Citrate-coated cobalt ferrite nanoparticles for the nano-enabled biofortification of wheat.

A pot experiment was conducted in an open greenhouse to explore the use of citrate-coated cobalt ferrite nanoparticles (CoFe2O4 NPs) as a source for Fe fortification of three wheat lines (Triticum aestivum L.). Two of the three wheat lines tested differ in their efficiency concerning Zn storage in their grains (efficient and inefficient), and one had inefficient P-absorption. The NPs were supplied by foliar or soil application of Fe at 330 mg L-1, and 46 or 68 mg kg-1 soil, respectively. A positive control (Fe-EDTA salt, a conventional iron fertilizer) and a negative control (no fertilization) were also included to compare the efficiency of NP fertilization. Soil fertilization with NPs improved the grain yield and Fe concentration in the grains compared with the foliar application of NPs and conventional Fe fertilizer. Application of soil NPs at 68 mg kg-1 increased the grain yield by 52% and 21% compared with the control and soil Fe-EDTA treatments, respectively. Likewise, grain Fe concentration increased by 96% and 72% compared with the control and soil Fe-EDTA treatments, respectively. The phytic acid concentration in grains and the phytic acid:Fe ratio decreased by 6% and 62%, respectively, due to the soil application of NPs (68 mg Fe per kg). The Fe grain concentration of lines inefficient for Zn storage and P-uptake in plants from soil fertilized with NPs (68 mg Fe per kg) was 1.37 and 0.26 fold above the target biofortification concentration (60 mg Fe per kg). Cobalt concentration in grains ranged from 9 to 16 mg kg-1. These concentrations were below the maximum allowable limit of Co in grains (50 mg kg-1) recommended by FAO and the WHO. Our results showed that Fe supplied as NPs may improve the nutritional quality of wheat grains, and the economic yield. However, there remains a long way to go to achieve effective and economic use of nanotechnology for the nutritional development of wheat.

Bioaccessibility of potentially toxic elements in mine residue particles.

Mining companies used to abandon tailing heaps in countryside regions of Mexico and other countries. Mine residues (MRs) contain a high concentration of potentially toxic elements (PTE). The wind can disperse dust particles (<100 µm) and once suspended in the atmosphere, can be ingested or inhaled; this is a common situation in arid climates. Nowadays, there is little information on the risk of exposure to PTEs from particulate matter dispersed by wind. The pseudo-total PTE in bulk and fractionated MR after aqua regia digestion, the inhalable bioaccessibility with Gamble solution (pH = 7.4), and the gastric bioaccessibility with 0.4 M glycine solution at pH 1.5 were determined. As and Pb chemical species were identified by X-ray absorption near-edge structure (XANES) spectroscopy. The highest rate of dispersion was observed with 74-100 µm particles (104 mg m-2 s-1); in contrast, particles <44 µm had the lowest rate (26 mg m-2 s-1). The highest pseudo-total As (35 961 mg kg-1), Pb (3326 mg kg-1), Cd (44 mg kg-1) and Zn (up to 4678 mg kg-1) concentration was in the <20 µm particles and As in the 50-74 µm (40 236 mg kg-1) particles. The highest concentration of inhaled bioaccessible As (343 mg kg-1) was observed in the <20 µm fraction and the gastric bioaccessible As was 744 mg kg-1, Pb was 1396 mg kg-1, Cd was 19.2 mg kg-1, and Zn was 2048 mg kg-1. The predominant chemical As species was arsenopyrite (92%), while 54% of Pb was in the adsorbed form. Erodible particle matter is a potential risk for humans in case of inhalation or ingestion.

Afforestation may influence changes in tailing heaps in a long time.

A soil and plant survey was carried out in a tailing heap afforested 30 years ago to gain information about the changes in the tailing and metal uptake by plants. A poor development of Technosol was found. It was observed accumulation of OM spatio temporarily. Metal concentrations in the soil profile varied between plots. Extractable Pb concentrations ranged from 0.4 to 2.9%; extractable Cd varied 9.7-46% of the total concentration. PCA analysis shows DTPA-Zn and DTPA-Cu, Na, K, and OM have the widest concentrations range between soil layers. Casuarina equisetifolia and Pennisetum clandestinum formed a pristine uniform litter layer, whereas Eucalyptus camaldulensis did not form a litter layer. Casuarina equisetifolia has a higher population density (756 p ha-1) compared to Populus nigra (528 p ha-1) and E. camaldulensis (621 p ha-1). Pennisetum clandestinum grew successfully and covered the tailing, but Cd and Pb concentrations were above the domestic animal toxicity limits, 0.5 and 10 mg kg-1, respectively. Populus nigra absorbed more Zn than Casuarina equisetifolia and Eucalyptus camaldulensis. Trees species did not accumulate high foliar Cu and Zn concentrations, but Pb (47.7-124.3 mg kg-1) and Cd (5.7-26.8 mg kg-1) concentrations are over those reported for mature leaf tissues. HighlightsPennisetum clandestinum formed soil cover on remediated plots.Casuarina equisetifolia was efficient in forming a litter soil horizon.Trasdescantia fluminensis accumulated Pb.Populus nigra accumulated Zn and Cd from the tailing heap.

Phytoremediation assisted by mycorrhizal fungi of a Mexican defunct lead-acid battery recycling site.

A field experiment was conducted during 15 months to study the effects of four arbuscular mycorrhizal fungi (AMF) on the growth of Ricinus communis accession SF7. Plants were established on amended soil (vermicompost:sawdust:soil 1:1:1) severely polluted by lead-acid batteries (LAB) located at Mexico State, Mexico. Plants inoculated with Acaulospora sp., Funneliformis mosseae and Gigaspora gigantea had 100% survival in comparison to non-inoculated plants (57%). These same AMF enhanced palmitic and linoleic acids content in seeds of R. communis. Acaulospora sp. modified rhizosphere soil pH and decreased 3.5 folds Pb foliar concentrations while F. mosseae BEG25 decreased three times Pb soil availability in comparison to non-inoculated plants. Spatial changes in Pb soil availability were observed at the end of this research. No fungal effect on P, Ca, Cu foliar concentrations, soluble sugars, proline, chlorophyll or on the activity of two oxidative stress enzymes was observed. Mycorrhizal colonization from the inoculated fungi was between 40% and 60%, while colonization by native fungi was between 16% and 22%. A similar percentage of foliar total phenolic compounds was observed in non-mycorrhizal plants and those inoculated with G. gigantea and Acaulospora sp. This is the first research reporting effects of AMF on R. communis (castor bean) shrubs when grown on a LAB recycling site suggesting the use of Acaulospora sp. and F. mosseae BEG25 in phytostabilization to ameliorate Pb pollution and decreasing its ecological risk.

Leaf Epiphytic Bacteria of Plants Colonizing Mine Residues: Possible Exploitation for Remediation of Air Pollutants.

Plant surfaces are known as an important sink for various air pollutants, including particulate matter and its associated potentially toxic elements (PTE). Moreover, leaves surface or phylloplane is a habitat that harbors diverse bacterial communities (epiphytic). However, little is known about their possible functions during phytoremediation of air pollutants like PTE. The study of leaf epiphytic bacteria of plants colonizing mine residues (MR) containing PTE is thus a key to understand and exploit plant-epiphytic bacteria interactions for air phytoremediation purposes. In this research, we aimed (i) to characterize the functions of epiphytic bacteria isolated from the phylloplane of Brickellia veronicifolia, Flaveria trinervia, Gnaphalium sp., and Allionia choisyi growing spontaneously on multi-PTE contaminated MR and (ii) to compare these against the same plant species in a non-polluted control site (NC). Concentrations (mg kg-1) of PTE on MR leaf surfaces of A. choisyi reached up to 232 for Pb, 13 for Cd, 2,728 for As, 52 for Sb, 123 for Cu in F. trinervia, and 269 for Zn in Gnaphalium sp. In the four plant species, the amount of colony-forming units per cm2 was superior in MR leaves than in NC ones, being A. choisyi the plant species with the highest value. Moreover, the proportion of isolates tolerant to PTE (Zn, Cu, Cd, and Sb), UV light, and drought was higher in MR leaves than in those in NC. Strain BA15, isolated from MR B. veronicifolia, tolerated 150 mg Zn L-1, 30 mg Sb L-1, 25 mg Cu L-1; 80 mg Pb L-1, and was able to grow after 12 h of continuous exposition to UV light and 8 weeks of drought. Plant growth promotion related traits [N fixation, indole acetic acid (IAA) production, and phosphate solubilization] of bacterial isolates varied among plant species isolates and between MR and NC sampling condition. The studied epiphytic isolates possess functions interesting for phytoremediation of air pollutants. The results of this research may contribute to the development of novel and more efficient inoculants for microbe-assisted phytoremediation applied to improve air quality in areas exposed to the dispersion of metal mine tailings.

Microscopic characterization of orchid mycorrhizal fungi: Scleroderma as a putative novel orchid mycorrhizal fungus of Vanilla in different crop systems.

Vanilla is an orchid of economic importance widely cultivated in tropical regions and native to Mexico. We sampled three species of Vanilla (V. planifolia, V. pompona, and V. insignis) in different crop systems. We studied the effect of crop system on the abundance, type of fungi, and quality of pelotons found in the roots using light and electron microscopy and direct sequencing of mycorrhizal structures. Fungi were identified directly from pelotons obtained from terrestrial roots of vanilla plants in the flowering stage. Root samples were collected from plants in crop systems located in the Totonacapan area in Mexico (states of Puebla and Veracruz). DNA was extracted directly from 40 pelotons and amplified using ITS rRNA sequencing. Peloton-like structures were observed, presenting a combination of active pelotons characterized by abundant hyphal coils and pelotons in various stages of degradation. The most active pelotons were observed in crop systems throughout living tutors (host tree) in comparison with roots collected from dead or artificial tutors. Fungi identified directly from pelotons included Scleroderma areolatum, a common ectomycorrhizal fungus that has not been reported as a mycorrhizal symbiont in orchids. Direct amplification of pelotons also yielded common plant pathogens, including Fusarium and Pyrenophora seminiperda, especially in those sites with low colonization rates, and where large numbers of degraded pelotons were observed. This research reports for the first time the potential colonization of Vanilla by Scleroderma, as a putative orchid mycorrhizal symbiont in four sites in Mexico and the influence of crop system on mycorrhizal colonization on this orchid.

Jatropha curcas and assisted phytoremediation of a mine tailing with biochar and a mycorrhizal fungus.

Soil pollution is an important ecological problem worldwide. Phytoremediation is an environmental-friendly option for reducing metal pollution. A greenhouse experiment was conducted to determine the growth and physiological response, metal uptake, and the phytostabilization potential of a nontoxic Jatropha curcas L. genotype when grown in multimetal-polluted conditions. Plants were established on a mine residue (MR) amended or not amended with corn biochar (B) and inoculated or not inoculated with the mycorrhizal fungus Acaulospora sp. (arbuscular mycorrhizal fungus, AMF). J. curcas was highly capable of growing in an MR and showed no phytotoxic symptoms. After J. curcas growth (105 days), B produced high desorption of Cd and Pb from the MR; however, no increases in metal shoot concentrations were observed. Therefore, Jatropha may be useful for phytostabilization of metals in mine tailings. The use of B is recommended because improved MR chemical properties conduced to plant growth (cation-exchange capacity, organic matter content, essential nutrients, electrical conductivity, water-holding capacity) and plant growth development (higher biomass, nutritional and physiological performance). Inoculation with an AMF did not improve any plant growth or physiological plant characteristic. Only higher Zn shoot concentration was observed, but it was not phytotoxic. Future studies of B use and its long-term effect on MR remediation should be conducted under field conditions.

Riparian plants on mine runoff in Zimapan, Hidalgo, Mexico: Useful for phytoremediation?

Dispersion and runoff of mine tailings have serious implications for human and ecosystem health in the surroundings of mines. Water, soils and plants were sampled in transects perpendicular to the Santiago stream in Zimapan, Hidalgo, which receives runoff sediments from two acidic and one alkaline mine tailing. Concentrations of potentially toxic elements (PTE) were measured in water, soils (rhizosphere and non-rhizosphere) and plants. Using diethylenetriaminepentaacetic acid (DTPA) extractable concentrations of Cu, Zn, Ni, Cd and Pb in rhizosphere soil, the bioconcentration and translocation factors were calculated. Ruderal annuals formed the principal element of the herbaceous vegetation. Accumulation was the most frequent strategy to deal with high concentrations of Zn, Cu, Ni, Cd and Pb. The order of concentration in plant tissue was Zn>Pb>Cu>Ni>Cd. Most plants contained concentrations of PTE considered as phytotoxic and behaved as metal tolerant species. Rorippa nasturtium-aquaticum accumulated particularly high concentrations of Cu. Parietaria pensylvanica and Commelina diffusa, common tropical weeds, behaved as Zn hyperaccumulators and should be studied further.

Inhibition of microorganisms involved in deterioration of an archaeological site by silver nanoparticles produced by a green synthesis method.

The Citadel, part of the pre-Hispanic city of Teotihuacan and listed as a World Heritage Site, harbors irreplaceable archaeological walls and murals. This city was abandoned by the 7th century and its potential deterioration represents a noteworthy loss of the world's cultural heritage. This research consisted of isolation and identification of bacteria and fungi contributing to this deterioration from walls of a pre-Hispanic city. In addition, silver nanoparticles (AgNP) produced, using a green synthesis method, were tested as potential inhibitors of microbes. AgNP of different sizes and concentrations were tested using in situ assays. Leaf aqueous extracts from two plants species (Foeniculum vulgare and Tecoma stans) and two extraction procedures were used in the NP synthesis. The potential of AgNP as preventive/corrective treatments to protect stucco materials from biodeterioration, as well as the microbial inhibition on three stone materials (stucco, basalt and calcite) was analyzed. Twenty-three bacterial species belonging to eight genera and fourteen fungal species belonging to seven genera were isolated from colored stains, patinas and biofilms produced on the surfaces of archaeological walls from the pre-Hispanic city, Teotihuacan. AgNP from F. vulgare were more effective for in vitro microbial growth inhibition than those from T. stans. Bacteria were less sensitive to AgNP than fungi; however, sensitivity mainly depended on the microbial strain and the plant extract used to prepare AgNP. The use of AgNP as a preventive or corrective treatment to decrease microbial colonization in three kinds of stone used in historical walls was successful. Calcite was more colonized by Alternaria alternata, but less by Pectobacterium carotovorum. This is the first study at different scales (in vitro and tests on different stone types) of inhibition of biodeterioration-causing microorganisms isolated from an archaeological site by green synthesized AgNP.

Localization and speciation of arsenic in Glomus intraradices by synchrotron radiation spectroscopic analysis.

The protective mechanisms employed by arbuscular mycorrhizal fungi (AMF) to reduce the toxic effects of arsenic on host plants remain partially unknown. The goal of this research was identifying the in situ localization and speciation of arsenic (As) in the AM fungus Rhizophagus intraradices [formerly named Glomus intraradices] exposed to arsenate [As(V)]. By using a two-compartment in vitro fungal cultures of R. intraradices-transformed carrot roots, microspectroscopic X-ray fluorescence (µ-XRF), and microspectroscopic X-ray absorption near edge structure (µ-XANES), we observed that As(V) is absorbed after 1 h in the hyphae of AMF. Three hours after exposure a decrease in the concentration of As was noticed and after 24 and 72 h no detectable As concentrations were perceived suggesting that As taken up was pumped out from the hyphae. No As was detected within the roots or hyphae in the root compartment zone three or 45 h after exposure. This suggests a dual protective mechanism to the plant by rapidly excluding As from the fungus and preventing As translocation to the plant root. µ-XANES data showed that gradual As(V) reduction occurred in the AM hyphae between 1 and 3 h after arsenic exposure and was completed after 6 h. Principal component analysis (PCA) and linear combination fitting (LCF) of µ-XANES data showed that the dominant species after reduction of As(V) by R. intraradices extra-radical hyphal was As(III) complexed with a reduced iron(II) carbonate compound. The second most abundant As species present was As(V)-iron hydroxides. The remaining As(III) compounds identified by the LCF analyses suggested these molecules were made of reduced As and S. These results increase our knowledge on the mechanism of As transport in AMF and validate our hypotheses that R. intraradices directly participates in arsenic detoxification. These fungal mechanisms may help AMF colonized plants to increase their tolerance to As at contaminated sites.

Potential of castor bean (Ricinus communis L.) for phytoremediation of mine tailings and oil production.

Bioenergy production combined with phytoremediation has been suggested to help in solving two critical world problems: the gradual reduction of fossil fuels and soil contamination. The aim of this research was to investigate the potential for the use of Ricinus communis L. (castor oil plant) as an energy crop and plant species to remediate metal-polluted sites. This study was performed in mine tailings containing high concentrations of Cu, Zn, Mn, Pb and Cd. Physico-chemical characterization, total, DTPA-extractable and water-soluble metals in rhizospheric tailings heap samples were carried. Metal concentrations in plant tissues and translocation factors (TFs) were also determined. The Ricinus seed-oil content was high between 41 and 64%, seeds from San Francisco site 6 had the highest oil content, while these from site 7 had the lowest. No trend between oil yield vs seed origin site was observed. Seed-oil content was negatively correlated with root concentration of Cu, Zn, Pb and Cd, but no correlation was observed with the extractable-metals. According to its shoot metal concentrations and TFs, castor bean is not a metal accumulator plant. This primary colonizing plant is well suited to cope with the local toxic conditions and can be useful for the stabilization of these residues, and for then decreasing metal bioavailability, dispersion and human health risks on these barren tailings heaps and in the surrounding area. Our work is the first report regarding combined oil production and a phytostabilization role for Ricinus plants in metal mine tailings and may give a new value to suitable metal-polluted areas.

Tolerance to and accumulation of cadmium by the mycelium of the fungi Scleroderma citrinum and Pisolithus tinctorius.

The behavior of ectomycorrhizal (ECM) fungi on exposure to cadmium dependent upon isolation remains a poorly understood phenomenon. The in vitro growth, tolerance, and accumulation of Cd were studied in three strains of ECM fungi exposed to six Cd concentrations (0-10 mg L(-1)). The fungi studied were a strain of Scleroderma citrinum Persoon (Sc) isolated from a tailings heap containing 5 mg kg(-1) available Cd, and two strains of Pisolithus tinctorius (Pers.) Coker and Couch from unpolluted sites (Pt1 and Pt2), both common ECM fungi used for remediation. The growth kinetic (36 days) of Sc was not affected by Cd concentration. By contrast, the ED(50) in Pt1 and Pt2 occurred at 4.8 and 6.9 mg L(-1) of Cd, respectively. The biomass of the three fungi exposed to the highest Cd concentration (10 mg L(-1)) was significantly different. Sc presented the highest biomass, while this was strongly reduced for Pt1 and Pt2. The tolerance index for Sc ranged from 78% to 95% at all Cd concentrations tested, while for Pt1 it was 49% and 31%, and for Pt2 it was 62% and 35% at 5 and 10 mg of Cd L(-1), respectively. The mycelium of both Pt strains accumulated more Cd than the Sc mycelium. At the highest Cd concentration, Pt1 and Pt2 accumulated 1.9 and 1.7 times more Cd than Sc. This study suggests that regardless of the differences in tolerance to Cd by the three ECM fungi, they could have biotechnological applications for soil remediation. However, Sc has greater possibilities of being used successfully when high concentrations of Cd prevail in the environment.

Arsenate induces the expression of fungal genes involved in As transport in arbuscular mycorrhiza.

We utilized the two-compartment system to study the effect of arsenic (As) on the expression of the Glomus intraradices high-affinity phosphate transporter GiPT, and the GiArsA gene, a novel protein with a possible putative role as part of an arsenite efflux pump and similar to ArsA ATPase. Our results show that induction of GiPT expression correlates with As(V) uptake in the extra-radical mycelium of G. intraradices. We showed a time-concerted induction of transcript levels first of GiPT, followed by GiArsA, as well as the location of gene expression using laser microdissection of these two genes not only in the extra-radical mycelium but also in arbuscules. This work represents the first report showing the dissection of the molecular players involved in arbuscular mycorrhizal fungus (AMF)-mediated As tolerance in plants, and suggests that tolerance mediated by AMF may be caused by an As exclusion mechanism, where fungal structures such as the extra-radical mycelium and arbuscules may be playing an important role. Our results extend knowledge of the mechanisms underlying As efflux in arbuscular mycorrhizal fungi and mechanisms related to As tolerance.

Plant and fungal biodiversity from metal mine wastes under remediation at Zimapan, Hidalgo, Mexico.

Plant establishment, presence of arbuscular mycorrhizal fungi (AMF) and other rhizospheric fungi were studied in mine wastes from Zimapan, Hidalgo state, Mexico, using a holistic approach. Two long-term afforested and three non-afforested mine tailings were included in this research. Fifty-six plant species belonging to 29 families were successfully established on the afforested sites, while unmanaged tailings had only a few native plant species colonizing the surrounding soils. Almost all plant roots collected were associated to AMF in these sites. The genus Glomus was the most abundant AMF species found in their rhizosphere; however, the Acaulospora genus was also observed. Other rhizospheric fungi were identified by 18S rDNA sequencing analysis. Their role in these substrates, i.e. biocontrol, pollutant- and organic matter-degradation, and aides that increase plant metal tolerance is discussed. Our results advance the understanding of fungal diversity in sites polluted with metals and present alternative plants for remediation use.