Aurora Neagoe

Calcium signaling mediates the response to cadmium toxicity in Saccharomyces cerevisiae cells

The involvement of Ca2+ in the response to high Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Hg2+ was investigated in Saccharomyces cerevisiae. The yeast cells responded through a sharp increase in cytosolic Ca2+ when exposed to Cd2+, and to a lesser extent to Cu2+, but not to Mn2+, Co2+, Ni2+, Zn2+, or Hg2+. The response to high Cd2+ depended mainly on external Ca2+ (transported through the Cch1p/Mid1p channel) but also on vacuolar Ca2+ (released into the cytosol through the Yvc1p channel). The adaptation to high Cd2+ was influenced by perturbations in Ca2+ homeostasis. Thus, the tolerance to Cd2+ often correlated with sharp Cd2+‐induced cytosolic Ca2+ pulses, while the Cd2+ sensitivity was accompanied by the incapacity to rapidly restore the low cytosolic Ca2+.

Bioprospecting at former mining sites across Europe: microbial and functional diversity in soils

The planetary importance of microbial function requires urgently that our knowledge and our exploitation ability is extended, therefore every occasion of bioprospecting is welcome. In this work, bioprospecting is presented from the perspective of the UMBRELLA project, whose main goal was to develop an integral approach for remediation of soil influenced by mining activity, by using microorganisms in association with plants. Accordingly, this work relies on the cultivable fraction of microbial biodiversity, native to six mining sites across Europe, different for geographical, climatic and geochemical characteristics but similar for suffering from chronic stress. The comparative analysis of the soil functional diversity, resulting from the metabolic profiling at community level (BIOLOG ECOPlates) and confirmed by the multivariate analysis, separates the six soils in two clusters, identifying soils characterised by low functional diversity and low metabolic activity. The microbial biodiversity falls into four major bacterial phyla: Actinobacteria, Proteobacteria, Firmicutes and Bacteroidetes, including a total of 47 genera and 99 species. In each soil, despite harsh conditions, metabolic capacity of nitrogen fixation and plant growth promotion were quite widespread, and most of the strains showed multiple resistances to heavy metals. At species-level, Shannon’s index (alpha diversity) and Sørensens Similarity (beta diversity) indicates the sites are indeed diverse. Multivariate analysis of soil chemical factors and biodiversity identifies for each soil well-discriminating chemical factors and species, supporting the assumption that cultured biodiversity from the six mining sites presents, at phylum level, a convergence correlated to soil factors rather than to geographical factors while, at species level, reflects a remarkable local characterisation.

The Role of Organic Matter in the Mobility of Metals in Contaminated Catchments

We have applied a concept framework for scale-specific processes in order to characterize the role of the organic matter in the mobility of metals. At very small scale, we identified roles by immobilization of metals (immobilization in litter, immobilization in soil aggregates, dissolved organic carbon chelates in fine pores), by mobilization of metals (organochemical weathering, soluble chelates, organocolloids, free enzymatic degradation of immobile organic carbon), and by supporting the mobilization or immobilization of metals by other compartments at the same scale (energy source for microorganisms, buffering of soil solution). These roles have effects on the fluxes of metals and can be characterized at a larger scale: transfer of metals to plants and to lower soil layers by hydrological fluxes. At scales ranging from contaminated sites to watershed, we identified the same roles as above, that however up-scaled differently as a function of the site type (contaminated soil in the slope area, mining dump or tailing dam, contaminated soil in the floodplain, contaminated stream ecotone), with corresponding effects on the fluxes of metals subsoil and groundwater to surface water, on the transfer to surface water by lateral types of flows, transfer to floodplains, and volatilization (also differentiated as a function of the type of site). The literature is comprehensively screened for each case. The extent and consistency of the available scientific knowledge decrease with the increase of the system scale and complexity. Based on this analysis, multiscale biogeochemical and ecotoxicological research directions are suggested.

Coupled pot and lysimeter experiments assessing plant performance in microbially assisted phytoremediation.

We performed an experiment at pot scale to assess the effect of plant growth-promoting bacteria (PGPB) on the development of five plant species grown on a tailing dam substrate. None of the species even germinated on inoculated unamended tailing material, prompting use of compost amendment. The effect of inoculation on the amended material was to increase soil respiration, and promote elements immobilisation at plant root surface. This was associated with a decrease in the concentrations of elements in the leaching water and an increase of plant biomass, statistically significant in the case of two species: Agrostis capillaris and Festuca rubra. The experiment was repeated at lysimeter scale with the species showing the best development at pot scale, A. capillaris, and the significant total biomass increase as a result of inoculation was confirmed. The patterns of element distribution in plants also changed (the concentrations of metals in the roots of A. capillaris and F. rubra significantly decreased in inoculated treatments, while phosphorus concentration significantly increased in roots of A. capillaris in inoculated treatment at lysimeter scale). Measured variables for plant oxidative stress did not change after inoculations. There were differences of A. capillaris plant–soil system response between experimental scales as a result of different substrate column structure and plant age at the sampling moment. Soil respiration was significantly larger at lysimeter scale than at pot scale. Leachate concentrations of As, Mn and Ni had significantly larger concentrations at lysimeter scale than at pot scale, while Zn concentrations were significantly smaller. Concentrations of several metals were significantly smaller in A. capillaris at lysimeter scale than at pot scale. From an applied perspective, a system A. capillaris—compost—PGPB selected from the rhizosphere of the tailing dam native plants can be an option for the phytostabilisation of tailing dams. Results should be confirmed by investigation at field plot scale.

Overexpression of the PHO84 gene causes heavy metal accumulation and induces Ire1p-dependent unfolded protein response in Saccharomyces cerevisiae cells

Pho84p, the protein responsible for the high-affinity uptake and transport of inorganic phosphate across the plasma membrane, is also involved in the low-affinity uptake of heavy metals in the Saccharomyces cerevisiae cells. In the present study, the effect of PHO84 overexpression upon the heavy metal accumulation by yeast cells was investigated. As PHO84 overexpression triggered the Ire1p-dependent unfolded protein response, abundant plasma membrane Pho84p could be achieved only in ire1Δ cells. Under environmental surplus, PHO84 overexpression augmented the metal accumulation by the wild type, accumulation that was exacerbated by the IRE1 deletion. The pmr1Δ cells, lacking the gene that encodes the P-type ATPase ion pump that transports Ca2+ and Mn2+ into the Golgi, hyperaccumulated Mn2+ even from normal medium when overexpressing PHO84, a phenotype which is rather restricted to metal-hyperaccumulating plants.

Vaccinium corymbosum L. (blueberry) extracts exhibit protective action against cadmium toxicity in Saccharomyces cerevisiae cells.

Blueberries (Vaccinium corymbosum L.) are a rich source of antioxidants and their consumption is believed to contribute to food-related protection against oxidative stress. In the present study, the chemoprotective action of blueberry extracts against cadmium toxicity was investigated using a cadmium-hypersensitive strain of Saccharomyces cerevisiae. Four varieties of blueberries were used in the study, and it was found that the extracts with high content of total anthocyanidins exhibited significant protective effect against the toxicity of cadmium and H2O2. Both the blueberry extracts and pure cyanidin exhibited protective effects against cadmium in a dose-dependent manner, but without significantly interfering with the cadmium accumulation by the yeast cells. The results imply that the blueberry extracts might be a potentially valuable food supplement for individuals exposed to high cadmium.

Plant growth promotion by inoculation with selected bacterial strains versus mineral soil supplements

In the process of remediation of mine sites, the establishment of a vegetation cover is one of the most important tasks. This study tests two different approaches to manipulate soil properties in order to facilitate plant growth. Mine waste from Ingurtosu, Sardinia, Italy rich in silt, clay, and heavy metals like Cd, Cu, and Zn was used in a series of greenhouse experiments. Bacteria with putative beneficial properties for plant growth were isolated from this substrate, propagated and consortia of ten strains were used to inoculate the substrate. Alternatively, sand and volcanic clay were added. On these treated and untreated soils, seeds of Helianthus annuus, of the native Euphorbia pithyusa, and of the grasses Agrostis capillaris, Deschampsia flexuosa and Festuca rubra were germinated, and the growth of the seedlings was monitored. The added bacteria established well under all experimental conditions and reduced the extractability of most metals. In association with H. annuus, E. pithyusa and D. flexuosa bacteria improved microbial activity and functional diversity of the original soil. Their effect on plant growth, however, was ambiguous and usually negative. The addition of sand and volcanic clay, on the other hand, had a positive effect on all plant species except E. pithyusa. Especially the grasses experienced a significant benefit. The effects of a double treatment with both bacteria and sand and volcanic clay were rather negative. It is concluded that the addition of mechanical support has great potential to boost revegetation of mining sites though it is comparatively expensive. The possibilities offered by the inoculation of bacteria, on the other hand, appear rather limited.

Environmental metal contamination and health impact assessment in two industrial regions of Romania

We investigated two Romanian industrial regions- Copşa Mică and Zlatna, to assess the current situation of soil pollution and bioaccumulation of Pb, Cd, Cu and Zn in different vegetable species and possible risks to consumers. Both total and mobile forms of the metals were determined in soil samples, and metal content in the edible parts of root vegetable samples was also assessed. The concentrations of Pb and Zn in soil were higher in Copşa Mică than in Zlatna (566mg/kg vs 271mg/kg for Pb and 1143mg/kg vs 368mg/kg for Zn)·The metal mobility in soil from Copsa Mica decreases in the order Zn>Cu>Cd>Pb (1.88mg/kg, 0.40mg/kg, 0.22mg/kg, 0.16mg/kg, respectively), while in Zlatna, the order was Cu>Zn>Pb>Cd (0.88mg/kg, 0.29mg/kg, 0.04mg/kg, 0.01mg/kg, respectively), apparently depending on metal and soil conditions. In Copsa Mica, the amount of Pb and Cd in vegetable samples exceeded the maximum permissible limits in carrots (median concentration 0.32mg/kg for Pb and Cd) and in yellow onions (median concentration 0.24mg/kg for Cd). In Zlatna region, the content of Cd exceeded the maximum limits in yellow onions (median concentration 0.11mg/kg). The amount of Pb was higher than the maximum acceptable level in carrots from the Zlatna region (median concentration 0.12mg/kg). Cu and Zn levels were within the normal range in all vegetable samples. In the Zlatna region, the transfer factors for Pb and Cd were higher in carrots (median values of 9.9 for Pb and 21.0 for Cd) compared to carrots harvested in Copsa Mica (median values of 4.0 for Pb and 2.0 for Cd). Daily intake rates of metals through local vegetable consumption exceeded the limit values established by the European Food Safety Authority for Pb (1.2 to 2.4 times) and Cd (5.5 to 9.1 times) in both regions, with potential adverse health effects for the local population. The results highlight the need for total soil remediation action before fruit and vegetables produced in these polluted areas can be safely consumed.

A Conceptual Framework for Up-Scaling Ecological Processes and Application to Ectomycorrhizal Fungi

After reviewing the limits of the current approaches, we introduce an analytical framework for up-scaling analyses of ecological processes. The framework attempts to produce a conceptual unification and leads to a ten-step approach for up-scaling from a source to a target scale. The literature on ectomycorrhizal fungi is then screened following each up-scaling step. We conclude that one needs to construct four (pseudo) hierarchical levels in order to understand the ecological role of ectomycorrhizal fungi in the ecological productivity of ecosystems (scale of 104-105 m2) and one more level, if one is interested in evolutionary processes such as gene flow or speciation. The modularization scales for understanding the role of ectomycorrhizal fungi are those applicable to bacteria (10-6-10-4 m2), fungi (functional dynamic modules occupying surfaces of tenths of m2, and a tree plot of 400–900m2), epigeous fungivorous invertebrates and mammals (104-106 m2), and, for speciation, to small catchments of several hundreds of km2. The analyses showed that the source for up-scaling has to be a plot of 400–900m2. This plot has an associated homomorphic model with a maximum number of nine functional dynamic modules for the structural and functional modeling of ectomycorrhizal communities. Only one modeling step is needed for up-scaling from the source scale (plot) to the ecosystem scale, but the model’s construction involves the previous construction of several up- and down-scaling models in order to quantify the effects of smaller- and larger scale organisms on fungi. The existing knowledge limits the up-scaling of processes, especially with respect to the available mathematical models, which in turn are limited by the data required.

Heavy metal accumulation by Saccharomyces cerevisiae cells armed with metal binding hexapeptides targeted to the inner face of the plasma membrane

Accumulation of heavy metals without developing toxicity symptoms is a phenotype restricted to a small group of plants called hyperaccumulators, whose metal-related characteristics suggested the high potential in biotechnologies such as bioremediation and bioextraction. In an attempt to extrapolate the heavy metal hyperaccumulating phenotype to yeast, we obtained Saccharomyces cerevisiae cells armed with non-natural metal-binding hexapeptides targeted to the inner face of the plasma membrane, expected to sequester the metal ions once they penetrated the cell. We describe the construction of S. cerevisiae strains overexpressing metal-binding hexapeptides (MeBHxP) fused to the carboxy-terminus of a myristoylated green fluorescent protein (myrGFP). Three non-toxic myrGFP-MeBHxP (myrGFP-H6, myrGFP-C6, and myrGFP-(DE)3) were investigated against an array of heavy metals in terms of their effect on S. cerevisiae growth, heavy metal (hyper) accumulation, and capacity to remove heavy metal from contaminated environments.