Long-term study of phytoplankton dynamics in a supply reservoir reveals signs of trophic state shift linked to changes in hydrodynamics associated with flow management and extreme events.

This study analyses over a decade (2009-2022) of monitoring data to understand the impact of hydrological characteristics on water quality and phytoplankton dynamics in Prospect Reservoir, a critical water supply for Greater Sydney, Australia, known for its excellent water quality. Water quality and phytoplankton dynamics were related to hydrodynamics, linked to flow management and the water quality of inflows. Phytoplankton biovolume increased after a prolonged drawdown and subsequent refill event, mainly driven by dinoflagellates, and corresponded to increases in total phosphorus and water temperature. The hydrological period following the 2019/2020 summer bushfires (post-bushfire) that impacted connected reservoirs, was marked by increased flow activity and nutrient loading, leading to significant shifts in the phytoplankton community. Functional group classification and ordination analysis indicated a transition from taxa typically dominant in oligotrophic conditions to meso­eutrophic. This transition correlated with elevated nutrient levels and chlorophyll-a (Chl-a), and reduced Secchi depth and dissolved oxygen, providing evidence of eutrophication. Q index indicated good water quality post-bushfire, contrasting with a eutrophic status assessment using Chl-a. Our findings highlight the importance of analysing long-term datasets encompassing varied hydroclimatological conditions for a deeper understanding of reservoir behaviour. A comprehensive approach to water quality assessment is recommended, combining functional group classification, Q index and Chl-a measurements for effective reservoir health assessment. This research provides novel insights into the effects of disturbances such as bushfires, on water quality and phytoplankton dynamics in an underrepresented geographic region, offering valuable knowledge for managing water resources amidst growing climate variability.

Simultaneous Analysis of Cyanotoxins ß-N-methylamino-L-alanine (BMAA) and Microcystins-RR, -LR, and -YR Using Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS).

ß-N-methylamino-L-alanine (BMAA) and its isomers, 2,4-diaminobutyric acid (2,4-DAB) and N-(2-aminoethyl)-glycine (AEG), along with microcystins (MCs)-RR, -LR, and -YR (the major MC congeners), are cyanotoxins that can cause detrimental health and environmental impacts during toxic blooms. Currently, there are no reverse-phase (RP) LC-MS/MS methods for the simultaneous detection and quantification of BMAA, its isomers, and the major MCs in a single analysis; therefore, multiple analyses are required to assess the toxic load of a sample. Here, we present a newly developed and validated method for the detection and quantification of BMAA, 2,4-DAB, AEG, MC-LR, MC-RR, and MC-YR using RP LC-MS/MS. Method validation was performed, assessing linearity (r2 > 0.996), accuracy (>90% recovery for spiked samples), precision (7% relative standard deviation), and limits of detection (LODs) and quantification (LOQs) (ranging from 0.13 to 1.38 ng mL-1). The application of this combined cyanotoxin analysis on a culture of Microcystis aeruginosa resulted in the simultaneous detection of 2,4-DAB (0.249 ng mg-1 dry weight (DW)) and MC-YR (4828 ng mg-1 DW). This study provides a unified method for the quantitative analysis of BMAA, its isomers, and three MC congeners in natural environmental samples.

Tributary Inflows to a Regulated River Influence Bacterial Communities and Increase Bacterial Carbon Assimilation.

Inflows from unregulated tributaries change the physical, chemical, and biotic conditions in receiving regulated rivers, impacting microbial community structure and metabolic function. Understanding how tributary inflows affect bacterial carbon production (BCP) is integral to understanding energy transfer in riverine ecosystems. To investigate the role of tributary inflows on bacterial community composition and BCP, a ~90th percentile natural flow event was sampled over 5 days along the Lachlan River and its tributaries within the Murray-Darling Basin of eastern Australia. Increased tributary inflows after rainfall corresponded with a significantly different and more diverse bacterial community in the regulated mainstem. The major contributor to this difference was an increase in relative abundance of bacterial groups with a potential metabolic preference for humic substances (Burkholderiaceae Polynucleobacter, Alcaligenaceae GKS98 freshwater group, Saccharimonadia) and a significant decrease in Spirosomaceae Pseudarcicella, known to metabolise algal exudates. Increases in orthophosphate and river discharge explained 31% of community change, suggesting a combination of resource delivery and microbial community coalescence as major drivers. BCP initially decreased significantly with tributary inflows, but the total load of carbon assimilated by bacteria increased by up to 20 times with flow due to increased water volume. The significant drivers of BCP were dissolved organic carbon, water temperature, and conductivity. Notably, BCP was not correlated with bacterial diversity or community composition. Tributary inflows were shown to alter mainstem bacterial community structure and metabolic function to take advantage of fresh terrestrial dissolved organic material, resulting in substantial changes to riverine carbon assimilation over small times scales.

Extraction of Non-Protein Amino Acids from Cyanobacteria for Liquid Chromatography-Tandem Mass Spectrometry Analysis.

Non-protein amino acids (NPAAs) are a large class of amino acids (AAs) that are not genetically encoded for translation into proteins. The analysis of NPAAs can provide crucial information about cellular uptake and/or function, metabolic pathways, and potential toxicity. ß-methylamino-L-alanine (BMAA) is a neurotoxic NPAA produced by various algae species and is associated with an increased risk for neurodegenerative diseases, which has led to significant research interest. There are numerous ways to extract AAs for analysis, with liquid chromatography-tandem mass spectrometry being the most common, requiring protein precipitation followed by acid hydrolysis of the protein pellet. Studies on the presence of BMAA in algal species provide contradictory results, with the use of unvalidated sample preparation/extraction and analysis a primary cause. Like most NPAAs, protein precipitation in 10% aqueous TCA and hydrolysis with fuming HCl is the most appropriate form of extraction for BMAA and its isomers aminoethylglycine (AEG) and 2,4-diaminobutyric acid (2,4-DAB). The present protocol describes the steps in a validated NPAA extraction method commonly used in research and teaching laboratories.

The Influence of Micronutrient Trace Metals on Microcystis aeruginosa Growth and Toxin Production.

Microcystis aeruginosa is a widespread cyanobacteria capable of producing hepatotoxic microcystins. Understanding the environmental factors that influence its growth and toxin production is essential to managing the negative effects on freshwater systems. Some micronutrients are important cofactors in cyanobacterial proteins and can influence cyanobacterial growth when availability is limited. However, micronutrient requirements are often species specific, and can be influenced by substitution between metals or by luxury uptake. In this study, M. aeruginosa was grown in modified growth media that individually excluded some micronutrients (cobalt, copper, iron, manganese, molybdenum) to assess the effect on growth, toxin production, cell morphology and iron accumulation. M. aeruginosa growth was limited when iron, cobalt and manganese were excluded from the growth media, whereas the exclusion of copper and molybdenum had no effect on growth. Intracellular microcystin-LR concentrations were variable and were at times elevated in treatments undergoing growth limitation by cobalt. Intracellular iron was notably higher in treatments grown in cobalt-deplete media compared to other treatments possibly due to inhibition or competition for transporters, or due to irons role in detoxifying reactive oxygen species (ROS).

The Changes in Cyanobacterial Concentration of ß-Methylamino-L-Alanine during a Bloom Event.

ß-N-methylamino L-alanine (BMAA) is a neurotoxin linked to high incidences of neurodegenerative disease. The toxin, along with two of its common isomers, 2,4-diaminobuytric acid (2,4-DAB) and N-(2-aminoethyl)glycine (AEG), is produced by multiple genera of cyanobacteria worldwide. Whilst there are many reports of locations and species of cyanobacteria associated with the production of BMAA during a bloom, there is a lack of information tracking changes in concentration across a single bloom event. This study aimed to measure the concentrations of BMAA and its isomers through the progression and end of a cyanobacteria bloom event using liquid chromatography-triple quadrupole-mass spectrometry. BMAA was detected in all samples analysed, with a decreasing trend observed as the bloom progressed. BMAA's isomers were also detected in all samples, however, they did not follow the same decreasing pattern. This study highlights the potential for current sampling protocols that measure a single time point as representative of a bloom's overall toxin content to underestimate BMAA concentration during a bloom event.

Leaf litter breakdown along an elevational gradient in Australian alpine streams.

The breakdown of allochthonous organic matter, is a central step in nutrient cycling in stream ecosystems. There is concern that increased temperatures from climate change will alter the breakdown rate of organic matter, with important consequences for the ecosystem functioning of alpine streams. This study investigated the rate of leaf litter breakdown and how temperature and other factors such as microbial and invertebrate activities influenced this over elevational and temporal gradients. Dried leaves of Snow Gum (Eucalyptus pauciflora) and cotton strips were deployed in coarse (6 mm), and fine (50 µm) mesh size bags along an 820 m elevation gradient. Loss of mass in leaf litter and cotton tensile strength per day (k per day), fungal biomass measured as ergosterol concentration, invertebrate colonization of leaf litter, and benthic organic matter (mass and composition) were determined. Both microbial and macroinvertebrate activities were equally important in leaf litter breakdown with the abundance of shredder invertebrate taxa. The overall leaf litter breakdown rate and loss of tensile strength in cotton strips (both k per day) were greater during warmer deployment periods and at lower elevations, with significant positive relationships between mean water temperature and leaf breakdown and loss of tensile strength rate, but no differences between sites, after accounting for the effects of temperature. Despite considerably lower amounts of benthic organic matter in streams above the tree line relative to those below, shredders were present in coarse mesh bags at all sites. Ergosterol concentration was greater on leaves in coarse mesh bags than in fine mesh bags, implying differences in the microbial communities. The importance of water temperatures on the rate of leaf litter breakdown suggests the potential effects of climate change-induced temperature increases on ecological processes in such streams.

Severe cyanobacterial blooms in an Australian lake; causes and factors controlling succession patterns.

Cyanobacterial blooms have major impacts on the ecological integrity and anthropogenic value of freshwater systems. Chrysosporum ovalisporum, a potentially toxic cyanobacteria has been rare in Australian waters until recently when is has bloomed in a number of lake and river systems. The aim of this study was to determine drivers of its growth and growing dominance. We performed regular monitoring of Mannus Lake, a small freshwater reservoir in South-Eastern Australia that has recently undergone extremely dense bloom events. Blooms of the diazotrophic Chrysosporum ovalisporum occurred in both summers of the 19 month study during periods of persistent thermal stratification. Following the C. ovalisporum blooms, non-diazotrophic taxa (Microcystis aeruginosa and Woronichinia sp.) dominated the phytoplankton community under less stratified conditions. Thermal stratification and nitrogen availability appeared to be the primary drivers of changes in cyanobacterial community structure. We propose that the observed transition from C. ovalisporum to M. aeruginosa and/or Woronichinia sp. may be a result of nitrogen limitation in early summer, which combined with persistent thermal stratification led to an ecological advantage for the nitrogen-fixing C. ovalisporum. Mixing events caused the senescence of the C. ovalisporum bloom, likely supplementing the nutrient budget of the lake with atmospherically derived N and alleviating N limitation to non-diazotrophic taxa. Non-diazotrophic cyanobacterial growth then increased, albeit at much lower biovolumes compared to the initial bloom. Overall, the results demonstrate the role of thermal stratification and nutrient cycling in structuring the cyanobacterial community and provide insights into the environmental factors driving the proliferation of the relatively new, potentially toxic cyanobacterium C. ovalisporum in Australian waters.

Assessing the importance of cobalt as a micronutrient for freshwater cyanobacteria.

Micronutrients play key roles in numerous metabolic processes in cyanobacteria. However, our understanding of whether the micronutrient cobalt influences the productivity of freshwater systems or the occurrence of cyanobacterial blooms is limited. This study aimed to quantify the concentration of Co necessary for optimal cyanobacterial growth by exposing Microcystis aeruginosa to a range of Co concentrations under culture conditions. Extended exposure to concentrations below ˜0.06 µg · L-1 resulted in notable inhibition of M. aeruginosa growth. A clear negative relationship was observed between Co concentration in solution and intracellular Fe quota of M. aeruginosa, possibly due to decreased transport of Fe at higher Co concentrations. Cyanocobalamin and any Co within the structure of cyanocobalamin appears to be non-bioavailable to M. aeruginosa, instead they likely rely on the synthesis of a structural variant - pseudocobalamin, which may have implications for the wider algal community as the variants of cobalamin are not necessarily functionally exchangeable. To evaluate the likelihood of Co limitation of cyanobacterial growth under field conditions, a survey of 10 freshwater reservoirs in South-Eastern Australia was conducted. Four of the ten sites had dissolved Co concentrations below the 0.06 µg · L-1 threshold value. All four of these sites rarely undergo cyanobacterial blooms, strengthening evidence of the potential for Co to limit growth, perhaps either alone or in combination with phosphorus.

Toxicity and bioaccumulation of two non-protein amino acids synthesised by cyanobacteria, ß-N-Methylamino-L-alanine (BMAA) and 2,4-diaminobutyric acid (DAB), on a crop plant.

In order to study the toxicity of the cyanobacterial non-protein amino acids (NPAAs) L-ß-N-methylamino-L-alanine (BMAA) and its structural isomer L-2,4-diaminobutyric acid (DAB) in the forage crop plant alfalfa (Medicago sativa), seedlings were exposed to NPAA-containing media for four days. Root growth was significantly inhibited by both treatments. The content of derivatised free and protein-bound BMAA and DAB in seedlings was then analysed by LC-MS/MS. Both NPAAs were detected in free and protein-bound fractions with higher levels detected in free fractions. Compared to shoots, there was approximately tenfold more BMAA and DAB in alfalfa roots. These results suggest that NPAAs might be taken up into crop plants from contaminated irrigation water and enter the food chain. This may present an exposure pathway for NPAAs in humans.

Erratum to: The effects of cold shock on freshwater fish larvae and early-stage juveniles: implications for river management.

[This corrects the article DOI: 10.1093/conphys/coaa092.].

The effects of cold shock on freshwater fish larvae and early-stage juveniles: implications for river management.

Temperature is essential to the maintenance of optimal physiological functioning in aquatic organisms. Fish can manage natural fluctuations in temperature; however, in freshwater ecosystems acute and rapid temperature changes can originate from sources such as large dams and industrial effluents. These rapid temperature changes may induce several physiological and behavioural responses that can result in lethal and sub-lethal consequences. The present study assessed immediate sub-lethal and short-term (10 days) lethal responses of three species of Australian freshwater fish larvae and early-stage juveniles to a range of different 'field-relevant' cold shocks (-4, -6, -8 and -10°C). Murray cod (Maccullochella peelii), silver perch (Bidyanus bidyanus) and golden perch (Macquaria ambigua) were tested at two age groups to elucidate the interaction between ontogeny and sensitivity to cold shock. Cold shock caused mortality and reductions in swimming ability (time to exhaustion and lines crossed) in all species of fish at both age groups. Sensitivity was correlated to the magnitude of cold shock; a 10°C drop in temperature caused the highest mortalities. Ontogeny interacted with the severity of cold shock; the younger fish experienced higher mortalities and greater impairment to swimming ability. This study demonstrates the potential lethal and sub-lethal impacts of cold shock on freshwater fish at a critical life-history stage. Understanding the impacts of cold shock will aid management of freshwater ecosystems for the benefit of fish populations, with the current study identifying critical life stages to be considered in remediation and guiding thresholds necessary to reduce the impact of cold shock on native fish populations.

Enchytraeus crypticus Avoid Soil Spiked with Microplastic.

Microplastics (MPs) of varying sizes are widespread pollutants in our environment. The general opinion is that the smaller the size, the more dangerous the MPs are due to enhanced uptake possibilities. It would be of considerably ecological significance to understand the response of biota to microplastic contamination both physically and physiologically. Here, we report on an area choice experiment (avoidance test) using Enchytraeus crypticus, in which we mixed different amounts of high-density polyethylene microplastic particles into the soil. In all experimental scenarios, more Enchytraeids moved to the unspiked sections or chose a lower MP-concentration. Worms in contact with MP exhibited an enhanced oxidative stress status, measured as the induced activity of the antioxidative enzymes catalase and glutathione S-transferase. As plastic polymers per se are nontoxic, the exposure time employed was too short for chemicals to leach from the microplastic, and as the microplastic particles used in these experiments were too large (4 mm) to be consumed by the Enchytraeids, the likely cause for the avoidance and oxidative stress could be linked to altered soil properties.

Highly heterogeneous temporal dynamics in the abundance and diversity of the emerging pathogens Arcobacter at an urban beach.

While the significance of Arcobacter in clinical settings grows, the ecological dynamics of potentially pathogenic Arcobacter in coastal marine environments remains unclear. In this study, we monitored the temporal dynamics of Arcobacter at an urban beach subject to significant stormwater input and wet weather sewer overflows (WWSO). Weekly monitoring of bacterial communities over 24 months using 16S rRNA amplicon sequencing revealed large, intermittent peaks in the relative abundance of Arcobacter. Quantitative PCR was subsequently employed to track absolute abundance of Arcobacter 23S rRNA gene copies, revealing peaks in abundance reaching up to 108 gene copies L-1, with these increases statistically correlated with stormwater and WWSO intrusion. Notably, peaks in Arcobacter abundance were poorly correlated with enterococci plate counts, and remained elevated for one week following heavy rainfall. Using oligotyping we discriminated single nucleotide variants (SNVs) within the Arcobacter population, revealing 10 distinct clusters of SNVs that we defined as Arcobacter "ecotypes", with each displaying distinct temporal dynamics. The most abundant ecotype during stormwater and modelled WWSO events displayed 16S rRNA sequence similarity to A. cryaerophilius, a species previously implicated in human illness. Our findings highlight the diverse environmental drivers of Arcobacter abundance within coastal settings and point to a potentially important, yet overlooked exposure risk of these potential pathogens to humans.

A Review of the Effect of Trace Metals on Freshwater Cyanobacterial Growth and Toxin Production.

Cyanobacterial blooms are becoming more common in freshwater systems, causing ecological degradation and human health risks through exposure to cyanotoxins. The role of phosphorus and nitrogen in cyanobacterial bloom formation is well documented and these are regularly the focus of management plans. There is also strong evidence that trace metals are required for a wide range of cellular processes, however their importance as a limiting factor of cyanobacterial growth in ecological systems is unclear. Furthermore, some studies have suggested a direct link between cyanotoxin production and some trace metals. This review synthesises current knowledge on the following: (1) the biochemical role of trace metals (particularly iron, cobalt, copper, manganese, molybdenum and zinc), (2) the growth limitation of cyanobacteria by trace metals, (3) the trace metal regulation of the phytoplankton community structure and (4) the role of trace metals in cyanotoxin production. Iron dominated the literature and regularly influenced bloom formation, with 15 of 18 studies indicating limitation or colimitation of cyanobacterial growth. A range of other trace metals were found to have a demonstrated capacity to limit cyanobacterial growth, and these metals require further study. The effect of trace metals on cyanotoxin production is equivocal and highly variable. Better understanding the role of trace metals in cyanobacterial growth and bloom formation is an essential component of freshwater management and a direction for future research.

Urban beaches are environmental hotspots for antibiotic resistance following rainfall.

To reveal the occurrence and mechanisms for dispersal of antibiotic resistance (AbR) among the microbial assemblages inhabiting impacted coastal environments, we performed a weekly, two-year duration time-series study at two urban beaches between 2014 and 2016. We combined quantitative PCR and multiplex PCR/reverse line blot techniques to track patterns in the occurrence of 31 AbR genes, including genes that confer resistance to antibiotics that are critically important antimicrobials for human medicine. Patterns in the abundance of these genes were linked to specific microbial groups and environmental parameters by coupling qPCR and 16S rRNA amplicon sequencing data with network analysis. Up to 100-fold increases in the abundance of several AbR genes, including genes conferring resistance to quinolones, trimethoprim, sulfonamides, tetracycline, vancomycin and carbapenems, occurred following storm-water and modelled wet-weather sewer overflow events. The abundance of AbR genes strongly and significantly correlated with several potentially pathogenic bacterial OTUs regularly associated with wastewater infrastructure, such as Arcobacter, Acinetobacter, Aeromonas and Cloacibacterium. These high-resolution observations provide clear links between storm-water discharge and sewer overflow events and the occurrence of AbR in the coastal microbial assemblages inhabiting urban beaches, highlighting a direct mechanism for potentially significant AbR exposure risks to humans.

Production of ß-methylamino-L-alanine (BMAA) and Its Isomers by Freshwater Diatoms.

ß-methylamino-L-alanine (BMAA) is a non-protein amino acid that has been implicated as a risk factor for motor neurone disease (MND). BMAA is produced by a wide range of cyanobacteria globally and by a small number of marine diatoms. BMAA is commonly found with two of its constitutional isomers: 2,4-diaminobutyric acid (2,4-DAB), and N-(2-aminoethyl)glycine (AEG). The isomer 2,4-DAB, like BMAA, has neurotoxic properties. While many studies have shown BMAA production by cyanobacteria, few studies have looked at other algal groups. Several studies have shown BMAA production by marine diatoms; however, there are no studies examining freshwater diatoms. This study aimed to determine if some freshwater diatoms produced BMAA, and which diatom taxa are capable of BMAA, 2,4-DAB and AEG production. Five axenic diatom cultures were established from river and lake sites across eastern Australia. Cultures were harvested during the stationary growth phase and intracellular amino acids were extracted. Using liquid chromatography triple quadrupole mass spectrometry (LC-MS/MS), diatom extracts were analysed for the presence of both free and protein-associated BMAA, 2,4-DAB and AEG. Of the five diatom cultures analysed, four were found to have detectable BMAA and AEG, while 2,4-DAB was found in all cultures. These results show that BMAA production by diatoms is not confined to marine genera and that the prevalence of these non-protein amino acids in Australian freshwater environments cannot be solely attributed to cyanobacteria.

Microplastic pollution in estuaries across a gradient of human impact.

Microplastic (MP) pollution is an emerging issue in aquatic sciences. Little comparative information currently exists about the problem in coastal systems exposed to different levels of human impact. Here we report a year-long study on the abundance of MP in the water column of three estuaries on the east-coast of Australia. The estuaries are subject to different scales of human impact; the Clyde estuary has little human modification, the Bega estuary has a small township and single wastewater treatment works discharging to its waters, and the Hunter estuary which has multiple townships, multiple wastewater treatment plants, and heavy industry. MP abundance followed an expected pattern with the lowest abundance in the low-impact Clyde estuary (98 part. m3), moderate levels of MP in the moderately impacted Bega estuary (246 part. m3), and high MP abundance in the highly impacted Hunter estuary (1032 part. m3). The majority of particles were <200 µm and fragment-like rather than fiber-like. MP abundance was positively related to maximum antecedent rainfall in the Bega estuary, however there are no clear environmental factors that could explain MP variation in the other systems. MP were generally higher in summer and following freshwater inflow events. On the Hunter estuary MP abundance was at times as high as zooplankton abundance, and within the range of numbers reported in other highly impacted systems globally. The results confirm that higher levels of human impact lead to greater plastic pollution and highlight the need to examine aquatic ecosystems under a range of conditions in order to adequately characterize the extent of MP pollution in rivers and coastal systems.

Prevalence of ß-methylamino-L-alanine (BMAA) and its isomers in freshwater cyanobacteria isolated from eastern Australia.

Environmental exposure to the amino acid ß-methylamino-L-alanine (BMAA) was linked to the high incidence of neurodegenerative disease first reported on the island of Guam in the 1940s and has more recently been implicated in an increased incidence of amyotrophic lateral sclerosis (ALS) in parts of the USA. BMAA has been shown to be produced by a range of cyanobacteria and some marine diatoms and dinoflagellates in different parts of the world. BMAA is commonly found with two of its constitutional isomers: 2,4- diaminobutyric acid (2,4-DAB) and N-(2-aminoethyl) glycine (AEG). These isomers are thought to be co-produced by the same organisms that produce BMAA and MS/MS analysis following LC separation can add an additional level of specificity over LC-FL. Although the presence of BMAA and 2,4-DAB in surface scum samples from several sites in Australia has been reported, which Australian cyanobacterial species are capable of BMAA, 2,4-DAB and AEG production remains unknown. The aims of the present studies were to identify some of the cyanobacterial genera or species that can produce BMAA, 2,4-DAB and AEG in freshwater cyanobacteria blooms in eastern Australia. Eleven freshwater sites were sampled and from these, 19 single-species cyanobacterial cultures were established. Amino acids were extracted from cyanobacterial cultures and analysed using liquid chromatography-tandem mass spectrometry. BMAA was detected in 17 of the 19 isolates, 2,4-DAB was detected in all isolates, and AEG was detected in 18 of the 19 isolates, showing the prevalence of these amino acids in Australian freshwater cyanobacteria. Concentrations of all three isomers in Australian cyanobacteria were generally higher than the concentrations reported elsewhere. This study confirmed the presence of BMAA and its isomers in cyanobacteria isolated from eastern Australian freshwater systems, and determined which Australian cyanobacterial genera or species were capable of producing them when cultured under laboratory conditions.

An examination of microcystin-LR accumulation and toxicity using tethered bilayer lipid membranes (tBLMs).

Microcystin-LR (MC-LR) is a potent cyanobacterial toxin responsible for animal and human poisonings worldwide. MC-LR is found in organisms throughout the foodweb, however there is conjecture regarding whether it biomagnifies. Few studies have investigated how MC-LR interacts with lipid membranes, a determinant of biomagnification potential. We tested whether 1 µM MC-LR irreversibly associates with lipid bilayers or causes the creation of pore defects upon short and long-term exposure. Using tethered bilayer lipid membranes (tBLMs), we observed an increase in membrane conduction in tBLMs, representing an interaction of microcystin-LR with the lipid bilayer and a change in membrane packing properties. However, there were minimal changes in membrane capacitance upon short and long-term exposure, and MC-LR exhibited a rapid off-rate. Upon 24 h exposure to the toxin, no lipophilic multimeric complexes were detected capable of altering the toxin's off-rate. There was no evidence of the creation of new pores. This study demonstrates that MC-LR does not irreversibly imbed itself into lipids membranes after short or long-term exposure and suggests MC-LR does not biomagnify through the food web via lipid storage.