Detection of saxitoxin-producing cyanobacteria and Anabaena circinalis in environmental water blooms by quantitative PCR

Presence of potential toxin-producing cyanobacteria in an oligo-mesotrophic lake in Baltic Lake District, Germany: an ecological, genetic and toxicological survey

Massive developments of potentially toxic cyanobacteria in Lake Stechlin, an oligo-mesotrophic lake in the Baltic Lake District of Germany raised concerns about toxic contamination of these important ecosystems. Field samples in the phase of mass developments of cyanobacteria were used for genetic and toxicological analyses. Microcystins and microcystin genes were detected in field samples of the lake for the first time. However, the toxins were not produced by the dominant taxa (Dolichospermum circinale and Aphanizomenon flos-aquae) but by taxa, which were present only in low biomass in the samples (Microcystis cf. aeruginosa and Planktothrix rubescens). The phytoplankton successions during the study period revealed an increase of cyanobacterial populations. The findings contribute to the changes that have been investigated in Lake Stechlin since the mid-1990s. The possible reasons behind these developments may be climate change, special weather conditions and an increased nutrient pool.

Hydrophobically-associating cationic polymers as micro-bubble surface modifiers in dissolved air flotation for cyanobacteria cell separation

Dissolved air flotation (DAF), an effective treatment method for clarifying algae/cyanobacteria-laden water, is highly dependent on coagulation-flocculation. Treatment of algae can be problematic due to unpredictable coagulant demand during blooms. To eliminate the need for coagulation-flocculation, the use of commercial polymers or surfactants to alter bubble charge in DAF has shown potential, termed the PosiDAF process. When using surfactants, poor removal was obtained but good bubble adherence was observed. Conversely, when using polymers, effective cell removal was obtained, attributed to polymer bridging, but polymers did not adhere well to the bubble surface, resulting in a cationic clarified effluent that was indicative of high polymer concentrations. In order to combine the attributes of both polymers (bridging ability) and surfactants (hydrophobicity), in this study, a commercially-available cationic polymer, poly(dimethylaminoethyl methacrylate) (polyDMAEMA), was functionalised with hydrophobic pendant groups of various carbon chain lengths to improve adherence of polymer to a bubble surface. Its performance in PosiDAF was contrasted against commercially-available poly(diallyl dimethyl ammonium chloride) (polyDADMAC). All synthesised polymers used for bubble surface modification were found to produce positively charged bubbles. When applying these cationic micro-bubbles in PosiDAF, in the absence of coagulation-flocculation, cell removals in excess of 90% were obtained, reaching a maximum of 99% cell removal and thus demonstrating process viability. Of the synthesised polymers, the polymer containing the largest hydrophobic functionality resulted in highly anionic treated effluent, suggesting stronger adherence of polymers to bubble surfaces and reduced residual polymer concentrations.

Nutrient-related changes in the toxicity of field blooms of the cyanobacterium, Cylindrospermopsis raciborskii

Nutrients have the capacity to change cyanobacterial toxin loads via growth-related toxin production, or shifts in the dominance of toxic and nontoxic strains. This study examined the effect of nitrogen (N) and phosphorus on cell division and strain-related changes in production of the toxins, cylindrospermopsins (CYNs) by the cyanobacterium, Cylindrospermopsis raciborskii. Two short-term experiments were conducted with mixed phytoplankton populations dominated by C. raciborskii in a subtropical reservoir where treatments had nitrate (NO3 ), urea (U) and inorganic phosphorus (P) added alone or in combination. Cell division rates of C. raciborskii were only statistically higher than the control on day 5 when U and P were co-supplied. In contrast, cell quotas of CYNs (QCYNS ) increased significantly in treatments where P was supplied, irrespective of whether N was supplied, and this increase was not necessarily related to cell division rates. Increased QCYNS did correlate with an increase in the proportion of the cyrA toxin gene to 16S genes in the C. raciborskii-dominated cyanobacterial population. Therefore, changes in strain dominance are the most likely factor driving differences in toxin production between treatments. Our study has demonstrated differential effects of nutrients on cell division and strain dominance reflecting a C. raciborskii population with a range of strategies in response to environmental conditions.

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.

Identification and enumeration of Microcystis using a sandwich hybridization assay

Based on sequence analyses of phycocyanin intergenic spacers (PC-IGS) from Microcystis, Anabaena, Aphanizomenon, and Planktothrix (Oscillatoria) strains, a genus-specific probe pair TF/TR was designed, and a sandwich hybridization assay was established to quantitatively detect Microcystis. Through BLAST and cyanobacterial culture tests, TF/TR was demonstrated to be specific for Microcystis. A calibration curve for the sandwich hybridization assay was established, and the lowest detected concentration was 100 cell/ml. Laboratory and field samples were analyzed with both sandwich hybridization assay and microscopy. The biotic and abiotic components of the samples were of little disturbance to the sandwich hybridization assay. The results showed no distinct difference between the two methods. In this study, a sandwich hybridization assay was established to detect Microcystis, providing an alternative to traditional microscopic, morphology-based methods.

Species-specific real-time PCR cell number quantification of the bloom-forming cyanobacterium Planktothrix agardhii

A species-specific method to detect and quantify Planktothrix agardhii was developed by combining the SYBR Green I real-time polymerase chain reaction technique with a simplified DNA extraction procedure for standard curve preparation. Newly designed PCR primers were used to amplify a specific fragment within the rpoC1 gene. Since this gene exists in single copy in the genome, it allows the direct achievement of cell concentrations. The cell concentration determined by real-time PCR showed a linear correlation with the cell concentration determined from direct microscopic counts. The detection limit for cell quantification of the method was 8 cells μL(-1), corresponding to 32 cells per reaction. Furthermore, the real-time qPCR method described in this study allowed a successful quantification of P. agardhii from environmental water samples, showing that this protocol is an accurate and economic tool for a rapid absolute quantification of the potentially toxic cyanobacterium P. agardhii.

Community composition, toxigenicity, and environmental conditions during a cyanobacterial bloom occurring along 1,100 kilometers of the Murray River

A cyanobacterial bloom impacted over 1,100 km of the Murray River, Australia, and its tributaries in 2009. Physicochemical conditions in the river were optimal to support a bloom at the time. The data suggest that at least three blooms occurred concurrently in different sections of the river, with each having a different community composition and associated cyanotoxin profile. Microscopic and genetic analyses suggested the presence of potentially toxic Anabaena circinalis, Microcystis flos-aquae, and Cylindrospermopsis raciborskii at many locations. Low concentrations of saxitoxins and cylindrospermopsin were detected in Anabaena and Cylindrospermopsis populations. A multiplex quantitative PCR was used, employing novel oligonucleotide primers and fluorescent TaqMan probes, to examine bloom toxigenicity. This single reaction method identified the presence of the major cyanotoxin-producing species present in these environmental samples and also quantified the various toxin biosynthesis genes. A large number of cells present throughout the bloom were not potential toxin producers or were present in numbers below the limit of detection of the assay and therefore not an immediate health risk. Potential toxin-producing cells, possessing the cylindrospermopsin biosynthesis gene (cyrA), predominated early in the bloom, while those possessing the saxitoxin biosynthesis gene (sxtA) were more common toward its decline. In this study, the concentrations of cyanotoxins measured via enzyme-linked immunosorbent assay (ELISA) correlated positively with the respective toxin gene copy numbers, indicating that the molecular method may be used as a proxy for bloom risk assessment.

Anatoxin-a synthetase gene cluster of the cyanobacterium Anabaena sp. strain 37 and molecular methods to detect potential producers

Cyanobacterial mass occurrences are common in fresh and brackish waters. They pose a threat to water users due to toxins frequently produced by the cyanobacterial species present. Anatoxin-a and homoanatoxin-a are neurotoxins synthesized by various cyanobacteria, e.g., Anabaena, Oscillatoria, and Aphanizomenon. The biosynthesis of these toxins and the genes involved in anatoxin production were recently described for Oscillatoria sp. strain PCC 6506 (A. Méjean et al., J. Am. Chem. Soc. 131:7512-7513, 2009). In this study, we identified the anatoxin synthetase gene cluster (anaA to anaG and orf1; 29 kb) in Anabaena sp. strain 37. The gene (81.6% to 89.2%) and amino acid (78.8% to 86.9%) sequences were highly similar to those of Oscillatoria sp. PCC 6506, while the organization of the genes differed. Molecular detection methods for potential anatoxin-a and homoanatoxin-a producers of the genera Anabaena, Aphanizomenon, and Oscillatoria were developed by designing primers to recognize the anaC gene. Anabaena and Oscillatoria anaC genes were specifically identified in several cyanobacterial strains by PCR. Restriction fragment length polymorphism (RFLP) analysis of the anaC amplicons enabled simultaneous identification of three producer genera: Anabaena, Oscillatoria, and Aphanizomenon. The molecular methods developed in this study revealed the presence of both Anabaena and Oscillatoria as potential anatoxin producers in Finnish fresh waters and the Baltic Sea; they could be applied for surveys of these neurotoxin producers in other aquatic environments.

On the origins and biosynthesis of tetrodotoxin

The potent neurotoxin tetrodotoxin (TTX) has been identified from taxonomically diverse marine organisms. TTX possesses a unique cage-like structure, however, its biosynthesis has yet to be elucidated. Biosynthetic studies in the TTX-producing newt Taricha torosa, and in bacterial genera, including Vibrio, have proven inconclusive. Indeed, very few studies have been performed that address the cellular production of TTX. Here we review the sources of TTX described to date and provide evidence for the biosynthesis of TTX by symbiotic microorganisms in higher taxa. Chemical and genetic based biosynthesis studies of TTX undertaken thus far are discussed and we outline approaches which may be useful for expanding upon the current body of knowledge. The complex biosynthesis of structurally similar toxins, that reveal clues into the biosynthetic pathway of TTX, is also presented.