Interactive effects of microcystin and ammonia on the reproductive performance and phenotypic traits of the rotifer Brachionus calyciflorus

Microcystin Contamination in Irrigation Water and Health Risk

Microcystins (MCs), natural hepatotoxic compounds produced by cyanobacteria, pose significant risks to water quality, ecosystem stability, and the well-being of animals, plants, and humans when present in elevated concentrations. The escalating contamination of irrigation water with MCs presents a growing threat to terrestrial plants. The customary practice of irrigating crops from local water sources, including lakes and ponds hosting cyanobacterial blooms, serves as a primary conduit for transferring these toxins. Due to their high chemical stability and low molecular weight, MCs have the potential to accumulate in various parts of plants, thereby increasing health hazards for consumers of agricultural products, which serve as the foundation of the Earth's food chain. MCs can bioaccumulate, migrate, potentially biodegrade, and pose health hazards to humans within terrestrial food systems. This study highlights that MCs from irrigation water reservoirs can bioaccumulate and come into contact with plants, transferring into the food chain. Additionally, it investigates the natural mechanisms that organisms employ for conjugation and the microbial processes involved in MC degradation. To gain a comprehensive understanding of the role of MCs in the terrestrial food chain and to elucidate the specific health risks associated with consuming crops irrigated with water contaminated with these toxins, further research is necessary.

Detrimental effects of hull cleaning wastewater on oxidative status, life cycle parameters, and population growth of the monogonont rotifer Brachionus manjavacas

While wastewater discharged from in-water cleaning process of ship hulls on rotifer consistently released into aquatic ecosystem, its detrimental effects on non-target animals are largely unclear. In this study, we provide evidence on detrimental effects of hull cleaning wastewater in the monogonont rotifer Brachionus manjavacas by analyzing biochemical and physiological parameters in its oxidative status, survival, lifespan, growth, fecundity, and population. The wastewater contained high concentrations of metals (Zn and Cu) and metal-based antifoulants (CuPT and ZnPT). Significant oxidative stress was observed in response to two wastewater samples [1) raw wastewater (RW) and 2) mechanical filtrated in the cleaning system (MF)]. Higher detrimental effects in survival, lifespan, fecundity, and population growth for 10 days were measured in the RW-exposed rotifers than those results analyzed in the MF-exposed rotifers. Two growth parameters, lorica length and width were also significantly modulated by both wastewater samples. These results indicate that even filtered hull cleaning wastewater would have deleterious effects on the maintenance of the rotifer population when they exposed constantly.

New insights into endocrine reproductive toxicity of Microcystis aeruginosa combined with ammonia exposure in zebrafish

The ecological risk posed by MCs-producing M. aeruginosa and elevated ammonia to fish in actual aquatic environments remains uncertain. To address this knowledge gap, we conducted simulations to investigate the endocrine-reproductive toxicity of prolonged exposure (45 d) to Microcystis aeruginosa (2 × 10^6 cells/mL) and 30 mg/L total ammonia nitrogen (TAN) in zebrafish under environmentally relevant conditions. Our results showed that exposure to M. aeruginosa significantly inhibited the body weight, increased gonadosomatic index (GSI), delayed oocyte development, and disrupted endocrine hormonal balance (reduced gonadotropin-releasing hormone (GnRH), and increased estradiol (E2) and testosterone (T)). Mechanistically, it should be attributed to the over-expression of hypothalamic-pituitary-gonadal-liver (HPGL) axis-related genes (cyp11a and cyp17) induced by M. aeruginosa. On the other hand, TAN exposure caused mild damage to zebrafish ovarian tissue and promoted an increase of T levels by inducing the upregulation of steroid hormone synthesis gene (3βhsd) expression in the ovary. It is worth noting that the dysregulation of E2/T ratio in zebrafish ovaries may be attributed to the inhibition of cyp19a1a by both M. aeruginosa and TAN. These results were further confirmed by changes in steroidogenic enzymes activities in the M. aeruginosa or TAN treated groups. Our findings indicated that exposure to M. aeruginosa and TAN had adverse impacts on the reproductive system of zebrafish. And the combined exposure of M. aeruginosa and TAN had more severe effects on the body weight, GSI, pathological changes, hormone levels and HPGL-axis related gene expression in female zebrafish. These results provide compelling evidence regarding the potential risks for reproductive health associated with M. aeruginosa and TAN in eutrophic water bodies experiencing M. aeruginosa blooms, and contribute to the development of effective strategies for monitoring and managing these toxins in aquatic ecosystems.

Integrated analysis of physiological, transcriptome, and metabolome analyses of the gills in Solenaia oleivora under ammonia exposure

Ammonia is a common toxicant in aquatic systems and one of the key factors affecting aquaculture. However, data on mollusks' toxic response and coping mechanisms to ammonia nitrogen, especially freshwater mollusks, are still lacking. In this study, we evaluated the tolerance of a freshwater mollusk Solenaia oleivora to ammonia and investigated its coping mechanisms by combining physiological, metabolic, and transcriptomic analyses in the gills. The acute toxicity test revealed that the LC50-96 h (temperature-20 ℃, pH-7.4) of ammonia in S. oleivora was 63.29 mg/L. The physiological and TUNEL results showed that although 10 mg/L ammonia exposure increased the activities of antioxidant, immune and ammonia detoxification-related enzymes, it still caused oxidative damage and cell apoptosis of gill tissues. A total of 97 differential metabolites (DMs) and 3431 differential expressed genes (DEGs) were identified after ammonia stress. Among them, most DMs and DEGs were involved in immune response, antioxidant, cell apoptosis, carbohydrate metabolism, amino acid metabolism, and lipid metabolism. The enhancement of glycolysis and lipid metabolisms may provide energy for immune response and ammonia detoxification. In addition, glutamine synthesis, alanine synthesis and urea cycle were involved in ammonia nitrogen detoxification in the gill tissue of S. oleivora. Our results indicate that ammonia leads to individual death in S. oleivora, as wells as oxidative damage, cell apoptosis, immune response, and metabolic changes of gill tissues. The findings will provide valuable information to assess the potential ecological risk of environmental ammonia to freshwater mollusks and theoretical guidance for the healthy aquaculture of S. oleivora.

A review of the toxic effects of ammonia on invertebrates in aquatic environments

Aquatic invertebrates are the organisms most susceptible to ammonia toxicity. However, the toxic effects of ammonia on invertebrates are still poorly understood. This study reviews the research progress in ammonia toxicology for the period from 1986 to 2023, focusing on the effects on invertebrates. Through examining the toxic effects of ammonia at different levels of organization (community, individual, tissue and physiology, and molecular) as well as the results from omics studies, we determined that the most significant effects were on the reproductive capacity of invertebrates and the growth of offspring, although different populations show variation in their tolerance to ammonia, and tissues have varied potential to respond to ammonia stress. A multicomponent analysis is an in-depth technique employed in toxicological studies, as it can be used to explore the enrichment pathways and functional genes expressed under ammonia stress. This study comprehensively discusses ammonia toxicity from multiple aspects in order to provide new insights into the toxic effects of ammonia on aquatic invertebrates.

Swimming behaviour as an alternative endpoint to assess differences in abiotic stress sensitivities between strains of Brachionus koreanus (Rotifera: Monogononta)

Brachionus plicatilis is a cosmopolitan rotifer used as a model organism in several research areas and as live food in aquaculture. Being a species complex, responses to stressors vary even among strains of the same species and, thus, the responses of one species are not representative of the whole complex. This study aimed to address the effects of extreme salinity ranges, and different concentrations of hydrogen peroxide, copper, cadmium, and chloramphenicol, in two strains of B. koreanus (MRS10 and IBA3) from B. plicatilis species complex, by assessing effects on their survival and swimming capacity. Neonates (0-4 h old) were exposed to the stressors in 48 well-microplates, for 24 and 6 h, to evaluate lethal and behavioural effects, respectively. Tested conditions of chloramphenicol did not show any effects on rotifers. The behavioural endpoint showed to be particularly sensitive to assess the effects of high salinity, hydrogen peroxide, and copper sulfate, as swimming capacity impairment was observed for both strains in the lowest concentrations used in lethal tests. Overall, results showed that IBA3 was more tolerant to the majority of stressors, comparing to MRS10, which may be due to differences in physiological characteristics, highlighting the importance of performing multiclonal experiments. Also, swimming capacity inhibition proved to be a good alternative to the classical lethality tests, being sensitive to lower concentrations and with shorter exposure periods.

Combined effects of increased water temperature and cyanobacterial compounds exert heterogeneous effects on survival and ecological processes in key freshwater species

Climate change is increasing water temperature and intensifying the incidence of cyanobacterial blooms worldwide. However, the combined effects of increased temperature and microcystin concentrations as co-stressors on survival and ecological processes in freshwater species are unclear. Here, using purified MC-LR and crude extract of toxigenic Microcystis aeruginosa, we tested the individual and combined effects of three water temperatures (15, 20, 25 °C) and a range of environmentally relevant concentrations of dissolved microcystin and crude extract (0.01–10 µg·L−1) on survival, growth inhibition, grazing and predation rates in three freshwater species: phytoplankton (Scenedesmus quadricauda), zooplankton (Daphnia pulex), and an invertebrate predator (Ischnura elegans). Purified MC-LR exerted a higher growth inhibitory effect on S. quadricauda compared to crude extract with the same concentration of MC-LR, while neither treatment affected its chlorophyll-a content or survival of D. pulex. Crude extract reduced grazing and survival of D. pulex and I. elegans, respectively. The combined effect of higher temperature and crude extract reduced I. elegans survival by 50%. Increased temperature reduced prey handing time in I. elegans by 49%, suggesting a higher predation rate. However, warming together with higher concentrations of crude extract jointly increased zooplankton grazing and reduced damselfly predation. Taken together, these results suggest crude extract, and not necessarily microcystin, can affect survival and productivity in freshwater species, although these effects may vary unevenly across trophic levels. Our findings highlight the importance of complex ecological mechanisms by which warming can exacerbate toxic effects of cyanobacterial bloom extracts on survival and functions among species in eutrophic freshwaters.

Effect of maternal ammonia stress on population dynamics of the rotifer Brachionus calyciflorus offspring

Maternal effects play important roles in phenotypic variations among individuals and are thus considered to regulate population performance in responses to environmental stress. High ammonia levels are known to suppress population growth of the rotifer Brachionus calyciflorus. However, it remains unclear whether maternal environmental ammonia stress influences the offspring phenotypic variation and, if so, how it affects the offspring population dynamics in the rotifer. The present work examined variations in life history, morphology, feeding and digestive activities of B. calyciflorus offspring affected by maternal ammonia stress and the effect of the above variations on offspring population dynamics. We observed increased fitness in the offspring population affected by the cumulative maternal effect. There was a trade-off between offspring (F₁) survival and reproductive investment under maternal (F₀) ammonia stress. Population growth of the offspring possibly increased via decreasing body size and posterolateral spine length while enhancing cellulase activity. Moreover, the absence of the posterolateral spine of the rotifer was a sensitive response to maternal ammonia stress. These findings underscore maternal environmental stress as an important source of phenotypic variations and highlight these multiple responses work together to affect population dynamics.

Cyanobacterial anabaenopeptin-B, microcystins and their mixture cause toxic effects on the behavior of the freshwater crustacean Daphnia magna (Cladocera)

Comparison of the toxic effects caused by the pure cyanobacterial cyclic hexapeptide anabaenopeptin-B (AN-B), the heptapeptides: microcystin-LR (MC-LR) and MC-LF as well as a binary mixture of AN-B with MC-LR on the swimming speed and hopping frequency - essential activities of Daphnia, was experimentally determined. Till now, no information on behavioral effects of AN-B and its mixture with microcystins, commonly produced by cyanobacteria, was available. Also MC-LF effect on aquatic crustaceans was determined for the first time. The results showed that AN-B exerted considerable inhibition of D. magna swimming speed and hopping frequency similar to MC-LR and MC-LF. The mixture of AN-B and MC-LR caused stronger toxic effects, than the individual oligopeptides used at the same concentration. The much lower 48 h- EC₅₀ value of the AN-B and MC-LR mixture (0.95 ± 0.12 μg/mL) than those of individual oligopeptides AN-B (6.3 ± 0.63 μg/mL), MC-LR (4.0 ± 0.27 μg/mL), MC-LF (3.9 ± 0.20 μg/mL) that caused swimming speed inhibition explains the commonly observed stronger toxicity of complex crude cyanobacterial extracts to daphnids than individual microcystins. The obtained results indicated that AN-B, microcystins and their mixture exerted time- and concentration-dependent motility disturbances of crustaceans and they can be good candidates for evaluation of toxicity in early warning systems. Other cyanobacterial oligopeptides beyond microcystins should be considered as a real threat for aquatic organisms.

Effects of acute ammonia exposure on antioxidant and detoxification metabolism in clam Cyclina sinensis

To investigate the defensive strategies of clam Cyclina sinensis in response to environmental ammonia exposure, we investigate the 96 h median lethal concentration (LC₅₀-96 h) and the 96 h safe concentration (SC) of total ammonia nitrogen (TAN) for C. sinensis, and on the basis we examined glutamine synthetase (GS) activity, glutamine content, urea content and the antioxidant enzyme activities of super oxide dismutase (SOD) and catalase (CAT) in 96 h at three different levels of TAN as 0 (control), 73.94 (T1) and 227.04 mg/L (T2). Results showed that LC₅₀-96 h and SC for C. sinensis were 65.79 and 6.58 mg/L, respectively. The LC₅₀-96 h and SC of NH₃ were 1.70 and 0.17 mg/L, respectively. Ammonia exposure had significantly effects on SOD and CAT activities in the hepatopancreas tissue. Both the level of SOD activity and CAT activity increased with increasing concentration of TAN. No significant differences between T1 and T2 were found in GS activity from 3 h to 96 h after exposed to ammonia, whereas they were significantly higher than those in the control. Both the level of glutamine content in T1 and T2 increased significantly from 6 h to 24 h after exposed to ammonia and they were significantly higher than those in the control. There were no significantly differences were found in the level of urea concentration between T1 and T2 from 6 h to 96 h, while they were significantly higher those in the control. In conclusion, enhancing hepatopancreas antioxidant responses as well as converting ammonia into glutamine and urea worked in combination to allow C. sinensi to defend against acute ammonia exposure.

Effects of bromate on life history parameters, swimming speed and antioxidant biomarkers in Brachionus calyciflorus

The baking industries and disinfection of tap water released a considerable amount of bromate into surface water, which has been reported as a carcinogenic compound to mammals. Rotifers play an important role in freshwater ecosystems and are model organisms to assess environmental contamination. In the present study, the effects of different concentrations (0.001, 0.01, 0.1, 1, 10, 100 and 200 mg/L) of bromate on the life-table and population growth parameters were investigated in the rotifer Brachionus calyciflorus. The results showed that the 24-h LC₅₀ of bromate to B. calyciflorus was 365.29 mg/L (95%Cl: 290.37-480.24). Treatments with 0.01, 10 and 200 mg/L bromate shorten the reproductive period. High levels of bromate (100 and 200 mg/L) significantly decreased net reproductive rate, intrinsic rate of population increase, life span, mictic rate of B. calyciflorus. To investigate the underlying mechanisms, swimming speed and antioxidative biomarkers were compared between bromate treatments and the control. The results showed that glutathione (GSH) and malondialdehyde (MDA) contents, total superoxide dismutase (T-SOD) and peroxidase (POD) activities decreased significantly in response to bromate exposure and the reasons required further investigation. Treatments with 0.001-200 mg/L bromate all significantly reduced swimming linear speed to rotifer larvae and treatments with 100-200 mg/L bromate significantly suppressed the swimming linear speed of adult rotifer. These changes would reduce filtration of algal food and could explain the decreased survival and reproduction. Overall, bromate may not show acute toxicity to rotifers, but still have potential adverse effects on rotifer behavior, which may then influence the community structure in aquatic ecosystems.

Growth performance, phenotypic traits, and antioxidant responses of the rotifer Brachionus plicatilis under different proportions of Phaeocystis globosa

Harmful Phaeocystis blooms disrupt seawater recreation and pose serious challenges to aquatic animals. The growth performance, phenotypic traits, and antioxidant responses of Brachionus plicatilis Müller to different proportions of Phaeocystis globosa were evaluated. B. plicatilis rotifers were exposed to cultures with Chlorella sp. and P. globosa alone and in mixtures of these two algae with proportions of 25%, 50%, and 75%. The total proportions of the two algae were maintained at 100%. Results showed that P. globosa inhibited the rotifer net reproduction rate, intrinsic growth rate, and finite rate of increase (P < 0.01). It induced the formation of defense phenotypic traits in terms of the increased posterolateral spine length and the reduced body length, swimming speed, and grazing rate of B. plicatilis (P < 0.001). Superoxide dismutase and catalase activities decreased, but the reactive oxygen species levels increased as the proportions of P. globosa increased (P < 0.01). The mixture of 50% Chlorella and 50% Phaeocystis positively affected the glutathione content, glutathione peroxidase activity, and generation time of rotifers (P < 0.01). Although P. globosa released toxicants with harmful effects on the growth performance of B. plicatilis, rotifers changed their antioxidant defense system and formed defense phenotypic traits in response to eutrophic conditions.

RAS based culture system for continuous production of Rotifers (Brachionus calyciflorus) in mass

The present study was undertaken to find out preferred food type, minimum effective algal cell requirement, effective harvest rate of rotifers and to design and construct re-circulatory aquaculture system (RAS) based rotifer, Brachionus calyciflorus production system at Aquatic Rainbow Technology Park, Dr MGR Fisheries College and Research Institute, TNJFU, Madhavaram campus, Chennai during 2017–2019. In the first experiment, food types, viz. Chlorella vulgaris, Spirulina major, Scenedismus obliquus and Baker’s yeast were extensively fed to rotifers with control (5000 L). The highest rotifer count was observed with C. vulgaris food type (365.33±2.18 rotifers/ml) followed by Baker’s yeast (245.33±5.36 rotifers/ml) on 8th day which started declining gradually to 30th day because of lower water quality. Second experiment on algal consumption rate by rotifer postulated that 22,000–25,000 cells/day/rotifer was the minimum cell requirement. Third experiment on standardizing effective harvest rate (10%, 30%, 50% and 70%) suggested that daily harvest at 30% maintained the rotifer culture at its stationary phase (381±19.45 rotifers/ml). After the experiments, we have designed, built and operated RAS based live food production unit for 17 months where the harvested water was treated using series of filters (rapidsand, cartridge, UV filters) and reused for algal culture. The seasonal data showed that temperature plays a major role with the highest production during summer (404.43±24.33 rotifers/ml) and consequently lower in winter (301.21±14.33 rotifers/ml). The system opens a new perspective of commercial scale production of rotifers with standard culture and harvesting practices.

The mechanisms in the altered ontogenetic development and lung-related pathology in microcystin-leucine arginine (MC-LR)-paternal-exposed offspring mice

A father's lifetime experience is a major risk factor for a range of diseases in an individual, and the consequences of the exposure can also be transmitted to his offspring. Our previous work has demonstrated that damage to testicular structures and decline in sperm quality in male mice can be caused by microcystin-leucine arginine (MC-LR), but the overall effects of the scope and extent of paternal exposure on health and disease in the offspring remain underexplored. Here, we report that MC-LR-paternal-exposed offspring mice showed reduced litter size and body weight accompanied by increased abnormalities in the lung. Analyses of the small noncoding RNAs (sncRNAs) in the sperm from MC-LR-exposed males demonstrated the downregulation of a wide range of piRNAs enriched for those target genes involved in the regulation of the embryo implantation pathways. Gene and protein expression analyses, as well as biochemical and functional studies, revealed suppressed expression of Hsp90α in testicular tissues from MC-LR-exposed males. Decreased Hsp90α in testicular tissues impaired the development of the offspring. In this study, we revealed that MC-LR alters the expression of Hsp90α in testicular tissues to cause changes in the expression profiles of sperm piRNAs produced by paternal mice. These changes lead to aberrant activation of the Wnt/β-catenin signaling pathway in pulmonary tissues of offspring mice, causing lung tissue damage and abnormal development. We hereby confirmed that MC-LR-induced alterations in epigenetic inheritance are capable of contributing to intergenerational developmental defects in paternal-exposed offspring mice.

Effect of acute ammonia exposure on the glutathione redox system in FFRC strain common carp (Cyprinus carpio L.)

Ammonia is one of the most common aquatic pollutants. To analyze the effect of ammonia exposure on the glutathione redox system, we investigated the levels of hydrogen peroxide (H₂O₂) and glutathione, and transcription and activities of glutathione-related enzymes in liver and gills of FFRC strain common carp (Cyprinus carpio L.) exposed to 0, 10, 20, and 30 mg/L of ammonia. The results showed that H₂O₂ content reached a maximum level at 48 h of exposure in the liver of fish. In gills, H₂O₂ increased rapidly at 6 h and reached to maximum levels at 24 h of exposure, indicating that gills experienced oxidative stress earlier than the liver of fish exposed to ammonia. Reduced glutathione (GSH) content and reduced glutathione/oxidized glutathione (GSH/GSSG) ratio increased significantly within 24 h of exposure. Meanwhile, the transcription and activities of glutathione S-transferase (GST) and glutathione reductase (GR) increased significantly in the liver, and glutathione peroxidase (GSH-Px) and GST increased in the gills of fish exposed to ammonia. Malondialdehyde (MDA) content kept at a low level after exposure to low concentration of ammonia, but increased significantly after exposure to 30 mg/L ammonia for 48 h along with a decrease in GSH content and GSH/GSSG ratio. These data showed that the glutathione redox system played an important role in protection against ammonia-induced oxidative stress in the liver and gills of FFRC strain common carp, though the defense capacity was not able to completely prevent oxidative damage occurring after exposure to higher concentration of ammonia. This research systematically studied the response of the glutathione redox system to ammonia stress and would provide novel information for a better understanding of the adaptive mechanisms of fish to environmental stress.