Vicia villosa Roth: a cover crop to phytoremediate arsenic polluted environments

Vicia villosa Roth is a legume species with a growing application in Argentina as a cover crop (CC), a practice that favors the sustainable development of agricultural systems. However, several areas where the use of this CC provides numerous advantages are affected by high concentrations of arsenic (As). Thus, in the present work we studied hairy vetch ability to cope with arsenate [As(V)], arsenite [As(III)], and the mixture of both along with oxidative stress indexes [chlorophyll content, malondialdehyde (MDA) equivalents] as well as anatomical and histological changes in the root structure. The results obtained suggested a different behavior of hairy vetch depending on its growth stage and on metal(oid) concentration. The roots treated with the contaminant showed less turgidity, thickening of the epidermal and subepidermal parenchymal outer layers, and the presence of dark deposits. The morpho-anatomic parameters (cortex length, vascular cylinder diameter, total diameter, and vascular cylinder area) were altered in plants treated with As(V) and As(V)/As(III) whereas the roots of plants treated with As(III) did not show significant differences respect to the control. Moreover V. villosa could tolerate and remove As from soil, thus the use of this legume species seems an attractive approach to remediate As while protecting contaminated soils.

Vicia: a green bridge to clean up polluted environments

Vicia species, commonly known as vetches, include legume plants which nowadays can be found in many countries around the world. Their use to improve soil health and productivity is crucial in management schemes that make sustainable agriculture possible, but they can also play a part in the phytoremediation of polluted environments. Furthermore, they harbor a large community of rhizospheric microorganisms, such as biodegradative bacteria and plant growth-promoting rhizobacteria, which can help to increase phytoremediation efficiency. Their mutualistic association with Rhizobium sp. has also been proposed as an attractive bioremediation tool. Thus, Vicia species could make a remarkable difference in the ecological restoration of polluted soils, thanks to their dual role as cover crops and phytoremediator plants. This mini-review discusses recent advances in the use of Vicia. Challenges and opportunities connect with the application of these species will also be revised, as well as aspects that remain to be explored.

Effect of arsenic on tolerance mechanisms of two plant growth-promoting bacteria used as biological inoculants

Bacterial ability to colonize the rhizosphere of plants in arsenic (As) contaminated soils is highly important for symbiotic and free-living plant growth-promoting rhizobacteria (PGPR) used as inoculants, since they can contribute to enhance plant As tolerance and limit metalloid uptake by plants. The aim of this work was to study the effect of As on growth, exopolysaccharide (EPS) production, biofilm formation and motility of two strains used as soybean inoculants, Bradyrhizobium japonicum E109 and Azospirillum brasilense Az39. The metabolism of arsenate (As(V)) and arsenite (As(III)) and their removal and/or possible accumulation were also evaluated. The behavior of both bacteria under As treatment was compared and discussed in relation to their potential for colonizing plant rhizosphere with high content of the metalloid. B. japonicum E109 growth was reduced with As(III) concentration from 10 μM while A. brasilense Az39 showed a reduction of growth with As(III) from 500 μM. EPS and biofilm production increased significantly under 25 μM As(III) for both strains. Moreover, this was more notorious for Azospirillum under 500 μM As(III), where motility was seriously affected. Both bacterial strains showed a similar ability to reduce As(V). However, Azospirillum was able to oxidize more As(III) (around 53%) than Bradyrhizobium (17%). In addition, both strains accumulated As in cell biomass. The behavior of Azospirillum under As treatments suggests that this strain would be able to colonize efficiently As contaminated soils. In this way, inoculation with A. brasilense Az39 would positively contribute to promoting growth of different plant species under As treatment.

Chromium (VI) remediation by a native strain: effect of environmental conditions and removal mechanisms involved

A native bacterial strain with high capability for Cr (VI) removal was isolated from tannery sediments located in Elena (Córdoba Province, Argentina). The strain was characterized by amplification of 16S rRNA gene and identified as Serratia sp. C8. It was able to efficiently remove different Cr (VI) concentrations in a wide range of pHs and temperatures. The addition of different carbon sources as well as initial inoculum concentration were analyzed, demonstrating that Serratia sp. C8 could reduce 80 % of 20 mg/L Cr (VI) in a medium containing glucose 1 g/L, at pH 6-7 and 28 °C as optimal conditions, using 5 % inoculum concentration. The mechanisms involved in Cr (VI) removal were also evaluated. The strain was capable of biosorpting around 7.5-8.5 % of 20 mg/L Cr on its cell surface and to reduce Cr (VI). In addition, approximately a 54 and 46 % of total Cr was detected in the biomass and in the culture medium, respectively, and in the culture medium, Cr (III) was the predominant species. In conclusion, Serratia sp. C8 removed Cr (VI) and the mechanisms involved in decreasing order of contribution were as follows: reduction catalyzed by intracellular enzymes, accumulation into the cells, and biosorption to the microbial biomass. This strain could be a suitable microorganism for Cr (VI) bioremediation of tannery sediments and effluents or even for other environments contaminated with Cr.

Use of hairy roots extracts for 2,4-DCP removal and toxicity evaluation by Lactuca sativa test

2,4-Dichlorophenol (2,4-DCP) is widely distributed in wastewaters discharged from several industries, and it is considered as a priority pollutant due to its high toxicity. In this study, the use of different peroxidase extracts for 2,4-DCP removal from aqueous solutions was investigated. Tobacco hairy roots (HRs), wild-type (WT), and double-transgenic (DT) for tomato basic peroxidases (TPX1 and TPX2) were used to obtain different peroxidase extracts: total peroxidases (TPx), soluble peroxidases (SPx), and peroxidases ionically bound to the cell wall (IBPx). All extracts derived from DT HRs exhibited higher peroxidase activity than those obtained from WT HRs. TPx and IBPx DT extracts showed the highest catalytic efficiency values. The optimal conditions for 2,4-DCP oxidation were pH 6.5, H2O2 0.5 mM, and 200 U mL(-1) of enzyme, for all extracts analyzed. Although both TPx extracts were able to oxidize different 2,4-DCP concentrations, the removal efficiency was higher for TPx DT. Polyethylene glycol addition slightly improved 2,4-DCP removal efficiency, and it showed some protective effect on TPx WT after 2,4-DCP oxidation. In addition, using Lactuca sativa test, a reduction of the toxicity of post removal solutions was observed, for both TPx extracts. The results demonstrate that TPx extracts from both tobacco HRs appear to be promising candidate for future applications in removing 2,4-DCP from wastewaters. This is particularly true considering that these peroxidase sources are associated with low costs and are readily available. However, TPx DT has increased peroxidase activity, catalytic efficiency, and higher removal efficiency than TPx WT, probably due to the expression of TPX1 and TPX2 isoenzymes.

Phytoremediation of 2,4-dichlorophenol using wild type and transgenic tobacco plants

INTRODUCTION

Transgenic plant strategies based on peroxidase expression or overexpression would be useful for phenolic compound removal since these enzymes play an important role in phenolic polymerizing reactions.

MATERIAL AND METHODS

Thus, double transgenic (DT) plants for basic peroxidases were obtained and characterized in order to compare the tolerance and efficiency for 2,4-dichlorophenol (2,4-DCP) removal with WT and simple transgenic plants expressing TPX1 or TPX2 gene. Several DT plants showed the expression of both transgenes and proteins, as well as increased peroxidase activity.

RESULTS

DT lines showed higher tolerance to 2,4-DCP at early stage of development since their germination index was higher than that of WT seedlings exposed to 25 mg/L of the pollutant. High 2,4-DCP removal efficiencies were found for WT tobacco plants. TPX1 transgenic plants and DT (line d) reached slightly higher removal efficiencies for 10 mg/L of 2,4-DCP than WT plants, while DT plants (line A) showed the highest removal efficiencies (98%). These plants showed an increase of 21% and 14% in 2,4-DCP removal efficiency for solutions containing 10 and 25 mg/L 2,4-DCP, respectively, compared with WT plants. In addition, an almost complete toxicity reduction of postremoval solutions using WT and DT plants was obtained through AMPHITOX test, which indicates that the 2,4-DCP degradation products would be similar for both plants.

CONCLUSION

These results are relevant in the field of phytoremediation application and, moreover, they highlight the safety of using DT tobacco plants because nontoxic products were formed after an efficient 2,4-DCP removal.

Phytoremediation of phenol using Vicia sativa L. plants and its antioxidative response

Common vetch (Vicia sativa L.) is a legume species with an extensive agricultural use. However, the phytoremediation potentiality of this species has not been sufficiently explored because little is known about its resistance to inorganic and organic pollutants. In the present work, phenol tolerance of common vetch was assayed at different stages of growth. Germination index and germination rate decreased only at high phenol concentrations (250 and 500 mg L(-1)), whereas 30-day-old plants were able to tolerate this pollutant, with high removal efficiencies. The activities of antioxidative enzymes, such as peroxidase (POD) and ascorbate peroxidase, increased significantly with the highest phenol concentration, whereas superoxide dismutase activity, malondialdehyde, and H(2)O(2) levels remained unaltered. Besides, an increase in two basic isoforms of POD was observed in plants treated with phenol. The results suggested that common vetch has an efficient protection mechanism against phenol-induced oxidative damage. Moreover, it could tolerate and remove high phenol concentrations, avoiding serious phytotoxic effects. Thus, V. sativa could be considered an interesting tool in the field of phytoremediation.

Antioxidant response of tobacco (Nicotiana tabacum) hairy roots after phenol treatment

Phenol is released to the environment from a wide variety of industrial effluents and it causes severe problems to human health and ecosystem. In the present study, we determined that Nicotiana tabacum hairy roots (HRs) double transgenic (DT) for two peroxidase genes (tpx1 and tpx2) showed higher phenol removal efficiency than wild type (WT) HRs after 120 h of phenol treatment at the expense of endogenous H(2)O(2). Besides, to determine whether phenol could induce oxidative stress on tobacco HRs, we analyzed the antioxidant response, superoxide anion (O(2)(-)) localization and malondialdehyde (MDA) levels. Both HRs treated with phenol, showed significant increases in peroxidase (PX) activity mainly at the end of the assay (120 h) being PX activity from transgenic HRs 40% higher than that of WT HRs. Superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities showed significant increases from 24 to 120 h of phenol treatment. PX, SOD and APX isoforms were also analyzed and slight changes were observed only in PX patterns. Both HRs showed significant differences in total glutathione (TGSH) content during treatment, being higher in DT HRs than in WT HRs. At the end of the assay, a greater accumulation of O(2)(-) in different root zones was observed in WT and DT HRs. Moreover, phenol was able to increase the MDA levels in WT HRs from 48 to 120 h of the treatment, but no significant changes were observed in DT HRs. Results suggest that under these experimental conditions, DT HRs would be more tolerant to phenol than WT HRs.

Phenol tolerance, changes of antioxidative enzymes and cellular damage in transgenic tobacco hairy roots colonized by arbuscular mycorrhizal fungi

Phytoremediation has been recognized as a cheap and eco-friendly technology which could be used for the remediation of organic pollutants, such as phenolic compounds. Besides, the extent to which plants react to environmental pollution might depend on rhizosphere processes such as mycorrhizal symbiosis. In the present work, phenol tolerance of transgenic tobacco hairy roots (HR), namely TPX1, colonized with an arbuscular mycorrhizal fungus (AMF) was studied. However, the question is whether AMF symbiosis can moderate adverse effects of phenol to the plant tissues. Thus, the antioxidative response as well as parameters of oxidative damage, like malondialdehyde (MDA) content, were determined. Antioxidative enzymes such as peroxidase, superoxide dismutase, ascorbate peroxidase were higher in TPX1 HR colonized with AMF, compared to wild type HR colonized by AMF, in the presence of increasing concentrations of the pollutant. Besides, MDA levels remained unaltered in TPX1 HR associated with AMF treated with the xenobiotic. These results, suggested that this culture could tolerate phenol and moreover, it has an efficient protective mechanism against phenol-induced oxidative damage, which is of great importance in the selection of species with remediation capacities. Thus, transgenic HR colonized with AMF could be considered as an interesting model system to study different processes which play a key role in the phytoremediation of organic pollutants.

Scale up of 2,4-dichlorophenol removal from aqueous solutions using Brassica napus hairy roots

Chlorophenols are harmful pollutants, frequently found in the effluents of several industries. For this reason, many environmental friendly technologies are being explored for their removal from industrial wastewaters. The aim of the present work was to study the scale up of 2,4-dichlorophenol (2,4-DCP) removal from synthetic wastewater, using Brassica napus hairy roots and H(2)O(2) in a discontinuous stirred tank reactor. We have analyzed some operational conditions, because the scale up of such process was poorly studied. High removal efficiencies were obtained (98%) in a short time (30 min). When roots were re-used for six consecutive cycles, 2,4-DCP removal efficiency decreased from 98 to 86%, in the last cycle. After the removal process, the solutions obtained from the reactor were assessed for their toxicity using an acute test with Lactuca sativa L. seeds. Results suggested that the treated solution was less toxic than the parent solution, because neither inhibition of lettuce germination nor effects in root and hypocotyl lengths were observed. Therefore, we provide evidence that Brassica napus hairy roots could be effectively used to detoxify solutions containing 2,4-DCP and they have considerable potential for a large scale removal of this pollutant. Thus, this study could help to design a method for continuous and safe treatment of effluents containing chlorophenols.

Removal of 2,4-diclorophenol from aqueous solutions using tobacco hairy root cultures

2,4-Dichlorophenol (2,4-DCP) is harmful for aquatic life and human health, so many attempts have focused on removing it through innocuous technologies. Hairy roots (HR) represent an interesting plant system to study the process and to remove efficiently this compound. In the present work, tobacco HR clones were obtained and one of them was selected for 2,4-DCP phytoremediation assays. These cultures removed 2,4-DCP in short time and with high efficiency (98%, 88% and 83%) for solutions initially containing 250, 500 and 1000 mg/L, respectively. Removal process was mainly associated with peroxidase activity. The highest efficiency for 2,4-DCP (500 mg/L) removal was reached at 60 min and using 10 mM H(2)O(2). Moreover, HR could be re-used, almost for three consecutive cycles. The diminution of pH and the increase of chloride ions in post-removal solutions suggested that 2,4-DCP dehalogenation was mediated by peroxidases. Moreover, changes in deposition pattern of lignin in HR exposed to 2,4-DCP suggested that cell walls of xylem and phloem elements would be the site of deposition of some products formed and they would be a lignin-type polymer. These findings contribute to understand 2,4-DCP removal process with tobacco HR and it might have implications in the use of this system for decontamination of polluted waters.

Establishment of transgenic tobacco hairy roots expressing basic peroxidases and its application for phenol removal

Transgenic hairy root (HR) systems constitute an interesting alternative to improve the efficiency of phytoremediation process. Since peroxidases (Px) have been associated with phenolic compounds removal, in the present work, transgenic tobacco HR, which expressed basic Px genes from tomato (tpx1 and tpx2), were established and assayed for phenol removal. Tobacco HR clones were obtained, including those transgenic for TPX1 or TPX2, those double transgenic (DT) for both Px and the corresponding controls. Based on growth index, the presence of rol C sequence, tpx1 and/or tpx2 genes and the coded proteins, as well as Px activity determinations, we selected 10 tobacco HR clones for phenol removal assays. The removal efficiencies were high for all the HR, although, some transgenic HR showed significantly higher removal efficiencies compared with controls. The results demonstrate that TPX1 is involved in phenol removal not only when it was overexpressed in tomato, but also when it was expressed in other plant, such as tobacco. The higher efficiency of TPX2 transgenic HR showed that this Px also participates in the process. The contribution of other mechanisms (adsorption, H2O2 independent enzymatic processes) could be considered depreciable, which establishes the great implication of Px in phenol removal.

Application of Brassica napus hairy root cultures for phenol removal from aqueous solutions

Phenolic compounds present in the drainage from several industries are harmful pollutants and represent a potential danger to human health. In this work we have studied the removal of phenol from water using Brassica napus hairy roots as a source of enzymes, such as peroxidases, which were able to oxidise phenol. These hairy roots were investigated for their tolerance to highly toxic concentrations of phenol and for the involvement of their peroxidase isoenzymes in the removal of phenol. Roots grew normally in medium containing phenol in concentrations not exceeding 100 mg l(-1), without the addition of H(2)O(2). However, roots were able to remove phenol concentrations up to 500 mg l(-1), in the presence of H(2)O(2), reaching high removal efficiency, within 1h of treatment and over a wide range of pH (4-9). Hairy roots could be re-used, at least, for three to four consecutive cycles. Peroxidase activity gradually decreased to approximately 20% of the control, at the fifth cycle. Basic and near neutral isoenzymes (BNP) decreased along time of recycling while acidic isoenzymes (AP) remained without changes. Although both group of isoenzymes would be involved in phenol removal, AP showed higher affinity and catalytic efficiency for phenol as substrate than BNP. In addition, AP retained more activity than BNP after phenol treatment. Thus, AP appears to be a promising isoenzyme for phenol removal and for application in continuous treatments. Furthermore, enzyme isolation might not be necessary and the entire hairy roots, might constitute less expensive enzymatic systems for decontamination processes.

Changes in ligno-suberization of cell walls of tomato hairy roots produced by salt treatment: the relationship with the release of a basic peroxidase

A highly basic peroxidase isoenzyme was shown to be released to the culture medium of tomato (Lycopersicon esculentum) hairy roots grown in Murashige-Skoog (MS) liquid medium when it was supplemented with 100 mM NaCl. In this paper we demonstrate that this enzyme is ionically bound to cell walls and that the release was a consequence of the continuous agitation of the tissue in a high ionic strength medium with salt addition. In order to establish the physiological role of this isoenzyme we partially purified it, and we analysed its kinetic properties as coniferyl alcohol peroxidase. The peroxidase isoenzyme showed a high catalytic efficiency for this substrate, which suggests that it would be associated with the ligno-suberization process. To confirm the involvement of this isoenzyme in that process, we studied the pattern of ligno-suberization of the tissue under different conditions of growth. Our results suggest that this basic peroxidase would be indeed involved in ligno-suberization since its leakage from cell walls, induced by 100 mM NaCl in liquid MS, caused less ligno-suberization of exo and endodermis. On the contrary, more ligno-suberization was seen in cell walls when the hairy roots were grown in a salt-supplemented MS solid medium without contact with it, a condition in which the release of the isoenzyme would be avoided. Thus, through the changes produced by the release of the enzyme from its site of action, we could demonstrate the physiological role of this peroxidase in the processing of root cell walls, being part of control mechanisms of ion and water fluxes through the root.

A tomato peroxidase involved in the synthesis of lignin and suberin

The last step in the synthesis of lignin and suberin has been proposed to be catalyzed by peroxidases, although other proteins may also be involved. To determine which peroxidases are involved in the synthesis of lignin and suberin, five peroxidases from tomato (Lycopersicon esculentum) roots, representing the majority of the peroxidase activity in this organ, have been partially purified and characterized kinetically. The purified peroxidases with isoelectric point (pI) values of 3.6 and 9.6 showed the highest catalytic efficiency when the substrate used was syringaldazine, an analog of lignin monomer. Using a combination of transgenic expression and antibody recognition, we now show that the peroxidase pI 9.6 is probably encoded by TPX1, a tomato peroxidase gene we have previously isolated. In situ RNA hybridization revealed that TPX1 expression is restricted to cells undergoing synthesis of lignin and suberin. Salt stress has been reported to induce the synthesis of lignin and/or suberin. This stress applied to tomato caused changes in the expression pattern of TPX1 and induced the TPX1 protein. We propose that the TPX1 product is involved in the synthesis of lignin and suberin.

Improved germination under osmotic stress of tobacco plants overexpressing a cell wall peroxidase

The cell wall is a fundamental component in the response of plants to environmental changes. To directly assess the role of the cell wall we have increased the expression and activity of a cell wall associated peroxidase (TPX2), an enzyme involved in modifying cell wall architecture. Overexpression of TPX2 had no effect on wild-type development, but greatly increased the germination rate under high salt or osmotic stress. Differential scanning calorimetry showed that transgenic seeds were able to retain more water available for germination than wild-type seeds. Thermoporometry calculations indicated that this could be due to a lower mean pore size in the walls of transgenic seeds. Therefore, the higher capacity of transgenic seeds in retaining water could result in higher germination rates in conditions where the availability of water is restricted.

[The value of immunological assays in the diagnosis of meningeal histoplasmosis]

INTRODUCTION

Between 1985 and 1995, 3,860 cerebrospinal fluid (CSF) samples from patients with mycotic meningitis were analyzed.

METHODS

Direct examination, cultures, complement fixation (CF) and immunodiffusion (ID) with Histoplasma capsulatum were carried out.

RESULTS

Seventy four samples from 31 patients (three of them with AIDS) were reactive at the immunological assays. Cultures were positive in five patients. In 26 patients the clinical diagnosis together with positive CSF assays gave indirect evidence of meningeal histoplasmosis. ID and CF reactivity were 93.5% and 100% respectively. For 23 patients who had simultaneous examination of blood and CSF the double positivity was 78.2%.

CONCLUSIONS

Because of the direct isolation of Histoplasma capsulatum is a difficult one, the diagnosis of subacute or chronic meningeal histoplasmosis may be confirmed by indirect immunological assays.

Expression of a highly basic peroxidase gene in NaCl-adapted tomato cell suspensions

A tomato peroxidase gene, TPX2, that is only weakly expressed in the roots of young tomato seedlings is highly expressed in tomato suspension cells adapted to high external NaCl concentration. The protein encoded by this gene, with an isolectric point value of approximately 9.6, is found in the culture medium of the growing cells. Our data suggest that the expression of TPX2 in the salt-adapted cells is not the result of the elicitation imposed by the in vitro culture or the presence of high NaCl concentration in the medium.

Induction of a tomato peroxidase gene in vascular tissue

Expression of a tomato peroxidase gene that is constitutively expressed only in roots was induced in stems and leaves as a result of mechanical wounding. However, wound-induction of TPX1 transcript accumulation in leaves was limited to the mid-rib. No TPX1 transcript was detected in the lamina of the leaf after wounding. Peroxidase isozyme studies indicated the presence of a unique basic isoform in stems after wounding.