyanotoxins in freshwaters from these countries are summarized. The presence of cyanotoxins has been confirmed in all countries but the information is still scarce and further monitoring is required. In this regard, remote sensing or metagenomics are good alternatives at reasonable cost. The risk management of freshwaters from those countries considering the most frequent uses (consumption and recreation) has been also evaluated. Only Spain and Peru include cyanotoxins in its drinking water legislation (only MC-LR) and thus, there is a need for regulatory improvements. The development of preventive strategies like diminishing nutrient loads to aquatic systems is also required. In the same line, corrective measures are urgently needed especially in drinking waters. Advanced Oxidation Processes (AOPs) have the potential to play a major role in this scenario as they are effective for the elimination of most cyanotoxins classes. The research on the field of AOPs is herein summarized considering the cost-effectiveness, environmental character and technical applicability of such technologies. Fenton-based processes and photocatalysis using solar irradiation or LED light represent very promising alternatives given their high cost-efficiency. Further research should focus on developing stable long-term operation systems, addressing their scale-up.

Phylogeographic, toxicological and ecological evidence for the global distribution of Raphidiopsis raciborskii and its northernmost presence in Lake Nero, Central Western Russia

Raphidiopsis raciborskii is a freshwater, potentially toxigenic cyanobacterium, originally described as a tropical species that is spreading to northern regions over several decades. The ability of R. raciborskii to produce cyanotoxins - in particular the alkaloid cylindrospermopsin (CYN), which is toxic to humans and animals - is of serious concern. The first appearance of R. raciborskii in Russia was noted in Lake Nero in the summer of 2010. This is the northernmost (57°N) recorded case of the simultaneous presence of R. raciborskii and detection of CYN. In this study, the data from long-term monitoring of the R. raciborskii population, temperature and light conditions in Lake Nero were explored. CYN and cyr/aoa genes present in environmental samples were examined using HPLC/MS-MS and PCR analysis. A R. raciborskii strain (R104) was isolated and its morphology, toxigenicity and phylogeography were studied. It is supposed that the trigger factor for the strong development of R. raciborskii in Lake Nero in summer 2010 may have been the relatively high water temperature, reaching 29-30 °C. Strain R. raciborskii R104 has straight trichomes and can produce akinetes, making it morphologically similar to European strains. Phylogeographic analysis based on nifH gene and 16S-23S rRNA ITS1 sequences showed that the Russian strain R104 grouped together with R. raciborskii strains isolated from Portugal, France, Germany and Hungary. The Russian strain R104 does not contain cyrA and cyrB genes, meaning that it - like all European strains - cannot produce CYN. Thus, while recent invasion of R. raciborskii into Lake Nero has occurred, morphological, genetic, and toxicological data supported the spreading of this cyanobacterium from other European lakes. Detection of CYN and cyr/aoa genes in environmental samples indicated the cyanobacterium Aphanizomenon gracile as a likely producer of CYN in Lake Nero. The article also discusses data on the global biogeography of R. raciborskii. Genetic similarity between R. raciborskii strains isolated from very remote continents might be related to the ancient origin of the cyanobacterium inhabiting the united continents of Laurasia and Gondwana, rather than comparably recent transoceanic exchange between R. raciborskii populations.

Biogeography of the cyanobacterium Raphidiopsis (Cylindrospermopsis) raciborskii: Integrating genomics, phylogenetic and toxicity data

Raphidiopsis (Cylindrospermopsis) raciborskii, a globally distributed bloom-forming cyanobacterium, produces either the cytotoxin cylindrospermopsin (CYL) in Oceania, Asia and Europe or the neurotoxin saxitoxin (STX) and analogues (paralytic shellfish poison, PSP) in South America (encoded by sxt genetic cluster) and none of them in Africa. Nevertheless, this particular geographic pattern is usually overlooked in current hypotheses about the species dispersal routes. Here, we combined genomics, phylogenetic analyses, toxicity data and a literature survey to unveil the evolutionary history and spread of the species. Phylogenies based on 354 orthologous genes from all the available genomes and ribosomal ITS sequences of the taxon showed two well-defined clades: the American, having the PSP producers; and the Oceania/Europe/Asia, including the CYL producers. We propose central Africa as the original dispersion center (non-toxic populations), reaching North Africa and North America (in former Laurasia continent). The ability to produce CYL probably took place in populations that advanced to sub-Saharan Africa and then to Oceania and South America. According to the genomic context of the sxt cluster found in PSP-producer strains, this trait was acquired once by horizontal transfer in South America, where the ability to produce CYL was lost.

Detection of Cyanotoxin-Producing Genes in a Eutrophic Reservoir (Billings Reservoir, São Paulo, Brazil)

CyanoHABs (cyanobacterial harmful algal blooms) are blooms of cyanobacteria capable of producing cyanotoxins, a large group of secondary metabolites that are toxic to most eukaryotes. In this work, the main aim was to evaluate the presence of multiple genes from each of the clusters responsible for biosynthesis of cyanotoxins (cylindrospermopsin, microcystin and saxitoxin) in total DNA obtained from sixteen environmental water samples by PCR. Microcystin gene mcyE was amplified in all analyzed samples. Among the cylindrospermopsin genes analyzed, only the cyrC gene was amplified from DNA obtained from three of sixteen samples. Of the three different saxitoxin genes analyzed, sxtB and sxtI were present in four and three of the sixteen samples studied, respectively, and sxtA did not show any positive result. Based on our results, we suggest caution when using only one gene from the full clusters responsible for biosynthesis of cyanotoxins, given that it may not be sufficient to confirm or exclude the toxigenic potential of a sample.

The Diversity of Cyanobacterial Toxins on Structural Characterization, Distribution and Identification: A Systematic Review

The widespread distribution of cyanobacteria in the aquatic environment is increasing the risk of water pollution caused by cyanotoxins, which poses a serious threat to human health. However, the structural characterization, distribution and identification techniques of cyanotoxins have not been comprehensively reviewed in previous studies. This paper aims to elaborate the existing information systematically on the diversity of cyanotoxins to identify valuable research avenues. According to the chemical structure, cyanotoxins are mainly classified into cyclic peptides, alkaloids, lipopeptides, nonprotein amino acids and lipoglycans. In terms of global distribution, the amount of cyanotoxins are unbalanced in different areas. The diversity of cyanotoxins is more obviously found in many developed countries than that in undeveloped countries. Moreover, the threat of cyanotoxins has promoted the development of identification and detection technology. Many emerging methods have been developed to detect cyanotoxins in the environment. This communication provides a comprehensive review of the diversity of cyanotoxins, and the detection and identification technology was discussed. This detailed information will be a valuable resource for identifying the various types of cyanotoxins which threaten the environment of different areas. The ability to accurately identify specific cyanotoxins is an obvious and essential aspect of cyanobacterial research.

Concentrations of cylindrospermopsin toxin in water and tilapia fish of tropical fishponds in Egypt, and assessing their potential risk to human health

Unlike microcystin, cylindrospermospin (CYN) concentrations in fishpond water and their accumulation in fish tissues have been largely unexplored. This study determined CYN levels in water and tilapia fish organs from three tropical fishponds in southern Egypt. Water and fish samples were collected monthly from fishponds for 12 months (Oct 2012 to Sep 2013). The results revealed that six CYN-producing species of cyanobacteria dominated phytoplankton populations and formed blooms in these fishponds during warm months. Among these species, Anabaena affinis, Planktothrix agardhii, Cylindrospermopsis catemaco, and C. philippinensis were assigned as CYN producers for the first time in the present study. The highest cell densities of CYN-producing species in fishponds were recorded in August and September 2013, correlating with high temperature, pH and nutrient concentrations. Dissolved CYN was found in fishpond waters at levels (0.3-2.76 μg L^-1) very close to those of particulate CYN (0.4-2.37 μg L^-1). CYN was also estimated in tilapia fish organs at levels up to 417 ng g^-1 in the intestines, 1500 ng g^-1 in the livers, and 280 ng g^-1in edible muscles. Compared to the recommended guideline (0.03 μg kg^-1 day^-1), the estimated daily intake (EDI) of CYN in our samples of edible muscles exceeded this limit by a factor of 1.3-14 during summer and autumn. This might represent a risk to human health upon consumption of such contaminated fish muscles. Therefore, fishponds worldwide should be monitored for the presence toxic cyanobacteria to protect humans from their potent toxins.

Development of sensitive and specific multiplex PCR method for the detection of microcystin producing cyanobacteria in spirulina food supplements

Spirulina has emerged as the next-generation dietary supplement owing to its health benefits. Despite the advantages, there have been reports of contamination by cyanotoxins such as microcystins that can adversely affect human health. Hence, there is a need to develop a robust, efficient, and cost-effective method to detect microcystin-producing cyanobacteria in these food supplements. In this study, we have demonstrated a multiplex polymerase chain reaction (PCR) method for identification of microcystin-contamination in spirulina dietary supplements. This method involves simultaneous amplification of phycocyanin and microcystin B encoding genes (pcb, mcyB). The sensitivity of the multiplex PCR was assessed, and the limit of detecting mcyB along with pcb was found to be 250 fg/µL. The presence of microcystin was detected in five out of seven fish food supplements indicating poor culture conditions. Hence, rigorous quality control is required for monitoring the spirulina food supplements.

Detection of microcystin-producing cyanobacteria in water samples using loop-mediated isothermal amplification targeting mcyB gene

Microcystin toxin-producing cyanobacteria are known to have harmful effects on humans and animals. We have developed a loop-mediated isothermal amplification (LAMP)-based detection method by targeting the microcystin synthetase B gene (mcyB), the gene responsible for the production of microcystin. The sensitivity of the method was found to be 1 fg per reaction, and it was 1000-fold higher than the conventional PCR. The LAMP method was able to amplify the target gene with a minimum amount of dNTP (0.4 mM), which further reduces the cost of reaction. The improved LAMP assay could detect the presence of the toxin-producing cyanobacteria in water samples within 2 h of time, which demonstrates the rapidness of the method. Freshwater samples were screened using the developed LAMP, and seven water samples collected from lakes and a bird sanctuary tested positive for mcyB gene harboring cyanobacteria, and negative in all other drinking waters. Hence, the developed LAMP could be a possible alternative to the existing molecular methods for screening for microcystin in environmental samples with greater sensitivity.

An Optical Biosensor-Based Quantification of the Microcystin Synthetase A Gene: Early Warning of Toxic Cyanobacterial Blooming

The monitoring and control of toxic cyanobacterial strains, which can produce microcystins, is critical to protect human and ecological health. We herein reported an optical-biosensor-based quantification of the microcystin synthetase A (mcyA) gene so as to discriminate microcystin-producing strains from nonproducing strains. In this assay, the mcyA-specific ssDNA probes were designed in silico with an on-line tool and then synthesized to be covalently immobilized on an optical-fiber surface. Production of fluorescently modified target DNA fragment amplicons was accomplished through the use of Cy5-tagged deoxycytidine triphosphates (dCTPs) in the polymerase chain reaction (PCR) method, which resulted in copies with internally labeled multiple sites per DNA molecule and delivered great sensitivity. With a facile surface-based hybridization process, the PCR amplicons were captured on the optical-fiber surface and were induced by an evanescent-wave field into fluorescence emission. Under the optimum conditions, the detection limit was found to be 10 pM (S/N ratio = 3) and equaled 10³ gene copies/mL. The assay was triumphantly demonstrated for PCR amplicons of mcyA detection and showed satisfactory stability and reproducibility. Moreover, the sensing system exhibited excellent selectivity with quantitative spike recoveries from 87 to 102% for M. aeruginosa species in the mixed samples. There results confirmed that the method would serve as an accurate, cost-effective, and rapid technique for in-field testing of toxic Microcystis sp. in water, giving early information for water quality monitoring against microcystin-producing cyanobacteria.

Stepwise strategy for monitoring toxic cyanobacterial blooms in lentic water bodies

Climate change has been causing the increase in frequency, severity, and duration of harmful algal blooms, which makes the establishment of water management strategies indispensable. For cyanobacteria, several methods are currently used in monitoring programs. However, these methods are time-consuming and require specialists, and results are usually not provided within an adequate timeframe for taking timely mitigation actions. This work proposes a strategy for a faster, easier, and more cost-effective monitoring of cyanobacterial blooms, using a stepwise approach based on fluorometric determination of phycocyanin at an early stage. Complementary parameters (chlorophyll a, enumeration of dominant cyanobacterial species and cyanotoxin potential and quantification) are determined when necessary, thus progressively allocating human and financial resources within the monitoring program. This strategy was applied and validated using nine lentic eutrophic freshwater bodies prone to the occurrence of cyanobacterial blooms. Samples were sequentially evaluated, and the study ended up with two samples that showed high health risks. However, according to WHO guidelines, eight of the nine samples would be classified as having "moderate risk of adverse health effects" and could lead to preventive measures that would have an important regional economic impact. Therefore, the present approach proved to be a promising alternative to increase the effectiveness and accuracy of the risk assessment process in water bodies where cyanobacterial blooms occur.

Influence of Glycine and Arginine on Cylindrospermopsin Production and aoa Gene Expression in Aphanizomenon ovalisporum

Arginine (Arg) and glycine (Gly) seem to be the only substrates accepted by the amidinotransferase that catalyze the first step of the synthesis pathway of the cyanotoxin cylindrospermopsin (CYN), leading to guanidinoacetate (GAA). Here, the effect of these amino acids on the production of CYN in cultures of the cylindrospermopsin-producing strain, Aphanizomenon ovalisporum UAM-MAO, has been studied. Arg clearly increased CYN content, the increment appearing triphasic along the culture. On the contrary, Gly caused a decrease of CYN, observable from the first day on. Interestingly, the transcript of the gene ntcA, key in nitrogen metabolism control, was also enhanced in the presence of Arg and/or Gly, the trend of the transcript oscillations being like that of aoa/cyr. The inhibitory effect of Gly in CYN production seems not to result from diminishing the activity of genes considered involved in CYN synthesis, since Gly, as Arg, enhance the transcription of genes aoaA-C and cyrJ. On the other hand, culture growth is affected by Arg and Gly in a similar way to CYN production, with Arg stimulating and Gly impairing it. Taken together, our data show that the influence of both Arg and Gly on CYN changes seems not to be due to a specific effect on the first step of CYN synthesis; it rather appears to be the result of changes in the physiological cell status.

The first detection of potentially toxic Microcystis strains in two Middle Atlas Mountains natural lakes (Morocco)

Aguelmam Azizgza (LAZ) and Dayet Afourgah (DAF) are two Moroccan natural lakes located in a humid hydrographic basin of the Middle Atlas Mountains. Both are considered important reservoirs of plant and animal biodiversity. In addition, they are extensively used for recreational and fishing activities and as a water source for irrigation of agricultural crops. Recurrent cyanobacteria scum episodes in the two water bodies have been reported, Microcystis being the main genus in the scums. Here, we report on the toxic potential of three Microcystis aeruginosa strains isolated from those lakes: Mic LAZ and Mic B7 from LAZ and Mic DAF isolated from DAF. The toxic potential was checked by their microcystin (MC) content and the presence of mcy genes involved in MC synthesis. The identification and quantification of MC variants were performed by high-performance liquid chromatography-photo-diode array. The detection of mcy genes was achieved by whole-cell multiplex PCR that allowed the simultaneous amplification of DNA sequences corresponding to specific mcy regions. MC content of cultured cells, as MC-LR equivalents per gram cell biomass, was slightly higher in Mic LAZ (ca. 860) than in Mic B7 (ca. 700) and Mic DAF (ca. 690). Four MC variants were identified in the three isolates: MC-WR, MC-RR, MC-DM-WR, and MC-YR. The presence of toxic Microcystis strains in the two studied lakes may be regarded as an environmental and health hazard, especially during periods of bloom proliferation. It would be recommended the use of two complementary techniques, as those utilized herein (HPLC and mcy detection) to alert on highly probable toxicity of such lakes.

The genetics, biosynthesis and regulation of toxic specialized metabolites of cyanobacteria

The production of toxic metabolites by cyanobacterial blooms represents a significant threat to the health of humans and ecosystems worldwide. Here we summarize the current state of the knowledge regarding the genetics, biosynthesis and regulation of well-characterized cyanotoxins, including the microcystins, nodularin, cylindrospermopsin, saxitoxins and anatoxins, as well as the lesser-known marine toxins (e.g. lyngbyatoxin, aplysiatoxin, jamaicamides, barbamide, curacin, hectochlorin and apratoxins).

In search of environmental role of cylindrospermopsin: a review on global distribution and ecology of its producers

Despite a significant interest in cyanotoxins over recent decades, their biological role is still poorly elucidated. Cylindrospermopsin (CYN) is a cyanobacterial metabolite that is globally identified in surface fresh- and brackish waters and whose producers are observed to spread throughout different climate zones. This paper provides a comprehensive review of the characteristics and global distribution of CYN-producing species, the variety of their chemotypes and the occurrence of strains which, while incapable of toxin synthesis, are able to produce other bioactive compounds including those that are hitherto unknown and yet to be identified. Environmental conditions that can trigger CYN production and promote growth of CYN-producers in aquatic ecosystems are also discussed. Finally, on the basis of existing experimental evidence, potential ecological role(s) of CYN are indicated. It is eventually concluded that CYN can be at least partially responsible for the ecological success of certain cyanobacteria species.

Phylogeny and biogeography of cyanobacteria and their produced toxins

Phylogeny is an evolutionary reconstruction of the past relationships of DNA or protein sequences and it can further be used as a tool to assess population structuring, genetic diversity and biogeographic patterns. In the microbial world, the concept that everything is everywhere is widely accepted. However, it is much debated whether microbes are easily dispersed globally or whether they, like many macro-organisms, have historical biogeographies. Biogeography can be defined as the science that documents the spatial and temporal distribution of a given taxa in the environment at local, regional and continental scales. Speciation, extinction and dispersal are proposed to explain the generation of biogeographic patterns. Cyanobacteria are a diverse group of microorganisms that inhabit a wide range of ecological niches and are well known for their toxic secondary metabolite production. Knowledge of the evolution and dispersal of these microorganisms is still limited, and further research to understand such topics is imperative. Here, we provide a compilation of the most relevant information regarding these issues to better understand the present state of the art as a platform for future studies, and we highlight examples of both phylogenetic and biogeographic studies in non-symbiotic cyanobacteria and cyanotoxins.

A review on cylindrospermopsin: the global occurrence, detection, toxicity and degradation of a potent cyanotoxin

Cylindrospermopsin is an important cyanobacterial toxin found in water bodies worldwide. The ever-increasing and global occurrence of massive and prolonged blooms of cylindrospermopsin-producing cyanobacteria poses a potential threat to both human and ecosystem health. Its toxicity is associated with metabolic activation and may involve mechanisms that adversely affect a wide variety of targets in an organism. Cylindrospermopsin has been shown to be cytotoxic, dermatotoxic, genotoxic, hepatotoxic in vivo, developmentally toxic, and may be carcinogenic. Human exposure may occur through drinking water, during recreational activities and by consuming foods in which the toxin may have bioaccumulated. Drinking water shortages of sufficient quality coupled with growing human pressures and climate variability and change necessitate an integrated and sustainable water management program. This review presents an overview of the importance of cylindrospermopsin, its detection, toxicity, worldwide distribution, and lastly, its chemical and biological degradation and removal by natural processes and drinking water treatment processes.

State of knowledge and concerns on cyanobacterial blooms and cyanotoxins

Cyanobacteria are ubiquitous microorganisms considered as important contributors to the formation of Earth's atmosphere and nitrogen fixation. However, they are also frequently associated with toxic blooms. Indeed, the wide range of hepatotoxins, neurotoxins and dermatotoxins synthesized by these bacteria is a growing environmental and public health concern. This paper provides a state of the art on the occurrence and management of harmful cyanobacterial blooms in surface and drinking water, including economic impacts and research needs. Cyanobacterial blooms usually occur according to a combination of environmental factors e.g., nutrient concentration, water temperature, light intensity, salinity, water movement, stagnation and residence time, as well as several other variables. These environmental variables, in turn, have promoted the evolution and biosynthesis of strain-specific, gene-controlled metabolites (cyanotoxins) that are often harmful to aquatic and terrestrial life, including humans. Cyanotoxins are primarily produced intracellularly during the exponential growth phase. Release of toxins into water can occur during cell death or senescence but can also be due to evolutionary-derived or environmentally-mediated circumstances such as allelopathy or relatively sudden nutrient limitation. Consequently, when cyanobacterial blooms occur in drinking water resources, treatment has to remove both cyanobacteria (avoiding cell lysis and subsequent toxin release) and aqueous cyanotoxins previously released. Cells are usually removed with limited lysis by physical processes such as clarification or membrane filtration. However, aqueous toxins are usually removed by both physical retention, through adsorption on activated carbon or reverse osmosis, and chemical oxidation, through ozonation or chlorination. While the efficient oxidation of the more common cyanotoxins (microcystin, cylindrospermopsin, anatoxin and saxitoxin) has been extensively reported, the chemical and toxicological characterization of their by-products requires further investigation. In addition, future research should also investigate the removal of poorly considered cyanotoxins (β-methylamino-alanine, lyngbyatoxin or aplysiatoxin) as well as the economic impact of blooms.

Characterization of Aphanizomenon ovalisporum amidinotransferase involved in cylindrospermopsin synthesis

An increasing abundance of Aphanizomenon ovalisporum in water bodies from diverse world regions has been reported in the last few years, with the majority of the isolated strains producing the toxin cylindrospermopsin (CYN), leading to a rise in ecological and health risks. The understanding of CYN synthesis is crucial in the control of CYN production. An amidinotransferase (AMDT) seems to be the first enzyme involved in the synthesis of CYN. In this study, we have cloned and overexpressed the aoaA gene from the constitutive CYN producer A. ovalisporum UAM-MAO. The recombinant purified AoaA was characterized, confirming that it is an l-arginine:glycine AMDT. It shows an optimal activity between 32 and 37°C, at pH from 8 to 9. The activity exhibits a mixed (ping-pong/sequential) kinetic mechanism, and is inhibited by the reaction product guanidine acetate (GAA) in a noncompetitive manner. Mg²⁺ stimulates AoaA activity while Co²⁺ and Mn²⁺ inhibit it. AoaA conserves the critical residues of the catalytic site and substrate specificity of AMDTs, as the previously reported AMDT from Cylindrospermopsis raciborskii Cyr. Both proteins can be included in a new group of prokaryotic AMDTs involved in CYN production.

Assessment of cylindrospermopsin toxin in an arid Saudi lake containing dense cyanobacterial bloom

This study reports the presence of the cyanobacterial toxin cylindrospermopisn (CYN) and its producer Cylindrospermopsis raciborskii for the first time in Saudi freshwater sources. C. raciborskii was found in Gazan Dam Lake water with two morphotypes (coiled and straight). The appearance and cell density of this species was significantly positively related to high temperature and high ammonium concentrations, and negatively with nitrate and phosphate concentrations in the lake. Intracellular concentrations of CYN (4-173 μg L(-1)) were associated with C. raciborskii rather than other cyanobacteria with a maximal value obtained in June 2011, coinciding with the highest bloom of this species (19 × 10(7) trichome L(-1)). CYN cell quotas (0.6-14.6 pg cell(-1)) varied significantly along the study period and correlated with most environmental factors. The results of ELISA and liquid chromatography-mass spectrometry proved that the CYN production by strains of this species was isolated from this lake during the present study, with an amount reaching 568 μg g(-1). Extracellular CYN was also detected in cell-free lake water at concentrations 0.03-23.3 μg L(-1), exceeding the drinking water guideline value of 1 μg L(-1) during the Apr-Jul period. As this lake is an important source for drinking and irrigation waters, CYN monitoring should be included in the environmental and health risk assessment plans of these water bodies.