Combined effects of nanoplastics and elevated temperature in the freshwater water flea Daphnia magna

Global warming and nanoplastics (NPs) are critical global issues. Among NPs, one of the most hazardous types of plastics, polystyrene (PS), poses ecotoxicological threats to several freshwater organisms. The degree of toxicity of PS-NPs is strongly influenced by various environmental factors. This study illustrates the combined effects of temperature and PS-NPs on the water flea Daphnia magna. The sensitivity of D. magna to PS-NPs was tested under control (23 °C) and elevated temperatures (28 °C). As a result, increased temperatures influenced the uptake and accumulation of PS-NPs. Co-exposure to both higher temperatures and PS-NPs resulted in a drastic decrease in reproductive performance. The level of oxidative stress was found to have increased in a temperature-dependent manner. Oxidative stress was stimulated by both stressors, leading to increased levels of reactive oxygen species and antioxidant enzyme activity supported by upregulation of antioxidant enzyme-related genes under combined PS-NPs exposure and elevated temperature. In the imbalanced status of intracellular redox, activation of the p38 mitogen-activated protein kinase signaling pathway was induced by exposure to PS-NPs at high temperatures, which supported the decline of the reproductive capacity of D. magna. Therefore, our results suggest that PS-NPs exposure along with an increase in temperature significantly affects physiological processes triggered by damage from oxidative stress, leading to severely inhibited reproduction of D. magna.

Thermal stress-stimulated ZnO toxicity inhibits reproduction of freshwater crustacean Daphnia magna

Elevated temperatures due to climate change pose a variety of environmental risks to the freshwater ecosystem. At the same time, zinc oxide (ZnO) has become widely used and has entered the freshwater environment. As thermal stress may potentially impact the physicochemical properties of ZnO, its toxicity to freshwater organisms in the face of global warming is poorly understood. The potential effects on reproductive performances, including oogenesis, are of particular concern. In this study, we investigate the reproductive performances and related mRNA abundance of the zooplankton Daphnia magna under conditions of ZnO exposure and heat stress. The results revealed that ZnO and elevated temperature delayed maturity and juvenile production of D. magna. Histological observations indicated that oogenesis was inhibited, and the number and size of oocytes were reduced in the condition of ZnO exposure under heat stress. Eventual offspring in the same treatment exhibited decreased numbers, size, and quality. Congenital juvenile anomalies were increased, such as deformed eye, and impaired antenna and tail spine. Moreover, both ZnO and elevated temperature treatments inhibited expression levels of reproduction-related genes (vtg, EcR and VMO1) and induced the dmrt93b gene involved in the production of male offspring. Furthermore, we found that D. magna tried to cope with ZnO and thermal stress by upregulating hsp90, HIF-1α and HIF-1β. ZnO and heat stress inhibited the reproductive capacity of D. magna, produced deleterious effects on reproduction-associated physiological pathways, and damaged reproductive outcomes.

Ecotoxicological, ecophysiological, and mechanistic studies on zinc oxide (ZnO) toxicity in freshwater environment

The world has faced climate change that affects hydrology and thermal systems in the aquatic environment resulting in temperature changes, which directly affect the aquatic ecosystem. Elevated water temperature influences the physico-chemical properties of chemicals in freshwater ecosystems leading to disturbing living organisms. Owing to the industrial revolution, the mass production of zinc oxide (ZnO) has been led to contaminated environments, and therefore, the toxicological effects of ZnO become more concerning under climate change scenarios. A comprehensive understanding of its toxicity influenced by main factors driven by climate change is indispensable. This review summarized the detrimental effects of ZnO with a single ZnO exposure and combined it with key climate change-associated factors in many aspects (i.e., oxidative stress, energy reserves, behavior and life history traits). Moreover, this review tried to point out ZnO kinetic behavior and corresponding mechanisms which pose a problem of observed detrimental effects correlated with the alteration of elevated temperature.

Disturbances in growth, oxidative stress, energy reserves and the expressions of related genes in Daphnia magna after exposure to ZnO under thermal stress

The toxicological effects of metal contamination are influenced by the ambient temperature. Therefore, global warming affects the toxicity of metal contamination in aquatic ecosystems. ZnO is widely used as a catalyst in many industries, and causes contamination in aquatic ecosystems. Here, we investigated the effects of ZnO concentration under elevated temperature by observing growth, oxidative stress, energy reserves and related gene expression in exposed Daphnia magna. Body length and growth rate increased in neonates exposed to ZnO for 2 days but decreased at 9 and 21 days under elevated temperature. ZnO concentration and elevated temperature induced oxidative stress in mature D. magna by reducing superoxide dismutase (SOD) activity and increasing malondialdehyde (MDA) levels. In contrast, juveniles were unaffected. Carbohydrate, protein and caloric contents were reduced throughout development in D. magna treated with ZnO and elevated temperature in all exposure periods (2, 9 and 21 days). However, lipid content also decreased in mature D. magna treated with ZnO cultured under elevated temperature, while that of juveniles showed an increase in lipid content. Therefore, energy was perhaps allocated to physiological processes for detoxification and homeostasis. Moreover, expression patterns of genes related to physiological processes changed under elevated temperature and ZnO exposure. Taken together, our results highlight that the combination of temperature and ZnO concentration induced toxicity in D. magna. This conclusion was confirmed by the Integrated Biological Response (IBR) index. This study shows that changes in biological levels of organization could be used to monitor environmental change using D. magna as a bioindicator.

Probiotics of Lacticaseibacillus paracasei SD1 and Lacticaseibacillus rhamnosus SD11 attenuate inflammation and β-cell death in streptozotocin-induced type 1 diabetic mice

Probiotics provide health benefits in various aspects and are believed to modulate the immune system by balancing gut microbiota homeostasis, termed the "microbiota-immune axis". Recent evidence supports that several Lactobacillus strains possess glucose-lowering and anti-inflammatory effects in an animal model of type 1 diabetes (T1D). Although probiotics of Lacticaseibacillus paracasei SD1 (SD1) and Lacticaseibacillus rhamnosus SD11 (SD11) exert human oral health benefits by reducing harmful bacterial populations, their clinical application regarding hypoglycemic-related traits as well as the underlying mechanisms are still lacking. In this report, we used multiple low doses of streptozotocin (STZ)-induced diabetic BALB/c mice to explore the effects of SD1 and SD11 supplementation on the regulation of markers related to T1D. Experimental mice were randomly assigned into five groups, non-STZ + V, STZ + V, STZ + SD1, STZ + SD11, and STZ + SDM (mixture of SD1 and SD11), and physiological data were measured every week. Blood and pancreas samples were collected at 4- and 8-weeks. Our results indicate that supplementation with SD1, SD11, or SDM for 8 weeks significantly improved body weights, glycemic levels, glucose tolerance, insulin levels, and lipid profiles. Probiotic administration also preserved islet integrity and increased β-cell mass in STZ-injected mice, as well as prevented infiltration of macrophages, CD4+, and CD8+ T cells into the islets. Significantly, SD1 and SD11 suppressed the levels of IL1-β, TNF-α and IFN-γ and increased IL-10, which is concomitant with the inhibition of cleaved caspase 3, caspase 9, caspase 8, proapoptotic Bax, NF-κBp65, pSTAT1, and iNOS. Additionally, the survival ability of β-cells was mediated by upregulated anti-apoptotic Bcl2. We conclude that SD1 and SD11 attenuate STZ-induced diabetic mice by stabilizing glycemic levels and reducing inflammation, thereby protecting β-cells. Among the probiotic treatment groups, SD11 revealed the best results in almost all parameters, indicating its potential use for alleviating hyperglycemia-associated symptoms.

Bacterial communities in Branchinella thailandensis and Streptocephalus sirindhornae

The fairy shrimp is a freshwater crustacean found in both temporary and permanent freshwaters. In Thailand, fairy shrimp are farmed as live food for ornamental fish. This study aimed to investigate the bacterial compositions in two fairy shrimp species, Branchinella thailandensis and Streptocephalus sirindhornae. Both species were cultured, and total DNA was extracted. The V3-V4 region of the 16S rRNA gene was amplified and sequenced using Illumina Miseq. All data were analyzed by Illumina 16S Metagenomics (version 1.0.1) workflow in Base Space- Illumina. Each read was blasted against the Illumina-curated version of the Greengenes database to determine the operational taxonomic units (OTUs) corresponding to the 16S rRNA gene sequence. The results showed that the Shanon-Weiner diversity index of bacterial compositions in B. thailandensis and S. sirindhornae were 2.135 and 3.122, respectively. The evenness and genus-level richness of the bacterial composition in B. thailandensis were 0.364 and 354 genera, respectively. The dominant bacterium found in B. thailandensis was Nevskia. In S. sirindhornae, the evenness and genus-level richness of the bacterial composition were 0.521 and 400 genera, respectively. Azohydromonas was the dominant bacterium. Our results showed that the compositions and proportions of bacterial communities were specific to each species of fairy shrimp. This study will be useful for further experiments in aquaculture and ecological studies related to symbiotic interaction.

Sargassum plagiophyllum Extract Enhances Colonic Functions and Modulates Gut Microbiota in Constipated Mice

Constipation is a symptom that is widely found in the world’s population. Various dietary supplementations are used to relieve and prevent constipation. Seaweed is widely used for its health benefits. In this study, we aimed to investigate the effects of Sargassum plagiophyllum extract (SPE) on functions of the gastrointestinal tract and gut microbiota. The results show that SPE pretreatment increased the frequency of gut contraction, leading to reduce gut transit time. SPE pretreatment also significantly increased the secretion of Cl− and reduced Na+ absorption, increasing fecal water content in constipated mice (p < 0.05). In addition, the Bifidobacteria population in cecal contents was significantly higher in constipated mice pretreated with 500 mg/kg SPE for 14 days than in untreated constipated mice (p < 0.05). Our findings suggest that SPE can prevent constipation in loperamide-induced mice. This study may be useful for the development of human food supplements from S. plagiophyllum, which prevent constipation.

Effects of Sargassum plagiophyllum extract pretreatment on tissue histology of constipated mice

Purpose: To evaluate the toxicity of the dried seaweed, Sargassum plagiophyllum, extract (SPE) pretreatment in constipated mice.Methods: The dried seaweed powder was mixed with distilled water and extracted by autoclave at 121°C. Antioxidant activity of the extract was determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. Human normal colon cells were pretreated with SPE at 0 - 100 μg/mL for 24 h before challenging them with 100 μM hydrogen peroxide (H2O2). Intracellular reactive oxygen species (ROS) were quantified using 2',7'- dichlorodihydrofluorescein diacetate (H2DCFDA). Male ICR mice were pretreated for 14 consecutive days with SPE at 100, 500 and 1,000 mg/kg or lactulose at 500 mg/kg. Body weight and food intake were recorded daily. Constipation was induced with loperamide on days 12, 13 and 14 and fecal pellets evacuated over a 4-hr period. The ileum, liver, kidney, and spleen were collected for histopathological examination.Results: The IC50 for the radical scavenging capacity of SPE was 343.90 ± 4.21 μg/mL compared to 14.14 ± 0.71 μg/mL for ascorbic acid. Pretreatment with SPE was significantly reduced ROS production in human normal colon cells. Oral administration of all doses of SPE and lactulose for 14 consecutive days had no effect on food intake or body weight when compared to the normal control group. Defecation was significantly more frequent in mice pretreated with SPE at 100 mg/kg than in the constipation control group. Histopathological examination of the ileum, liver, kidney and spleen of pretreated constipated mice revealed no toxic effect from either SPE or lactulose. On the other hand, the loss of mucus-producing cells in the ileum of constipated mice was significantly lower in mice pretreated with SPE.Conclusions: These findings support the safety of SPE supplementation and may broaden itsapplication in clinical fields as an alternative drug or supplement for constipation management.

Bacteria Associated with Echinodorus cordifolius and Lepironia articulata Enhance Nitrogen and Phosphorus Removal from Wastewater

Phytoremediation and bioremediation are eco-friendly methods of wastewater treatment that are widely used throughout the world to reduce anthropogenic water contamination. This study was conducted to assess the effectiveness of symbiotic bacteria in phytoremediation using two aquatic plants, Echinodorus cordifolius and Lepironia articulata, that were tested in sterilized and unsterilized groups. The results showed that unsterilized plants removed more phosphate, ammonium, nitrate and nitrite than the sterilized plants. In untreated and unsterilized E. cordifolius groups, the dominant bacterium was Calothrix (46.90 and 49.69%, respectively), which was higher than in the sterilized E. cordifolius group (38.88%). In untreated and unsterilized groups of L. articulata, Clostridium was a dominant bacterium. The proportion of Clostridium was much lower in the sterilized L. articulata group (1.31%) than in the untreated (13.71%) and unsterilized (49.02%) groups. Our results suggested that root-associated bacteria in E. cordifolius and L. articulata were effective in the removal of phosphorus and nitrogen from domestic wastewater.

Oligosaccharides derived from dragon fruit modulate gut microbiota, reduce oxidative stress and stimulate toll-pathway related gene expression in freshwater crustacean Daphnia magna

Dragon fruit oligosaccharide (DFO) is an indigestible prebiotic. In this study, we aimed to investigate the effects of DFO on gut microbiota, oxidative stress and immune-related gene expression in Daphnia magna. The 10-day-old D. magna were treated with 0, 9, and 27 mg l^-1 DFO for 85 h. The gut bacterial communities, superoxide dismutase (SOD) activity, lipid peroxidation and the expressions of genes in Toll signaling pathway were observed. The results showed that D. magna treated with 9 and 27 mg l^-1 DFO altered gut microbiota composition by increasing Limnohabitans and Lactobacillus, and significantly increased SOD activity and reduced lipid peroxidation. Moreover, the expressions of Toll2, Toll3, Toll5, Toll7 and Pelle genes were significantly increased in D. magna treated with 9 and 27 mg l^-1 DFO. Our results suggested that DFO changed the composition of the gut microbiota of D. magna by increasing the beneficial bacteria. DFO also had the ability to stimulate innate immunity in D. magna by increasing SOD activity, reducing lipid peroxidation, and increasing the expression of immune-related genes.

Temperature and concentration of ZnO particles affect life history traits and oxidative stress in Daphnia magna

Temperature affects physiological processes in organisms and the toxicity of chemicals. The widespread industrial use of ZnO causes contamination in aquatic ecosystems. This study aimed to investigate the chronic toxicity of ZnO at different temperatures using Daphnia magna as a model organism. The chronic toxicity of five different concentrations of ZnO was assessed at 23 °C and 28 °C. The results showed that higher concentrations of ZnO inhibited growth, production of first clutch eggs and juvenile accumulation at both 23 °C and 28 °C. Growth rate, numbers of first clutch eggs and juvenile accumulation were lower at 28 °C than at 23 °C. We also observed the levels of malondialdehyde (MDA) and superoxide dismutase (SOD) activity. At higher concentrations of ZnO, oxidative stress was induced leading to increase MDA level and decrease SOD activity at 28 °C. These findings indicated that high temperature and high concentration of ZnO inhibited the activity of enzymatic proteins. Nonetheless, among all treatments, the accumulation of zinc in D. magna was not significantly different. Our results suggested that both ZnO and higher temperature induced oxidative stress in D. magna. As a result, MDA concentration increased, SOD activity changed and the growth and reproduction of D. magna was adversely affected.

Effects of symbiotic bacteria on chemical sensitivity of Daphnia magna

The crustacean zooplankton Daphnia magna has been widely used for chemical toxicity tests. Although abiotic factors have been well documented in ecotoxicological test protocols, biotic factors that may affect the sensitivity to chemical compounds remain limited. Recently, we identified symbiotic bacteria that are critical for the growth and reproduction of D. magna. The presence of symbiotic bacteria on Daphnia raised the question as to whether these bacteria have a positive or negative effect on toxicity tests. In order to evaluate the effects of symbiotic bacteria on toxicity tests, bacteria-free Daphnia were prepared, and their chemical sensitivities were compared with that of Daphnia with symbiotic bacteria based on an acute immobilization test. The Daphnia with symbiotic bacteria showed higher chemical resistance to nonylphenol, fenoxycarb, and pentachlorophenol than bacteria-free Daphnia. These results suggested potential roles of symbiotic bacteria in the chemical resistance of its host Daphnia.

Symbiotic bacteria contribute to increasing the population size of a freshwater crustacean, Daphnia magna

The filter-feeding crustacean Daphnia is a key organism in freshwater ecosystems. Here, we report the effect of symbiotic bacteria on ecologically important life history traits, such as population dynamics and longevity, in Daphnia magna. By disinfection of the daphniid embryos with glutaraldehyde, aposymbiotic daphniids were prepared and cultured under bacteria-free conditions. Removal of bacteria from the daphniids was monitored by quantitative polymerase chain reaction for bacterial 16S rRNA gene. The population of aposymbiotic daphniids was reduced 10-folds compared with that of the control daphniids. Importantly, re-infection with symbiotic bacteria caused daphniids to regain bacteria and increase their fecundity to the level of the control daphniids, suggesting that symbiotic bacteria regulate Daphnia fecundity. To identify the species of symbiotic bacteria, 16S rRNA genes of bacteria in daphniids were sequenced. This revealed that 50% of sequences belonged to the Limnohabitans sp. of the Betaproteobacteria class and that the diversity of bacterial taxa was relatively low. These results suggested that symbiotic bacteria have a beneficial effect on D. magna, and that aposymbiotic Daphnia are useful tools in understanding the role of symbiotic bacteria in the environmental responses and evolution of their hosts.