Detection of secondary cyanobacterial metabolites using LC-HRMS in Lake Karaoun

Nanozyme and bifunctional nanobody-based colorimetric-SERS dual-mode Immunosensor for microcystin-LR detection

Microcystin-LR (MC-LR), a potent cyanotoxin in freshwater, poses a risk of severe liver damage and other health issues, making its detection vital. However, the detection capabilities of conventional antibodies are constrained, which limited their use in immunoassays. In this work, we designed a new bifunctional nanobody, named A2.3-SBP (comprised of nanobody and streptavidin binding peptide), capable of binding with MC-LR and streptavidin. Based on A2.3-SBP and Fe3O4@Au-Pt nanozyme, we introduced an enzyme-free immunosensor that operated in microplate with colorimetric and surface-enhanced Raman scattering (SERS) detection modes. The dual-mode assay showed color changes and SERS intensity directly correlating to MC-LR concentrations with a range from 1.0 to 500 ng/mL and a limit of detection of 0.26 and 0.032 ng/mL, respectively. This strategy eliminated the need for complex enzymatic reactions and realized dual-signal detection of MC-LR in 96 water samples (0.03 μg/kg) within 30 min, suggesting its potential in drinking water detection.

Bloom-forming planktonic Microcystis and benthic Oscillatoria-induced oxidative stress and inflammatory responses in juvenile silver carp and bighead carp

As global warming and water eutrophication, the multiple proliferation of harmful cyanobacteria can form algal blooms and cause serious ecological problems. In recent years, the large-scale and persistent cyanobacterial blooms occur frequently worldwide and have attracted widespread attention due to the harmful impacts. Among these harmful bloom-forming cyanobacteria, the ecological and toxicological impacts of planktonic cyanobacteria have been extensively studied. However, research on the ecological risks and adverse effects of harmful benthic cyanobacteria is lagging. Filter-feeding fish could suffer from more toxic stimuli than other fish due to their special feeding habits. To investigate and compare the complex toxic effects of different kinds of harmful cyanobacteria on fish, three different-sized (i.e. small, medium, and large) juvenile silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis) were exposed to cyanobacterial blooms-related density (1 × 106 cells/mL) of Microcystis aeruginosa (i.e. generating microcystins) and Oscillatoria sp. (i.e. generating cylindrospermopsin) for 3 d, after which biomarkers of oxidative stress and inflammation in the liver of fish were detected. The silver carp and bighead carp can effectively ingest Microcystis cells but cannot effectively ingest Oscillatoria cells through the measurement of the levels of cyanotoxins. Both Microcystis and Oscillatoria cells can induce different levels of oxidative stress and inflammatory responses in the liver of these juvenile filter-feeding fish via altering the biochemical parameters of the antioxidant system (e.g. superoxide dismutase activity) and immune system (e.g. interleukin-1β level). Therefore, our research identified potential data gaps that how the different types of cyanobacteria induce toxic effects in the liver of juvenile filter-feeding fish in a short time. This study contributes to a better understanding of the short-term adverse effects of different cyanobacterial species on juvenile fish, suggesting that the benthic toxic cyanobacteria-induced ecological and health risks require further attention.

Identification and occurrence of microcystins in freshwaters and fish from a eutrophic dam through LC-HRMS

Microcystins (MCs) are cyclic heptapeptides originating from various cyanobacteria in eutrophic aquatic environments. Their potential consequences on ecosystems and public health underscores the need to explore MCs' occurrence. In this study, liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS) analysis and a suspect screening workflow supported by open-source tools were employed for the determination of MCs in freshwater and biota samples from a eutrophic dam in Uruguay. MS2 spectra were acquired using higher-energy collisional dissociation (HCD), data-dependent acquisition (DDA), and stepped NCE of [M + H]+ and [M + 2H]2+ ions. In addition to the confirmation of 3 MCs in the samples, a comprehensive study of the acquired spectra led to the tentative identification of 30 MCs, including 2 partially described variants not previously reported. 33 MCs were determined in freshwaters, exhibiting a maximum MC concentration in a sample of 12731 μg/L. Regarding fish, the 61 % of the samples exhibited at least a positive determination. 8 MCs were detected and [D-Leu1]MC-LR, [seco-4/5]MC-LR, MC-LR, MC-RR, MC-WR, and [D-Asp3]MC-RR could be semi-quantified (3-127 μg/kg, w.w). In 2 samples, the MC-LR content per 100 g of fish was found to be close to 80 % the tolerable daily intake for chronic exposure recommended by the WHO. The identification of [seco-4/5]MC-LR in biota highlights the labile byproducts of MCs and the need for wide-scope analytical approaches. This study emphasizes the extensive range of MCs present in eutrophic freshwater environments, their accumulation in exposed biota, and their potential entry into the food web.

The toxicological effects of life-cycle exposure to harmful benthic cyanobacteria Oscillatoria on zebrafish growth and reproduction: A comparative study with planktonic Microcystis

The risks of planktonic cyanobacteria blooms have been the focus of much scientific research, but studies on the ecotoxicological effects of benthic cyanobacteria are lagging. The impacts of cyanobacteria cells on fish populations might be more complex in contrast to purified cyanotoxins or cyanobacteria extracts. This study systematically compared the chronic effects of benthic Oscillatoria sp. (producing cylindrospermopsins) and planktonic Microcystis aeruginosa (producing microcystins) on the growth and reproduction of zebrafish through life-cycle exposure (5- 90 days post fertilization). The results showed that both Oscillatoria sp. and M. aeruginosa exposure caused growth inhibition and fecundity reduction in F0 generation by disrupting sex hormone levels, delayed ovarian and sperm development, and induced pathological lesions in zebrafish gonads. Furthermore, exposure to Oscillatoria sp. or M. aeruginosa in adult zebrafish increased mortality and teratogenicity in F1 embryos (without exposure), indicating a parental transmission effect of developmental toxicity. The difference was that M. aeruginosa exposure led to significant alterations in pathways, such as tissue development, redox processes, and steroid hormone synthesis. In contrast, Oscillatoria sp. exposure primarily disrupted the PPAR signaling pathway, cell adhesion molecules, and lipid transport pathways. Interestingly, the differentially expressed genes revealed that male fish were more sensitive to harmful cyanobacteria than females, whether exposed to Oscillatoria sp. or M. aeruginosa. These findings contribute to a better mechanistic understanding of the chronic toxic effects of distinct types of harmful cyanobacteria, suggesting that the ecological risk of benthic cyanobacteria requires further attention.