Evaluation of heavy metal acute toxicity and bioaccumulation in soil ciliated protozoa

Removal and assessment of cadmium contamination based on the toxic responds of a soil ciliate Colpoda sp

Bioremediation of cadmium (Cd) pollution, a recognized low-carbon green environmental protection technology, is significantly enhanced by the discovery of Cd-tolerant microorganisms and their underlying tolerance mechanisms. This study presents Colpoda sp., a soil ciliate with widespread distribution, as a novel bioindicator and bioremediator for Cd contamination. With a 24 h-LC50 of 5.39 mg l-1 and an IC50 of 24.85 μg l-1 in Cd-contaminated water, Colpoda sp. achieves a maximum bioaccumulation factor (BAF) of 3.58 and a Cd removal rate of 32.98 ± 0.74 % within 96 h. The toxic responses of Colpoda sp. to Cd stress were assessed through cytological observation with transmission electron microscopy (TEM), oxidative stress kinase activity, and analysis of Cd-metallothionein (Cd-MTs) and the cd-mt gene via qRT-PCR. The integrated biomarker response index version 2 (IBRv2) and structural equation models (SEM) were utilized to analyze key factors and mechanisms, revealing that the up-regulation of Cd-MTs and cd-mt expression, rather than the oxidative stress system, is the primary determinant of Cd accumulation and tolerance in Colpoda sp. The ciliate's ability to maintain growth under 24.85 μg l-1 Cd stress and its capacity to absorb and accumulate Cd particles from water into cells are pivotal for bioremediation. A new mathematical formula and regression equations based on Colpoda sp.'s response parameters have been established to evaluate environmental Cd removal levels and design remediation schemes for contaminated sites. These findings provide a novel bioremediation and monitoring pathway for Cd remobilization and accumulation in soil and water, potentially revolutionizing the governance of Cd pollution.

MicroRNAs in Tetrahymena thermophila: An epigenetic regulatory mechanism in the response to cadmium stress

Among the epigenetic mechanisms based on non-coding RNA are microRNAs (miRNAs) that are involved in the post-transcriptional regulation of mRNAs. In many organisms, the expression of genes involved in the cellular response to biotic or abiotic stress depends on the regulation, generally inhibitory, performed by miRNAs. For the first time in the eukaryotic microorganism (ciliate-model) Tetrahymena thermophila, miRNAs involved in the post-transcriptional regulation of transcripts linked to the response to cadmium have been isolated and analyzed. Forty de novo miRNAs (we named tte-miRNAs) have been isolated from control and Cd-treated populations (1 or 24 h exposures). An exhaustive comparative analysis of the features of these mature tte-miRNAs and their precursor sequences (pre-tte-miRNAs) confirms that they are true miRNAs. In addition to the three types of miRNA isoforms previously described in other organisms, two new types are also described among the tte-miRNAs studied. A certain percentage of the pre-tte-miRNA sequences are in introns from genes with many introns, and have been defined as 5', 3'-tailed mirtrons. A qRT-PCR analysis of selected tte-miRNAs together with some of their targets has validated them. Cd is one of the most toxic metals for the cell, which must defend itself against its toxicity by various mechanisms, such as expulsion by membrane pumps, chelation by metallothioneins, among others. Like other toxic metals, Cd also causes a well-known series of cellular effects such as intense proteotoxicity. Many of the targets that are regulated by the tte-miRNAs are transcripts encoding proteins that fit into these defense mechanisms and toxic metal effects.

Soil protists are more resilient to the combined effect of microplastics and heavy metals than bacterial communities

Heavy metals and micro-/nanoplastic pollution seriously threaten the environment and ecosystems. While many studies investigated their effects on diverse microbes, few studies have focused on soil protists, and it is unclear how soil protists respond to the combined effect of micro-/nanoplastics and heavy metals. This study investigated how soil protistan and bacterial communities respond to single or combined copper and micro-/nanoplastics. The bacterial community exhibited an instantaneous response to single copper pollution, whereas the combined pollution resulted in a hysteresis effect on the protistan community. Single and combined pollution inhibited the predation of protists and changed the construction of ecological networks. Though single and combined pollution did not significantly affect the overall community structure, the exposure experiment indicated that combined pollution harmed soil amoeba's fitness. These findings offer valuable new insights into the toxic effects of single and combined pollution of copper and plastics on soil protistan and bacterial communities. Additionally, this study shows that sequencing-based analyses cannot fully reflect pollutants' adverse effects, and both culture-independent and dependent methods are needed to reveal the impact of pollutants on soil microbes.

Integral Study of Paramecium caudatum Acute and Chronic Toxicity, Sites of Entry and Distribution, Bioconcentration and Body Burdens of Five Metals

An integral analysis of the acute and chronic toxicity, bioaccumulation, sites of entry, and distribution of four trace metals: copper, iron, lead, and nickel, and the non-trace metal mercury were performed in the ciliate Paramecium caudatum. Mercury was the fastest metal accumulated, and the most toxic. The sensitivity of Paramecium caudatum to the five metals tested (Cu, Fe, Hg, Ni, and Zn) falls in the range of other ciliate species. We observed similarities between the toxicity of the five metals to the ciliate P. caudatum with the rotifer Euchlanis dilatata: (a) Mercury was the most toxic metal in terms of acute and body burdens. (b) Acute values were very similar in both species, Hg as the most toxic and Fe as the less toxic, (c) the vacuole/ingestion chronic tests were more sensitive than growth inhibition chronic tests. These analyses would ideally help generate safer guidelines for protecting aquatic biota.

Green, non-toxic and efficient adsorbent from hazardous ash waste for the recovery of valuable metals and heavy metal removal from waste streams

As compared to alkali-activated geopolymers with phosphoric acid which may be used in high concentrations resulting in disposal concerns, acid-based geopolymers may have superior properties. A novel green method of converting waste ash to a geopolymer for use in adsorption applications such as water treatment is presented here. We use methanesulfonic acid, a green chemical with high acid strength and biodegradability to form geopolymers from coal and wood fly ashes. The geopolymer is characterized for its physico-chemical properties and tested for heavy metal adsorption. The material specifically adsorbs iron and lead. The geopolymer is coupled to activated carbon forming a composite, which adsorbs silver (precious metal) and manganese (hazardous metal) significantly. The adsorption pattern complies with pseudo-second order kinetics and Langmuir isotherm. Toxicity studies show while activated carbon is highly toxic, the geopolymer and the carbon-geopolymer composite have relatively less toxicity concerns.

Intracellular bioaccumulation of the rare earth element Gadolinium in ciliate cells resulting in biogenic particle formation and excretion

Ciliates are abundant unicellular organisms capable of resisting high concentrations of metal ions in the environment caused by various anthropogenic activities. Understanding the cellular pathways involved in resistance to and detoxification of elements is required to predict the impact of ciliates on environmental element cycles. Here, we investigated the so far unknown process of tolerance, cellular uptake and bioaccumulation of the emerging rare earth element gadolinium (Gd) in the common ciliate Tetrahymena pyriformis. Gd treatment results in the intracellular formation and excretion of biogenic Gd-containing particles. This cellular process effectively removes dissolved Gd from the organic growth medium by 53.37% within 72 h. Based on light and electron microscopic observations, we postulate a detoxification pathway: Cells take up toxic Gd³⁺ ions from the medium by endocytosis, process them into stable Gd-containing particles within food vacuoles, and exocytose them. Stable biogenic particles can be isolated, which are relatively homogeneous and have a diameter of about 3 µm. They consist of the elements Gd, C, O, P, Na, Mg, K, and Ca. These findings broaden the view of metal ion accumulation by protists and are of relevance to understand environmental elemental cycles and may inspire approaches for metal recovery or bioremediation.

Microbial community shifts induced by plastic and zinc as substitutes of tire abrasion

Aquatic environments serve as a sink for anthropogenic discharges. A significant part of the discharge is tire wear, which is increasingly being released into the environment, causing environmental disasters due to their longevity and the large number of pollutants they contain. Main components of tires are plastic and zinc, which therefore can be used as substitutes for tire abrasion to study the effect on microbial life. We investigate environmentally realistic concentrations of plastic and zinc on a freshwater microeukaryotic community using high-throughput sequencing of the 18S V9 region over a 14-day exposure period. Apart from a generally unchanged diversity upon exposure to zinc and nanoplastics, a change in community structure due to zinc is evident, but not due to nanoplastics. Evidently, nanoplastic particles hardly affect the community, but zinc exposure results in drastic functional abundance shifts concerning the trophic mode. Phototrophic microorganisms were almost completely diminished initially, but photosynthesis recovered. However, the dominant taxa performing photosynthesis changed from bacillariophytes to chlorophytes. While phototrophic organisms are decreasing in the presence of zinc, the mixotrophic fraction initially benefitted and the heterotrophic fraction were benefitting throughout the exposure period. In contrast to lasting changes in taxon composition, the functional community composition is initially strongly imbalanced after application of zinc but returns to the original state.

Interactions between soil protists and pollutants: An unsolved puzzle

Soil protists are essential but often overlooked in soils, although they play crucial functional roles in the terrestrial ecosystem. While soil protists have drawn increased attention to their functional role in soils, their interaction with soil pollutants remains unresolved. This review provides a first overview of the current understanding of interactions between soil protists and major pollutants (heavy metals, organic pollutants, nanoparticles, and soil pathogens). We summarize how soil pollutants affect protists and vice versa, showing that we are just beginning to understand their complex interactions. In addition, we identify five research gaps, including hidden diversity, adaptive mechanisms, species interactions, soil bioindicators and environmental applications, and we hope that our review will help promote and build research guidelines for the future. In conclusion, a better understanding of soil pollutant-protist interactions will significantly increase our knowledge of the pollution ecology in the soil and how soil organisms respond and adapt to environmental pollution, which will contribute to the bioremediation and environmental applications of protists in soil.

Identification of glutathione-S-transferase m19 and m34 among responsive GST genes against 1-chloro-2,4-dinitrobenzene treatment of Tetrahymena thermophila

Industrial xenobiotic pollutants have toxic effects on diverse organisms in their natural environments. This study aims to identify the Glutathione-S-transferases (GST) from Tetrahymena thermophila that are highly responsive to the treatment of synthetic substrate 1-chloro-2,4-dinitrobenzene (CDNB). The LD50 value of CDNB was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test as 0.079 mM at 9 h exposure. The glutathione affinity-purified 22 kDa and 23 kDa GSTs from CDNB-treated cells were identified as GSTm19 and GSTm34 with 2D-gel electrophoresis coupled MALDI-Tof MS/MS analysis. The specific activitiy of the affinity-purified GSTs was upregulated upon the treatment of 0.072 mM CDNB with the decreased cell survival. GSTm19 and GSTm34 had also upregulated the mRNA expression under the highest dose treatment. The high cell survival and elevated total GST enzyme activity at 9 h under CDNB doses could be the result of both transcriptional upregulations as well as post-translational modifications. As a result, the cell survival of Tetrahymena thermophila was significantly affected by CDNB exposure in a concentration-dependent manner with the effect of low-dose stimulation and high-dose inhibition.

Development of immunoassay methods based on monoclonal antibody and its application in the determination of cadmium ion

Owing to the threat of cadmium (Cd²⁺) to public health, it is an urgent demand to develop effective, sensitive, and rapid methods for the detection of cadmium. In this study, indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) and immunochromatographic test strips (ICTS) were established for the determination of Cd²⁺ based on the obtained mAb with high specificity and high affinity (Kaff = 3.0 × 10⁹ L/moL). The linear range of ic-ELISA detection was 0.03-1.11 ng/mL and 50% inhibitive concentration (IC50) of cadmium ion was determined to be 0.15 ng/mL. The visual limit of detection (vLOD) of the AuNS-based strip was 0.375 ng/mL. The vLOD of AuNF-based strip using higher intensity reporter determined to be 0.03 ng/mL, which was enhanced 12 times compared to the traditional strip. In summary, the developed immunoassays based on mAb shows great potential for monitoring the cadmium ion in environmental samples.

Arsenite induce neurotoxicity of common carp: Involvement of blood brain barrier, apoptosis and autophagy, and subsequently relieved by zinc (Ⅱ) supplementation

Arsenic pollution is a common threat to aquatic ecosystems. The effects of chronic exposure to arsenite on the brains of aquatic organisms are unknown. This study was designed to evaluate arsenic-induced brain damage in common carp (Cyprinus carpio) and the ameliorating effects of divalent zinc ion (Zn2+) supplementation from the aspects of oxidative stress (OxS), tight junction (TJ), apoptosis and autophagy. After arsenite exposure (2.83 mg/L) for 30 days, oxidative damage to the brain was determined, as indicated by inhibited antioxidants system (catalase-superoxide dismutase system, and glutathione system) and elevated levels of biomacromolecule peroxidation (malondialdehyde and 8-hydroxydeoxyguanosine). Moreover, we also found functional damage to the brain as suggested by injuries to the blood-brain barrier (decreases in tight junction) and nerve conduction (depletion of AChE). Mechanisticly, apoptotic and autophagic cell death were indicated by typical morphologies including karyopyknosis and autophagosome, accompanying by key bio-indicators (Bcl-2, caspase and autophagy related gene family proteins). In contrast, the coadministration of Zn2+ (1 mg/L) with arsenite effectively alleviated this damage as suggested by the recovery of the aforementioned bioindicators. This study provides new insight into the brain toxicity caused by arsenite and suggests the application of zinc preparations in the aquatic pollution of arsenic.

Indicators for assessment of soil quality: a mini-review

Soil quality is the competence of soil to perform necessary functions that are able to maintain animal and plant productivity of the soil. Soil consists of various physical, chemical, and biological parameters, and all these parameters are involved in the critical functioning of soil. There is a need for continuous assessment of soil quality as soil is a complex and dynamic constituent of Earth's biosphere that is continuously changing by natural and anthropogenic disturbances. Any perturbations in the soil cause disturbances in the physical (soil texture, bulk density, etc.), chemical (pH, salinity, organic carbon, etc.), and biological (microbes and enzymes) parameters. These physical, chemical, and biological parameters can serve as indicators for soil quality assessment. However, soil quality assessment cannot be possible by evaluating only one parameter out of physical, chemical, or biological. So, there is an emergent need to establish a minimum dataset (MDS) which shall include physical, chemical, and biological parameters to assess the quality of the given soil. This review attempts to describe various physical, chemical, and biological parameters, combinations of which can be used in the establishment of MDS.

Assessing the Cadmium Effects on the Benthic Foraminifer Ammonia cf. parkinsoniana: An Acute Toxicity Test

Heavy metals are one of the most hazardous pollutants in marine environments because of their bioaccumulation and biomagnification capabilities. Among them, cadmium (Cd) has been considered as one of the most dangerous for marine organisms. Here we incubated Ammonia cf. parkinsoniana specimens, a benthic foraminiferal taxon used in previous experiments, for up to 48 h in natural seawater with different concentrations of Cd to unravel the physiological change. We document a reduced pseudopodial activity of the Cd-treated specimens at concentrations >10–100 ppb in comparison with the control specimens. Moreover, confocal images of Cd-treated specimens using Nile Red as a fluorescent probe reveal an enhanced intracellular neutral lipid accumulation in the form of lipid droplets at 6 h and 12 h. This bioassay experiment allows for the direct evaluation of Cd-dose to A. cf. parkinsoniana-response relationships under laboratory controlled conditions and provides complementary information to field observations as well as to water quality guidelines and thresholds.

Expression and molecular characterization of stress-responsive genes (hsp70 and Mn-sod) and evaluation of antioxidant enzymes (CAT and GPx) in heavy metal exposed freshwater ciliate, Tetmemena sp

Response of heavy metals namely cadmium (Cd) and copper (Cu) on the expression of stress responsive genes in the fresh water ciliate, Tetmemena sp. (single cell eukaryote) was studied. Stress responsive genes include heat shock protein genes and genes involved in antioxidant defence system. Quantitative real time PCR (qRT-PCR) was employed to evaluate the effects of Cd and Cu on the expression of cytosolic hsp70 and Mn-sod genes. Increase in the expression of these genes was observed after exposure with the heavy metals. The macronuclear cytosolic hsp70 and Mn-sod (SOD2) genes were also sequenced and characterized using various bioinformatics tools. In antioxidant defence system, the superoxide dismutase (SOD) family is a first line antioxidant enzyme group involved in catalysing reactive oxygen species (ROS) to hydrogen peroxide and molecular oxygen. Influence of Cd and Cu on the activity of SOD has already been reported by our group. Therefore, the enzymatic activities of antioxidant enzymes, catalase (CAT) and glutathione peroxidase (GPx) were studied in the presence of Cd and Cu and there was significant increase in activity of these enzymes in concentration dependent manner. This study suggests that cytosolic hsp70, Mn-sod and the antioxidant enzymes such as CAT and GPx can be used as effective molecular biomarkers for heavy metal toxicity and Tetmemena sp. can be used as potential model for understanding the molecular response to heavy metal contamination in aquatic ecosystems.

Wood ash decreases cadmium toxicity to the soil nematode Caenorhabditis elegans

Wood ash is a beneficial fertilizer and liming agent in nutrient depleted soils, but it also contains considerable amounts of cadmium (Cd), which can be toxic to organisms in the environment. Therefore, risk assessments regarding utilization of wood ash is required. Here, we studied how wood ash (applied in doses equivalent to 0, 3 and 6 t ha^-1) and Cd (applied in doses of 0, 10, 150, 300, 600, 1200 and 2000 mg kg^-1) affected growth of the soil nematode Caenorhabditis elegans. The treatments were combined in a full factorial design. Wood ash alone greatly stimulated both soil respiration and growth of C. elegans, whereas Cd alone had a toxic effect. However, unrealistically high Cd levels were needed to severely affect growth of C. elegans and soil respiration, especially soil respiration was very resilient to Cd amendment. Ash addition decreased Cd toxicity to C. elegans, with an EC₅₀ value of 390 mg Cd kg^-1 in the 3 t ash ha^-1 treatment, and an increase of EC₅₀ to 1894 mg Cd kg^-1 in the 6 t ash ha^-1 treatment. This is probably because ash increases the Cd sorption capacity of the soil, and thereby decreases the bio-availability of Cd. The results suggest that there is no acute toxic effect of Cd to nematodes associated with wood ash recycling; in fact, our results suggest that ash actually decrease Cd toxicity.

Effects of heavy metals identified in Chascomús shallow lake on the endocrine-reproductive axis of pejerrey fish (Odontesthes bonariensis)

Some heavy metals related to human activities were measured in the water of Chascomús lake. The maximum concentrations were: 0.23 μg/L for Cd, 4.28 μg/L for Cr, 22.09 μg/L for Cu, 2.49 μg/L for Ni, 3.24 μg/L for Pb and 210.76 μg/L for Zn. The values of Cd, Cr, Cr, Pb and Zn were above the Argentine National Guidelines for the Protection of the Aquatic life. The analysis of gonadal condition of pejerrey fish (Odontesthes bonariensis) from this lake did not revealed any reproductive damages. However, exposures with environmental concentrations of Cd, Cr, Cu and Zn under laboratory conditions of pejerrey males (14 days), caused a significant increase of the expression of the three variants of gnrh in the brain (within Cd exposure) and a decrease in cyp19a1b mRNA (within Cu exposure). Furthermore, at pituitary level, a decrease in fshb transcript levels was observed in the fish exposed to Cd and Cr and a decrease in the expression of both gonadotropin receptors at gonadal level in Zn exposure. Moreover, the gonads of the fish exposed to all the tested metals suffered structural damages showing shortness of the spermatic lobules, fibrosis, testis ova and the presence of piknotic cells. All these findings alert that heavy metals pollution affects the expression of key reproductive genes and gonadal structure of fish species that represent the predominant group of organisms and are considered sentinel species in the aquatic ecosystems.

Toxicity of cadmium and zinc to small soil protists

Small heterotrophic protists (flagellates and naked amoebae) are very abundant in soil and play a key role in maintaining soil services. Hence, knowledge on how xenobiotics affect these organisms is essential in ecosystem management. Cadmium (Cd) is an increasing environmental issue as both industrial deposition and recycling of heavy metal rich waste products have led to Cd enrichment of soils. Evaluation of toxicity of Cd to micro-organisms is often performed using a solution of pure Cd (e.g. CdCl) in liquid culture. This approach may be highly misleading as interactions between Cd and other substances, e.g. various ions or inherent soil components often strongly modify Cd toxicity. Hence, we compared the toxic effect of Cd to small heterotrophic protists in soil microcosms and liquid culture. We also evaluated how zinc (Zn) affects Cd toxicity, as Zn usually accompanies Cd in a ratio of c. 100:1, and is known to impede Cd toxicity. In the soil microcosms, we also monitored the primary food source of the protists, i.e. culturable bacteria, and used soil respiration as a proxy of soil functioning. Finally, we examined to what extent Cd actually sorbs to soil. We found 1) that c. 10³ times more Cd was required to obtain the same effect in the soil microcosms compared to the liquid culture, 2) that soil sorption explains why Cd, even though highly toxic in aqueous solutions, has very limited effect when applied to soil, and 3) (very surprisingly) that in our experimental systems Zn was as toxic as Cd. Our study suggests that Cd toxicity to soil protists will be small because most Cd in soil will be sorbed to the soil matrix and because the Zn:Cd ratio of 100:1 in most substances, incl. pollutants, will mean that lethal Zn effects will occur before Cd reaches toxic levels.

Discrepancies Between Molecular and Morphological Databases of Soil Ciliates Studied for Temperate Grasslands of Central Europe

By measuring the change in soil protist communities, the effect of human land use on grasslands can be monitored to promote sustainable ecosystem functioning. Protists form the active link in the rhizosphere between the plant roots and higher trophic organisms; however, only few morphological species and their ecological values have yet been described in this context. To investigate the communicability between morphological and molecular databases used in the molecular barcoding of protists and in the biomonitoring of grassland soil, the present high-throughput sequencing (HTS) study (N=150) covered the area of central Europe (mesoscale) known to be well studied for ciliated protists. HTS delivered 2,404 unique reads identifying taxa in all major ciliophoran classes but exact reference matches were few. The study identified clear discrepancies between databases for well-studied taxa, where molecular databases contained multiple gene variants for single morphospecies of dominant taxa. Gene variants presented own biogeography - the eukaryotic microdiversity along gradients (e.g., land-use intensity, soil water). It is possible that many of the so called novel phylogenetic lineages and hidden diversity pointed out in environmental surveys could be evidence for the severe lack of molecular data for already known and morphologically described species, present in morphological databases.

Complexation of Eu(III), Pb(II), and U(VI) with a Paramecium glycoprotein: Microbial transformation of heavy elements in the aquatic environment

This study investigated the interaction of inorganic aqueous Eu(III), Pb(II), and U(VI) with Paramecium sp., a representative single-celled protozoan that lives in freshwater. Living and prekilled Paramecium cells were tested. The prekilled cells were killed with a fixative. After 24 h exposure of the cells to inorganic aqueous solutions containing Eu(III) or U(VI), analyses by microparticle-induced X-ray emission with a focused beam (<1 μm) did not detect Eu and U in the living cells, whereas Eu and U were detected in the prekilled cells. Size exclusion chromatography coupled with on-line ultraviolet-visible detection and elemental detection by inductively coupled plasma mass spectrometry of the aqueous phases collected after the living cell experiments revealed that a fraction of the Eu, Pb, and U in the aqueous phase bound to a large (ca. 250 kDa) Paramecium biomolecule and formed a metal-organic complex. The characteristics of the biomolecule were consistent with those of the soluble glycoproteins covering the surfaces of Paramecium cells. These results show that Paramecium cells transform inorganic aqueous Eu, Pb, and U to organic complexes. This paper discusses the relation between this novel complexation and the sorption of these heavy elements on Paramecium cells.

Laboratory Scale Microbial Food Chain To Study Bioaccumulation, Biomagnification, and Ecotoxicity of Cadmium Telluride Quantum Dots

The increasing applications of engineered nanomaterials (ENMs) in consumer products warrant a careful evaluation of their trophic transfer and consequent ecological impact. In the present study, a laboratory scale aquatic microbial food chain was established using bacteria (Escherichia coli (E. coli)) as a prey and ciliated protozoan (Paramecium caudatum) as a predator organism to determine the impact of cadmium telluride quantum dots (CdTe QDs). We observed that 29% of bacterivory potential of paramecium was lost, including an ∼12 h delay in doubling time on exposure to 25 mg/L CdTe QD (∼4 nm) as compared to control. The fluorescence based stoichiometric analysis revealed that 65% of the QDs bioaccumulated when paramecia were exposed to 25 mg/L QDs at 24 h. There was a significant (p < 0.05) increase in cellular cadmium (Cd) concentration at 24 h (306 ± 192 mg/L) as compared to 1 h (152 ± 50 mg/L). Moreover, the accumulation of Cd in E. coli (147 ± 25 mg/L) at 1 h of exposure to 25 mg/L QDs transferred 1.4 times higher Cd (207 ± 24 mg/L; biomagnification factor = 1.4) to its predator, paramecium.

Influence of waterborne arsenic on nutritive and potentially harmful elements in gilthead seabream (Sparus aurata)

Fish are an important source of nutrients in human nutrition. Although arsenic (As) is considered potentially carcinogenic for human being, very little is known about its toxicity in fish biology. To increase our knowledge of the effect of exposure to waterborne As on fish, gilthead seabream (Sparus aurata) were exposed to 5 μM As₂O₃ and the bioaccumulation of macronutrients (Ca, K, Mg, Na, P), micronutrients (Fe, Mn, Zn) and Potentially Harmful Elements (As, Cd) was determined using spectrometric techniques. All elements were determined in the muscle and liver of non-exposed fish and those exposed to As for 2, 10 or 30 days. The concentrations of K, Na, Mg, Mn and Zn (in muscle) and Fe and Mn (in liver) of control (non-exposed) fish were higher than those determined in exposed fish. Furthermore, neither As nor Cd accumulated in the edible part (muscle) of seabream and were only evident in liver after 30 days of continuous exposure to As, but both concentrations remained below legally established limits.

Metal Concentrations in Sediment And Biota of the Huludao Coast in Liaodong Bay and Associated Human and Ecological Health Risks

This study assessed the contamination extent and potential ecological and human health impacts for chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb) in sediments and indigenous benthic organisms along the coastal area of Huludao, China. We analyzed a total of eight species: two benthic fish species, two bivalves, two snails, and two decapod crustaceans. Cu, Zn, and Cd levels in sediment exceeded the Chinese marine sediment quality criteria. The geoaccumulation index was highest for Cd followed in a decreasing order by Zn, Pb, Cu, Ni, and Cr. Metal levels were highest in the four mollusk species. The oyster and veined rapa whelk had the highest bioaccumulation factors, indicating that these two species would be well suited for monitoring the metal pollution in this area. Our comparison of estimated daily intake values for human consumption of the seafood species to the Food and Agricultural Organization-recommended daily dietary allowances indicate potential health risks from the intake of Cd from all shellfish other than our crab species and Zn intake from oyster consumption. An analysis of target hazard quotients identified noncarcinogenic health risks from Cd (in all shellfish analyzed except for our crab species), Cu, and Zn (in oysters and veined rapa whelks). Moreover, an analysis of cancer risk from Pb ingestion detected an increased risk for consumption of all shellfish except for the crab species. Health risks seem especially pronounced for the consumption of oysters and the veined rapa whelks; a seafood advisory may be warranted for these mollusks.

Bio-recovery of non-essential heavy metals by intra- and extracellular mechanisms in free-living microorganisms

Free-living microorganisms may become suitable models for recovery of non-essential and essential heavy metals from wastewater bodies and soils by using and enhancing their accumulating and/or leaching abilities. This review analyzes the variety of different mechanisms developed mainly in bacteria, protists and microalgae to accumulate heavy metals, being the most relevant those involving phytochelatin and metallothionein biosyntheses; phosphate/polyphosphate metabolism; compartmentalization of heavy metal-complexes into vacuoles, chloroplasts and mitochondria; and secretion of malate and other organic acids. Cyanide biosynthesis for extra-cellular heavy metal bioleaching is also examined. These metabolic/cellular processes are herein analyzed at the transcriptional, kinetic and metabolic levels to provide mechanistic basis for developing genetically engineered microorganisms with greater capacities and efficiencies for heavy metal recovery, recycling of heavy metals, biosensing of metal ions, and engineering of metalloenzymes.

Molecular Characterization of a Copper Metallothionein Gene From a Ciliate Tetrahymena farahensis

A new copper metallothionein (TfCuMT) gene has been identified from a locally isolated ciliate Tetrahymena farahensis. It contains 327 nucleotides encoding a peptide chain of 108 amino acids and belongs to class MTT2 and subfamily 7b. Amplification from both gDNA and mRNA confirmed the intronless nature of this gene. Like most of the metallohtioneins, cysteine residues contribute nearly 30% content with the specific CKC motifs. Structural repeats present in peptide sequence of TfCuMT indicate internal duplication of gene at some stage of gene evolution. The predicted model of copper metallothionein protein showed that copper ions are mainly chelated by thiol sulfur of cysteine residues and are embedded in the folds of polypeptide chain. For in vivo expression of TfCuMT in Escherichia coli host cells the classical stop codons, which coded for glutamine in the ciliate were mutated to CAA and CAG through site directed mutagenesis. The mutated gene showed higher expression in pET28a expression vector compared with pET21a. Optimum expression was obtained after 6-8 h of 0.1 mM IPTG induction. Stability of His tagged TfCuMT in 5% SDS was low, with half-life of about 104 min. Presence of 1.0 μM copper increased the expression level by 1.65-fold. Presence of 100 μM Cysteine in culture medium caused 2.4-fold increase in expression level. His tagged TfCuMT was purified through affinity chromatography using NTN-His binding resin in the presence of 0.1 M imidazole and NaCl. The modeled structure of the TfCuMT showed a cleft for Cu binding with correct orientation of Cys residues in the motif CKC. J. Cell. Biochem. 117: 1843-1854, 2016. © 2016 Wiley Periodicals, Inc.

Evaluation of the sensitivity to zinc of ciliates Euplotes vannus and Euplotes crassus and their naturally associated bacteria isolated from a polluted tropical bay

The aim of this study was to evaluate the Zn sensitivity of Euplotes vannus, Euplotes crassus, and their naturally associated bacteria sampled from sediments in the northwest and east regions of Guanabara Bay. The unexposed ciliates and bacteria did not appear to be negatively affected by 96 h of assay. In the control group, E. vannus exhibited an increase in the biomass content from 2.3 × 10(2) to 2.3 × 10(3) μg C cm(-3) between 0 and 96 h, and E. crassus increased up to 7.07 × 10(2) μg C cm(-3) at 48 h. The maximum biomass was pointed by E. crassus (1.33 × 10(3) μg C cm(-3)) in the presence of 0.005 mg Zn L(-1) and E. vannus was naturally associated bacteria (2.40 × 10(-1) μg C cm(-3)) in the presence of 1.0 mg Zn L(-1) (96 h). The growth of E. vannus from the northwest region showed concentration-dependent manners, and it is more sensitive to zinc than E. crassus from the southeast. Naturally associated bacteria showed better adaptation to increasing concentrations of Zn, and the Dunnett test showed that previous environmental selection is important. These results show that new bioremediation tools are necessary.

Effects of elevated temperature on the toxicity of copper and oxytetracycline in the marine model, Euplotes crassus: a climate change perspective

Trace metals and broad-spectrum antibiotic drugs are common environmental contaminants, the importance of which is increasing due to global climate change-related effects. In the present study, the biological model organism E. crassus was first acclimated to five temperatures, from 25 °C to 33 °C, followed by exposure to nominal concentrations of copper, the antibiotic model compound oxytetracycline and mixtures of both, at increasing thermal conditions. Variations of temperature-related toxicity were assessed by two high-level endpoint tests, survival and replication rates, and two sublethal parameters: endocytosis rate and lysosomal membrane stability. The selected toxicants presented opposite behaviours as the protozoa's survival rates increased following an increasing thermal gradient in the oxytetracycline-related treatments, and a decline of tolerance in metal-related treatments was observed. Results of tests combining binary mixtures of tested toxicants showed a complex pattern of responses.

Effect of nickel on nutrient removal by selected indigenous protozoan species in wastewater systems

Nutrient and heavy metal pollutions are major concern worldwide. This study aimed at comparing the effect of Ni(2+) on nutrient removal efficiency of four indigenous wastewater protozoan species (Aspidisca sp., Paramecium sp., Peranema sp., Trachelophyllum sp.). Specific physicochemical parameters and microbial growth/die-off were measured using standard methods. The results revealed that protozoan species were able to simultaneously remove phosphate, nitrate and Ni(2+) at concentrations ranging between 66.4-99.36%, 56.19-99.88% and 45.98-85.69%, respectively. Peranema sp. appeared to be the isolates with the highest removal of nutrients (Phosphate-99.36% and Nitrate-99.88%) while Paramecium sp. showed higher removal of Ni(2+) at 85.69% and low removal of nutrients. Aspidisca sp. was the most sensitive isolate to Ni(2+) but with significant nutrient removal (Phosphate-66.4% and Nitrate-56.19%) at 10 mg-N(2+)/L followed by an inhibition of nutrient removal at Ni(2+) concentration greater than 10 mg/L. Significant correlation between the growth rate and nutrient removal (r = 0.806/0.799, p < 0.05 for phosphate and nitrate, respectively) was noted. Except for Peranema sp. which revealed better nutrient removal ability at 10 mg-Ni(2+)/L, an increase in Ni(2+) concentration had a significant effect on nutrient removal efficiency of these indigenous protozoan species. This study suggests that although Ni(2+) appeared to be toxic to microbial isolates, its effect at a low concentration (10 mg-Ni(2+)/L) towards these isolates can be used to enhance the wastewater treatment process for the removal of nutrients. Peranema sp., which was able to remove both Ni(2+) and nutrients from wastewater mixed-liquor, can also be used for bioremediation of wastewater systems.

Acute effects of heavy metals on the expression of glutathione-related antioxidant genes in the marine ciliate Euplotes crassus

Euplotes crassus, a single-celled eukaryote, is directly affected by environmental contaminants. Here, exponentially cultured E. crassus were exposed to cadmium, copper, lead, and zinc and then the reactive oxygen species (ROS) and total glutathione (GSH) levels were measured. Subsequently, the transcriptional modulation of glutathione peroxidase (GPx) and glutathione reductase (GR) were estimated by quantitative RT-PCR. After an 8-h exposure, significantly higher increases in the relative ROS and total GSH levels were observed in exposed group, compared to the controls. Real-time PCR data revealed that the expression levels of GPx and GR mRNA were sensitively modulated within 8h of exposure to all heavy metals. These findings suggest that these genes may be involved in cellular defense mechanisms by modulating their gene expression against heavy metal-induced oxidative stress. Thus, they may be useful as potential molecular biomarkers to assess sediment environments for contaminants.

Effects of cadmium and mercury on the upper part of skeletal muscle glycolysis in mice

The effects of pre-incubation with mercury (Hg(2+)) and cadmium (Cd(2+)) on the activities of individual glycolytic enzymes, on the flux and on internal metabolite concentrations of the upper part of glycolysis were investigated in mouse muscle extracts. In the range of metal concentrations analysed we found that only hexokinase and phosphofructokinase, the enzymes that shared the control of the flux, were inhibited by Hg(2+) and Cd(2+). The concentrations of the internal metabolites glucose-6-phosphate and fructose-6-phosphate did not change significantly when Hg(2+) and Cd(2+) were added. A mathematical model was constructed to explore the mechanisms of inhibition of Hg(2+) and Cd(2+) on hexokinase and phosphofructokinase. Equations derived from detailed mechanistic models for each inhibition were fitted to the experimental data. In a concentration-dependent manner these equations describe the observed inhibition of enzyme activity. Under the conditions analysed, the integral model showed that the simultaneous inhibition of hexokinase and phosphofructokinase explains the observation that the concentrations of glucose-6-phosphate and fructose-6-phosphate did not change as the heavy metals decreased the glycolytic flux.

Effect of disinfectant, water age, and pipe materials on bacterial and eukaryotic community structure in drinking water biofilm

Availability of safe, pathogen-free drinking water is vital to public health; however, it is impossible to deliver sterile drinking water to consumers. Recent microbiome research is bringing new understanding to the true extent and diversity of microbes that inhabit water distribution systems. The purpose of this study was to determine how water chemistry in main distribution lines shape the microbiome in drinking water biofilms and to explore potential associations between opportunistic pathogens and indigenous drinking water microbes. Effects of disinfectant (chloramines, chlorine), water age (2.3 days, 5.7 days), and pipe material (cement, iron, PVC) were compared in parallel triplicate simulated water distribution systems. Pyrosequencing was employed to characterize bacteria and terminal restriction fragment polymorphism was used to profile both bacteria and eukaryotes inhabiting pipe biofilms. Disinfectant and water age were both observed to be strong factors in shaping bacterial and eukaryotic community structures. Pipe material only influenced the bacterial community structure (ANOSIM test, P < 0.05). Interactive effects of disinfectant, pipe material, and water age on both bacteria and eukaryotes were noted. Disinfectant concentration had the strongest effect on bacteria, while dissolved oxygen appeared to be a major driver for eukaryotes (BEST test). Several correlations of similarity metrics among populations of bacteria, eukaryotes, and opportunistic pathogens, as well as one significant association between mycobacterial and proteobacterial operational taxonomic units, provides insight into means by which manipulating the microbiome may lead to new avenues for limiting the growth of opportunistic pathogens (e.g., Legionella) or other nuisance organisms (e.g., nitrifiers).

A modified nanoporous stir bar for simultaneous determination of Cu(II) and Cd(II) ions in natural samples prior to flame atomic absorption spectroscopy

In this work, the application of stir bar sorptive extraction (SBSE), as a fast and conventional method, has been investigated for the simultaneous preconcentration and determination of trace amounts of Cd(II) and Cu(II) ions in natural samples. For this purpose, the surface of stir bar was functionalized by amine functionalized nanoporous silica and characterized by IR spectroscopy, X-ray powder diffraction (XRD), Atomic force microscopy (AFM) and N2adsorption. In this approach, after the preconcentration of Cd(II) and Cu(II) ions and removing the matrix interferences using modified stir bar, the amounts of these ions were determined in eluent by flame atomic absorption spectroscopy (FAAS). Various parameters on adsorption and elution steps including pH of sample, adsorption kinetic, eluent parameters (type, volume and concentration) and elution time, have been optimized in this study. The limits of detection (LOD) were 1.6 and 13.8 ng mL-1(recovery of 83.5 and 88.1%) for cadmium and copper ions, respectively. The preconcentration factors were 133 and 137 and the relative standard deviations (RSD) of the method were 5.7 and 4.6% for Cd(II) and Cu(II) ions, respectively. As the key point in this study seems to be stir bar nanoporous structure, the analytical performance of this stir bar was compared to non-porous ones. The accuracy of this novel method has been confirmed using some standard references materials. Finally the potential of this method was investigated by determination of Cd(II) and Cu(II) ions in some real samples with complicated matrixes.

Assessing the resistance and bioremediation ability of selected bacterial and protozoan species to heavy metals in metal-rich industrial wastewater

BACKGROUND

Heavy-metals exert considerable stress on the environment worldwide. This study assessed the resistance to and bioremediation of heavy-metals by selected protozoan and bacterial species in highly polluted industrial-wastewater. Specific variables (i.e. chemical oxygen demand, pH, dissolved oxygen) and the growth/die-off-rates of test organisms were measured using standard methods. Heavy-metal removals were determined in biomass and supernatant by the Inductively Couple Plasma Optical Emission Spectrometer. A parallel experiment was performed with dead microbial cells to assess the biosorption ability of test isolates.

RESULTS

The results revealed that the industrial-wastewater samples were highly polluted with heavy-metal concentrations exceeding by far the maximum limits (in mg/l) of 0.05-Co, 0.2-Ni, 0.1-Mn, 0.1-V, 0.01-Pb, 0.01-Cu, 0.1-Zn and 0.005-Cd, prescribed by the UN-FAO. Industrial-wastewater had no major effects on Pseudomonas putida, Bacillus licheniformis and Peranema sp. (growth rates up to 1.81, 1.45 and 1.43 d-1, respectively) compared to other test isolates. This was also revealed with significant COD increases (p < 0.05) in culture media inoculated with living bacterial isolates (over 100%) compared to protozoan isolates (up to 24% increase). Living Pseudomonas putida demonstrated the highest removal rates of heavy metals (Co-71%, Ni-51%, Mn-45%, V-83%, Pb-96%, Ti-100% and Cu-49%) followed by Bacillus licheniformis (Al-23% and Zn-53%) and Peranema sp. (Cd-42%). None of the dead cells were able to remove more than 25% of the heavy metals. Bacterial isolates contained the genes copC, chrB, cnrA3 and nccA encoding the resistance to Cu, Cr, Co-Ni and Cd-Ni-Co, respectively. Protozoan isolates contained only the genes encoding Cu and Cr resistance (copC and chrB genes). Peranema sp. was the only protozoan isolate which had an additional resistant gene cnrA3 encoding Co-Ni resistance.

CONCLUSION

Significant differences (p < 0.05) observed between dead and living microbial cells for metal-removal and the presence of certain metal-resistant genes indicated that the selected microbial isolates used both passive (biosorptive) and active (bioaccumulation) mechanisms to remove heavy metals from industrial wastewater. This study advocates the use of Peranema sp. as a potential candidate for the bioremediation of heavy-metals in wastewater treatment, in addition to Pseudomonas putida and Bacillus licheniformis.

Bioreactor function under perturbation scenarios is affected by interactions between bacteria and protozoa

This study investigated the impact of transient cadmium perturbations on the structure and function of the microbial community in an activated sludge system. The impact of cadmium perturbation on the bioreactor performance, bacterial activity, bacterial community structure, and bacteria-protozoa interactions was examined. The bacterial community exhibited a short-term inhibition following a pulse perturbation of cadmium. Process recovery was associated with an increase in bacterial abundance above the unperturbed control reactor, followed by high biomass activity after the washout of cadmium. This trend was seen for multiple experiments at both laboratory- and pilot-scale. The increase in biomass activity could not be explained by changes in bacterial community structure. Independent experiments showed that the increase in bacterial abundance, and by association biomass activity, was caused by the decrease in the protozoal grazing due to the higher inhibition of ciliated protozoa as compared to bacteria when exposed to cadmium. This paper highlights the importance of expanding the investigative boundaries of the microbial ecology of bioengineered systems to include protozoal grazing, especially under perturbation scenarios.

The use of multiple endpoints to assess cellular responses to environmental contaminants in the interstitial marine ciliate Euplotes crassus

This paper presents the results of investigations on the suitability of Euplotes crassus, an interstitial marine ciliate, to be used as model organism in ecotoxicology and thereafter to evaluate the toxicity of estuarine and coastal sediments upon laboratory exposure. Nowadays, anthropogenic activities have resulted in accumulation of metals and organic pollutants in the environment as well as in the food chain hence leading to serious ecological and human health problems. This may pose a risk to benthic and epibenthic organisms and it is crucial to discover toxicity tests that will identify adverse effects of sediment-associated chemicals on benthic organisms. Due to their nature as a eukaryotic cell/organism and their position in the food web, ciliated protozoa are suitable models for evaluating the effects of pollution on aquatic communities. Lethal and sublethal effects of exposure to inorganic and organic pollutants were tested on the cell mortality, replication rate, lysosomal membrane stability and endocytosis rate of E. crassus. Increasing nominal concentrations of individual and mixtures of mercury, copper, and benzo(a)pyrene were investigated in this study as they might be bioavailable in naturally occurring polluted sites. A significant decrease in the mean replication rate (p<0.05) was found after 24h exposures to m/μM concentrations of all tested pollutants. At the same time, significant decreases of lysosomal membrane stability (p<0.05) were observed for Cu (5 μM), Hg (10 nM), and B(a)P (200 nM). Among the entire suite of tests, endocytosis rate test demonstrated the highest sensitivity. Exposures to binary mixtures of all studied pollutants were performed showing both inorganic-organic and inorganic-inorganic additive and/or antagonist effects. Moreover, medium salinity was also varied to mimic estuarine-like environmental conditions linking biological response to ionic strengths. Under these conditions significant increases of both endocytosis rate and lysosomal membrane stability were observed and related to the increment of some Hg- and Cu-related toxic complexes. The studied biomarkers were always able to discriminate between the effects of organic and inorganic pollutants. Together with the short time and simplicity of the test procedures, results obtained in this study indicate that E. crassus is a promising and convenient bioindicator for evaluating the toxicity of different environmental matrixes like pore water, sediments and wastewaters--polluted by metals and organic pollutants.

Metals in the tissues of two fish species from the rare and endemic fish nature reserve in the upper reaches of the Yangtze River, China

Concentrations of copper, zinc, mercury, and arsenic were measured in the muscle, gill and liver tissues of Coreius heterodon and Pelteobagrus vachelli collected from the rare and endemic fish nature reserve in the upper reaches of the Yangtze River. The concentrations of copper and zinc in the tissues of these two fish species were higher than those of mercury and arsenic. Highest metal concentrations were generally found in fish samples from Yibin. The concentrations of copper, zinc, mercury, and arsenic in C. heterodon were higher than that in P. vachelli. The fish from this study area were not safe for human consumption.

Heavy metal concentrations in some macrobenthic fauna of the Sundarbans mangrove forest, south west coast of Bangladesh

Heavy metal concentrations in some macrobenthic fauna have been reported for the first time from the Sundarbans mangrove forest, south west coast of Bangladesh, in the northern part of Bay of Bengal. The concentration of Fe, Cu, Zn, Cd and Pb in macrobenthos ranged from 235 ± 10.11 to 1,051 ± 38.42, 3.66 ± 0.89 to 7.55 ± 1.29, 76.8 ± 8.55 to 98.5 ± 6.49, 0.46 ± 0.11 to 0.859 ± 0.2 and 4.66 ± 1.17 to 6.77 ± 2.1 μg/g, respectively. Significant variations (p ≤ 0.05) in heavy metal concentrations have been observed among the mud crab, mudskipper and gastropod. However, heavy metal burdens did not vary significantly among the hermit and horseshoe crabs. In mud crab, horseshoe crab and gastropod, heavy metal concentrations were recorded in the sequence: Fe > Zn > Pb > Cu > Cd. Hermit crab and mudskipper contained heavy metals in the order of Fe > Zn > Cu > Pb > Cd. Fe and Zn concentrations were found significantly (p ≤ 0.05) higher in macrobenthos. The lead (Pb) concentration found in the edible portion of macrobenthos exceeded the international permissible limits certified by the WHO. Bioconcentration factors >1.00 obtained for Fe (17.05 in mudskipper) and Cd (1.87 in gastropod) indicated that these metals were highly bioaccumulated and biomagnified in benthic fauna of Sundarbans. The findings of this study refer to the potential impact of heavy metals in the mangrove ecosystem of Bangladesh.

Hematological, biochemical and ionoregulatory responses of Indian major carp Catla catla during chronic sublethal exposure to inorganic arsenic

In the present study the acute toxicity of arsenic trioxide in fingerlings of Catla catla an Indian major carp was evaluated with renewal bioassay method. The median lethal concentration of arsenic trioxide to the fish C. catla for 96 h was found to be 20.41 ppm (with 95% confidence limits). From this a non-lethal dose of (2.041 ppm; 1/10th of LC 50 96 value) was selected and fingerlings were exposed to 35 d and hematological, biochemical and ionoregulatory responses were studied at days 7, 14, 21, 28 and 35. Arsenic trioxide produced a significant increase in hemoglobin, hematocrit, WBC count, plasma GPT levels and reduction in RBC count, plasma sodium, chloride, potassium, glucose, protein, GOT, LDH levels as compared to the control group. Gill Na(+)/K(+)-ATPase activity was influenced by arsenic trioxide exposure. A biphasic response was noted in the value of MCH and MCV. However the MCHC level was not altered in arsenic trioxide treated fish throughout the study period. Results of the present investigation suggest that arsenic trioxide affects the hematological, biochemical and ionoregulatory parameters of fish and alterations of these parameters can be useful in environmental biomonitoring of arsenic contamination.

Concentration of four heavy metals (cadmium, lead, mercury, and arsenic) in organs of two cyprinid fish (Cyprinus carpio and Capoeta sp.) from the Kor River (Iran)

Concentration of heavy metals in aquatic animals mainly occurs due to industrial contamination. In this study, the concentrations of four heavy metals (cadmium, lead, mercury, and arsenic) in organs of two cyprinid fish and in water collected from three sections of the Kor River, Iran were determined using the inductively coupled plasma method. Pathological and hormonal changes due to metal contamination were also measured. The concentrations of heavy metals in tissue of fish from the middle sampling zone were significantly higher (p < 0.05) than those from the other two sampling zones, whereas no significant differences (p > 0.05) were detected between the two sexes and species. High levels of metals were found in the ovaries and testes; estradiol in females and progesterone and testosterone in males from the middle study site were significantly (p < 0.05) lower than values from the other two sites. Pathological changes in blood cells, liver, and kidneys of fishes were significantly higher in highly polluted areas (middle sampling zone). These results show that industrial activities have polluted the river and that the maximum concentrations of Cd, Pb, and Hg were higher than the permissible levels for human consumption.

A combination method to study microbial communities and activities in zinc contaminated soil

Zinc (Zn) plays a special role in soil ecology and fertility because it can support the growth of soil organisms or inhibit their growth depending on its concentrations. In this work, the effects of different concentrations of Zn on soil microbial communities and activities were analyzed by loading five different doses of Zn (160-6000 microg g(-1)) into a wheat surface soil. The microbial metabolic process revealed a significant bimodal pattern at high concentrations of Zn (>1920 microg g(-1)). This phenomenon suggested that soil microorganisms were very sensitive to zincous poisoning. A variety of soil quality properties were also measured and assessed. The results showed slower bacterial growth in soil cultures polluted with high levels of Zn. In addition, two kinds of fungi were identified by morphology and glomalin-related soil protein content in the Zn-contaminated soil. The growth of the first kind was inhibited with increase in Zn concentration. By contrast, the second kind could survive and continue to grow with increasing doses of Zn at 160-1920 microg g(-1) and its growth began to decline with further increase in Zn concentration. Finally, the fungus could not survive at very high (6000 microg g(-1)) Zn concentration. In this work, we conclude that soil microbial communities and activities can adapt to Zn pollution to a certain extent.

Heavy metal uptake by Euplotes mutabilis and its possible use in bioremediation of industrial wastewater

A ciliate protozoan, Euplotes mutabilis, isolated from heavy metal laden industrial wastewater, has been shown to tolerate multiple heavy metals thus suggesting its significance in bioremediation of industrial effluents. This ciliate tolerated Zn(2+) up to 33 microg/mL, Cd(2+) up to 22 microg/mL and Ni(2+) up to 18 microg/mL. The ciliate could uptake 85% Zn(2+), 84% of Cd(2+) and 87% of Ni(2+) after 96 h of inoculation of growth medium containing 10 microg/mL of Zn(2+) and 5 microg/mL of Cd(2+) and Ni(2+), with actively growing ciliates. After 6 days of incubation the ciliate removed 87% Cd(2+), 92% Ni(2+), and 93% Zn(2+) from the wastewater. The heavy metal uptake capability of Euplotes mutabilis may be employed for metal detoxification operations.