Harmful effects of metal(loid) oxide nanoparticles

The incorporation of nanomaterials (NMs), including metal(loid) oxide (MOx) nanoparticles (NPs), in the most diversified consumer products, has grown enormously in recent decades. Consequently, the contact between humans and these materials increased, as well as their presence in the environment. This fact has raised concerns and uncertainties about the possible risks of NMs to human health and the adverse effects on the environment. These concerns underline the need and importance of assessing its nanosecurity. The present review focuses on the main mechanisms underlying the MOx NPs toxicity, illustrated with different biological models: release of toxic ions, cellular uptake of NPs, oxidative stress, shading effect on photosynthetic microorganisms, physical restrain and damage of cell wall. Additionally, the biological models used to evaluate the potential hazardous of nanomaterials are briefly presented, with particular emphasis on the yeast Saccharomyces cerevisiae, as an alternative model in nanotoxicology. An overview containing recent scientific advances on cellular responses (toxic symptoms exhibited by yeasts) resulting from the interaction with MOx NPs (inhibition of cell proliferation, cell wall damage, alteration of function and morphology of organelles, presence of oxidative stress bio-indicators, gene expression changes, genotoxicity and cell dead) is critically presented. The elucidation of the toxic modes of action of MOx NPs in yeast cells can be very useful in providing additional clues about the impact of NPs on the physiology and metabolism of the eukaryotic cell. Current and future trends of MOx NPs toxicity, regarding their possible impacts on the environment and human health, are discussed.This work was supported by National funds through FCT - Foundation for Science and Technology under the scope of the projects UIDB/50006/2020, UID/BIO/04469/2020 unit and BioTecNorte opera tion (NORTE-01-0145-FEDER-000004) funded by the European Regional Development Fund under the scope of Norte2020 - Programa Operacional Regional do Norte.info:eu-repo/semantics/publishedVersio

Lead induces oxidative stress and apoptotic response in Saccharomyces cerevisiae

Background: Heavy metals are found in the environment mainly due to anthropogenic activities. The presence of metals in surface waters and soils can create an environmental hazard and pose a serious risk to public health. Lead is a non essential metal for biological functions, displays a toxic effect and is classified as probable human carcinogen. Objectives: In the present work, the mode of cell death induced by Pb in Saccharomyces cerevisiae was studied. Methods: Cell proliferation capacity was evaluated by colony-forming units counting. Membrane integrity was assessed by the fluorescent probes bis(1,3-dibutylbarbituric acid trimethine oxonol) [DiBAC4(3)] and propidium iodide. Reactive oxygen species (ROS) accumulation was examined by using 2,7-dichlorodihydrofluorescein diacetate (H2DCFDA). Nuclear morphological modifications were revealed by diaminophenylindole (DAPI) staining. Conclusions: Yeast cells, Pb-exposed, up to 6 hours, lost progressively the capacity to proliferate and maintained the membrane integrity. The exposition of yeast cells to Pb resulted in the intracellular accumulation of ROS. The addition of ascorbic acid (a ROS scavenger) strongly reduced the oxidative stress and impaired the loss of proliferation capacity in Pbtreated cells. Pb-induced death is an active process, which requires the participation of cellular metabolism, since the simultaneous addition of cycloheximide attenuated the loss of cell proliferation capacity. Pb-exposed cells displayed nuclear morphological alterations, like chromatin fragmentation. Together, the obtained data indicate that exposition of yeast cells to 1 mmol/l Pb results in a severe oxidative stress, which can be the trigger of programmed cell death by apoptosis

Population dynamics of flocculating yeasts

The problem of understanding the recognition and specific interactions in a population of yeast flocculating cells is discussed. The biochemistry, physiology and genetics of flocculation is briefly reviewed. Yeast flocculation requires the expression of a specific protein (lectin) on flocculent cells, and carbohydrate (receptors) on neighbouring cells. Adhesion experiments performed with cells whose flocculation is repressed by growth conditions, indicating that the inhibition of flocculation is due to inhibition or inactivation of lectin-like component. Additionally, using adhesion experiments, it is demonstrated that cells of non-flocculent strain interact by establishing a true bond with flocculent cells rather than by entrapment inside the floc matrix. As phenotypic expression of flocculation, for several strains, is shown to be repressed, modulated or induced by modifying growth conditions, the constitutiveness and inducibility of flocculation are also discussed

Using a flocculent brewer’s yeast strain of Saccharomyces cerevisiae in the removal of heavy metals

Fundação para a Ciência e a Tecnologia (FCT) - POCTI/CTA/47875/2002, (SFRH/BD/31755/2006)Fundo Europeu de Desenvolvimento Regional (FEDER

Removal of heavy metals using cells of Saccharomyces cerevisiae as a green technology

Anthropogenic activities are largely responsible for the release of heavy metals in the environment. Unlike organic pollutants, heavy metals are not degraded and remain indefinitely in the ecosystem, which poses a different kind of challenge for remediation. Municipal sanitary sewers are not designed to treat toxic wastes, such as industrial effluents containing heavy metals. Thus, heavy metals should be removed in a “previous step”, from these metalladen effluents before they are released into the water body or sent to a municipal treatment plant. Conventional physicochemical technologies are not environmental friendly, fully efficient or present very high costs when applied to large volume of wastewaters containing low metal concentration (1- 100 mg/l). The disadvantages of these available “best treatment technologies”, associated with the increase of environmental regulations, have compelled the search for alternative, low-cost and efficient processes for the detoxification of metal-bearing wastewaters. The advantages and the current knowledge of the mechanisms of metal removal by yeast cells of Saccharomyces cerevisiae will be presented. The use of live or dead biomass and the influence of biomass inactivation processes or the modification of the yeast surface on the metal accumulation characteristics will be outlined. The importance of the physico-chemical characteristics of the effluents and the role of chemical speciation as a tool for predicting and optimising metal removal will be highlighted. The use of yeast cells as the only treatment process of real effluents or in a “polishing” step, after the chemical treatment of the raw effluent to remove the bulk of the metal will be presented. The problem of biomass separation, after treatment of the effluents, and the use of flocculent characteristics of yeast cells, as an alternative process of cell-liquid separation, will also be discussed. The convenient management of the contaminated biomass and the advantages of the selective recovery of heavy metals in the development of a closed cycle without residues (green technology) will be presented

Removal of heavy metals from real electroplating effluents using a brewer's yeast strain of Saccharomyces cerevisiae

Background: The release of heavy metals in aquatic systems due to the discharge of industrial wastewaters is a matter of environmental concern. The use of yeast cells has been raised as an alternative to the conventional technologies. Objectives: To evaluate the feasibility of flocculent brewing cells of S. cerevisiae to remove several metals from real electroplating effluents. Methods: Flocculation was assessed using a sedimentation test. The occurrence of structural or molecular changes in the yeast cells during heat treatment (at 45ºC), were evaluated using fluorescence, scanning electron microscopy and infrared spectroscopy. Heavy metals concentrations were determined by atomic absorption spectroscopy with flame atomization. Conclusions: Yeast cells were able to sediment in the presence of most of the heavy metals, as well as in the industrial effluents. Cells inactivated at 45ºC maintained the sedimentation characteristics and showed a higher degree of heavy metal removal than the live cells. Effluents containing Cu, Ni and Zn (effluent A) or Cr, Cu and Ni (effluent B) were used. In both effluents, pH was adjusted to 6.0; in effluent B, Cr(VI) was previously reduced to Cr(III). Subsequently, effluents were treated with a serial batch of heat-inactivated yeast biomass. After the third batch, metal concentrations were lowered to below the legal limits of discharge; removals 89%, were attained for all metals. The usefulness of using heat-inactivated flocculent brewing cells for detoxifying complex industrial effluents loaded with several heavy metals was demonstrated. This approach combines an efficient metal removal with a fast and off-cost yeast separation

Responses of the green alga Pseudokirchneriella subcapitata to short- and long-term exposure to heavy metals

Book of Abstracts of CEB Annual Meeting 2017[Excerpt] Algal cells can be exposed to toxicants for a short-term due to accidental discharges or, more commonly, for a long term. The green alga Pseudokirchneriella subcapitata has been widely used in ecological risk assessment, usually based on the impact of the toxicants in the alga growth. However, the physiological causes that lead algal growth inhibition are not completely understood. [...]info:eu-repo/semantics/publishedVersio

Impact of nickel oxide nanoparticles on yeast physiology

[Excerpt] In the recent years, nickel oxide (NiO) nanoparticles (NPs), have been used in different fields, such as in biosensors, catalysis, ceramics, electrochromic film, electronics, conductive and magnetic materials, energy storage devices, fuel cells, printing inks and wastewater treatment [1-2]. Due to the increasing use of these NPs, concerns about their possible toxic effects have been raised. In the present study, the yeast Saccharomyces cerevisiae was used as a cell model to evaluate the possible hazards of NiO NPs. Physicochemical characteristics of NiO in MES buffer, namely NPs agglomeration (examined by dynamic light scattering – DLS), surface charge (determination of zeta potential) and dissolution of the NPs (quantification of Ni2+ released in medium) were evaluated in order to be correlated with their toxicity. [...]info:eu-repo/semantics/publishedVersio

Optimization of a microplate-based assay to assess esterase activity in the alga Pseudokirchneriella subcapitata

The present work describes the optimization of a short-term assay, based on the inhibition of the esterase activity of the alga Pseudokirchneriella subcapitata, in a microplate format. The optimization of the staining procedure showed that the incubation of the algal cells with 20 μmol L−1 fluorescein diacetate (FDA) for 40 min allowed discrimination between metabolic active and inactive cells. The short-term assay was tested using Cu as toxicant. For this purpose, algal cells, in the exponential or stationary phase of growth, were exposed to the heavy metal in growing conditions. After 3 or 6 h, cells were subsequently stained with FDA, using the optimized procedure. For Cu, the 3- and 6-h EC50 values, based on the inhibition of the esterase activity of algal cells in the exponential phase of growth, were 209 and 130 μg L−1, respectively. P. subcapitata cells, in the stationary phase of growth, displayed higher effective concentration values than those observed in the exponential phase. The 3- and 6-h EC50 values for Cu, for cells in the stationary phase, were 443 and 268 μg L−1, respectively. This short-term microplate assay showed to be a rapid endpoint for testing toxicity using the alga P. subcapitata. The small volume required, the simplicity of the assay (no washing steps), and the automatic reading of the fluorescence make the assay particularly well suited for the evaluation of the toxicity of a high number of environmental samples.The authors thank the Fundacao para a Ciencia e a Tecnologia (FCT) through the Portuguese Government for their financial support of this work through the grant PEST-OE/EQB/LA0023/2011 to IBB. Manuela D. Machado gratefully acknowledges the postdoctoral grant from FCT (SFRH/BPD/72816/2010)

Nickel oxide nanoparticles induce toxicity in yeasts via oxidative stress

[Excerpt] The increasing use of nickel oxide (NiO) nanoparticles (NPs) raises concerns about their potential toxicity. In the present study, the yeast Saccharomyces cerevisiae was used, as a cell model, in order to elucidate whether the toxicity of NiO NPs is associated with the oxidative stress (OS). In abiotic conditions (cell free), NiO NPs were unable to induce the generation of reactive oxygen species (ROS), which excludes the possibility of exerting a pro-oxidant effect. However, yeast cells exposed to NiO NPs accumulated intracellularly superoxide anions (assessed with dihydroethidium) and hydrogen peroxide (evaluated with 2′,7′-dichlorodihydrofluorescein diacetate or dihydrorhodamine 123) when incubated in normal (oxygen) atmosphere. Yeast cells exposed to NiO also presented reduced cell viability (measured through a clonogenic assay). Yeasts co-exposed to NiO NPs and the antioxidants L-ascorbic acid (a scavenger of free radicals) or N-tertbutyl-α-phenylnitrone (a spin trapping agent) presented ROS quenching and increased cell viability, which suggests that NiO toxicity is linked to ROS production. [...]info:eu-repo/semantics/publishedVersio