Lipid signaling and proline catabolism are activated in barley roots (Hordeum vulgare L.) during recovery from cold stress

Previous findings have shown that phospholipase D (PLD) contributes to the response to long-term chilling stress in barley by regulating the balance of proline (Pro) levels. Although Pro accumulation is one of the most prominent changes in barley roots exposed to this kind of stress, the regulation of its metabolism during recovery from stress remains unclear. Research has mostly focused on the responses to stress per se, and not much is known about the dynamics and mechanisms underlying the subsequent recovery. The present study aimed to evaluate how PLD, its product phosphatidic acid (PA), and diacylglycerol pyrophosphate (DGPP) modulate Pro accumulation in barley during recovery from long-term chilling stress. Pro metabolism involves different pathways and enzymes. The rate-limiting step is mediated by pyrroline-5-carboxylate synthetase (P5CS) in its biosynthesis, and by proline dehydrogenase (ProDH) in its catabolism. We observed that Pro levels decreased in recovering barley roots due to an increase in ProDH activity. The addition of 1-butanol, a PLD inhibitor, reverted this effect and altered the relative gene expression of ProDH. When barley tissues were treated with PA before recovery, the fresh weight of roots increased and ProDH activity was stimulated. These data contribute to our understanding of how acidic membrane phospholipids like PA help to control Pro degradation during recovery from stress.

Biohybrid Adsorbent for the Preconcentration of Lead and Its Determination in Fruit Juices by Electrothermal Atomic Absorption Spectrometry

BACKGROUND

Fruit juices are one of the most non-alcoholic beverages consumed in the world. Essential elements and other nutrients present in fruit juices play an important role in human well-being. However, fruit juices may also contain potentially toxic elements at trace levels, causing health risks.

OBJECTIVE

The objective of this work was to develop an analytical methodology based on the preconcentration of lead using a new biodegradable hybrid material (BHM) composed of Rhodococcus erythropolis AW3 bacteria and Brassica napus hairy roots.

METHODS

The BHM was implemented in an online solid-phase extraction (SPE) system for the determination of lead in fruit juices by electrothermal atomic absorption spectrometry (ETAAS).

RESULTS

Effects of critical parameters on lead retention were studied. Under optimal experimental conditions, extraction efficiency higher than 99.9% and an enrichment factor of 62.5 were achieved. The dynamic capacity of the BHM was 36 mg/g, which favored the reuse of the column for at least eight biosorption-desorption cycles. The LOD and LOQ for preconcentration of 5 mL of sample were 5.0 and 16.5 ng/L lead, respectively. The RSD was 4.8% (at 1 µg/L lead and n = 10).

CONCLUSION

The developed method was suitable for application to lead determination in different types of fruit juice.

HIGHLIGHTS

A novel microextraction procedure based on the use of a biohybrid adsorbent. Highly sensitive determination of Pb at trace levels. Analysis of Pb in fruit juices samples. An eco-friendly microextraction technique for Pb determination.

Proteomic analysis to unravel the biochemical mechanisms triggered by Bacillus toyonensis SFC 500-1E under chromium(VI) and phenol stress

Bacillus toyonensis SFC 500-1E is a member of the consortium SFC 500-1 able to remove Cr(VI) and simultaneously tolerate high phenol concentrations. In order to elucidate mechanisms utilized by this strain during the bioremediation process, the differential expression pattern of proteins was analyzed when it grew with or without Cr(VI) (10 mg/L) and Cr(VI) + phenol (10 and 300 mg/L), through two complementary proteomic approaches: gel-based (Gel-LC) and gel-free (shotgun) nanoUHPLC-ESI-MS/MS. A total of 400 differentially expressed proteins were identified, out of which 152 proteins were down-regulated under Cr(VI) and 205 up-regulated in the presence of Cr(VI) + phenol, suggesting the extra effort made by the strain to adapt itself and keep growing when phenol was also added. The major metabolic pathways affected include carbohydrate and energetic metabolism, followed by lipid and amino acid metabolism. Particularly interesting were also ABC transporters and the iron-siderophore transporter as well as transcriptional regulators that can bind metals. Stress-associated global response involving the expression of thioredoxins, SOS response, and chaperones appears to be crucial for the survival of this strain under treatment with both contaminants. This research not only provided a deeper understanding of B. toyonensis SFC 500-1E metabolic role in Cr(VI) and phenol bioremediation process but also allowed us to complete an overview of the consortium SFC 500-1 behavior. This may contribute to an improvement in its use as a bioremediation strategy and also provides a baseline for further research.

Functional response of Acinetobacter guillouiae SFC 500-1A to tannery wastewater as revealed by a complementary proteomic approach

Acinetobacter guillouiae SFC 500-1 A is a promising candidate for the bioremediation of tannery wastewater. In this study, we applied shotgun proteomic technology in conjunction with a gel-based assay (Gel-LC) to explore the strain's intracellular protein profile when grown in tannery wastewater as opposed to normal culture conditions. A total of 1775 proteins were identified, 52 of which were unique to the tannery wastewater treatment. Many of them were connected to the degradation of aromatic compounds and siderophore biosynthesis. On the other hand, 1598 proteins overlapped both conditions but were differentially expressed in each. Those that were upregulated in wastewater (109) were involved in the processes mentioned above, as well as in oxidative stress mitigation and intracellular redox state regulation. Particularly interesting were the downregulated proteins under the same treatment (318), which were diverse but mainly linked to the regulation of basic cellular functions (replication, transcription, translation, cell cycle, and wall biogenesis); metabolism (amino acids, lipids, sulphate, energetic processes); and other more complex responses (cell motility, exopolysaccharide production, biofilm formation, and quorum sensing). The findings suggest that SFC 500-1 A engages in survival and stress management strategies to cope with the toxic effects of tannery wastewater, and that such strategies may be mostly oriented at keeping metabolic processes to a minimum. Altogether, the results might be useful in the near future to improve the strain's effectiveness if it will be applied for bioremediation.

Promising co-inoculation strategies to reduce arsenic toxicity in soybean

Arsenic (As) is the cause for concern worldwide due to its high toxicity. Its presence in agricultural soils and groundwater adversely affects soybean (Glycine max L.) growth and yield and also endangers food safety. Plant growth-promoting rhizobacteria (PGPR) could be used as part of cost-effective and eco-friendly strategies to mitigate As phytotoxicity. However, simple inoculation of soybean with PGPR Bradyrhizobium japonicum E109 (E109), a common practice in Argentina, is not effective in counteracting the effects of As exposure. Our aim was to assess whether the response of soybean to arsenate (AsV) and arsenite (AsIII) could be helpfully modulated by co-inoculating E109 with the free-living PGPRs Azospirillum brasilense Cd (Cd) or Bacillus pumilus SF5 (SF5). Co-inoculation with E109 + SF5 alleviated As-induced depletion of chlorophyll a and b, and carotenoid content, reaching an increase of 26, 28 y 31%, respectively. It also enhanced nodulation (15-19%) under As exposure. E109 + Cd and E109 + SF5 induced changes in the antioxidant system, which could be related to the maintenance of redox homeostasis. Moreover, As accumulation was reduced by 53% in aerial parts of plants inoculated with E109 + Cd, and by 16% in the roots of those inoculated with E109 + SF5. The strains selected show interesting potential for the development of biotechnological schemes to improve soybean yield while guaranteeing safer food production.

Groundwater quality and vulnerability in farms from agricultural-dairy basin of the Argentine Pampas

Agricultural and livestock activities strongly influence groundwater quality and conditioning its use as water supply in rural areas. The aim was to determine the quality and suitability of the groundwater supply used in dairy farms of an agricultural area of Pampa plain of Córdoba (Argentina). Piper's diagram showed that the groundwater types were sodium bicarbonate, sodium bicarbonate-chloride, sodium chloride-sulfate, and sodium sulfate. Physicochemical parameters revealed that cations and anions showed a high and significant correlation in water samples, indicating a strong water-rock interaction. Nitrate (NO₃^-) content was significantly correlated with pH, water well depth, and distance from contamination sources. A high positive correlation between arsenic (As) and bicarbonate, sulfate, sodium, and chloride (p < 0.05) indicates a similar origin. Among the pesticides monitored, 2,4-D was detected in 25% of groundwater samples (0.4 to 0.8 µg/L) coinciding with the ordinary application practices. In general, most of the groundwater samples did not comply with national and international regulations for drinking water and dairy hygiene, due to the high content of As, NO₃^-, bacteria, and the presence of 2,4-D herbicide. However, the quality of water was suitable for livestock drink. The data obtained in this study contribute to a better understanding of the contamination processes taking place and improve the agricultural and livestock management for an efficient use of this resource by dairy farmers.

Tobacco hairy root's peroxidases are rhythmically controlled by phenol exposure

Plants like almost all living organisms, have developed a biological clock or circadian clock (CC) capable of synchronizing and adjusting various metabolic and physiological processes at certain times of the day and in a period of 24 h. This endogenous timekeeping is able to predict the environmental changes providing adaptive advantages against stressful conditions. Therefore, the aim of this work was to analyze the possible link between metabolism of xenobiotic compounds (MXC) and the CC. Synchronized Nicotiana tabacum hairy roots (HRs) were used as a validated plant model system, and peroxidases (PODs), key enzymes of the phase I in the MCX, were evaluated after phenol treatment. Two POD genes were selected and their temporal expression profiles as well as the total POD activity were analyzed in order to find circadian oscillations either under control conditions or phenol treatment. It was demonstrated that these PODs genes showed oscillatory profiles with an ultradian period (period length shorter than the circadian period), and preserving the same phases and expression peaks still under phenol treatment. The total PODs activity showed also a marked oscillatory behavior mainly in phenol-treated HRs with the highest levels at ZT23. Untreated HRs showed decrease and increase in the intensity of some basic isoforms at light and dark phase, respectively, while in phenol- treated HRs, an increase in the intensity of almost all isoforms was observed, mainly during the dark phase, being coincident with the high PODs activity detected at ZT23. The periodic analysis determined an ultradian period either in total POD activity or in the POD activity of isoform VI, being 18.7 and 15.3 h, respectively. Curiously, in phenol treated HRs, the period length of total POD activity was longer than in untreated HRs, suggesting that phenol could induce a marked oscillatory behavior in the POD activity with better performance during the dark phase, which explain the higher phenol removal efficiencies at ZT23. These findings showed novel information about the performance of PODs, which would be rhythmically controlled at biochemical level, by phenol exposure.

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.

Monitoring of Atrazine Pollution and its Spatial-Seasonal Variation on Surface Water Sources of an Agricultural River Basin

Surface water sources are greatly impacted in areas with major agricultural land use. The atrazine quantification in surface waters as well as the spatial-temporal patterns of this herbicide was studied to detect pollution hotspots and to understand the putative factors responsible of its occurrence at the Ctalamochita river basin. The samples were collected on the aeolian fluvial plain of the river basin during five consecutive years. The results showed the high ubiquity of this compound and several sites with hazardous concentration (exceeding 0.1 µg/L international guidelines). The frequencies of quantification range from 67 to 100% in spring and 33%-67% in autumn. The atrazine content in surface water increased during the warm-rainy season, as consequence of atrazine application events (coinciding to the prevalent crop type). Overall, the study highlights the factors that could have favored atrazine pollution in the river basin such as land use, transport by runoff processes and atmospheric deposition.

Application of two bioassays as potential indicators of phenol phytoremediation efficiency by tobacco hairy roots

Phenol is one of the contaminants most frequently found in the environment and it is considered a priority pollutant due to their toxic effects. Hairy roots (HR) constitute a good model tool for the removal of this contaminant. In this work, phenol removal using wild type (WT) and double transgenic (DT) Nicotiana tabacum HR was performed with high efficiency (60-80%, for 25-250 mg L-1 phenol solutions, respectively). After phytoremediation process, the toxicity of post removal solutions (PRS) was evaluated through two-toxicity test belonging to two trophic levels, Lactuca sativa test and Rhinella arenarum (AMPHITOX). Toxicity of PRS showed variable results since these solutions were less toxic to L. sativa seeds compared to R. arenarum embryos, which could be attributed to different sensitivities of the exposed organisms. Although PRS obtained using WT and DT HR reduced phenol phytotoxicity on L. sativa seeds, WT PRS were even less toxic than DT PRS according to this test. Regarding AMPHITOX, HR culture medium without phenol but incubated with HR and phenol PRS exerted a toxic effect on the embryos, which could be related to the presence of toxic products derived from HR metabolism. The results demonstrated that an efficient phenol removal is not always accompanied by a considerable reduction of the solution toxicity and therefore, the use of organisms from different trophic levels to evaluate the toxicity after the removal process gains importance.

Biohybrid membranes for effective bacterial vehiculation and simultaneous removal of hexavalent chromium (CrVI) and phenol

The aim of the present study was to obtain an effective vehiculation system in which bacterial agents could maintain viability improving their removal capacity. Herein, we present a novel biohybrid membrane of polymeric nanofibers and free-living bacteria for the simultaneous removal of pollutants. In this system, bacteria are free within the pores between the nanofibers and adsorbed to the surface of the membranes. Association between bacteria and the membranes was performed through a self-formulated medium, and the presence of the bacteria in the polymeric matrix was evidenced through atomic force microscopy (AFM). Biohybrid membranes associated with the remediation agents Bacillus toyonensis SFC 500-1E and Acinetobacter guillouiae SFC 500-1A promoted a reduction of up to 2.5 mg/L of hexavalent chromium and up to 200 mg/L of phenol after 24 h of treatment in synthetic medium containing the contaminants. Similarly, more than 46% of the hexavalent chromium and all of the phenol content were removed after treatment of a tannery effluent with initial concentrations of 7 mg/L of Cr(VI) and 305 mg/L of phenol. Counts of the remediation agents from the membranes were always above 1.10⁷ CFU/g, also in the reutilization assays performed without reinoculation. Biohybrid membranes were hydrolysis-resistant, reusable, and effective in the simultaneous removal of contaminants for more than 5 cycles. Viability of the microorganisms was maintained after long-term storage of the membranes at 4 °C, without the use of microbiological media or the addition of cryoprotectants. Graphical abstract KEY POINTS: • Polymeric membranes were effectively associated with the SFC 500-1 remediation consortium • Biohybrid membranes removed hexavalent chromium and phenol from different matrices • Removal of contaminants was achieved in many successive cycles without reinoculation.

Improving soybean growth under arsenic stress by inoculation with native arsenic-resistant bacteria

Certain metal (loid)-resistant bacteria that inhabit the rhizosphere have shown to improve plant growth and tolerance under toxic metal stress. In this study, we tested if six native, arsenic-resistant and plant growth promoting bacteria (PGPB) were able to enhance soybean (Glycine max L.) growth and modulate arsenic (As) uptake. As a previous work, we tested all single isolates and all possible binary combinations without arsenic stress to identify the combinations that would have the greatest plant growth promoting effect. In this study, a screening assay was performed with only five inoculation options selected after first stage (Pseudomonas sp. AW4, Pseudomonas sp. AW6, AW4+AW6, Rhodococcus sp. AW3+Pseudomonas sp. AW5 and Enterobacter sp. AW1+AW6). In both stages, inoculation was implemented by imbibition of soybean seeds with bacterial suspensions, and plant growth was carried out in pots using perlite as substrate in a chamber with controlled conditions. In the third stage, we performed similar assays, under As stress, using the three most promising inoculation options (AW4, AW6 and AW3+AW5). Treatments were performed by irrigation with 25 μM arsenite (As3+), 25 μM arsenate (As5+), 25 μM equimolar As3+/As5+ solution or water (control). Biometric and biochemical parameters indicated that inoculation with Pseudomonas sp. AW4 significantly promoted soybean growth under As3+/As5+ treatment and did not modified As accumulation pattern. Further field studies are needed to determine if some of these inoculation options are useful to improve in situ soybean growth under arsenic stress and could become a tool for the development of sustainable agriculture in As-impacted environments.

Impact assessment of bioaugmented tannery effluent discharge on the microbiota of water bodies

Effluents are commonly discharged into water bodies, and in order for the process to be as environmentally sound as possible, the potential effects on native water communities must be assessed alongside the quality parameters of the effluents themselves. In the present work, changes in the bacterial diversity of streamwater receiving a tannery effluent were monitored by high-throughput MiSeq sequencing. Physico-chemical and microbiological parameters and acute toxicity were also evaluated through different bioassays. After the discharge of treated effluents that had been either naturally attenuated or bioaugmented, bacterial diversity decreased immediately in the streamwater samples, as evidenced by the over-representation of taxa such as Brachymonas, Arcobacter, Marinobacterium, Myroides, Paludibacter and Acinetobacter, typically found in tannery effluents. However, there were no remarkable changes in diversity over time (after 1 day). In terms of the physico-chemical and microbiological parameters analyzed, chemical oxygen demand and total bacterial count increased in response to discharge of the treated effluents. No lethal effects were observed in Lactuca sativa L. seeds or Rhinella arenarum embryos exposed to the streamwater that had received the treated effluents. All of these results contribute to the growing knowledge about the environmental safety of effluent discharge procedures.

Polyphasic characterization and identification of the bioremediation agent Bacillus sp. SFC 500-1E

Bacillus sp. SFC 500-1E is used for the effective treatment of tannery effluents since it consistently removes hexavalent chromium from diverse contaminated matrices. The aim of the present study was to complete identification of the strain through a polyphasic characterization, which included the pattern of carbohydrate utilization, fatty acids profile, multilocus sequence analysis, multiplex PCR profile and the analysis of the complete genome sequence. Morpho-physiological and biochemical characterization results and analysis of 16S rRNA sequences were not conclusive. The strain formed a monophyletic clade with B. toyonensis BCT-7112, B. thuringiensis MC28 and B. cereus Rock 1-3. However, genomic comparisons with type strains of B. cereus and B. thuringiensis showed that the isolated belonged to a different species. Results of this study highlight the relevance of the genome sequence of this strain, identified as Bacillus toyonensis SFC 500-1E, to expand knowledge of its bioremediation potential and to explore unknown decontamination activities.

Impact of phenol on the glycerophospholipid turnover and potential role of circadian clock in the plant response against this pollutant in tobacco hairy roots

Glycerophospholipids (GPLs) from cell membranes (CM) are a proper source for the synthesis of lipid messengers able to activate signal pathways that will define the plant survival under changing and stressful environmental conditions. Little is known about how GPLs metabolism (GPLsM) is regulated and the effects of phenol treatment on GPLs composition. In this work, we studied the effects of phenol both on GPLs turnover and on the expression of GPLsM-related genes potentially regulated by the circadian clock, using tobacco hairy root cultures (HRC). Phenol decreased the total PC levels and increased PE, PG and CL levels in the dark phase. Different molecular species of PC and PE showed the same trend than the total PC and PE upon phenol treatment. Besides, significant differences in the expression of all studied genes related to GPLsM were found. NtCCT2 expression was affected at all analyzed times while NtPECT1 and NtAAPT1 showed similar expression patterns. NtCDS1, NtPGPS2 and NtCLS genes showed significant and differential expression profiles both in untreated and treated HRC. PECT1 and NtPGPS2 genes seem to conserve a circadian expression profile mainly in untreated HRC. However, phenol was able to modify the GPLs composition and the expression of genes related to GPLs synthesis. The GPLs modification could be explained by the up-regulation of NtPECT1, NtAAPT1 and NtCLS genes during the dark phase, suggesting for being a crucial moment for HRC to trigger an adaptive response against this organic pollutant.

Morphological and structural response of Bacillus sp. SFC 500-1E after Cr(VI) and phenol treatment

Bacillus sp. SFC 500-1E, a bacterial strain isolated from tannery sediments, is able to remove Cr(VI) and simultaneously tolerate high concentrations of phenol. In this study, we used high-resolution microscopies, fluorescence polarization techniques, and several biochemical approaches to improve our understanding about the adaptive mechanisms of this strain to survive in the presence of Cr(VI) and phenol, both individually and simultaneously. Among adaptive strategies developed by Bacillus sp. SFC 500-1E, an increase in bacterial size, such as length, width, and height, and ultrastructural alterations, such as electron-dense precipitates, the presence of exopolymers, and cell lysis, are noteworthy. The exopolymers observed were consistent with the extensive biofilm formation and exopolysaccharides and extracellular protein quantification. At the cell membrane level, a rapid rigidity was induced in Cr(VI) + phenol treatment. This effect was counteracted after 16 h by changes at the level of phospholipids, mainly in the composition of fatty acids (FAs); in particular, an increase in the unsaturated fatty acid/saturated fatty acid ratio was detected. This study shows evidence of some adaptive responses displayed by Bacillus sp. SFC 500-1E, which allows it to survive in stressful conditions.

Deepening the knowledge on the removal of Cr(VI) by L. minuta Kunth: removal efficiency and mechanisms, lipid signaling pathways, antioxidant response, and toxic effects

Lemna minuta Kunth was used to remove Cr(VI) from aqueous solutions, and some of the mechanisms involved in this process were analyzed. In addition, the cellular signaling mediated by phospholipase D activity as well as antioxidant responses was also evaluated during the process. Cr(VI) removal efficiencies were 40% for 0.5 mg/L, after 24 h, and up to 18% at metal concentrations as high as 5 mg/L. Removal mechanisms displayed by these macrophytes include bioadsorption to cell surfaces and, to a greater extent, Cr internalization and bioaccumulation within cells. Inside of them, Cr(VI) was reduced to Cr(III), a less toxic form of this metal. At the first hours of Cr(VI) exposure, plants were able to sense chromium, activating membrane signal transduction pathways mediated by phospholipase D and phosphatidic acid. Moreover, an increase in the activity of antioxidant enzymes such as superoxide dismutases and peroxidases was observed in the same time. These and other components of the antioxidant defense system would help to reduce the stress generated by the metal. The toxicity of the products formed during the removal process was assessed through Lactuca sativa L. and AMPHIAGU test. It was evidenced that Cr(VI) phytoremediation process by L. minuta plants did not generate acute toxicity neither for L. sativa seeds nor for embryos of Rhinella arenarum (Hensel, 1876). Thus, L. minuta plants could be considered as valuable species for the treatment of waters contaminated with Cr(VI).

CR(VI) phytoremediation by hairy roots of Brassica napus: assessing efficiency, mechanisms involved, and post-removal toxicity

Industrial activities such as leather tanning involve the use of highly toxic inorganic pollutants, like Chromium (Cr). This work evaluated Cr(VI) remediation by hairy roots (HR) of Brassica napus, paying close attention to the mechanisms involved and the toxicity of post-removal solutions. Results showed that these roots were capable of tolerating concentrations of up to 10 mg L^-1 Cr(VI), while higher concentrations were toxic for HR development. Removal efficiency was assessed through the use of synthetic solutions containing different initial Cr(VI) concentrations (2, 5, or 10 mg L^-1). Regardless of these initial concentrations, the highest removal efficiency values were between 80 and 90% after 24 and 48 h of treatment, using a 2.0 g inoculum. The mechanisms involved were Cr accumulation (60%) and to a lesser extent, adsorption to the root biomass (30%). A fraction of Cr(VI) was intracellularly reduced to Cr(III), which suggests reductases may have played a role. Additionally, post-removal toxicity was evaluated through two bioassays (Lactuca sativa L. and AMPHITOX test) after the removal of 10 mg L^-1 Cr(VI). The treated solutions showed moderate phytotoxicity for L. sativa L. and no toxicity for R arenarum. The ability of HR to remove 10 mg L^-1 Cr(VI) from real tannery effluents collected from a regional industry (Córdoba province, Argentina) was also determined. The high removal efficiency observed (98%) demonstrates this system can be successful in treating complex wastewaters.

Phytoremediation processes of domestic and textile effluents: evaluation of the efficacy and toxicological effects in Lemna minor and Daphnia magna

Phytoremediation has been proposed as a potential biotechnological strategy to remediate effluents before their release into the environment. The use of common aquatic plant species, such as macrophytes (e.g., Lemna spp.) as a cleanup solution has been proposed decades ago. However, the effectiveness of such processes must be assessed by analyzing the toxicity of resulting effluents, for the monitoring of wastewater quality. To attain this purpose, this work intended to quantify the efficacy of a Lemna-based wastewater phytoremediation process, by analyzing toxicological effects of domestic and textile effluents. The toxic effects were measured in Lemna minor (same organisms used in the phytoremediation process, by quantifying toxicological endpoints such as root length, pigment content, and catalase activity) and by quantifying individual parameters of Daphnia magna (immobilization, reproduction, and behavior analysis). Phytoremediation process resulted in a decrease of chemical oxygen demand in both effluents and in an increase in root length of exposed plants. Moreover, textile effluent decreased pigments content and increased catalase activity, while domestic effluent increased the anthocyanin content of exposed plants. D. magna acute tests allowed calculating a EC₅₀ and Toxic Units interval of 53.82-66.89%/1.85-1.49, respectively, to raw textile effluent; however, it was not possible to calculate these parameters for raw and treated domestic effluent (RDE and TDE). Therefore, in general, the acute toxicity of effluent toward D. magna was null for RDE, and mild for the treated textile effluent (TTE), probably due to the effect of phytoremediation. Exposure to textile effluents (raw and treated) increased the total number of neonates of D. magna and, in general, both textile effluents decreased D. magna distance swim. Moreover, although both effluents were capable of causing morphological and physiological/biochemical alterations in L. minor plants, organisms of this species were able to survive in the presence of both effluents and to remediate them.

Biochemical and molecular characterization of arsenic response from Azospirillum brasilense Cd, a bacterial strain used as plant inoculant

Azospirillum brasilense Cd is a bacterial strain widely used as an inoculant of several crops due to its plant growth promoting properties. However, its beneficial effects depend on its viability and functionality under adverse environmental conditions, including the presence of arsenic (As) in agricultural soils. Therefore, the aim of this work was to evaluate the response of A. brasilense Cd to arsenate (AsV) and arsenite (AsIII). This bacterium was tolerant to As concentrations frequently found in soils. Moreover, properties related to roots colonization (motility, biofilm, and exopolymers) and plant growth promotion (auxin, siderophore production, and N₂ fixation) were not significantly affected by the metalloid. In order to deepen the understanding on As responses of A. brasilense Cd, As resistance genes were sequenced and characterized for the first time in this work. These genes could mediate the redox As transformation and its extrusion outside the cell, so they could have direct association with the As tolerance observed. In addition, its As oxidation/reduction capacity could contribute to change the AsV/AsIII ratio in the environment. In conclusion, the results allowed to elucidate the As response of A. brasilense Cd and generate interest for its potential use in polluted environments.

Catanionic nanocarriers as a potential vehicle for insulin delivery

Diabetes is a disease that affects millions of people in the World, constituting a global problem. Patients are administered insulin subcutaneous injections, resulting in high costs and frequent infections in the injection site. A possible solution to this problem may be the use of nanotechnology. Nanotransporters can act as specific release systems able to overcome the current limitations to drug delivery. Liposomes and vesicles can deliver drugs directly and efficiently to the site of action, decreasing toxicity and adverse effects. In previous studies, we demonstrated the biocompatibility and safety of catanionic benzyl n-hexadecyldimethylammonium 1,4 -bis-2-ethylhexylsulfosuccinate (BHD-AOT) vesicles using both in vitro and in vivo tests. Thus, the aims of this work were to evaluate the ability of the BHD-AOT vesicles to encapsulate insulin; to analyze the structural properties and stability of the system, vesicle-Insulin (VIn), at different pH conditions; and to study the ability of VIn to decrease the glycemia in miceby different administration routes. Our results showed that 2 and 5 mg mL^-1 of vesicles were able to encapsulate about 55 % and 73 % of insulin, respectively. The system VIn showed a significant increase in size from 120 to 350 nm, changes in the surface zeta potential value, and high stability to different pH conditions. A significant decrease of the glycemia after VIn administration was demonstrated in in vivo assays, including the oral route. Our results reveal that BHD-AOT vesicles may be an appropriate system to encapsulate and protect insulin, and may be a potential system to be administrated in different ways as an alternative strategy to conventional therapy.

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.

Targeting Acr3 from Ensifer medicae to the plasma membrane or to the tonoplast of tobacco hairy roots allows arsenic extrusion or improved accumulation. Effect of acr3 expression on the root transcriptome

Transgenic tobacco hairy roots expressing the bacterial arsenite efflux pump Acr3 from Ensifer medicae were generated. The gene product was targeted either to the plasma membrane (ACR3 lines) or to the tonoplast by fusing the ACR3 protein to the tonoplast integral protein TIP1.1 (TIP-ACR3 lines). Roots expressing Acr3 at the tonoplast showed greater biomass than those expressing Acr3 at the plasma membrane. Furthermore, higher contents of malondialdehyde (MDA) and RNA degradation in ACR3 lines were indicative of higher oxidative stress. The determination of ROS-scavenging enzymes depicted the transient role of peroxidases in ROS detoxification, followed by the action of superoxide dismutase during both short- and medium-term exposure periods. Regarding As accumulation, ACR3 lines accumulated up to 20-30% less As, whereas TIP-ACR3 achieved a 2-fold increase in As accumulation in comparison to control hairy roots. Strategies that presumably induce As uptake, such as phosphate deprivation or dehydration followed by rehydration in the presence of As, fostered As accumulation up to 10 800 μg g-1. Finally, the effects of the heterologous expression of acr3 on the root transcriptome were assessed. Expression at the plasma membrane induced drastic changes in gene expression, with outstanding overexpression of genes related to electron transport, ATP synthesis and ATPases, suggesting that As efflux is the main detoxification mechanism in these lines. In addition, genes encoding heat shock proteins and those related to proline synthesis and drought tolerance were activated. On the other hand, TIP-ACR3 lines showed a similar gene expression profile to that of control roots, with overexpression of the glutathione and phytochelatin synthesis pathways, together with secondary metabolism pathways as the most important resistance mechanisms in TIP-ACR3, for which As allocation into the vacuole allowed better growth and stress management. Our results suggest that modulation of As accumulation can be achieved by subcellular targeting of Acr3: expression at the tonoplast enhances As accumulation in roots, whereas expression at the plasma membrane could promote As efflux. Thus, both approaches open the possibilities for developing safer crops when grown on As-polluted paddy soils, but expression at the tonoplast leads to better growth and less stressed roots, since the high energy cost of As efflux likely compromises growth in ACR3 lines.

How the bacterial community of a tannery effluent responds to bioaugmentation with the consortium SFC 500-1. Impact of environmental variables

Bioaugmentation with the consortium SFC 500-1 is a promising alternative to remediate wastewaters, such as tannery effluents. With the aim of assessing the changes produced in response to bioaugmentation, bacterial 16S rDNA genes were sequenced with Illumina MiSeq Platform. Additionally, bacterial and fungal groups were analyzed through standard culture dependent methods. The impact of diverse physico-chemical and microbiological parameters on the prokaryotic diversity was also evaluated throughout. Bacteroidetes, Firmicutes and Proteobacteria, represented together up to 91% of the total number of sequences obtained from the tannery effluent. Diversity decreased immediately after inoculation, due to an increase in the representation of the taxa to which the added consortium belongs. However, bioaugmentation produced no greater variations since only a 10% of unique operational taxonomic units were found in the inoculated treatment. An increase in the abundance of Myroides and a reduction in the representation of Proteiniclasticum and Halomonas were major observed variations. On the other hand, pH and dissolved oxygen constituted main environmental factors affecting the structure of the prokaryotic communities. In all treatments yeasts increased over time, to the detriment of filamentous fungi. Together, data from this report may contribute to the development of improved bioremediation strategies of industrial wastewaters.

Membrane Rigidity and Phosphatidic Acid (PtdOH) Signal: Two Important Events in Acinetobacter guillouiae SFC 500-1A Exposed to Chromium(VI) and Phenol

The remodeling of membrane lipids is a mechanism that allows microorganisms to survive in unfavorable environments such as industrial effluents, which often contain inorganic and organic pollutants, like chromium and phenol. In the present work, we evaluated the effect of Cr(VI) and phenol on the membrane of Acinetobacter guillouiae SFC 500-1A, a bacterial strain isolated from tannery sediments where such pollutants can be found. The presence of lipid kinases and phospholipases and the changes in their activities under exposure to these pollutants were determined. Cr(VI) and Cr(VI) + phenol caused the membrane to become more rigid for up to 16 h after exposure. This could be due to an increase in cardiolipin (Ptd₂ Gro) and a decrease in phosphatidylethanolamine (PtdEtn), which are indicative of more order and rigidity in the membrane. Increased phospholipase A activity (PLA, EC 3.1.1.4) could be responsible for the decrease in PtdEtn levels. Moreover, our results indicate that Cr(VI) and Cr(VI) + phenol trigger the phosphatidic acid (PtdOH) signal. The finding of significantly increased phosphatidylinositol-4-phosphate (PtdIns-4-P) levels means this is likely achieved via PtdIns-PLC/DGK. This report provides the first evidence that A. guillouiae SFC 500-1A is able to sense Cr(VI) and phenol, transduce this signal through changes in the physical state of the membrane, and trigger lipid-signaling events.

Impact of double inoculation with Bradyrhizobium japonicum E109 and Azospirillum brasilense Az39 on soybean plants grown under arsenic stress

Inoculation practice with plant growth-promoting bacteria (PGPB) has been proposed as a good biotechnological tool to enhance plant performance and alleviate heavy metal/metalloid stress. Soybean is often cultivated in soil with high arsenic (As) content or irrigated with As-contaminated groundwater, which causes deleterious effects on its growth and yield, even when it was inoculated with rhizobium. Thus, the effect of double inoculation with known PGPB strains, Bradyrhizobium japonicum E109 and Azospirillum brasilense Az39 was evaluated in plants grown in pots under controlled conditions and treated with As. First, the viability of these co-cultivated bacteria was assayed using a flow cytometry analysis using SYTO9 and propidium iodide (PI) dyes. This was performed in vitro to evaluate the bacterial population dynamic under 25 μM AsV and AsIII treatment. A synergistic effect was observed when bacteria were co-cultured, since mortality diminished, compared to each growing alone. Indole acetic acid (IAA) produced by A. brasilense Az39 would be one of the main components involved in B. japonicum E109 mortality reduction, mainly under AsIII treatment. Regarding in vivo assays, under As stress, plant growth improvement, nodule number and N content increase were observed in double inoculated plants. Furthermore, double inoculation strategy reduced As translocation to aerial parts thus improving As phytostabilization potential of soybean plants. These results suggest that double inoculation with B. japonicum E109 and A. brasilense Az39 could be a safe and advantageous practice to improve growth and yield of soybean exposed to As, accompanied by an important metalloid phytostabilization.

Laboratory and field microcosms as useful experimental systems to study the bioaugmentation treatment of tannery effluents

Tannery effluents require effective treatment prior to their final disposal, and the use of native bacterial consortia could be an appropriate strategy for this purpose. In the present work, consortium SFC 500-1 was found to be highly tolerant to different metals, metalloids and aromatic compounds like phenols. It was also able to remove the black dye commonly used in tanneries. Moreover, it promoted a significant reduction in chemical oxygen demand and exhibited high capability for the simultaneous removal of Cr(VI) and phenol. However, the effectiveness of the remediation processes markedly varied from one experimental system (Erlenmeyer flasks) to another (field microcosm system), highlighting the importance of moving from a small-scale study system to one involving more realistic environmental scenarios. In addition, we found a decrease in the toxicity of the effluent treated with consortium SFC 500-1. Taken together, our results indicate that this consortium possesses great potential for the treatment of tannery effluents. We conclude that for the development of a bioremediation strategy, it is necessary to develop experiments at a larger scale under conditions similar to those of the original system, in order to complete the scenario first created by in vitro approaches.

What makes A. guillouiae SFC 500-1A able to co-metabolize phenol and Cr(VI)? A proteomic approach

Acinetobacter guillouiae SFC 500-1A is an environmental bacterium able to efficiently co-remediate phenol and Cr(VI). To further understand the molecular mechanisms triggered in this strain during the bioremediation process, variations in the proteomic profile after treatment with phenol and phenol plus Cr(VI) were evaluated. The proteomic analysis revealed the induction of the β-ketoadipate pathway for phenol oxidation and the assimilation of degradation products through TCA cycle and glyoxylate shunt. Phenol exposure increased the abundance of proteins associated to energetic processes and ATP synthesis, but it also triggered cellular stress. The lipid bilayer was suggested as a target of phenol toxicity, and changing fatty acids composition seemed to be the bacterial response to protect the membrane integrity. The involvement of two flavoproteins in Cr(VI) reduction to Cr(III) was also proposed. The results suggested the important role of chaperones, antioxidant response and SOS-induced proteins in the ability of the strain to mitigate the damage generated by phenol and Cr(VI). This research contributes to elucidate the mechanisms involved in A. guillouiae SFC 500-1A tolerance and co-remediation of phenol and Cr(VI). Such information may result useful not only to improve its bioremediation efficiency but also to identify putative markers of resistance in environmental bacteria.

Identification of the main mechanisms involved in the tolerance and bioremediation of Cr(VI) by Bacillus sp. SFC 500-1E

Chromium pollution is a problem that affects different areas worldwide and, therefore, must be solved. Bioremediation is a promising alternative to treat environmental contamination, but finding bacterial strains able to tolerate and remove different contaminants is a major challenge, since most co-polluted sites contain mixtures of organic and inorganic substances. In the present work, Bacillus sp. SFC 500-1E, isolated from the bacterial consortium SFC 500-1 native to tannery sediments, showed tolerance to various concentrations of different phenolic compounds and heavy metals, such as Cr(VI). This strain was able to efficiently remove Cr(VI), even in the presence of phenol. The detection of the chrA gene suggested that Cr(VI) extrusion could be a mechanism that allowed this strain to tolerate the heavy metal. However, reduction through cytosolic NADH-dependent chromate reductases may be the main mechanism involved in the remediation. The information provided in this study about the mechanisms through which Bacillus sp. SFC 500-1E removes Cr(VI) should be taken into account for the future application of this strain as a possible candidate to remediate contaminated environments.

Arsenic stress effects on root water absorption in soybean plants: Physiological and morphological aspects

Soybean (Glycine max L.) is often cultivated in areas contaminated with arsenic (As), which negatively affects plant growth and reduces crop yield. The deleterious effects may be due, at least in part, to disturbances in the water status, as was reported for some plants exposed to heavy metals. However, to our knowledge, these mechanisms have not been studied in depth in soybean plants exposed to As. The aim of the present work was to analyze possible changes in water relations and the responses developed in soybean plants under arsenate (AsV) and arsenite (AsIII) stress. We discuss physiological and morphological aspects of the As stress response, such as root absorption rate, water content, stomatal conductance, water and osmotic potential, accumulation of compatible solutes, leaf conducting tissues and stomata characteristics. AsV and AsIII caused a significant decrease in root absorption rate, which could reduce metalloid uptake. On the other hand, water content decreased at the beginning of the treatment but was re-established after 4 and 8 d. This was correlated with a decrease in stomatal conductance and a reduction in leaf water and osmotic potential due to the accumulation of proline and soluble sugars. Besides, smaller leaf xylem vessels and abnormal stomata were observed in plants under As treatment. These mechanisms increased the plant's ability to retain water and therefore to avoid dehydration. Thus, the results of the present work contribute to the understanding of how soybean responds to As, by describing key tolerance strategies to the metalloid.

Identification and characterization of key circadian clock genes of tobacco hairy roots: putative regulatory role in xenobiotic metabolism

The circadian clock is an endogenous system that allows organisms to daily adapt and optimize their physiology and metabolism. We studied the key circadian clock gene (CCG) orthologs in Nicotiana tabacum seedlings and in hairy root cultures (HRC). Putative genes involved in the metabolism of xenobiotic compounds (MXC) were selected and their expression profiles were also analyzed. Seedlings and HRC displayed similar diurnal variations in the expression profiles for the CCG examined under control conditions (CC). MXC-related genes also showed daily fluctuations with specific peaks of expression. However, when HRC were under phenol treatment (PT), the expression patterns of the clock and MXC-related genes were significantly affected. In 2-week-old HRC, PT downregulated the expression of NtLHY, NtTOC1, and NtPRR9 while NtFKF1 and NtGI genes were upregulated by phenol. In 3-week-old HRC, PT also downregulated the expression of all CCG analyzed and NtTOC1 was the most affected. Following PT, the expression of the MXC-related genes was upregulated or displayed an anti-phasic expression profile compared to the expression under CC. Our studies thus provide a glimpse of the circadian expression of clock genes in tobacco and the use of HRC as a convenient system to study plant responses to xenobiotic stresses.

Removal of copper from aqueous solutions by rhizofiltration using genetically modified hairy roots expressing a bacterial Cu-binding protein

The aim of this work was to develop a biotechnological tool to hyperaccumulate high copper (Cu) concentrations from wastewaters. Transgenic tobacco hairy roots were obtained by expressing, either the wild-type version of the gene copC from Pseudomonas fluorescens in the cytoplasm of plant cells (CuHR), or a modified version targeted to the vacuole (CuHR-V). Control hairy roots transformed with the empty vector (HR) were also generated. The roots were incubated in the presence of solutions containing Cu (from 1 to 50 mM). At 5 mM external copper, transgenic hairy roots accumulated twice the amount of copper accumulated by control hairy roots. However, at 50 mM Cu, accumulation in both transgenic and control roots reached similar values. Maximum Cu accumulation achieved by transgenic hairy roots was 45,000 µg g-1 at 50 mM external Cu. Despite the high Cu accumulation, transgenic hairy roots, particularly CuHR-V, showed less toxicity symptoms, in correlation with lower activity of several antioxidant enzymes and lower malondialdehyde (MDA) levels. Moreover, CuHR-V roots displayed low values of the oxidative stress index (OSI) - a global parameter proposed for oxidative stress - indicating that targeting CopC to the vacuole could alleviate the oxidative stress caused by Cu. Our results suggest that expressing copC in transgenic hairy roots is a suitable strategy to obtain Cu-hyperaccumulator hairy roots with less toxicity stress symptoms.

ABBREVIATIONS

APX: ascorbate peroxidase; ATSDR: Agency for Toxic Substances and Disease Registry (U.S.); BCF: bioconcentration factor; CuHR: copper-hairy roots; EDTA: ethylenediamine tetracetic acid; EPA: Environmental Protection Agency (U.S.); GSH: glutathione; HM: heavy metals; HR: control hairy roots; ICP-OES: Inductively Coupled Plasma/Optical Emission Spectrometry; MDA: malondialdehyde; NBT: nitroblue tetrazolium; OD: optical density; OSI: oxidative stress index; PCR: polymerase chain reaction; PVP: polyvynilpirrolidone; PX: peroxidase; ROS: reactive oxygen species; SOD: superoxide dismutase.

An approach to study ultrastructural changes and adaptive strategies displayed by Acinetobacter guillouiae SFC 500-1A under simultaneous Cr(VI) and phenol treatment

Acinetobacter guillouiae SFC 500-1A, a native bacterial strain isolated from tannery sediments, is able to simultaneously remove high concentrations of Cr(VI) and phenol. In this complementary study, high-resolution microscopy techniques, such as atomic force microscopy (AFM) and transmission electron microscopy (TEM), were used to improve our understanding of some bacterial adaptive mechanisms that enhance their ability to survive. AFM contributed in gaining insight into changes in bacterial size and morphology. It allowed the unambiguous identification of pollutant-induced cellular disturbances and the visualization of bacterial cells with depth sensitivity. TEM analysis revealed that Cr(VI) produced changes mainly at the intracellular level, whereas phenol produced alterations at the membrane level. This strain tended to form more extensive biofilms after phenol treatment, which was consistent with microscopy images and the production of exopolysaccharides (EPSs). In addition, other exopolymeric substances (DNA, proteins) significantly increased under Cr(VI) and phenol treatment. These exopolymers are important for biofilm formation playing a key role in bacterial aggregate stability, being especially useful for bioremediation of environmental pollutants. This study yields the first direct evidences of a range of different changes in A. guillouiae SFC 500-1A which seems to be adaptive strategies to survive in stressful conditions.

Synergistic effect of chickpea plants and Mesorhizobium as a natural system for chromium phytoremediation

The presence of chromium in soils not only affects the physiological processes of plants but also the microbial rhizosphere composition and metabolic activities of microorganisms. Hence, the inoculation of plants with Cr(VI)-tolerant rhizospheric microorganisms as an alternative to reduce Cr phytotoxicity was studied. In this work, chickpea germination was reduced by Cr(VI) concentrations of 150 and 250 mg/L (6 and 33%, respectively); however lower Cr(VI) concentrations negatively affected the biomass. On the other hand, its symbiont, Mesorhizobium ciceri, was able to grow and remove different Cr(VI) concentrations (5-20 mg/L). The inoculation of chickpea plants with this strain exposed to Cr(VI) showed a significantly enhanced plant growth. In addition, inoculated plants accumulated higher Cr concentration in roots than those noninoculated. It is important to note that Cr was not translocated to shoots independently of inoculation. These results suggest that Mesorhizobium's capability to remove Cr(VI) could be exploited for bioremediation. Moreover, chickpea plants would represent a natural system for phytoremediation or phytostabilization of Cr in situ that could be improved with M. ciceri inoculation. This strategy would be considered as a phytoremediation tool with great economic and ecological relevance.

Plant tissue cultures as sources of new ene- and ketoreductase activities

While many redox enzymes are nowadays available for synthetic applications, the toolbox of ene-reductases is still limited. Consequently, the screening for these enzymes from diverse sources in the search of new biocatalyst suitable for green chemistry approaches is needed. Among 13 plant tissue cultures, Medicago sativa and Tessaria absinthioides calli, as well as Capsicum annuum hairy roots, were selected due to their ability to hydrogenate the CC double bond of the model substrate 2-cyclohexene-1-one. The three axenic plant cultures showed more preference toward highly activated molecules such as nitrostyrene and maleimide rather than the classical substrates of the well-known Old Yellow Enzymes, resembling the skills of the NAD(P)H-dependent flavin-independent enzymes. When the three biocatalytic systems were applied in the reduction of chalcones, T. absinthioides showed high chemoselectivity toward the CC double bond whereas the other two demonstrated abilities to biohydrogenate the CC double bounds and the carbonyl groups in a sequential fashion.

Biotechnological tools to improve bioremediation of phenol by Acinetobacter sp. RTE1.4

The use of native bacteria is a useful strategy to decontaminate industrial effluents as well as the environment. Acinetobacter sp. RTE1.4 was previously isolated from polluted environments and constitutes a promising alternative for this purpose due to its capability to remove phenol from synthetic solutions and industrial effluents. In this work, this strain was identified at species level as A. tandoii RTE1.4. Phenol degradation pathway was studied and some reaction intermediates were detected, confirming that this strain degraded phenol through ortho-cleavage of the aromatic ring. Phenol removal assays were carried out in a stirred tank bioreactor and a complete degradation of the contaminant was achieved after only 7 h, at an aeration rate of 3 vvm and at agitation of 600 rpm. Moreover, this bacterium was immobilized into calcium alginate beads and an increase in phenol biodegradation with respect to free cells was observed. The immobilized cells were reused for four consecutive cycles and stored at 4°C for 9 months, during which phenol removal efficiency was maintained. Post-removal solutions were evaluated by Microtox® test, showing a toxicity reduction after bacterial treatment. These findings demonstrated that A. tandoii RTE1.4 might be considered as a useful biotechnological tool for an efficient treatment of different solutions contaminated with phenol in bioreactors, using either free or immobilized cells.

Arsenic stress induces changes in lipid signalling and evokes the stomata closure in soybean

Soybean (Glycine max) is often exposed to high arsenic (As) level in soils or through irrigation with groundwater. In previous studies on As-treated soybean seedlings we showed deleterious effect on growth, structural alterations mainly in root vascular system and induction of antioxidant enzymes. However, there are not reports concerning signal transduction pathways triggered by the metalloid in order to develop adaptive mechanisms. Phosphatidic acid (PA), a key messenger in plants, can be generated via phospholipase D (PLD) or via phospholipase C (PLC) coupled to diacylglycerol kinase (DGK). Thus, changes in PA and in an enzyme involved in its metabolism (PLD) were analysed in soybean seedlings treated with 25 μM AsV or AsIII. The present study demonstrated that As triggers the PA signal by PLD and also via PLC/DGK mainly after 48 h of As treatment. DGPP, other lipid messenger produced by phosphorylation of PA by PAK increased in As treated roots. Arsenic also induced rapid and significant stomatal closure after 1.5 h of treatment, mainly with AsIII, probably as an adaptive response to the metalloid to reduce water loss by transpiration. This report constitute the first evidence that shows the effects of As on lipid signalling events in soybean seedlings which would be crucial in adaptation and survival of soybean seedlings under As stress.

Arsenic toxicity in soybean seedlings and their attenuation mechanisms

Even though vast areas contaminated with arsenic (As) are under soybean (Glycine max) cultivation, little is known about the growth and intrinsic antioxidant metabolism of soybean in response to As exposure. Thus, an evaluation was carried out of plant growth, root anatomy, antioxidant system and photosynthetic pigment content under arsenate (As(V)) and arsenite (As(III)) treatment. Soybean seedling growth was significantly affected at 25 μM or higher concentrations of As(V) or As(III), and the toxic effect on root growth was associated with cell death of root tips. Microscopic analysis of cross-sections of As-treated root showed a reduction in the cortex area, dark deposits in cortex cells and broken cells in the outer layer. Similarly, in the vascular cylinder, dark deposits within xylem vessel elements and phloem cell walls were observed. In all the analyzed parameters, the deleterious effect was more evident under As(III) than As(V) treatment. Arsenic-treated soybean seedlings showed increased activity of antioxidant enzymes [total peroxidases (Px) and superoxide dismutase (SOD)] in root and shoot harvested after 2 and 5 d of treatment. However, a reduction in chlorophyll content and an increase in membrane lipids peroxidation were observed. It is suggested that root structural alterations induced by As, such as the particular pattern of dark depositions in the vascular system, could be associated with an adaptation or detoxification mechanism to prevent As translocation to the aboveground tissues.

Optimization of simultaneous removal of Cr (VI) and phenol by a native bacterial consortium: its use for bioaugmentation of co-polluted effluents

AIMS

This study was designed to isolate, identify and characterize micro-organisms or mixed cultures capable of simultaneously removing Cr (VI) and phenol in the surrounding area of a tannery localized in Elena, Córdoba, Argentina. In addition, nutritional and physical factors were optimized in order to improve the removal efficiency in a real effluent.

METHODS AND RESULTS

The consortium SFC 500-1, composed of two bacterial strains belonging to Acinetobacter and Bacillus genus, was isolated from the heavily polluted wastewater discharge channel of a local tannery. SFC 500-1 was able to remove phenol at environmentally relevant concentrations (1000 mg l(-1) ) and reduce Cr (VI) to Cr (III), which was immobilized in the bacterial biomass. The consortium simultaneously removed these contaminants under a wide range of physicochemical conditions and different growth media, even in a tannery effluent.

CONCLUSION

The ability of SFC 500-1 to simultaneously reduce Cr (VI) and degrade phenol in different synthetic growth media and even in the effluent from which it was isolated with high efficiency makes this consortium a potential candidate for the biotreatment of effluents.

SIGNIFICANCE AND IMPACT OF THE STUDY

This finding is important, taking into account that industrial effluents present complex mixtures of toxic substances as well as native flora which often affect the bioremediation process. Considering the ecological advantages of using native bacteria for bioremediation, as well as the high efficiency of the consortium SFC 500-1 to simultaneously remove Cr (VI) and phenol, this could be a suitable biological system to improve the biotreatment of polluted effluents through a bioaugmentation strategy.

Biochemical and molecular mechanisms involved in simultaneous phenol and Cr(VI) removal by Acinetobacter guillouiae SFC 500-1A

Bioremediation has emerged as an environmental friendly strategy to deal with environmental pollution. Since the majority of polluted sites contain complex mixtures of inorganic and organic pollutants, it is important to find bacterial strains that can cope with multiple contaminants. In this work, a bacterial strain isolated from tannery sediments was identified as Acinetobacter guillouiae SFC 500-1A. This strain was able to simultaneously remove high phenol and Cr(VI) concentrations, and the mechanisms involved in such process were evaluated. The phenol biodegradation was catalized by a phenol-induced catechol 1,2-dioxygenase through an ortho-cleavage pathway. Also, NADH-dependent chromate reductase activity was measured in the cytosolic fraction. The ability of this strain to reduce Cr(VI) to Cr(III) was corroborated by detection of Cr(III) in cellular biomass after the removal process. While phenol did not affect significantly the chromate reductase activity, Cr(VI) was a major disruptor of catechol dioxygenase activity. Nevertheless, this activity was high even in presence of high Cr(VI) concentrations. Our results suggest the potential application of A. guillouiae SFC 500-1A for wastewaters treatment, and the obtained data provide the insights into the removal mechanisms, dynamics, and possible limitations of the bioremediation.

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.

Application of two bacterial strains for wastewater bioremediation and assessment of phenolics biodegradation

The use of native bacteria is a useful strategy to decontaminate industrial effluents. In this work, two bacterial strains isolated from polluted environments constitutes a promising alternative since they were able to remove several phenolic compounds not only from synthetic solutions but also from effluents derived from a chemical industry and a tannery which are complex matrices. Acinetobacter sp. RTE 1.4 showed ability to completely remove 2-methoxyphenol (1000 mg/L) while Rhodococcus sp. CS 1 not only degrade the same concentration of this compound but also removed 4- chlorophenol, 2,4-dichlorophenol and pentachlorophenol with high efficiency. Moreover, both bacteria degraded phenols naturally present or even exogenously added at high concentrations in effluents from the chemical industry and a tannery in short time (up to 5 d). In addition, a significant reduction of biological oxygen demand and chemical oxygen demand values was achieved after 7 d of treatment for both effluents using Acinetobacter sp. RTE 1.4 and Rhodococcus sp. CS1, respectively. These results showed that Acinetobacter sp. RTE1.4 and Rhodococcus sp. CS 1 might be considered as useful biotechnological tools for an efficient treatment of different effluents, since they showed wide versatility to detoxify these complex matrices, even supplemented with high phenol concentrations.