Species composition and cyanotoxin production in periphyton mats from three lakes of varying trophic status

Proliferation and anatoxin production of benthic cyanobacteria associated with canine mortalities along a stream-lake continuum

Proliferations of benthic cyanobacteria are increasingly in the public eye, with rising animal deaths associated with benthic rather than planktonic blooms. In early June 2021, two dogs died after consuming material on the shore of Shubenacadie Grand Lake, Nova Scotia. Preliminary investigations indicated anatoxins produced by benthic cyanobacterial mats were responsible for the deaths. In this study, we monitored the growth of a toxic benthic cyanobacterial species (Microcoleus sp.) along a stream-lake continuum where the canine poisonings occurred. We found that the species was able to proliferate in both lentic and lotic environments, but temporal growth dynamics and the predominant sub-species were influenced by habitat type, and differed with hydrodynamic setting, nutrient and sunlight availability. Toxin concentration was greatest in cyanobacterial mats growing in the oligotrophic lakeshore environment (maximum measured total anatoxins (ATXs) >20 mg·kg-1 wet weight). This corresponded with a shift in the profile of ATX analogues, which also indicated changing sub-species dominance along the stream-lake transition.

A Review of In Situ Methods-Solid Phase Adsorption Toxin Tracking (SPATT) and Polar Organic Chemical Integrative Sampler (POCIS) for the Collection and Concentration of Marine Biotoxins and Pharmaceuticals in Environmental Waters

Solid Phase Adsorption Toxin Tracking (SPATT) and Polar Organic Chemical Integrative Sampler (POCIS) are in situ methods that have been applied to pre-concentrate a range of marine toxins, pesticides and pharmaceutical compounds that occur at low levels in marine and environmental waters. Recent research has identified the widespread distribution of biotoxins and pharmaceuticals in environmental waters (marine, brackish and freshwater) highlighting the need for the development of effective techniques to generate accurate quantitative water system profiles. In this manuscript, we reviewed in situ methods known as Solid Phase Adsorption Toxin Tracking (SPATT) and Polar Organic Chemical Integrative Sampler (POCIS) for the collection and concentration of marine biotoxins, freshwater cyanotoxins and pharmaceuticals in environmental waters since the 1980s to present. Twelve different adsorption substrates in SPATT and 18 different sorbents in POCIS were reviewed for their ability to absorb a range of lipophilic and hydrophilic marine biotoxins, pharmaceuticals, pesticides, antibiotics and microcystins in marine water, freshwater and wastewater. This review suggests the gaps in reported studies, outlines future research possibilities and guides researchers who wish to work on water contaminates using Solid Phase Adsorption Toxin Tracking (SPATT) and Polar Organic Chemical Integrative Sampler (POCIS) technologies.

Microalgae colonization of different microplastic polymers in experimental mesocosms across an environmental gradient

A variety of organisms can colonize microplastic surfaces through biofouling processes. Heterotrophic bacteria tend to be the focus of plastisphere research; however, the presence of epiplastic microalgae within the biofilm has been repeatedly documented. Despite the relevance of biofouling in determining the fate and effects of microplastics in aquatic systems, data about this process are still scarce, especially for freshwater ecosystems. Here, our goal was to evaluate the biomass development and species composition of biofilms on different plastic polymers and to investigate whether plastic substrates exert a strong enough selection to drive species sorting, overcoming other niche-defining factors. We added microplastic pellets of high-density polyethylene (HDPE), polyethylene terephthalate (PET), and a mix of the two polymers in 15 lentic mesocosms in five different locations of the Iberian Peninsula, and after one month, we evaluated species composition and biomass of microalgae developed on plastic surfaces. Our results, based on 45 samples, showed that colonization of plastic surfaces occurred in a range of lentic ecosystems covering a wide geographical gradient and different environmental conditions (e.g., nutrient concentration, conductivity, macrophyte coverage). We highlighted that total biomass differed based on the polymer considered, with higher biomass developed on PET substrate compared to HDPE. Microplastics supported the growth of a rich and diversified community of microalgae (242 species), with some cosmopolite species. However, we did not observe species-specificity in the colonization of the different plastic polymers. Local species pool and nutrient concentration rather than polymeric composition seemed to be the determinant factor defying the community diversity. Regardless of specific environmental conditions, we showed that many species could coexist on the surface of relatively small plastic items, highlighting how microplastics may have considerable carrying capacity, with possible consequences on the wider ecological context.

Biodegradation of Nodularin by a Microcystin-Degrading Bacterium: Performance, Degradation Pathway, and Potential Application

Currently, studies worldwide have comprehensively recognized the importance of Sphingomonadaceae bacteria and the mlrCABD gene cluster in microcystin (MC) degradation. However, knowledge about their degradation of nodularin (NOD) is still unclear. In this study, the degradation mechanism of NOD by Sphingopyxis sp. m6, an efficient MC degrader isolated from Lake Taihu, was investigated in several aspects, including degradation ability, degradation products, and potential application. The strain degraded NOD of 0.50 mg/L with a zero-order rate constant of 0.1656 mg/L/d and a half-life of 36 h. The average degradation rate of NOD was significantly influenced by the temperature, pH, and initial toxin concentrations. Moreover, four different biodegradation products, linear NOD, tetrapeptide H-Glu-Mdhb-MeAsp-Arg-OH, tripeptide H-Mdhb-MeAsp-Arg-OH, and dipeptide H-MeAsp-Arg-OH, were identified, of which the latter two are the first reported. Furthermore, the four mlr genes were upregulated during NOD degradation. The microcystinase MlrA encoded by the mlrA gene hydrolyzes the Arg-Adda bond to generate linear NOD as the first step of NOD biodegradation. Notably, recombinant MlrA showed higher degradation activity and stronger environmental adaptability than the wild strain, suggesting future applications in NOD pollution remediation. This research proposes a relatively complete NOD microbial degradation pathway, which lays a foundation for exploring the mechanisms of NOD degradation by MC-degrading bacteria.

Toxic benthic freshwater cyanobacterial proliferations: Challenges and solutions for enhancing knowledge and improving monitoring and mitigation

1. This review summarises knowledge on the ecology, toxin production, and impacts of toxic freshwater benthic cyanobacterial proliferations. It documents monitoring, management, and sampling strategies, and explores mitigation options. 2. Toxic proliferations of freshwater benthic cyanobacteria (taxa that grow attached to substrates) occur in streams, rivers, lakes, and thermal and meltwater ponds, and have been reported in 19 countries. Anatoxin- and microcystin-containing mats are most commonly reported (eight and 10 countries, respectively). 3. Studies exploring factors that promote toxic benthic cyanobacterial proliferations are limited to a few species and habitats. There is a hierarchy of importance in environmental and biological factors that regulate proliferations with variables such as flow (rivers), fine sediment deposition, nutrients, associated microbes, and grazing identified as key drivers. Regulating factors differ among colonisation, expansion, and dispersal phases. 4. New -omics-based approaches are providing novel insights into the physiological attributes of benthic cyanobacteria and the role of associated microorganisms in facilitating their proliferation. 5. Proliferations are commonly comprised of both toxic and non-toxic strains, and the relative proportion of these is the key factor contributing to the overall toxin content of each mat. 6. While these events are becoming more commonly reported globally, we currently lack standardised approaches to detect, monitor, and manage this emerging health issue. To solve these critical gaps, global collaborations are needed to facilitate the rapid transfer of knowledge and promote the development of standardised techniques that can be applied to diverse habitats and species, and ultimately lead to improved management.

Tools for successful proliferation: diverse strategies of nutrient acquisition by a benthic cyanobacterium

Freshwater cyanobacterial blooms have increased worldwide, channeling organic carbon into these systems, and threatening animal health through the production of cyanotoxins. Both toxic and nontoxic Microcoleus proliferations usually occur when there are moderate concentrations of dissolved inorganic nitrogen, but when phosphorus is scarce. In order to understand how Microcoleus establishes thick biofilms (or mats) on riverbeds under phosphorus-limiting conditions, we collected Microcoleus-dominated biofilms over a 19-day proliferation event for proteogenomics. A single pair of nitrogen-dependent Microcoleus species were consistently present in relatively high abundance, although each followed a unique metabolic trajectory. Neither possessed anatoxin gene clusters, and only very low concentrations of anatoxins (~2 µg kg-1) were detected, likely originating from rarer Microcoleus species also present. Proteome allocations were dominated by photosynthesizing cyanobacteria and diatoms, and data indicate biomass was actively recycled by Bacteroidetes and Myxococcales. Microcoleus likely acquired nutrients throughout the proliferation event by uptake of nitrate, urea, and inorganic and organic phosphorus. Both species also harbored genes that could be used for inorganic phosphate solubilization with pyrroloquinoline quinone cofactors produced by cohabiting Proteobacteria. Results indicate that Microcoleus are equipped with diverse mechanisms for nitrogen and phosphorus acquisition, enabling them to proliferate and out-compete others in low-phosphorus waters.

Multiple cyanotoxin congeners produced by sub-dominant cyanobacterial taxa in riverine cyanobacterial and algal mats

Benthic cyanobacterial proliferations in rivers are have been reported with increasing frequency worldwide. In the Eel and Russian rivers of California, more than a dozen dog deaths have been attributed to cyanotoxin toxicosis since 2000. Periphyton proliferations in these rivers comprise multiple cyanobacterial taxa capable of cyanotoxin production, hence there is uncertainty regarding which taxa are producing toxins. In this study, periphyton samples dominated by the cyanobacterial genera Anabaena spp. and Microcoleus spp. and the green alga Cladophora glomerata were collected from four sites in the Eel River catchment and one site in the Russian River. Samples were analysed for potential cyanotoxin producers using polymerase chain reaction (PCR) in concert with Sanger sequencing. Cyanotoxin concentrations were measured using liquid chromatography tandem-mass spectrometry, and anatoxin quota (the amount of cyanobacterial anatoxins per toxigenic cell) determined using droplet digital PCR. Sequencing indicated Microcoleus sp. and Nodularia sp. were the putative producers of cyanobacterial anatoxins and nodularins, respectively, regardless of the dominant taxa in the mat. Anatoxin concentrations in the mat samples varied from 0.1 to 18.6 μg g-1 and were significantly different among sites (p < 0.01, Wilcoxon test); however, anatoxin quotas were less variable (< 5-fold). Dihydroanatoxin-a was generally the most abundant variant in samples comprising 38% to 71% of the total anatoxins measured. Mats dominated by the green alga C. glomerata contained both anatoxins and nodularin-R at concentrations similar to those of cyanobacteria-dominated mats. This highlights that even when cyanobacteria are not the dominant taxa in periphyton, these mats may still pose a serious health risk and indicates that more widespread monitoring of all mats in a river are necessary.

Spatial and Temporal Variation in Paralytic Shellfish Toxin Production by Benthic Microseira (Lyngbya) wollei in a Freshwater New York Lake

Butterfield Lake is a mesotrophic lake in New York State where residents and pets have experienced unexplained health issues. Microseira wollei (basionym Lyngbya wollei) was found at two of 15 sites in Butterfield Lake and analyzed for microcystins, anatoxins, cylindrospermopsins, and paralytic shellfish poisoning toxins (PSTs). Only PSTs and trace levels of anatoxin-a were detected in these samples. This is the first published report of PSTs within a New York State lake. To evaluate the environmental and temporal drivers leading to the observed toxicity, PST content at the two sites was examined in detail. There were distinct differences in the total PST content, filament nutrient, filament chlorophyll, and relationship to environmental drivers between the sites, as well as distinct differences in the total PST content measured using different analytical techniques. A multivariate model containing site, temperature, and filament chlorophyll explained 85% of the variation in PSTs observed over the growing season. This work emphasizes the importance of proper site selection and choice of analytical technique in the development of monitoring programs to protect lake users from the occurrence of benthic cyanobacteria toxins.

Anatoxins are consistently released into the water of streams with Microcoleus autumnalis-dominated (cyanobacteria) proliferations

Proliferations of potentially toxic, mat-forming Microcoleus are increasing in streams globally. A range of cyanotoxins are produced by Microcoleus, with the neurotoxic anatoxins (anatoxin-a, dihydro-anatoxin-a, homoanatoxin-a and dihydro-homoanatoxin-a) the most commonly reported. The anatoxins produced by Microcoleus are thought to be largely contained within the cells. More knowledge on whether anatoxins are been released into the overlying stream water is required to better assess health risks to human, animals, and aquatic organisms. Field studies were conducted in three streams experiencing toxic Microcoleus autumnalis (basionym Phormidium autumnale)-dominated proliferations. Samples were collected every 1.5-3 h over a 24- or 26-h sampling period. Water samples were analyzed for total (intracellular and dissolved) and dissolved anatoxins, and time-integrated anatoxin samples were collected using solid phase adsorption tracking technology (SPATT). Anatoxins were detected in all stream water and SPATT samples (max. 0.91 ng mL^-1 and 95 ng g^-1 of strata-x hr^-1). At two sites, anatoxins were largely dissolved, whereas at the third site only total anatoxins could be detected. Temporal variability in anatoxin concentrations was observed, but there were no evident patterns between sampling sites. Linear regression showed a very weakstatistically significant relationship (R² = 0.24, p = 0.002) between total anatoxin concentrations in water and SPATT, however, when tested per site, only one of the three showed a significant relationship. These results highlight the potential for chronic exposure to anatoxins for humans (i.e., through drinking water) and aquatic organisms in streams with M. autumnalis proliferations. The health implications of this are unknown.

The predominant phytoplankton of Pseudoanabaena holding specific biosynthesis gene-derived occurrence of 2-MIB in a drinking water reservoir

With the increasing occurrence of water eutrophication and blooms, earthy-musty odor problems caused by cyanobacteria have been more and more apparent. These problems have a serious impact on aquatic ecosystems and drinking water safety and become one of the priorities of the water environment researches and managements. In the present study, genes associated with 2-MIB synthesis in cyanobacteria were studied by systematic investigation on molecular characterization and quantity of 2-MIB-producing cyanobacteria in China. Our results founded that Pseudoanabaena is an important 2-MIB-producing phytoplankton and predominant in summer in Qingcaosha reservoir, and the copy number of mic and 2-MIB concentration have strongly positive correlation. We also demonstrated that abundance of mic in water was significant correlation with that in sediment. These results will help us to understand the main taxa of the odoriferous cyanobacteria in the water bodies in China, understand the genetic basis of the odor substances in the cyanobacteria. Rapid, reliable monitoring and ecological research methods for the production of odor cyanobacteria in water bodies can be established based on these results.

Solid Phase Adsorption Toxin Tracking (SPATT) Technology for the Monitoring of Aquatic Toxins: A Review

The Solid Phase Adsorption Toxin Tracking (SPATT) technology, first introduced in 2004, uses porous synthetic resins capable of passively adsorbing toxins produced by harmful microalgae or cyanobacteria and dissolved in the water. This method allows for the detection of toxic compounds directly in the water column and offers numerous advantages over current monitoring techniques (e.g., shellfish or fish testing and microalgae/cyanobacteria cell detection), despite some limitations. Numerous laboratory and field studies, testing different adsorbent substrates of which Diaion^® HP20 resin appears to be the most versatile substrate, have been carried out worldwide to assess the applicability of these passive monitoring devices to the detection of toxins produced by a variety of marine and freshwater microorganisms. SPATT technology has been shown to provide reliable, sensitive and time-integrated sampling of various aquatic toxins, and also has the potential to provide an early warning system for both the occurrence of toxic microalgae or cyanobacteria and bioaccumulation of toxins in foodstuffs. This review describes the wide range of lipophilic and hydrophilic toxins associated with toxin-producing harmful algal blooms (HABs) that are successfully detected by SPATT devices. Implications in terms of monitoring of emerging toxic risks and reinforcement of current risk assessment programs are also discussed.

Spatiotemporal dynamics of Phormidium cover and anatoxin concentrations in eight New Zealand rivers with contrasting nutrient and flow regimes

Toxic benthic cyanobacterial proliferations, particularly of the genus Phormidium, are a major concern in many countries due to their increasing extent and severity. The aim of this study was to improve the current understanding of the dominant physicochemical variables associated with high Phormidium cover and toxin concentrations. Phormidium cover and anatoxin concentrations were assessed weekly for 30weeks in eight predominately cobble-bed rivers in the South Island of New Zealand. Phormidium cover was highly variable both spatially (among and within sites) and temporally. Generalized additive mixed models (GAMMs) identified site, month of the year, conductivity and nutrient concentrations over the accrual period as significant variables associated with Phormidium cover. Cover was greatest under low to intermediate accrual dissolved inorganic nitrogen (DIN) and dissolved reactive phosphorus (DRP) concentrations. Accrual nutrients had a strong, negative effect on cover at concentrations>0.2mgL^-1 DIN and 0.014mgL^-1 DRP. The effect of flow was generally consistent across rivers, with cover accruing with time since the last flushing flow. Total anatoxins were detected at all eight study sites, at concentrations ranging from 0.008 to 662.5mgkg^-1 dried weight. GAMMs predicted higher total anatoxin concentrations between November and February and during periods of accrual DRP<0.02mgL^-1. This study suggests that multiple physicochemical variables may influence Phormidium proliferations and also evidenced large site-to-site variability. This result highlights a challenge from a management perspective, as it suggests that mitigation options are likely to be site-specific.

Attached Algae: The Cryptic Base of Inverted Trophic Pyramids in Freshwaters

It seems improbable that a thin veneer of attached algae coating submerged surfaces in lakes and rivers could be the foundation of many freshwater food webs, but increasing evidence from chemical tracers supports this view. Attached algae grow on any submerged surface that receives enough light for photosynthesis, but animals often graze attached algae down to thin, barely perceptible biofilms. Algae in general are more nutritious and digestible than terrestrial plants or detritus, and attached algae are particularly harvestable, being concentrated on surfaces. Diatoms, a major component of attached algal assemblages, are especially nutritious and tolerant of heavy grazing. Algivores can track attached algal productivity over a range of spatial scales and consume a high proportion of new attached algal growth in high-light, low-nutrient ecosystems. The subsequent efficient conversion of the algae into consumer production in freshwater food webs can lead to low-producer, high-consumer biomass, patterns that Elton (1927) described as inverted trophic pyramids. Human perturbations of nutrient, sediment, and carbon loading into freshwaters and of thermal and hydrologic regimes can weaken consumer control of algae and promote nuisance attached algal blooms.

Nodularin from benthic freshwater periphyton and implications for trophic transfer

In 2013 and 2015, the Pennsylvania Department of Environmental Protection conducted a survey of lotic habitats within the Susquehanna, Delaware, and Ohio River basins in Pennsylvania, USA, to screen for microcystins/nodularins (MCs/NODs) in algae communities and smallmouth bass (Micropterus dolomieu). Periphyton (68 from 41 sites), juvenile whole fish (153 from 19 sites) and adult fish liver (115 from 16 sites) samples were collected and screened using an Adda enzyme-linked immunosorbent assay (ELISA). Samples that were positive for MCs/NODs were further analyzed using LC-MS/MS, including 14 variants of microcystin and NOD-R and the MMPB technique. The ELISA was positive for 47% of the periphyton collections, with NOD-R confirmed (0.7-82.2 ng g^-1 d.w.) in 20 samples. NOD-R was confirmed in 10 of 15 positive juvenile whole fish samples (0.8-16.7 ng g^-1 w.w.) and in 2 of 8 liver samples (1.7 & 2.8 ng g^-1 w.w.). The MMPB method resulted in total MCs/NODs measured in periphyton (2.2-1269 ng g^-1 d.w.), juvenile whole fish (5.0-210 ng g^-1 d.w.) and adult livers (8.5-29.5 ng g^-1 d.w.). This work illustrates that NOD-R is present in freshwater benthic algae in the USA, which has broader implications for monitoring and trophic transfer.

Production of High Amounts of Hepatotoxin Nodularin and New Protease Inhibitors Pseudospumigins by the Brazilian Benthic Nostoc sp. CENA543

Nostoc is a cyanobacterial genus, common in soils and a prolific producer of natural products. This research project aimed to explore and characterize Brazilian cyanobacteria for new bioactive compounds. Here we report the production of hepatotoxins and new protease inhibitors from benthic Nostoc sp. CENA543 isolated from a small, shallow, saline-alkaline lake in the Nhecolândia, Pantanal wetland area in Brazil. Nostoc sp. CENA543 produces exceptionally high amounts of nodularin-R. This is the first free-living Nostoc that produces nodularin at comparable levels as the toxic, bloom-forming, Nodularia spumigena. We also characterized pseudospumigins A-F, which are a novel family of linear tetrapeptides. Pseudospumigins are structurally related to linear tetrapeptide spumigins and aeruginosins both present in N. spumigena but differ in respect to their diagnostic amino acid, which is Ile/Leu/Val in pseudospumigins, Pro/mPro in spumigins, and Choi in aeruginosins. The pseudospumigin gene cluster is more similar to the spumigin biosynthetic gene cluster than the aeruginosin gene cluster. Pseudospumigin A inhibited trypsin (IC₅₀ 4.5 μM after 1 h) in a similar manner as spumigin E from N. spumigena but was almost two orders of magnitude less potent. This study identifies another location and environment where the hepatotoxic nodularin has the potential to cause the death of eukaryotic organisms.

Sustained High Nutrient Supply As an Allelopathic Trigger between Periphytic Biofilm and Microcystis aeruginosa

Allelopathy among aquatic organisms, especially microorganisms, has received growing attention in recent years for its role in shaping interactions with bloom-forming algae. Many studies have shown that allelopathy occurs and increases under nutrient limiting conditions. However, to date there is no reported direct evidence to indicate that allelopathy occurs under the condition of constant high nutrient supply. Here we report the allelopathic action of periphytic biofilm on bloom-forming cyanobacteria (Microcystis aeruginosa), which was triggered by the stress of high nutrient conditions, and continues while nutrients are maintained at high levels (trophic state index at 159 and 171). The experimental evidence indicates that the electron transport from photosystem II (PS II) to photosystem I (PS I) in M. aeruginosa is interrupted by the identified allelochemicals, (9Z)-Octadec-9-enoic acid and (9Z)-Hexadec-9-enoic acid, leading to the failure of photosynthesis and the subsequent death of M. aeruginosa. Our findings indicate that the nutrient stress of constant high nutrient supply may be a newly recognized trigger causing allelopathy between microbial competitors, and therefore opening a new direction for the better management of ecological processes in cyanobacteria-dominated and hyper-eutrophic waters.

Iningainema pulvinus gen nov., sp nov. (Cyanobacteria, Scytonemataceae) a new nodularin producer from Edgbaston Reserve, north-eastern Australia

A new nodularin producing benthic cyanobacterium Iningainema pulvinus gen nov., sp nov. was isolated from a freshwater ambient spring wetland in tropical, north-eastern Australia and characterised using combined morphological and phylogenetic attributes. It formed conspicuous irregularly spherical to discoid, blue-green to olive-green cyanobacterial colonies across the substratum of shallow pools. Morphologically Iningainema is most similar to Scytonematopsis Kiseleva and Scytonema Agardh ex Bornet & Flahault. All three genera have isopolar filaments enveloped by a firm, often layered and coloured sheath; false branching is typically geminate, less commonly singly. Phylogenetic analyses using partial 16S rRNA sequences of three clones of Iningainema pulvinus strain ES0614 showed that it formed a well-supported monophyletic clade. All three clones were 99.7-99.9% similar, however they shared less than 93.9% nucleotide similarity with other cyanobacterial sequences including putatively related taxa within the Scytonemataceae. Amplification of a fragment of the ndaF gene involved in nodularin biosynthesis from Iningainema pulvinus confirmed that it has this genetic determinant. Consistent with these results, analysis of two extracts from strain ES0614 by HPLC-MS/MS confirmed the presence of nodularin at concentrations of 796 and 1096μgg^-1 dry weight. This is the third genus of cyanobacteria shown to produce the cyanotoxin nodularin and the first report of nodularin synthesis from the cyanobacterial family Scytonemataceae. These new findings may have implications for the aquatic biota at Edgbaston Reserve, a spring complex which has been identified as a priority conservation area in the central Australian arid and semiarid zones, based on patterns of endemicity.

Presence of the Cyanotoxin Microcystin in Arctic Lakes of Southwestern Greenland

Cyanobacteria and their toxins have received significant attention in eutrophic temperate and tropical systems where conspicuous blooms of certain planktonic taxa release toxins into fresh water, threatening its potability and safe use for recreation. Although toxigenic cyanobacteria are not confined to high nutrient environments, bloom-forming species, or planktonic taxa, these other situations are studied les often studied. For example, toxin production in picoplankton and benthic cyanobacteria—the predominant photoautotrophs found in polar lakes—is poorly understood. We quantified the occurrence of microcystin (MC, a hepatotoxic cyanotoxin) across 18 Arctic lakes in southwestern Greenland. All of the focal lakes contained detectable levels of MC, with concentrations ranging from 5 ng·L⁻¹ to >400 ng·L⁻¹ during summer, 2013–2015. These concentrations are orders of magnitude lower than many eutrophic systems, yet the median lake MC concentration in Greenland (57 ng·L⁻¹) was still 6.5 times higher than the median summer MC toxicity observed across 50 New Hampshire lakes between 1998 and 2008 (8.7 ng·L⁻¹). The presence of cyanotoxins in these Greenlandic lakes demonstrates that high latitude lakes can support toxigenic cyanobacteria, and suggests that we may be underestimating the potential for these systems to develop high levels of cyanotoxins in the future.

The rise of toxic benthic Phormidium proliferations: A review of their taxonomy, distribution, toxin content and factors regulating prevalence and increased severity

There has been a marked increase in the distribution, intensity and frequency of proliferations of some species of the benthic mat-forming, toxin-producing genus Phormidium in rivers globally over the last decade. This review summarises current knowledge on their taxonomy, distribution, toxin content, environmental drivers of proliferations, and monitoring and management strategies in New Zealand. Although toxic Phormidium proliferation occurs in rivers worldwide little is known about these factors in most countries. Proliferations, defined as >20% cover of a riverbed, have been identified in 103 rivers across New Zealand. Morphological and molecular data indicate the main species responsible is Phormidium autumnale. In New Zealand Phormidium produces anatoxins (anatoxin-a, homoanatoxin-a, dihydroanatoxin-a, and dihydrohomoanatoxin-a) and these were detected in 67% of 771 samples from 40 rivers. The highest concentration measured was 712mgkg^-1 dried weight (Oreti River, Southland), with considerable spatial and temporal variability in anatoxin concentrations between and within rivers. A synthesis of field based studies suggests that Phormidium proliferations are most likely when there is some enrichment of dissolved inorganic nitrogen but when water-column dissolved reactive phosphorus is less than 0.01mgL^-1. Once established Phormidium-dominated mats trap sediment and internal mat biogeochemistry can mobilise sediment-bound phosphorus, which is then available for growth. Removal of Phormidium-dominated mats is primarily due to shear stress and substrate disturbance, although there is also evidence for autogenic detachment. A combination of factors including; changes to riparian margins, increased nitrate and fine sediment loads, and alterations in flow regimes are likely to have contributed to the rise in Phormidium proliferations.

Nutrient capture and recycling by periphyton attached to modified agrowaste carriers

The reuse of periphytic biofilm from traditional wastewater treatment (i.e., active sludge process) is inefficient to recycle nutrients due to low accumulation of nutrients. Then, in this study, peanut shell (PS), rice husk (RH), decomposed peanut shell (DPS), acidified rice husks (ARH), and a commonly used carrier-ceramsite (C, as the control)-were used to support the growth of periphyton. Results showed that DPS and ARH supported significantly higher periphyton biomass and metabolic versatility than PS and RH, respectively, due to the increased presence of positive groups. The total nitrogen (TN) and total phosphorus (TP) captured by periphyton were enhanced by 600-657 and 833-3255 % for DPS, and 461-1808 and 21-308 % for ARH, respectively. The removal of nutrients from simulated eutrophic surface waters using periphyton attached to DPS was improved by 24-47 % for TP, 12-048 % for TN, and 15-78 % for nitrate compared to the control. The results indicate that the periphyton attached to modified agrowaste was capable of efficiently entrapping and storing N and P from eutrophic water. This study also implies that the mixture of periphyton and the modified agrowaste carriers are promising raw materials of biofertilizer.

Comparison of the properties of periphyton attached to modified agro-waste carriers

Periphyton is a valuable, environmentally benign resource widely used in environmental remediation. A protocol for reusing agro-wastes to improve the metabolic activity and versatility of periphyton was tested in this study. Peanut shell (PS), decomposed peanut shell (DPS), acidified peanut shell (APS), rice husks (RHs), acidified rice husks (ARHs), and a commonly used synthetic carrier, ceramsite (C), were used to support periphyton attachment and growth. The results show that the modified carriers have more hydrophilic groups, higher periphyton biomass, and autotrophic indices than the unmodified carriers. As a consequence, they promote the metabolic versatility of periphyton microbial communities. Thus, the periphyton attached to modified agro-wastes (DPS, APS, and ARH) grew in a stable and sustainable manner. This study suggests that modified PS and RH are effective and environmentally benign carriers that enhance periphyton activity and functionality. Development of periphytic carriers using agro-wastes is also a sustainable method of reusing these materials.

Successional change in microbial communities of benthic Phormidium-dominated biofilms

Benthic cyanobacterial blooms are increasing worldwide and can be harmful to human and animal health if they contain toxin-producing species. Microbial interactions are important in the formation of benthic biofilms and can lead to increased dominance and/or toxin production of one or few taxa. This study investigated how microbial interactions contribute to proliferation of benthic blooms dominated by the neurotoxin-producing Phormidium autumnale. Following a rainfall event that cleared the substrate, biofilm succession was characterised at a site on the Hutt River (New Zealand) by sampling every 2-3 days over 32 days. A combination of morphological and molecular community analyses (automated ribosomal intergenic spacer analysis and Illumina™ MiSeq sequencing) identified three distinct phases of succession in both the micro-algal and bacterial communities within P. autumnale-dominated biofilms. Bacterial composition shifted between the phases, and these changes occurred several days before those of the micro-algal community. Alphaproteobacteria and Betaproteobacteria dominate in the early phase; Alphaproteobacteria, Betaproteobacteria, Sphingobacteria and Flavobacteria in the mid-phase; and Sphingobacteria and Flavobacteria in the late phase. Collectively, the results suggest that succession is driven by bacteria in the early stages but becomes dependent on micro-algae in the mid- and late stages of biofilm formation.

MIB-producing cyanobacteria (Planktothrix sp.) in a drinking water reservoir: distribution and odor producing potential

The production of odorant 2-methylisoborneol (MIB) in water bodies by Planktothrix sp. have not been understood very well. Through a four-year investigation in Miyun Reservoir, a huge mesotrophic drinking water reservoir known to have the MIB episodes, we found that the Planktothrix sp. bloomed during September and October causing the high levels of MIB in the reservoir. The concentration of MIB and the biomass of MIB-producing cyanobacteria Planktothrix were measured (n = 887) at different sites and depths during different seasons. The results indicated that the shallow region of the reservoir is the major habitat for Planktothrix sp. due to that the light is able to penetrate down to the relatively high concentrations of nutrients close to the sediments. Quantile regression analysis between Planktothrix biomass and MIB concentration shows that the risk of MIB exceeding the odor threshold (15 ng L⁻¹) in water was as high as 90% when the Planktothrix density was more than 4.0 × 10⁵ cells L⁻¹, while the risk was reduced to 10% when the Planktothrix density remained below 1.6 × 10⁴ cells L⁻¹. This study will improve the understanding of the environmental behaviors of Planktothrix sp., and can provide useful information for better management of drinking water lakes/reservoirs experiencing the taste and odor (T&O) problems caused by deep living cyanobacterial species.

Impact of environmental factors on the regulation of cyanotoxin production

Cyanobacteria are capable of thriving in almost all environments. Recent changes in climatic conditions due to increased human activities favor the occurrence and severity of harmful cyanobacterial bloom all over the world. Knowledge of the regulation of cyanotoxins by the various environmental factors is essential for effective management of toxic cyanobacterial bloom. In recent years, progress in the field of molecular mechanisms involved in cyanotoxin production has paved the way for assessing the role of various factors on the cyanotoxin production. In this review, we present an overview of the influence of various environmental factors on the production of major group of cyanotoxins, including microcystins, nodularin, cylindrospermopsin, anatoxins and saxitoxins.

First report of microcystin-producing Fischerella sp. (Stigonematales, Cyanobacteria) in tropical Australia

A polyphasic study of four Stigonematales cyanobacteria from tropical Australia (Queensland) revealed production of the hepatotoxins microcystins (MC-LR, MC-LA, MC-LF, MC-FR and demethyl-MC-LR) by Fischerella sp. NQAIF311 isolated from a seasonal creek. Total microcystin content reached 43 μg g(-1) dry weight. Phylogeny demonstrated high sequence similarities for 16S rRNA (99%), mcyE (97%) and mcyD (95%) genes with microcystin-producing Fischerella sp. CENA161 from Brazil. This is the first report of a cyanotoxin-producing Stigonematal in Australia.

Toxicity thresholds for juvenile freshwater mussels Echyridella menziesii and crayfish Paranephrops planifrons, after acute or chronic exposure to Microcystis sp

Survival of juvenile freshwater mussels (Echyridella menziesii (Gray, 1843) formerly known as Hyridella menziesi) and crayfish (Paranephrops planifrons, White, 1842) decreased after four days exposure to microcystin-containing cell-free extracts (MCFE) of Microcystis sp. at concentrations typical of severe cyanobacterial blooms. Crayfish survival was 100, 80, and 50% in microcystin concentrations of 1339, 2426, and 11146 μg L(-1) respectively, and shade- and shelter-seeking behavior was negatively affected when concentrations were ≥2426 μg L(-1) . Mussel survival decreased to 92% and reburial rates decreased to 16% after exposure for 96 h to MCFE containing microcystins at concentrations of 5300 μg L(-1) . Crayfish survival was 100% when fed freeze-dried Microcystis sp. incorporated into an artificial diet (6-100 μg microcystin kg(-1) ww) at dietary doses from 0.03 to 0.55 μg g(-1) body weight d(-1) for 27 days. Specific growth rate was significantly lower in crayfish fed ≥0.15 μg g(-1) body weight day(-1) compared with controls, but not compared with a diet incorporating nontoxic cyanobacteria. Microcystins accumulated preferentially in crayfish hepatopancreas and mussel digesta as MCFE or dietary concentrations increased. These laboratory data indicate that, assuming dissolved oxygen concentrations remain adequate, and no simultaneous exposure to live Microcystis sp. cells, cell-free microcystins will only be a significant stressor to juvenile crayfish and mussels in severe Microcystis sp. blooms. In contrast, crayfish were negatively affected by relatively low concentrations of microcystins in artificial diets compared with those measured locally in benthic cyanobacterial mats.

Climate change and regulation of hepatotoxin production in Cyanobacteria

Harmful, bloom-forming cyanobacteria (CyanoHABs) are occurring with increasing regularity in freshwater and marine ecosystems. The most commonly occurring cyanobacterial toxins are the hepatotoxic microcystin and nodularin. These cyclic hepta- and pentapeptides are synthesised nonribosomally by the gene products of the toxin gene clusters mcy and nda, respectively. Understanding of the regulation of hepatotoxin production is incomplete, although there is strong evidence supporting the roles of iron, light, higher nitrate availability and inorganic carbon in modulating microcystin levels. The majority of these studies have focused on the unicellular freshwater, microcystin-producing strain of Microcystis aeruginosa, with little attention being paid to terrestrial or marine toxin producers. This review intends to investigate the regulation of microcystin and nodularin production in unicellular and filamentous diazotrophic cyanobacteria against the background of changing climate conditions. Special focus is given to diazotrophic filamentous cyanobacteria, for example Nodularia spumigena, capable of regulating their nitrogen levels by actively fixing dinitrogen. By combining data from significant studies, an overall scheme of the regulation of toxin production is presented, focussing specifically on nodularin production in diazotrophs against the background of increasing carbon dioxide concentrations and temperatures envisaged under current climate change models. Furthermore, the risk of sustaining and spreading CyanoHABs in the future ocean is evaluated.

A review of current knowledge on toxic benthic freshwater cyanobacteria--ecology, toxin production and risk management

Benthic cyanobacteria are found globally in plethora of environments. Although they have received less attention than their planktonic freshwater counterparts, it is now well established that they produce toxins and reports of their involvement in animal poisonings have increased markedly during the last decade. Most of the known cyanotoxins have been identified from benthic cyanobacteria including: the hepatotoxic microcystins, nodularins and cylindrospermopsins, the neurotoxic saxitoxins, anatoxin-a and homoanatoxin-a and dermatotoxins, such as lyngbyatoxin. In most countries, observations of toxic benthic cyanobacteria are fragmented, descriptive and in response to animal toxicosis events. Only a limited number of long-term studies have aimed to understand why benthic proliferations occur, and/or how toxin production is regulated. These studies have shown that benthic cyanobacterial blooms are commonly a mixture of toxic and non-toxic genotypes and that toxin concentrations can be highly variable spatially and temporally. Physiochemical parameters responsible for benthic proliferation vary among habitat type with physical disturbance (e.g., flow regimes, wave action) and nutrients commonly identified as important. As climatic conditions change and anthropogenic pressures on waterways increase, it seems likely that the prevalence of blooms of benthic cyanobacteria will increase. In this article we review current knowledge on benthic cyanobacteria: ecology, toxin-producing species, variables that regulate toxin production and bloom formation, their impact on aquatic and terrestrial organisms and current monitoring and management strategies. We suggest research needs that will assist in filling knowledge gaps and ultimately allow more robust monitoring and management protocols to be developed.

Cultivation and characterization of the MaMV-DC cyanophage that infects bloom-forming cyanobacterium Microcystis aeruginosa

The MaMV-DC cyanophage, which infects the bloom-forming cyanobacterium Microcystis aeruginosa, was isolated from Lake Dianchi, Kunming, China. Twenty-one cyanobacterial strains were used to detect the host range of MaMV-DC. Microcystic aeruginosa FACHB-524 and plaque purification were used to isolate individual cyanophages, and culturing MaMV-DC with cyanobacteria allowed us to prepare purified cyanophages for further analysis. Electron microscopy demonstrated that the negatively stained viral particles are tadpole-shaped with an icosahedral head approximately 70 nm in diameter and a contractile tail approximately 160 nm in length. Using one-step growth experiments, the latent period and burst size of MaMV-DC were estimated to be 24-48 hours and approximately 80 infectious units per cell, respectively. Restriction endonuclease digestion and agarose gel electrophoresis were performed using purified MaMV-DC genomic DNA, and the genome size was estimated to be approximately 160 kb. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis revealed four major structural proteins. These results support the growing interest in using freshwater cyanophages to control bloom-forming cyanobacterium.

Cyanobacteria, Lyngbya aestuarii and Aphanothece bullosa as antifungal and antileishmanial drug resources

OBJECTIVE

To investigate two cyanobacteria isolated from different origins i.e. Lyngbya aestuarii (L. aestuarii) from brackish water and Aphanothece bullosa (A. bullosa) from fresh water paddy fields for antifungal and antileishmanila activity taking Candida albicans and Leishmania donovain as targets.

METHODS

Biomass of L. aestuarii and A. bullosa were harvested after 40 and 60 d respectively and lyophilized twice in methanol (100%) and redissolved in methanol (5%) for bioassay. Antifungal bioassay was done by agar well diffusion method while antileishmanial, by counting cell numbers and flageller motility observation of promastigotes and amastigotes from L. donovani. Fluconazole and 5% methanol were used as control.

RESULTS

Both the cyanobacteria were found to be potent source of antifungal activity keeping fluconazole as positive control, however, methanolic crude extract (15 mg/mL) of A. bullosa was found more potent (larger inhibition zone) over that of methanolic crude extract of L. aestuarii. Similarly antileishmanial activity of crude extract (24.0 mg/mL) of A. bullosa was superior over that of methanolic crude extract of L. aestuarii (25.6 mg/mL).

CONCLUSIONS

Antifungal and antileishmanial drugs are still limited in the market. Screening of microbes possessing antifungal and antileishmanial activity drug is of prime importance. Cyanobacteria are little explored in this context because most of the drugs in human therapy are derived from microorganisms, mainly bacterial, fungal and actinomycetes. Thus in the present study two cyanobacterial strains from different origins showed potent source of antifungal and antileishmanial biomolecules.

Within-mat variability in anatoxin-a and homoanatoxin-a production among benthic Phormidium (cyanobacteria) strains

Benthic Phormidium mats can contain high concentrations of the neurotoxins anatoxin-a and homoanatoxin-a. However, little is known about the co-occurrence of anatoxin-producing and non-anatoxin-producing strains within mats. There is also no data on variation in anatoxin content among toxic genotypes isolated from the same mat. In this study, 30 Phormidium strains were isolated from 1 cm(2) sections of Phormidium-dominated mats collected from three different sites. Strains were grown to stationary phase and their anatoxin-a, homoanatoxin-a, dihydroanatoxin-a and dihydrohomoanatoxin-a concentrations determined using liquid chromatography-mass spectrometry. Each strain was characterized using morphological and molecular (16S rRNA gene sequences) techniques. Eighteen strains produced anatoxin-a, dihydroanatoxin-a or homoanatoxin-a. Strains isolated from each mat either all produced toxins, or were a mixture of anatoxin and non-anatoxin-producing genotypes. Based on morphology these genotypes could not be separated. The 16S rRNA gene sequence comparisons showed a difference of at least 17 nucleotides among anatoxin and non-anatoxin-producing strains and these formed two separate sub-clades during phylogenetic analysis. The total anatoxin concentration among toxic strains varied from 2.21 to 211.88 mg kg(-1) (freeze dried weight), representing a 100 fold variation in toxin content. These data indicate that both the relative abundance of anatoxin and non-anatoxin-producing genotypes, and variations in anatoxin producing capability, can influence the overall toxin concentration of benthic Phormidium mat samples.