AgNP Treatment Research Articles

Role of hematin and sodium nitroprusside in regulating Brassica nigra seed germination under nanosilver and silver nitrate stresses

Silver nanoparticles (AgNPs) are one of the most widely used nanomaterials, although the mechanisms of AgNP toxicity in terrestrial plants is still unclear. We compared the toxic effects of AgNPs and AgNO3 on Brassica nigra seed germination at physiological and molecular levels. Both AgNPs and AgNO3 inhibited seed germination, lipase activity, soluble and reducing sugar contents in germinating seeds and seedlings. These reductions were more pronounced in AgNP treatments than AgNO3 treatments. Application of 200–400mg/L both AgNPs and AgNO3 increased transcription of heme oxygenase-1. However, at 800, 1600mg/L, AgNPs or AgNO3 suppressed HO-1 expression. At 400mg/L, AgNPs or AgNO3-induced inhibitory effects on seed germination and were ameliorated by the HO-1 inducer, hematin, or NO donor, sodium nitroprusside (SNP). Additionally, 4μM hematin and 400μM SNP were able to markedly boost the HO/NO system. However, the addition of the HO-1 inhibitor (ZnPPIX) or the specific scavenger of NO (cPTIO) not only reversed the protective effects conferred by hematin, but also blocked the up-regulation of HO activity. In addition, hematin-drived NO production in B. niger seeds under AgNPs was confirmed. Our results at physiological and molecular levels suggested that AgNPs were more toxic than AgNO3. Based on these results, for the first time, we suggest that endogenous HO is needed to alleviate AgNPs-induced germination inhibition, which might have a possible interaction with NO.

Silver nanoparticles affect on gene expression of inflammatory and neurodegenerative responses in mouse brain neural cells

Silver nanoparticles (AgNPs) have antibacterial characteristics, and currently are applied in Ag-containing products. This study found neural cells can uptake 3–5nm AgNPs, and investigated the potential effects of AgNPs on gene expression of inflammation and neurodegenerative disorder in murine brain ALT astrocytes, microglial BV-2 cells and neuron N2a cells. After AgNPs (5, 10, 12.5μg/ml) exposure, these neural cells had obviously increased IL-1β secretion, and induced gene expression of C-X-C motif chemokine 13 (CXCL13), macrophage receptor with collagenous structure (MARCO) and glutathione synthetase (GSS) for inflammatory response and oxidative stress neutralization. Additionally, this study found amyloid-β (Aβ) plaques for pathological feature of Alzheimer's disease (AD) deposited in neural cells after AgNPs treatment. After AgNPs exposure, the gene expression of amyloid precursor protein (APP) was induced, and otherwise, neprilysin (NEP) and low-density lipoprotein receptor (LDLR) were reduced in neural cells as well as protein level. These results suggested AgNPs could alter gene and protein expressions of Aβ deposition potentially to induce AD progress in neural cells. It's necessary to take notice of AgNPs distribution in the environment.

Silver nanoparticles augment releasing of pyrogenic factors by blood cells stimulated with LPS

Abstract Silver nanoparticles (AgNPs) have cytotoxic properties via generation of reactive oxygen species which are involved in the generalized sickness behavior of the host, including fever and lethargy among others. The aim of the present study was to investigate the impact of AgNPs on the ability of rat peripheral blood mononuclear cells (PBMCs) to release fever mediating factors after stimulation with lipopolysaccharide (LPS). Body temperature and motor activity of the Wistar rats were measured by biotelemetry system. Rat PBMCs were stimulated with LPS and after that the cells were washed and incubated alone or with AgNPs. The final supernatants were injected intraperitoneally. The levels of endogenous pyrogens such as interleukin-1β (IL−1β), IL-6 and tumor necrosis factor-α (TNF-α) released from the PBMCs into the final supernatants were also estimated. The results indicated that injection of the supernatants from the cells stimulated with LPS induced fever and inhibited motor activity. These effects were potentiated by the presence of AgNPs during the final incubation. The presence of the AgNPs also resulted in significant increases in levels of endogenous pyrogens. The augmentation of fever in the rats by the AgNPs treatment of the cultures seemed to be primarily associated with the changes in interleukin-1β levels.

Toxicity and bioaccumulation of sediment-associated silver nanoparticles in the estuarine polychaete, Nereis (Hediste) diversicolor

In this study, the toxicities of sediment-associated silver added to sediment as commercially available silver nanoparticles (Ag NPs, 20 and 80nm) and aqueous Ag (AgNO3) to the estuarine polychaete, Nereis (Hediste) diversicolor, were investigated for both individual and subcellular endpoints after 10 d of exposure. Both Ag NP types were characterized in parallel to the toxicity studies and found to be polydispersed and overlapping in size. Burrowing activity decreased (marginally) with increasing Ag concentration and depended on the form of Ag added to sediment. All worms accumulated Ag regardless of the form in which it was added to the sediment, and worm size (expressed as dry weight) was found to significantly affect bioaccumulation such that smaller worms accumulated more Ag per body weight than larger worms. Lysosomal membrane permeability (neutral red retention time, NRRT) and DNA damage (comet assay tail moment and tail DNA intensity %) of Nereis coelomocytes increased in a concentration-dependent manner in all three Ag treatments. Ag NP treatments were more toxic than aqueous Ag for all toxicity endpoints, even though bioaccumulation did not differ significantly among Ag forms. No significant difference in toxicity was observed between the two Ag NP treatments which was attributed to their overlap in particle size.

Potential of Kalopanax septemlobus leaf extract in synthesis of silver nanoparticles for selective inhibition of specific bacterial strain in mixed culture.

Silver nanoparticles (AgNPs) were synthesised using Kalopanax septemlobus plant leaf extracts. UV-visible spectrophotometric, Fourier-transform infrared, electron dispersive X-ray spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses confirmed synthesis of AgNPs. TEM micrographs revealed presence of well-dispersed AgNPs predominantly of small size and different shapes with an average particle size of 30.8 nm. Antimicrobial susceptibility tests of AgNP treatments revealed variability in sensitivity of bacteria Bacillus cereus and Saccharophagus degradans under study. Minimum inhibitory concentration (MIC) values of the AgNPs for B. cereus and S. degradans were found to be 30 and 10 μg/mL, respectively. The mixed culture of B. cereus and S. degradans treated with AgNPs at 10 μg/mL showed increase in growth with time, suggesting survival of bacteria in liquid media. The plating of mixed culture before AgNP treatment showed presence of both bacteria, but 24-h-old mixed culture treated with AgNPs at the concentration of 10 μg/mL showed presence of B. cereus colonies. SEM micrographs revealed damage to S. degradans cells but no effect on B. cereus cells after AgNP treatment. Confocal microscopic observations of AgNP-treated mixed cultures by Nile blue A staining indicated intact polyhydroxyalkanoates producing flourescent cells of B. cereus but damage and deformities in S. degradans cells. This study suggests that AgNPs can selectively inhibit growth of S. degradans and retain B. cereus at MIC of S. degradans. This report is a case study for selective inhibition of one bacteria and growth of the other in a culture using plant-synthesized silver nanoparticles.

The effect of silver nanoparticles on seasonal change in arctic tundra bacterial and fungal assemblages.

The impact of silver nanoparticles (NPs) and microparticles (MPs) on bacterial and fungal assemblages was studied in soils collected from a low arctic site. Two different concentrations (0.066% and 6.6%) of Ag NPs and Ag MPs were tested in microcosms that were exposed to temperatures mimicking a winter to summer transition. Toxicity was monitored by differential respiration, phospholipid fatty acid analysis, polymerase chain reaction-denaturing gradient gel electrophoresis and DNA sequencing. Notwithstanding the effect of Ag MPs, nanosilver had an obvious, additional impact on the microbial community, underscoring the importance of particle size in toxicity. This impact was evidenced by levels of differential respiration in 0.066% Ag NP-treated soil that were only half that of control soils, a decrease in signature bacterial fatty acids, and changes in both richness and evenness in bacterial and fungal DNA sequence assemblages. Prominent after Ag NP-treatment were Hypocreales fungi, which increased to 70%, from only 1% of fungal sequences under control conditions. Genera within this Order known for their antioxidant properties (Cordyceps/Isaria) dominated the fungal assemblage after NP addition. In contrast, sequences attributed to the nitrogen-fixing Rhizobiales bacteria appeared vulnerable to Ag NP-mediated toxicity. This combination of physiological, biochemical and molecular studies clearly demonstrate that Ag NPs can severely disrupt the natural seasonal progression of tundra assemblages.

Effects of silver nanoparticles (AgNPs) on hematological parameters of rainbow trout, Oncorhynchus mykiss

Silver nanoparticles (AgNPs) are potentially toxic materials that are used today in numerous consumer products. Releasing of AgNPs to aquatic environment may affect adversely aquatic animal health including fish. In this study, we examined the effects of AgNPs on hematological parameters of rainbow trout, Oncorhynchus mykiss. The parameters include red blood cells (RBCs) and hemoglobin (Hb), hematocrit (Hct), white blood cells (WBCs), mean corpuscular hemoglobin (MCH), mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC), alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), lactate dehydrogenase (LDH), total protein (TP), and albumin (AL). Three treatment groups included fish treated with 0.1 mg/l AgNP solution (T1), 0.2 mg/l AgNP (T2), and 0.4 mg/l AgNP (T3), and one group without AgNP treatment was considered as control group. In the fourth and eighth days of the experiment, the values of RBCs and WBCs were higher in all treatments than those in the control group (P < 0.05). The Hct in the T3 group showed lower values than that of the control group in the eighth day (P < 0.05). Although the Hb concentrations were higher in the T2 and T3 groups than those in the control group in the first blood sampling, a significant decrease compared to the control group was observed in Hb values in the second sampling for the T3 group (P < 0.05). The MCV and MCH in the treatment groups decreased as the concentration of AgNPs increased (P < 0.05). In contrast, the MCHC values showed an increasing trend as the concentration of AgNPs increased (P < 0.05). The concentrations of liver enzymes (i.e., ALT, AST, ALP, and LDH) were higher in all treatment groups than those in the control group (P < 0.05). The TP and AL concentrations decreased compared to the control group as the concentration of AgNPs increased (P < 0.05). Our results demonstrated that silver nanoparticles induce significant changes in hematologic parameters of rainbow trout.

Silver nanoparticles induced accumulation of reactive oxygen species and alteration of antioxidant systems in the aquatic plant Spirodela polyrhiza

Silver nanoparticles (AgNPs) are widely used commercially because of their antibacterial properties. Oxidative stress is known to be involved in the toxicity of AgNPs to bacteria, animals, and algae. The authors used Spirodela polyrhiza to investigate whether AgNPs can induce oxidative stress in higher plants. Results showed that there was a dose-dependent increase in levels of reactive oxygen species, superoxide dismutase and peroxidase activity, and the antioxidant glutathione content in 6-nm AgNP treatments. Catalase activity and malondialdehyde content in 6-nm AgNP treatments was significantly higher than the control at silver concentrations of 5 mg L(-1) . Superoxide dismutase and catalase activity and antioxidant glutathione and malondialdehyde content were not significantly different at 10 mg L(-1) of AgNPs (6 nm and 20 nm). Treatment with 20 µg L(-1) Ag(+) (the amount almost equal to 10 mg L(-1) AgNPs released) did not change the reactive oxygen species level or antioxidant enzymes activity. Micron-sized Ag particles had no effect on S. polyrhiza. Transmission electron microscopy showed that, compared with the control, chloroplasts in S. polyrhiza treated with 6-nm and 20-nm AgNPs accumulated starch grains and had reduced intergranal thylakoids. These results clearly indicate that AgNPs are able to cause oxidative stress and affect the chloroplast structure and function of S. polyrhiza, and this effect was not caused by Ag(+) released from particles.

Effects of silver nanoparticles (NM‐300K) onLumbricus rubellusearthworms and particle characterization in relevant test matrices including soil

The impact of silver nanoparticles (AgNP; at 0 mg Ag/kg, 1.5 mg Ag/kg, 15.4 mg Ag/kg, and 154 mg Ag/kg soil) and silver nitrate (AgNO3 ; 15.4 mg Ag/kg soil) on earthworms, Lumbricus rubellus, was assessed. A 4-wk exposure to the highest AgNP treatment reduced growth and reproduction compared with the control. Silver nitrate (AgNO3 ) exposure also impaired reproduction, but not as much as the highest AgNP treatment. Long-term exposure to the highest AgNP treatment caused complete juvenile mortality. All AgNP treatments induced tissue pathology. Population modeling demonstrated reduced population growth rates for the AgNP and AgNO3 treatments, and no population growth at the highest AgNP treatment because of juvenile mortality. Analysis of AgNP treated soil samples revealed that single AgNP and AgNP clusters were present in the soil, and that the total Ag in soil porewater remained high throughout the long-term experiment. In addition, immune cells (coelomocytes) of earthworms showed sensitivity to both AgNP and AgNO3 in vitro. Overall, the present study indicates that AgNP exposure may affect earthworm populations and that the exposure may be prolonged because of the release of a dissolved Ag fraction to soil porewater.

The cellular uptake and cytotoxic effect of silver nanoparticles on chronic myeloid leukemia cells.

Several studies have suggested that silver nanoparticles (AgNPs) have the potential to treat human cancers, including leukemia. However, the detailed cellular mechanisms for AgNPs to inhibit the growth of leukemic cells and their efficacy on clinical isolates of leukemic patients are not elucidated. In this study, the cellular uptake and cytotoxic mechanism of AgNPs in chronic myeloid leukemia (CML) cells were investigated. AgNPs were synthesized with a modified polyol method, which were stable under cell culture conditions with fetal bovine serum (FBS). AgNPs were demonstrated to be able to enter K562 cells (a CML cell line) in a dose-dependent manner and locate in endosomes. Reactive oxygen species (ROS) could be generated upon AgNPs exposure and cause cytotoxicity and apoptosis. It was also found that AgNPs treatment inhibited the viability of cells from CML patients (n = 4). The cell cycle status and several critical regulators were altered upon AgNPs treatment as well. All these cellular and molecular alterations caused by AgNPs exposure could be reversed by the addition of Vitamin C (an antioxidant). These results suggested that proper usage of AgNPs would be of great significance for CML treatment in future.

Silver nanoparticles induced changes in the expression of NF-κB related genes are cell type specific and related to the basal activity of NF-κB

Silver nanoparticles (AgNPs) are widely used in industry and medicine but the recent evidence for their cytotoxicity rise a concern about the safety of their use. We have previously shown that human A549 cells are resistant to AgNPs cytotoxicity, as compared with similarly treated HepG2 cells. In order to check for the role of the NF-κB signaling pathway in response of A549 and HepG2 cell lines to the treatment with 20nm and 200nm AgNps, we analyzed the expression of 84 key genes related to the functionality of the NF-κB signaling pathway. We observed considerable alternations in gene expression in HepG2 cells treated with 20nm AgNPs, and minor changes when exposed to 200nm AgNPs. Surprisingly, no changes in gene expression were observed in A549 cells treated with both size AgNPs. Using the NF-κB luciferase reporter system, we further tested the basal activity and inducibility of the NF-κB pathway in both cell lines and found that the inducibility of NF-κB signaling in A549 cells is approximately 5 times lower than this of HepG2 cells, but the basal activity is approximately 3.5 times higher. In accordance, the NF-κB activation after AgNPs treatment was observed in HepG2 but not in A549. Altogether indicate that NF-kB mediated cellular response to AgNPs is cell type specific and related to the basal activity of NF-κB.

Monitoring the developmental impact of copper and silver nanoparticle exposure in Drosophila and their microbiomes

There is concern that waste waters containing manufactured metal nanoparticles (NPs) originating from consumer goods, will find their way into streams and larger water bodies. Aquatic invertebrates could be vulnerable to such pollution, and here we have used fruit flies, Drosophila melanogaster, as a model invertebrate, to test for the effect of NPs on fitness. Both copper NP and microparticle (MP)-containing medium slowed development, reduced adult longevity and decreased sperm competition. In contrast, ingestion of silver resulted in a significant reduction in developmental success only if the metal particles were nanosized. Ag NP-treatments resulted in reduced developmental success as assessed by larval and pupal survival as well as larval climbing ability, but there was no impact of silver on adult longevity and little effect on reproductive success. However, Cu NPs generally appeared to be no more toxic to this invertebrate model than the bulk counterpart. The impact of silver ingestion in larvae was further investigated by 454 pyrosequencing of the 16S rRNA genes of the midgut flora. There was a striking reduction in the diversity of the gut microbiota of Ag NP-treated larvae with a rise in the predominance of Lactobacillus brevis and a decrease in Acetobacter compared to control or Ag MP-treatment groups. Importantly, these experiments show that perturbation of the microbial assemblage within a metazoan model may contribute to Ag NP-mediated toxicity. These observations have implications for impact assessments of nanoparticles as emerging contaminants.

The Immediate Mitochondrial Stress Response in Coping with Systemic Exposure of Silver Nanoparticles in Rat Liver

Silver nanoparticles (Ag-nps) induce hepatotoxicities via oxidative stress. The oxidative stress-induced mitochondrial damages are known to be regulated by mitochondrial unfolded protein response (mtUPR) and autophagy/mitophagy systems. The present study was undertaken to investigate role of mtUPR and autophagy/mitophagy on the Ag-nps induced mitochondrial dysfunction. Experiments consisted of two groups of Sprague Dawley rats: control and Ag-nps treated. The Ag-nps treated group received an intraperitoneally injection of 1.5 ml deionized water containing 500 mg/ kg of Ag-nps. Control group received equal volume of deionized water. All animals were sacrificed at different time points (6, 12, 18 and 24 hr post treatment), followed by removal of livers for determination of ATP content and protein expression. The results show that multi-ubiquitinated proteins (Ub-proteins) in liver mitochondria were increased at 12 hr and the increases were sustained up to 24 hr following Ag-nps treatment. Expressions of mtUPR-associated proteins including transcriptional factors (C/EBP homologous protein (CHOP) and CAAT/enhancer-binding protein-β (C/EBPβ)), molecular chaperones (heat shock protein (Hsp) 70 and Hsp60) and protease (caseinolytic Clp protease (ClpP)) remained unchanged during the entire experimental period, except that Hsp10 was upregulated. Expression of LC3-II (autophagy marker) and BNIP3 (mitophagy marker) were upregulated at 6 hr and the upregulation remained throughout the experimental period. ATP content was reduced at 6 hr after Ag-nps exposure and the reductions were sustained during the entire experimental period. These results demonstrate that activation of autophagy/mitophagy markers co-existed with upregulation of Ub-proteins and reduction of ATP content without changing mtUPR in rat liver following Ag-nps administration. These findings indicate that protective effects of autophagy/mitophagy markers were overwhelmed by detrimental actions of Ub-proteins on the control of mitochondrial function, and the counter-balance of the two systems eventually resulting in impaired mitochondrial function, i.e., reduction of ATP content.

Impacts of different nanoparticles on functional bacterial community in activated sludge

Rapidly developing industry raises concerns about the environmental impacts of nanoparticles, but the effects of inorganic nanoparticles on functional bacterial community in wastewater treatment remain unclear. The discriminated effects of silver nanoparticles (Ag-NP) and zinc oxide nanoparticles (ZnO-NP) in a simulated sequencing batch reactor (SBR) system were therefore evaluated by the RNA-based terminal restricted fragment length polymorphism (T-RFLP), 16S rcDNA gene clone library and real-time reverse transcription-PCR (RT-PCR) analyses. Although the COD and NH4-N removal efficiencies were not or slightly reduced by the addition of ZnO-NP and Ag-NP, the functional bacterial community changed remarkably. The denitrification related species were inhibited by high dosage of ZnO-NP and Ag-NP, including Diaphorobacter species, Thauera species and those in the Sphaerotilus-Leptothrix group. However, the bacteria related to sludge bulking, heavy metal resistant and biosorption were increased, especially by ZnO-NPs treatment, including those closely related to Haliscomenobacter hydrossis, Zoogloea ramigera and Methyloversatilis universalis. In addition, Ag-NP and ZnO-NP treatments influenced the functional bacterial community differently. Increasing of bulking related bacteria may help to compensate the COD removal efficiency and to maintain functional redundancy, but could lead to operation failure of activated sludge system when expose to ZnO-NPs.

Time-course profiling of molecular stress responses to silver nanoparticles in the earthworm Eisenia fetida

The molecular mechanism of silver nanoparticle (AgNP) toxicity, particularly its temporal aspect, is currently limited in the literature. This study seeks to identify and profile changes in molecular response patterns over time during soil exposure of the earthworm Eisenia fetida to AgNPs (82±27nm) with reference to dissolved silver salt (AgNO3). Principal component analysis of selected gene and enzyme response profiles revealed dissimilar patterns between AgNO3 and AgNP treatments and also over time. Despite the observed difference in molecular profiles, the body burdens of total Ag were within the same range (10–40mg/kg dry weight worm) for both treatments with apparent correlation to the induction pattern of metallothionein. AgNO3 induced the genes and enzymes related to oxidative stress at day 1, after which markers of energy metabolism were all suppressed at day 2. Exposure to AgNPs likewise led to induction of oxidative stress genes at day 2, but with a temporal pattern shift to immune genes at day 14 following metabolic upregulation at day 7. The involvement of oxidative stress and subsequent alterations in immune gene regulation were as predicted by our in vitro study reported previously, highlighting the importance of immunological endpoints in nanosilver toxicity.

Silver-Based Nanoparticles Induce Apoptosis in Human Colon Cancer Cells Mediated Through P53

The authors have systematically investigated the anticancer potentiality of silver-based nanoparticles (AgNPs) and the mechanism underlying their biological activity in human colon cancer cells. Starch-capped AgNPs were synthesized, characterized and their biological activity evaluated through multiple biochemical assays. AgNPs decreased the growth and viability of HCT116 colon cancer cells. AgNP exposure increased apoptosis, as demonstrated by an increase in 4´,6-diamidino-2-phenylindole-stained apoptotic nuclei, BAX/BCL-XL ratio, cleaved poly(ADP-ribose) polymerase, p53, p21 and caspases 3, 8 and 9, and by a decrease in the levels of AKT and NF-κB. The cell population in the G1 phase decreased, and the S-phase population increased after AgNP treatment. AgNPs caused DNA damage and reduced the interaction between p53 and NF-κB. Interestingly, no significant alteration was noted in the levels of p21, BAX/BCL-XL and NF-κB after AgNP treatment in a p53-knockout HCT116 cell line. AgNPs are bona fide anticancer agents that act in a p53-dependent manner. Original submitted 16 March 2012; Revised submitted 25 August 2012; Published online 21 March 2013.

Development of biomarker for detecting silver nanoparticles exposure using a GAL4 enhancer trap screening in Drosophila

Silver nanoparticles (AgNPs) have been widely used in commercial goods ranging from medical devices to home appliances. Their widespread application increase the risk related to their potential toxicity. Although several studies showed their acute hazardous effects on living animals, our understanding of chronic effects of AgNPs exposed by the environment we encounter in our everyday lives is still very limited. This is partly because of the lack of versatile animal model system for studying AgNPs effects on terrestrial animals including human. In this study, we used Drosophila model to study AgNPs toxicity in terrestrial animals, and found that long-term exposure of AgNPs, but not Ag ions, at low level (0.1 and 1μg/mL) significantly shortened the lifespan. By taking advantage of the power of Drosophila genetics, we also isolated a GAL4 enhancer trap line called M95, in which the expression of GAL4 is up-regulated in response to ingestion of AgNPs at concentrations as low as 0.1μg/mL. Interestingly M95 flies showed significantly increased tolerance to both AgNPs treatment and dry starvation probably due to up-regulation of JNK signaling. These findings suggest not only that M95 may be a very useful biomarker of AgNPs because of its high sensitivity and tolerance to AgNPs, but also that Drosophila may be a versatile terrestrial invertebrate model for studying the effects of AgNPs on human health.

Low Concentrations of Silver Nanoparticles in Biosolids Cause Adverse Ecosystem Responses under Realistic Field Scenario

A large fraction of engineered nanomaterials in consumer and commercial products will reach natural ecosystems. To date, research on the biological impacts of environmental nanomaterial exposures has largely focused on high-concentration exposures in mechanistic lab studies with single strains of model organisms. These results are difficult to extrapolate to ecosystems, where exposures will likely be at low-concentrations and which are inhabited by a diversity of organisms. Here we show adverse responses of plants and microorganisms in a replicated long-term terrestrial mesocosm field experiment following a single low dose of silver nanoparticles (0.14 mg Ag kg−1 soil) applied via a likely route of exposure, sewage biosolid application. While total aboveground plant biomass did not differ between treatments receiving biosolids, one plant species, Microstegium vimeneum, had 32 % less biomass in the Slurry+AgNP treatment relative to the Slurry only treatment. Microorganisms were also affected by AgNP treatment, which gave a significantly different community composition of bacteria in the Slurry+AgNPs as opposed to the Slurry treatment one day after addition as analyzed by T-RFLP analysis of 16S-rRNA genes. After eight days, N2O flux was 4.5 fold higher in the Slurry+AgNPs treatment than the Slurry treatment. After fifty days, community composition and N2O flux of the Slurry+AgNPs treatment converged with the Slurry. However, the soil microbial extracellular enzymes leucine amino peptidase and phosphatase had 52 and 27% lower activities, respectively, while microbial biomass was 35% lower than the Slurry. We also show that the magnitude of these responses was in all cases as large as or larger than the positive control, AgNO3, added at 4-fold the Ag concentration of the silver nanoparticles.

Silver nanoparticle toxicity effect on growth and cellular viability of the aquatic plant Lemna gibba

The toxicity effect of silver nanoparticles (AgNPs) on growth and cellular viability was investigated on the aquatic plant Lemna gibba exposed over 7 d to 0, 0.01, 0.1, 1, and 10 mg/L of AgNPs. Growth inhibition was demonstrated by a significant decrease of frond numbers dependent on AgNP concentration. Under these conditions, reduction in plant cellular viability was detected for 0.1, 1, and 10 mg/L of AgNPs within 7 d of AgNPs treatment. This effect was highly correlated with the production of intracellular reactive oxygen species (ROS). A significant increase of intracellular ROS formation was triggered by 1 and 10 mg/L of AgNP exposure. The induced oxidative stress was related to Ag accumulation within L. gibba plant cells and with the increasing concentration of AgNP exposure in the medium. The authors' results clearly suggested that AgNP suspension represented a potential source of toxicity for L. gibba plant cells. Due to the low release capacity of free soluble Ag from AgNP dissolution in the medium, it is most likely that the intracellular uptake of Ag was directly from AgNPs, triggering cellular oxidative stress that may be due to the release of free Ag inside plant cells. Therefore, the present study demonstrated that AgNP accumulation in an aquatic environment may represent a potential source of toxicity and a risk for the viability of duckweeds.

Effect of silver nanoparticles on Oryza sativa L. and its rhizosphere bacteria

Silver nanoparticles (AgNPs) are widely used as antibacterial and antifungal agents in agriculture. Nevertheless, these nanoparticles with newborn properties pose a potential risk to the environment, Due to contact with crops and bacteria that are beneficial to the soil. This study is based on the examination of the phytotoxic effects of AgNPs on Oryza sativa L. and some of its rhizosphere bacteria, by physiological and biochemical assays. In order to study the complex interaction of the AgNPs life expectancy that are mixed with culture medium, the incubation time for the fresh mixture, 7, 14 and 21 days old of AgNPs, on the seedlings growth was investigated. Results indicated that plant’s response to the treatment with AgNPs affected on the cell wall, and that with an increase in its concentration (up to 60μg/mL). The obtained results of transmission electron microscopy (TEM) exhibited that those particles not only penetrated the cell wall, but they could also damage the cell morphology and its structural features. AgNPs treatment up to 30μg/mL accelerated root growth and at 60μg/mL was able to restrict a root’s ability to grow. The 30μg/mL treatment had significant effect on root branching and dry weight. In contrast, shoot growth was more susceptible to the effects of AgNPs treatment. The root content for total soluble carbohydrates and starch demonstrated that despite stable starch content, total soluble carbohydrates showed the tendency to significantly decline in response to AgNPs. However, induction of root branching and photosynthetic pigments can attributed to AgNPs stress based on evidence from the production of the reactive oxygen species (ROS) and local root tissue death. Nine isolates of the genus Bacillus selected and identified according to morphological and chemotaxonomic methods. The AgNPs treatment revolutionized the populations of bacteria as Bacillus thuringiensis SBURR1 was totally eliminated, and Bacillus amyloliquefaciens SBURR5 became the most populated one. Images from an electron microscope and the leakage of reducing sugars and protein through the bacterial membrane, similarly confirmed the “pit” formation mechanism of the AgNPs. Moreover the hypothesis from the growth curve study demonstrated that AgNPs may damage bacterium cell wall and transform them to protoplasts.