Simultaneous Cd2+, Zn2+, and Pb2+ uptake and accumulation by photosynthetic Euglena gracilis

Competition of Cd(II) and Pb(II) on the bacterial cells: a new insight from bioaccumulation based on NanoSIMS imaging

Polymetallic exposure causes complex toxicity to microorganisms. In this study, we investigated the responses of Escherichia coli under co-existence of cadmium (Cd) and lead (Pb), primarily based on biochemical analysis and RNA sequencing. Cd completely inhibited bacterial growth at a concentration of 2.41 mmol/L, with its removal rate as low as <10%. In contrast, the Pb removal rate was >95% under equimolar sole Pb stress. In addition, the Raman analysis confirmed the loss of proteins for the bacterial cells. Under the co-existence of Cd and Pb, the Cd toxicity to E. coli was alleviated. Meanwhile, the biosorption of Pb cations was more intense during the competitive sorption with Cd. Transmission electron microscopy images showed that a few cells were elongated during incubation, i.e., the average cellular length increased from 1.535 ± 0.407 to 1.845 ± 0.620 µm. Moreover, NanoSIMS imaging showed that the intracellular distribution of Cd and Pb was coupled with sulfur. Genes regulating sulfate transporter were also upregulated to promote sulfate assimilation. Then, the subsequent production of biogenic sulfide and sulfur-containing amino acids was enhanced. Although this strategy based on S enrichment could resist the polymetallic stress, not all related genes were induced to upregulate under sole Cd stress. Therefore, the S metabolism might remodel the microbial resistance to variable occurrence of heavy metals. Furthermore, the competitive sorption (in contrast to sole Cd stress) could prevent microbial cells from strong Cd toxicity.IMPORTANCEMicrobial tolerance and resistance to heavy metals have been widely studied under stress of single metals. However, the polymetallic exposure seems to prevail in the environment. Though microbial resistance can alleviate the effects of exogenous stress, the taxonomic or functional response to polymetallic exposure is still not fully understood. We determined the strong cytotoxicity of cadmium (Cd) on growth, and cell elongation would be driven by Cd stress. The addition of appropriate lead (Pb) showed a stimulating effect on microbial bioactivity. Meanwhile, the biosorption of Pb was more intense during co-existence of Pb and Cd. Our work also revealed the spatial coupling of intracellular S and Cd/Pb. In particular, the S assimilation was promoted by Pb stress. This work elucidated the microbial responses to polymetallic exposure and may provide new insights into the antagonistic function during metal stresses.

Fatty Acid Accumulations and Transcriptome Analyses Under Different Treatments in a Model Microalga Euglena gracilis

With the continuous growth of the world’s population and the increasing development of industrialization, the demand for energy by human beings has been expanding, resulting in an increasingly severe energy crisis. Microalgae are considered the most potential alternatives to traditional fossil fuels due to their many advantages, like fast growth rate, strong carbon sequestration capacity, and low growth environment requirements. Euglena can use carbon sources such as glucose, ethanol, and others for heterotrophic growth. Moreover, Euglena is highly adaptable to the environment and has a high tolerance to various environmental stresses, such as salinity, heavy metals, antibiotics, etc. Different treatments of Euglena cells could affect their growth and the accumulation of bioactive substances, especially fatty acids. To expand the industrial application of Euglena as a potential biodiesel candidate, we determine the physiological responses of Euglena against environmental stresses (antibiotics, heavy metals, salinity) or carbon resources (glucose and ethanol), and evaluate the potential for higher quality and yield of fatty acid with a high growth rate. Adding glucose into the culture media increases cell biomass and fatty acid production with high-quality biodiesel characters. The transcriptome analysis helped explore the possible regulation and biosynthesis of fatty acids under different treatments and exploited in the improvement of biodiesel production. This study provides insights for further improvement and various culture treatments for Euglena-based biodiesel and jet fuels.

Morphological Indicator for Directed Evolution of Euglena gracilis with a High Heavy Metal Removal Efficiency

In the past few decades, microalgae-based bioremediation methods for treating heavy metal (HM)-polluted wastewater have attracted much attention by virtue of their environment friendliness, cost efficiency, and sustainability. However, their HM removal efficiency is far from practical use. Directed evolution is expected to be effective for developing microalgae with a much higher HM removal efficiency, but there is no non-invasive or label-free indicator to identify them. Here, we present an intelligent cellular morphological indicator for identifying the HM removal efficiency of Euglena gracilis in a non-invasive and label-free manner. Specifically, we show a strong monotonic correlation (Spearman's ρ = -0.82, P = 2.1 × 10^-5) between a morphological meta-feature recognized via our machine learning algorithms and the Cu²⁺ removal efficiency of 19 E. gracilis clones. Our findings firmly suggest that the morphology of E. gracilis cells can serve as an effective HM removal efficiency indicator and hence have great potential, when combined with a high-throughput image-activated cell sorter, for directed-evolution-based development of E. gracilis with an extremely high HM removal efficiency for practical wastewater treatment worldwide.

Lead accumulation in photosynthetic Euglena gracilis depends on polyphosphates and calcium

Worldwide increasing levels of lead in water systems require the search for efficient ecologically friendly strategies to remove it. Hence, lead accumulation by the free-living algae-like Euglena gracilis and its effects on cellular growth, respiration, photosynthesis, chlorophyll, calcium, and levels of thiol- and phosphate-molecules were analyzed. Photosynthetic cells were able to accumulate 4627 mg lead/kg_DW after 5 days of culture with 200 μM Pb²⁺. Nevertheless, exposure to 50, 100 and 200 μM Pb²⁺ for up to 8 days did not modify growth, viability, chlorophyll content and oxygen consumption/production. Enhanced biosynthesis of thiol molecules and polyphosphates, i.e. the two canonical metal ion chelation mechanisms in E. gracilis, was not induced under such conditions. However, in cells cultured in the absence of phosphate, lead accumulation and polyphosphate content markedly decreased, while culturing in the absence of sulfate did not modify the accumulation of this metal. In turn, the total amount of intracellular calcium slightly increased as the amount of intracellular lead increased, whereas under Ca²⁺ deficiency lead accumulation doubled. Therefore, the results indicated that E. gracilis is highly resistant to lead through mechanisms mediated by polyphosphates and Ca²⁺ and can in fact be classified as a lead hyperaccumulator microorganism.

Growth and photosynthetic responses of Ochromonas gloeopara to cadmium stress and its capacity to remove cadmium

Cadmium (Cd) is one of the predominant anthropogenic pollutants in aquatic systems. As Cd has negative effects on species at all trophic levels, the community composition in aquatic habitats can be changed as a result of Cd stress. The response of mixotrophic protists to environmental stressors is particularly important as they act as both producers and consumers in complex planktonic communities. In this study, we used mixotrophic Ochromonas gloeopara to study its growth and photosynthetic responses to Cd, and specially focused on the effects of initial Cd concentrations and nutrient levels on its capacity to remove Cd. Results showed that when Cd concentration reached 0.5 mg L-1, the growth rate and carrying capacity were significantly inhibited, whereas the photosynthesis was markedly decreased when Cd concentration reached 0.15 mg L-1. Moreover, under Cd concentration 0.15, 0.5, 0.9, 1.6, and 2.0 mg L-1, the removal efficiencies of Cd by O. gloeopara were 83.2%, 77.7%, 74.6%, 70.1%, and 68.8%, respectively. The increase of nitrogen did not cause significant effect on the removal capacity of Cd by O. gloeopara, but increased concentration of phosphorus significantly enhanced the removal capacity of Cd. Our findings indicated that the mixotrophic O. gloeopara has strong tolerance and capacity to remove Cd, and increasing concentration of phosphorus can increase its removal capacity, suggesting that O. gloeopara has great potential application value in mitigating Cd pollution in waters.

Variations in the Phytoremediation Efficiency of Metal-polluted Water with Salvinia biloba: Prospects and Toxicological Impacts

The occurrence of heavy metals in industrial wastewater is unanimously considered a major concern since these pollutants cannot be chemically or biologically degraded and therefore have long residence times. Phytoremediation is one of the most widespread biotechnological applications worldwide, which consists in the use of plants to adsorb or accumulate a broad range of inorganic and organic contaminants from water, air, and soil. To improve the cost-effectiveness and sustainability of phytoremediation-based wastewater treatment systems, it is essential to use plants that are not only efficient in pollutants removal, but also abundant and easily accessible at the target site, requiring no-special culture conditions. In this study, we have evaluated the capacity of naturally-occurring aquatic macrophytes of the genus Salvinia (classified as Salvinia biloba) to phytoremediate water artificially contaminated with cadmium (Cd), copper (Cu), lead (Pb), or zinc (Zn) at equal molar concentrations (50 ± 2 and 100 ± 1 µM), during 48 h. Additionally, photosynthetic and antioxidant pigments (carotenoids, chlorophylls, anthocyanins, and flavonoids), and soluble carbohydrate content was also measured in floating leaves of Salvinia specimens to appraise heavy metals phytotoxicity. Elemental analyses to plant tissue indicate that S. biloba was able to bioconcentrate all four metals analyzed, albeit with different degrees of affinity. In addition, the mechanisms of uptake and detoxification were dissimilar for each ion, resulting in greater removal of Cu and Pb (≥96%, at both concentrations), in comparison to Cd (79 ± 4% and 56 ± 2% for 50 ± 2 and 100 ± 1 µM, respectively) and Zn (77 ± 5% and 70 ± 4% for 50 ± 2 and 100 ± 1 µM, respectively). Accordingly, the assessment of the selected physiological parameters in floating leaves suggests that different response mechanisms are triggered by each metal in S. biloba to counteract the corresponding toxicological stress.

Nickel accumulation by the green algae-like Euglena gracilis

Nickel accumulation and nickel effects on cellular growth, respiration, photosynthesis, ascorbate peroxidase (APX) activity, and levels of thiols, histidine and phosphate-molecules were determined in Euglena gracilis. Cells incubated with 0.5-1mM NiCl₂ showed impairment of O₂ consumption, photosynthesis, Chl a+b content and APX activity whereas cellular integrity and viability were unaltered. Nickel accumulation was depressed by Mg²⁺ and Cu²⁺, while Ca²⁺, Co²⁺, Mn²⁺ and Zn²⁺ were innocuous. The growth half-inhibitory concentrations for Ni²⁺ in the culture medium supplemented with 2 or 0.2mM Mg²⁺ were 0.43 or 0.03mM Ni²⁺, respectively. Maximal nickel accumulation (1362mg nickel/Kg DW) was achieved in cells exposed to 1mM Ni²⁺ for 24h in the absence of Mg²⁺ and Cu²⁺; accumulated nickel was partially released after 72h. GSH polymers content increased or remained unchanged in cells exposed to 0.05-1mM Ni²⁺; however, GSH, cysteine, γ-glutamylcysteine, and phosphate-molecules all decreased after 72h. Histidine content increased in cells stressed with 0.05 and 0.5mM Ni²⁺ for 24h but not at longer times. It was concluded that E. gracilis can accumulate high nickel levels depending on the external Mg²⁺ and Cu²⁺ concentrations, in a process in which thiols, histidine and phosphate-molecules have a moderate contribution.

Biochemistry and Physiology of Heavy Metal Resistance and Accumulation in Euglena

Free-living microorganisms may become suitable models for removal of heavy metals from polluted water bodies, sediments, and soils by using and enhancing their metal accumulating abilities. The available research data indicate that protists of the genus Euglena are a highly promising group of microorganisms to be used in bio-remediation of heavy metal-polluted aerobic and anaerobic acidic aquatic environments. This chapter analyzes the variety of biochemical mechanisms evolved in E. gracilis to resist, accumulate and remove heavy metals from the environment, being the most relevant those involving (1) adsorption to the external cell pellicle; (2) intracellular binding by glutathione and glutathione polymers, and their further compartmentalization as heavy metal-complexes into chloroplasts and mitochondria; (3) polyphosphate biosynthesis; and (4) secretion of organic acids. The available data at the transcriptional, kinetic and metabolic levels on these metabolic/cellular processes are herein reviewed and analyzed to provide mechanistic basis for developing genetically engineered Euglena cells that may have a greater removal and accumulating capacity for bioremediation and recycling of heavy metals.

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.

Cadmium removal by Euglena gracilis is enhanced under anaerobic growth conditions

The facultative protist Euglena gracilis, a heavy metal hyper-accumulator, was grown under photo-heterotrophic and extreme conditions (acidic pH, anaerobiosis and with Cd(2+)) and biochemically characterized. High biomass (8.5×10(6)cellsmL(-1)) was reached after 10 days of culture. Under anaerobiosis, photosynthetic activity built up a microaerophilic environment of 0.7% O₂, which was sufficient to allow mitochondrial respiratory activity: glutamate and malate were fully consumed, whereas 25-33% of the added glucose was consumed. In anaerobic cells, photosynthesis but not respiration was activated by Cd(2+) which induced higher oxidative stress. Malondialdehyde (MDA) levels were 20 times lower in control cells under anaerobiosis than in aerobiosis, although Cd(2+) induced a higher MDA production. Cd(2+) stress induced increased contents of chelating thiols (cysteine, glutathione and phytochelatins) and polyphosphate. Biosorption (90%) and intracellular accumulation (30%) were the mechanisms by which anaerobic cells removed Cd(2+) from medium, which was 36% higher versus aerobic cells. The present study indicated that E. gracilis has the ability to remove Cd(2+) under anaerobic conditions, which might be advantageous for metal removal in sediments from polluted water bodies or bioreactors, where the O₂ concentration is particularly low.

Euglenoid flagellates: a multifaceted biotechnology platform

Euglenoid flagellates are mainly fresh water protists growing in highly diverse environments making them well-suited for a multiplicity of biotechnology applications. Phototrophic euglenids possesses complex chloroplasts of green algal origin bounded by three membranes. Euglena nuclear and plastid genome organization, gene structure and gene expression are distinctly different from other organisms. Our observations on the model organism Euglena gracilis indicate that transcription of both the plastid and nuclear genome is insensitive to environmental changes and that gene expression is regulated mainly at the post-transcriptional level. Euglena plastids have been proposed as a site for the production of proteins and value added metabolites of biotechnological interest. Euglena has been shown to be a suitable protist species to be used for production of several compounds that are used in the production of cosmeceuticals and nutraceuticals, such as α-tocopherol, wax esters, polyunsaturated fatty acids, biotin and tyrosine. The storage polysaccharide, paramylon, has immunostimulatory properties and has shown a promise for biomaterials production. Euglena biomass can be used as a nutritional supplement in aquaculture and in animal feed. Diverse applications of Euglena in environmental biotechnology include ecotoxicological risk assessment, heavy metal bioremediation, bioremediation of industrial wastewater and contaminated water.

Accumulation of arsenic, lead, copper, and zinc, and synthesis of phytochelatins by indigenous plants of a mining impacted area

Several native plants, able to grow in an unconfined mining impacted area that is now in close vicinity with urban areas, were evaluated for their ability to accumulate heavy metals. The main soil contaminants were As, Pb, Cu, and Zn. Sampling of the rhizospheric metal polluted soil showed that Euphorbia prostrata Aiton, Parthenium incanum Kunth, and Zinnia acerosa (DC.) A. Gray were able to grow in the presence of high amounts of mixtures of these elements. The plants accumulated the metals in the above ground parts and increased the synthesis of thiol molecules. E. prostrata showed the highest capacity for accumulation of the mixture of elements (588 μg g DW(-1)). Analysis of the thiol-molecules profile showed that these plants synthesized high amounts of long-chain phytochelatins, accompanied by low amounts of monothiol molecules, which may be related to their higher resistance to As and heavy metals. The three plants showed translocation factors from roots to leaves >1 for As, Pb, Cu, and Zn. Thus, by periodically removing aerial parts, these plants could be useful for the phytoremediation of semi-arid and arid mining impacted areas, in which metal hyper-accumulator plants are not able to grow.

Sulfate uptake in photosynthetic Euglena gracilis. Mechanisms of regulation and contribution to cysteine homeostasis

BACKGROUND

Sulfate uptake was analyzed in photosynthetic Euglena gracilis grown in sulfate sufficient or sulfate deficient media, or under Cd(2+) exposure or Cys overload, to determine its regulatory mechanisms and contribution to Cys homeostasis.

RESULTS

In control and sulfate deficient or Cd(2+)-stressed cells, one high affinity and two low affinity sulfate transporters were revealed, which were partially inhibited by photophosphorylation and oxidative phosphorylation inhibitors and ionophores, as well as by chromate and molybdate; H(+) efflux also diminished in presence of sulfate. In both sulfate deficient and Cd(2+)-exposed cells, the activity of the sulfate transporters was significantly increased. However, the content of thiol-metabolites was lower in sulfate-deficient cells, and higher in Cd(2+)-exposed cells, in comparison to control cells. In cells incubated with external Cys, sulfate uptake was strongly inhibited correlating with 5-times increased intracellular Cys. Re-supply of sulfate to sulfate deficient cells increased the Cys, γ-glutamylcysteine and GSH pools, and to Cys-overloaded cells resulted in the consumption of previously accumulated Cys. In contrast, in Cd(2+) exposed cells none of the already elevated thiol-metabolites changed.

CONCLUSIONS

(i) Sulfate transport is an energy-dependent process; (ii) sulfate transporters are over-expressed under sulfate deficiency or Cd(2+) stress and their activity can be inhibited by high internal Cys; and (iii) sulfate uptake exerts homeostatic control of the Cys pool.

Individual and joint toxicity effects of Cu, Cr(III), and Cr(VI) on pakchoi: a comparison between solution and soil cultures

The single and joint toxicity effects of Cu, Cr(III), and Cr(VI) on the root elongation of pakchoi in solution and soil were investigated. The median effective concentration (EC(50)) was determined to examine the toxic thresholds of the test elements. The results showed that individual contamination by Cu, Cr(III), or Cr(VI) can inhibit the root elongation of pakchoi. The EC(50) values of the test elements were 2.02 mg/L and 195.8 mg/kg, 62.2 mg/L and 1,773 mg/kg, and 6.88 mg/L and 8.08 mg/kg in solution and soil, respectively. Toxic unit (TU) was introduced to determine the outcome in combined tests, and different behaviors were observed in both solution and soil. The coexistence of Cu and Cr(III) in solution exhibited an antagonistic effect (EC(50mix) = 1.76 TU(mix)), whereas a synergistic effect was observed in soil (EC(50mix) = 0.76 TU(mix)). In contrast, combined Cu-Cr(VI) showed a less than additive toxicity both in solution and soil, with EC(50mix) values of 3.31 and 1.24 TU(mix). In conclusion, the coexistence of toxicity in Cu-Cr(III) and Cu-Cr(VI) differs from the toxicity exhibited individually by Cu, Cr(III), and Cr(VI). Heavy metal interaction also changes depending on the medium.

Removal, accumulation and resistance to chromium in heterotrophic Euglena gracilis

The removal, uptake and toxicity of chromium in Euglena gracilis cultured in absence and presence of malate with Cr(VI) or Cr(III) was evaluated. The malate extrusion and the extra- and intracellular Cr(VI) reduction capacity were determined and the contents of molecules with thiol group and ascorbate were also evaluated. Absence of malate in the medium decreased cell growth, increased Cr(III) toxicity, induced faster Cr(VI) disappearance from medium, and increased intracellular and intramitochondrial chromium accumulation. Both chromium species induced soluble and particulate ascorbate-dependent chromate reductase activities. Cells also secreted large amounts of malate and increased intracellular contents of thiol-molecules to bind extracellular and intracellular Cr(III), respectively. The former process was supported by significant increase in malate-producing enzyme activities and the assessment of the Cr-complexes indicated the in situ formation with thiol-molecules. The present results establish new paradigms regarding chromium stress on algae-like microorganisms: (i) Cr(III) may be more toxic than Cr(VI), depending on the culture (or environmental) conditions; (ii) several simultaneous mechanisms are turned on to inactivate chromium species and their toxic effects. These mechanisms, now well understood may further optimize, by genetically modifying E. gracilis, and facilitate the development of strategies for using this protist as potential bio-remediator of chromium-polluted water systems.

Lead, chromium and manganese removal by in vitro root cultures of two aquatic macrophytes species: Typha latifolia L. and Scirpus americanus pers

The ability of in vitro roots cultures of Typha latifolia and Scirpus americanus to remove metals was studied. Roots were cultivated on Murashige-Skoog medium with 15 microg L(-1) Cr 11, 60 microg L(-1) Pb II or 1.8 mg L(-1) Mn II. Adsorbed metal to root surface was removed by washing with 0.042% HNO3. T. latifolia roots were able to uptake 68.8 microg Pb g(-1), 22.1 microg Cr g(-1) and 1680 microg Mn g(-1), while the S. americanus roots removed 148.3 microg Pb g(-1), 40.7 microg Cr g(-1) and 4037 microg Mn g(-1). About 80-90% of Pb and Cr were absorbed in both cultures. On the contrary, the Mn removal was due mainly to an adsorption process (82-86%). In comparison to the T. latifolia cultures, S. americanus cultures were twofold more efficient to remove Pb and Cr, and threefold more efficient to remove Mn. Both plant species capture metals in the following order: Cr >Pb >Mn. This investigation confirms that in vitro roots cultures could be an alternative as a phytoremediation approach for contaminated water with heavy metals.

Toxic effects of Cr(VI) and Cr(III) on energy metabolism of heterotrophic Euglena gracilis

To assess the toxic effect of Cr on energy metabolism, heterotrophic Euglena gracilis was grown in a medium that prompts high yield biomass and in the presence of different Cr(VI) or Cr(III) concentrations. The cell growth IC₅₀ value was 12 and >250μM for Cr(VI) and Cr(III), respectively; in these cells chromium was accumulated and a fraction compartmentalized into mitochondria, and synthesis of cysteine and glutathione was induced. Respiration of control isolated mitochondria was strongly inhibited by added Cr(VI) or Cr(III) with L-lactate or succinate as substrates. In turn, cellular and mitochondrial respiration, respiratory Complexes I, III and IV, glycolysis and cytosolic NAD(+)-alcohol and -lactate dehydrogenases from cells cultured with Cr(VI) were significantly lower than control, whereas AOX and external NADH dehydrogenase activities were unaltered or increased, respectively. Addition of Cr(VI) or Cr(III) to isolated mitochondria or cytosol from control- or Cr(VI)-grown cells induced inhibition of respiration, respiratory Complexes III, IV and AOX, and glycolytic pyruvate kinase; whereas Complex I, external NADH dehydrogenase, and other glycolytic enzymes were unaffected. Protein contents of mitochondrial Complexes I, III, IV and V, and ANT were diminished in Cr(VI)-grown cells. Decreased respiration and glycolysis induced by Cr(VI) resulted in lower cellular ATP content. Results suggested that Cr(VI) cytotoxicity altered gene expression (as widely documented) and hence enzyme content, and induced oxidative stress, but it was also related with direct enzyme inhibition; Cr(III) was also cytotoxic although at higher concentrations. These findings establish new paradigms for chromium toxicity: Cr(VI) direct enzyme inhibition and non-innocuous external Cr(III) toxicity.

Combined effects of Cu, Cd, Pb, and Zn on the growth and uptake of consortium of Cu-resistant Penicillium sp. A1 and Cd-resistant Fusarium sp. A19

Microorganisms can be important biosorbents for heavy metal remediation of contaminated soils and wastewaters. With different types and concentrations of heavy metals, strains display different resistance and removal abilities to the heavy metals. The objective of this study was to investigate the effects of single and multiple heavy metals on the growth and uptake of consortium of two types of fungal strains, Penicillium sp. A1 and Fusarium sp. A19. These fungal strains were tested to be tolerant to several heavy metals. A1, A19, and their combination (A1+A19) were inoculated on potato dextrose agar (PDA), Czapek Dox agar (CDA), and potato dextrose broth (PDB) containing Cu(2+), Cd(2+), Pb(2+), and Zn(2+). Experimental results showed that the combined inoculation of A1 and A19 had profound effects on the growth of the two fungi in PDA and CDA under the treatments with Cu(2+) and mixed Cd(2+)+Zn(2+). The amount of metals through bioaccumulation by A1, A19, and A1+A19 was significantly higher than that through biosorption by these fungi. The highest amount of Cd, Cu, and Zn accumulated by fungal biomass was obtained in the presence of Cd(2+)+Cu(2+)+Zn(2+) in PDB. Compared with the individual A1 or A19 used in PDB, A1+A19 accumulated higher amount of Cu and Pb in the presence of Cd(2+)+Cu(2+)+Pb(2+) and higher amount of Pb in the presence of Cd(2+)+Cu(2+)+Zn(2+)+Pb(2+). Our results indicated that there was no simple relationship between the metal biosorption by fungal biomass and the fungal metal tolerance. The biomass of A1+A19 cultivated in PDB absorbed higher amount of metals than A1 or A19 in the presence of single metals and their combinations. The results suggested that the applicability of growing fungi tolerant to heavy metals provided a potential biotechnology for treatment of wastewaters with heavy metal pollutions.

Removal and accumulation of cadmium and lead by Typha latifolia exposed to single and mixed metal solutions

We investigated the effect of Cd and Pb on the growth of the aquatic macrophyte Typha latifolia; the removal from the solution and the accumulation of these elements by the plant were also studied. Thus, small plants of T. latifolia, collected from a noncontaminated site, were exposed for 10 days to Cd and Pb, in a single solution or in mixture solutions, at two concentrations of the metals (5 and 7.5 mg/L). Our results showed that T. latifolia removed effectively Cd and Pb from solutions and was able to accumulate these metals in the roots and, to a lesser extent, in the leaves. Our findings suggested a synergistic effect of Cd and Pb with respect to the toxicity to T. latifolia. Additionally, Cd diminished the Pb absorption by T. latifolia. Our results confirmed, using scanning electron microscopy, the internalization of Cd and Pb in T. latifolia.

The Pb-hyperaccumulator aquatic fern Salvinia minima Baker, responds to Pb(2+) by increasing phytochelatins via changes in SmPCS expression and in phytochelatin synthase activity

The relationship between accumulation of Pb(2+) and the activation of chelation and metal sequestration mechanisms mediated by phytochelatins (PC) was analyzed in the Pb(2+) hyperaccumulator aquatic fern Salvinia minima, after exposure to 40microM Pb(NO(3))(2). The tissue accumulation pattern of lead and the phytochelatin biosynthesis responses were analyzed in both, S. minima submerged root-like modified fronds (here named "roots"), and in its aerial leaf-like fronds ("leaves"). S. minima roots accumulated a significantly higher concentrations of Pb(+2) than leaves did. Accumulation of Pb(2+) in roots was bi-phasic with a first uptake phase reached after 3h exposure and a second higher uptake phase reached after 24h exposure. In leaves, a single delayed, smaller uptake phase was attained only after 9h of exposure. In roots lead accumulation correlated with an increased phytochelatin synthase (PCS) activity and an enhanced PC production. A higher proportion of polymerized PC(4) was observed in both tissues of exposed S. minima plants relative to unexposed ones, although a higher concentration of PC(4) was found in roots than in leaves. PCS activity and Pb(2+) accumulation was also higher in roots than in leaves. The expression levels of the S. minima PCS gene (SmPCS), in response to Pb(2+) treatment, were also evaluated. In S. minima leaves, the accumulation of Pb(2+) correlated with a marked increase in expression of SmPCS, suggesting a transcriptional regulation in the PCS activation and PC accumulation in this S. minima tissue. However, in roots, the basal expression of SmPCS was down-regulated after Pb(2+) treatment. This fact did not correlate with the later but strong increase in both, PCS activity and PC production; suggesting that the PC biosynthesis activation in S. minima roots occurs only by post-translational activation of PCS. Taken together, our data suggest that the accumulation of PC in S. minima is a direct response to Pb(2+) accumulation, and phytochelatins do participate as one of the mechanism to cope with Pb(2+) of this Pb-hyperaccumulator aquatic fern.

Enhanced alternative oxidase and antioxidant enzymes under Cd2+ stress in Euglena

To identify some of the mechanisms involved in the high resistance to Cd(2+) in the protist Euglena gracilis, we studied the effect of Cd(2+) exposure on its energy and oxidative stress metabolism as well as on essential heavy metals homeostasis. In E. gracilis heterotrophic cells, as in other organisms, CdCl(2) (50 microM) induced diminution in cell growth, severe oxidative stress accompanied by increased antioxidant enzyme activity and strong perturbation of the heavy metal homeostasis. However, Cd(2+) exposure did not substantially modify the cellular respiratory rate or ATP intracellular level, although the activities of respiratory complexes III and IV were strongly decreased. In contrast, an enhanced capacity of the alternative oxidase (AOX) in both intact cells and isolated mitochondria was determined under Cd(2+) stress; in fact, AOX activity accounted for 69-91% of total respiration. Western blotting also revealed an increased AOX content in mitochondria from Cd(2+)-exposed cells. Moreover, AOX was more resistant to Cd(2+) inhibition than cytochrome c oxidase in mitochondria from control and Cd(2+)-exposed cells. Therefore, an enhanced AOX seems to be a relevant component of the resistance mechanism developed by E. gracilis against Cd(2+)-stress, in addition to the usual increased antioxidant enzyme activity, that enabled cells to maintain a relatively unaltered the energy status.

Molecular mechanisms of resistance to heavy metals in the protist Euglena gracilis

The biochemical mechanisms of resistance to several heavy metals, which are associated with their accumulation (binding by high-affinity chelating molecules such as thiol-compounds together with their compartmentalization into organelles), are analyzed for the photosynthetic, free-living protist Euglena gracilis. The complete understanding of these mechanisms may facilitate the rational design of strategies for bioremediation of heavy metal polluted water and soil systems.