RESUMO

A chromate of copper and cobalt (Φy) was synthesized and characterized. Φy activated peroxymonosulfate (PMS) to degrade ciprofloxacin (CIP) in water. The Φy/PMS combination showed a high degrading capability toward CIP (~100% elimination in 15 min). However, Φy leached cobalt (1.6 mg L-1), limiting its use for water treatment. To avoid leaching, Φy was calcinated, forming a mixed metal oxide (MMO). In the combination of MMO/PMS, no metals leached, the CIP adsorption was low (<20%), and the action of SO4•- dominated, leading to a synergistic effect on pollutant elimination (>95% after 15 min of treatment). MMO/PMS promoted the opening and oxidation of the piperazyl ring, plus the hydroxylation of the quinolone moiety on CIP, which potentially decreased the biological activity. After three reuse cycles, the MMO still presented with a high activation of PMS toward CIP degradation (90% in 15 min of action). Additionally, the CIP degradation by the MMO/PMS system in simulated hospital wastewater was close to that obtained in distilled water. This work provides relevant information on the stability of Co-, Cu-, and Cr-based materials under interaction with PMS and the strategies to obtain a proper catalyst to degrade CIP.

Assuntos

Poluentes Químicos da Água , Purificação da Água , Antibacterianos/farmacologia , Cobre , Poluentes Químicos da Água/análise , Peróxidos , Óxidos , Ciprofloxacina/farmacologia , Cobalto

RESUMO

The interfacial barrier of charge transfer from semiconductors to cocatalysts means that the photogenerated charges cannot be fully utilized, especially for the challenging water oxidation reaction. Using cobalt cubane molecules (Co4 O4 ) as water oxidation cocatalysts, we rationally assembled partially oxidized graphene (pGO), acting as a charge-transfer mediator, on the hole-accumulating {-101} facets of lead chromate (PbCrO4 ) crystal. The assembled pGO enables preferable immobilization of Co4 O4 molecules on the {-101} facets of the PbCrO4 crystal, which is favorable for the photogenerated holes transferring from PbCrO4 to Co4 O4 molecules. The surface charge-transfer efficiency of PbCrO4 was boosted by selective assembly of pGO between PbCrO4 and Co4 O4 molecules. An apparent quantum efficiency for photocatalytic water oxidation on the Co4 O4 /pGO/PbCrO4 photocatalyst exceeded 10 % at 500 nm. This strategy of rationally assembling charge-transfer mediator provides a feasible method for acceleration of charge transfer and utilization in semiconductor photocatalysis.

RESUMO

Soil contamination caused by improper waste disposal can affect plant growth. Tropical forage plants have rapid growth, high biomass production and vigorous regrowth. Chromium (Cr) is one of the most common contaminants in the environment. Sulfur (S) is a nutrient involved in various cell detoxification processes. The objective was to assess the effects of excess Cr on biomass production and concentrations of this metal, S and cationic micronutrients, under conditions of varying supply of S for Tanzania guinea grass. The experiment was conducted in randomized complete blocks in a 3 × 4 factorial scheme, corresponding to three levels of S (0.1, 1.9 and 3.7 mmol L-1) and four levels of Cr (0.0, 0.5, 1.0 and 2.0 mmol L-1) in three replicates. Root surface area, shoot and root biomass production, concentrations of total S, sulfate-S, Cr and cationic micronutrients, and Cr transport factor were determined. S level of 1.9 mmol L-1 reduced the toxicity by Cr in Tanzania guinea grass, expressed by the higher shoot and root dry weight production, greater stability in the cellular concentration of sulfate-S and higher concentrations of micronutrients. It was concluded that the high availability of S reduced the toxicity by Cr(VI) in Tanzania guinea grass, expressed by the higher shoot and root dry weight production, greater stability in the cellular concentration of sulfate-S and higher concentration of micronutrients in the grass shoots.

Assuntos

Cromo , Poluentes do Solo , Cromo/toxicidade , Cromo/análise , Tanzânia , Biomassa , Micronutrientes , Guiné , Poaceae/metabolismo , Enxofre/metabolismo , Raízes de Plantas/metabolismo , Poluentes do Solo/análise

RESUMO

BACKGROUND: Acidophilic microorganisms like Leptospirillum sp. CF-1 thrive in environments with extremely low pH and high concentrations of dissolved heavy metals that can induce the generation of reactive oxygen species (ROS). Several hypothetical genes and proteins from Leptospirillum sp. CF-1 are known to be up-regulated under oxidative stress conditions. RESULTS: In the present work, the function of hypothetical gene ABH19_09590 from Leptospirillum sp. CF-1 was studied. Heterologous expression of this gene in Escherichia coli led to an increase in the ability to grow under oxidant conditions with 5 mM K2CrO4 or 5 mM H2O2. Similarly, a significant reduction in ROS production in E. coli transformed with a plasmid carrying ABH19_09590 was observed after exposure to these oxidative stress elicitors for 30 min, compared to a strain complemented with the empty vector. A co-transcriptional study using RT-PCR showed that ABH19_09590 is contained in an operon, here named the "och" operon, that also contains ABH19_09585, ABH19_09595 and ABH19_09600 genes. The expression of the och operon was significantly up-regulated in Leptospirillum sp. CF-1 exposed to 5 mM K2CrO4 for 15 and 30 min. Genes of this operon potentially encode a NADH:ubiquinone oxidoreductase, a CXXC motif-containing protein likely involved in thiol/disulfide exchange, a hypothetical protein, and a di-hydroxy-acid dehydratase. A comparative genomic analysis revealed that the och operon is a characteristic genetic determinant of the Leptospirillum genus that is not present in other acidophiles. CONCLUSIONS: Altogether, these results suggest that the och operon plays a protective role against chromate and hydrogen peroxide and is an important mechanism required to face polyextremophilic conditions in acid environments.

Assuntos

Cromatos , Peróxido de Hidrogênio , Bactérias/genética , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Cromatos/metabolismo , Escherichia coli , Peróxido de Hidrogênio/metabolismo , Peróxido de Hidrogênio/farmacologia , Óperon , Estresse Oxidativo/genética , Espécies Reativas de Oxigênio/metabolismo

RESUMO

BACKGROUND: Acidophilic microorganisms like Leptospirillum sp. CF 1 thrive in environments with extremely low pH and high concentrations of dissolved heavy metals that can induce the generation of reactive oxygen species (ROS). Several hypothetical genes and proteins from Leptospirillum sp. CF 1 are known to be up regulated under oxidative stress conditions. RESULTS: In the present work, the function of hypothetical gene ABH19_09590 from Leptospirillum sp. CF 1 was studied. Heterologous expression of this gene in Escherichia coli led to an increase in the ability to grow under oxidant conditions with 5 mM K2CrO4 or 5 mM H2O2. Similarly, a significant reduction in ROS production in E. coli transformed with a plasmid carrying ABH19_09590 was observed after exposure to these oxidative stress elicitors for 30 min, compared to a strain complemented with the empty vector. A co transcriptional study using RT PCR showed that ABH19_09590 is contained in an operon, here named the "och" operon, that also contains ABH19_09585, ABH19_09595 and ABH19_09600 genes. The expression of the och operon was significantly up regulated in Leptospirillum sp. CF 1 exposed to 5 mM K2CrO4 for 15 and 30 min. Genes of this operon potentially encode a NADH:ubiquinone oxidoreductase, a CXXC motif containing protein likely involved in thiol/disulfide exchange, a hypothetical protein, and a di hydroxy acid dehydratase. A comparative genomic analysis revealed that the och operon is a characteristic genetic determinant of the Leptospirillum genus that is not present in other acidophiles. CONCLUSIONS: Altogether, these results suggest that the och operon plays a protective role against chromate and hydrogen peroxide and is an important mechanism required to face polyextremophilic conditions in acid environments.

Assuntos

Cromatos/metabolismo , Peróxido de Hidrogênio/metabolismo , Peróxido de Hidrogênio/farmacologia , Óperon , Bactérias/genética , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Estresse Oxidativo/genética , Escherichia coli

RESUMO

Hexavalent chromium is a highly toxic element generated due to indiscriminate chromite mining in Sukinda, Odisha. In the present research investigation a relatively higher Cr(VI) resistant (900 mg L-1) bacterium CWB-54 was isolated from the chromite mine water. Based on the biochemical and molecular analysis the strain (CWB-54) was identified as Exiguobacterium mexicanum. When this bacterium was grown at 35 °C, 100 rpm, pH~8.0, and fructose as an electron donor, it could reduce the total hexavalent chromium (100 mg L-1) supplemented in the medium within 33 h of incubation period. Though experiment was carried out to study the effect of Mn, Ni, Cd, Hg and Zn on Cr(VI) reduction by the strain E. mexicanum it has been observed that in the presence of Cd and Hg, Cr(VI) reduction drastically decreased. Characterization of Cr(VI) reduced product by SEM-EDX and TEM analysis revealed intracellular and extracellular Cr(III) deposition in the bacterium, which is assumed to be Cr(OH)3 precipitate in nanometric size. But the extracellular chromate reductase enzyme production is found to be negligible as compared to the intracellular enzyme production. The increased concentration of Cr(VI) above (1000 mg L-1) also showed the genotoxic effect on the DNA. Several reports have been published on Exiguobacterium sp. on different scientific aspect but the current report on the reduction of toxic Cr(VI) by a new species E. mexicanum is a novel one which established the potentiality of this microorganism for a broad area of application.

Assuntos

Exiguobacterium , Solo , Biodegradação Ambiental , Cromo , Oxirredução

RESUMO

Klebsiella sp. strain AqSCr, isolated from Cr(VI)-polluted groundwater, reduces Cr(VI) both aerobically and anaerobically and resists up 34 mM Cr(VI); this resistance is independent of the ChrA efflux transporter. In this study, we report the whole genome sequence and the transcriptional profile by RNA-Seq of strain AqSCr under Cr(VI)-adapted conditions and found 255 upregulated and 240 downregulated genes compared to controls without Cr(VI) supplementation. Genes differentially transcribed were mostly associated with oxidative stress response, DNA repair and replication, sulfur starvation response, envelope-osmotic stress response, fatty acid (FA) metabolism, ribosomal subunits, and energy metabolism. Among them, genes not previously associated with chromium resistance, for example, cybB, encoding a putative superoxide oxidase (SOO), gltA2, encoding an alternative citrate synthase, and des, encoding a FA desaturase, were upregulated. The sodA gene encoding a manganese superoxide dismutase was upregulated in the presence of Cr(VI), whereas sodB encoding an iron superoxide dismutase was downregulated. Cr(VI) resistance mechanisms in strain AqSCr seem to be orchestrated by the alternative sigma factors fecl, rpoE, and rpoS (all of them upregulated). Membrane lipid analysis of the Cr(IV)-adapted strain showed a lower proportion of unsaturated lipids with respect to the control, which we hypothesized could result from unsaturated lipid peroxidation followed by degradation, together with de novo synthesis mediated by the upregulated FA desaturase-encoding gene, des. This report helps to elucidate both Cr(VI) toxicity targets and global bacterial response to Cr(VI).

RESUMO

Cr(VI) is mutagenic and teratogenic and considered an environmental pollutant of increasing concern. The use of microbial enzymes that convert this ion into its less toxic reduced insoluble form, Cr(III), represents a valuable bioremediation strategy. In this study, we examined the Bacillus subtilis YhdA enzyme, which belongs to the family of NADPH-dependent flavin mononucleotide oxide reductases and possesses azo-reductase activity as a factor that upon overexpression confers protection on B. subtilis from the cytotoxic effects promoted by Cr(VI) and counteracts the mutagenic effects of the reactive oxygen species (ROS)-promoted lesion 8-OxoG. Further, our in vitro assays unveiled catalytic and biochemical properties of biotechnological relevance in YhdA; a pure recombinant His10-YhdA protein efficiently catalyzed the reduction of Cr(VI) employing NADPH as a cofactor. The activity of the pure oxidoreductase YhdA was optimal at 30°C and at pH 7.5 and displayed Km and Vmax values of 7.26 mM and 26.8 µmol·min-1·mg-1 for Cr(VI), respectively. Therefore, YhdA can be used for efficient bioremediation of Cr(VI) and counteracts the cytotoxic and genotoxic effects of oxygen radicals induced by intracellular factors and those generated during reduction of hexavalent chromium.IMPORTANCE Here, we report that the bacterial flavin mononucleotide/NADPH-dependent oxidoreductase YhdA, widely distributed among Gram-positive bacilli, conferred protection to cells from the cytotoxic effects of Cr(VI) and prevented the hypermutagenesis exhibited by a MutT/MutM/MutY-deficient strain. Additionally, a purified recombinant His10-YhdA protein displayed a strong NADPH-dependent chromate reductase activity. Therefore, we postulate that in bacterial cells, YhdA counteracts the cytotoxic and genotoxic effects of intracellular and extracellular inducers of oxygen radicals, including those caused by hexavalent chromium.

Assuntos

Bacillus subtilis/efeitos dos fármacos , Bacillus subtilis/fisiologia , Proteínas de Bactérias/metabolismo , Cromo/toxicidade , FMN Redutase/metabolismo , Bacillus subtilis/enzimologia , Bacillus subtilis/genética , Proteínas de Bactérias/química , FMN Redutase/química

RESUMO

Plants adapt to soil injury and biotic stress via cell regeneration. In Arabidopsis, root tip damage by genotoxic agents, antibiotics, UV light and cutting induces a program that recovers the missing tissues through activation of stem cells and involves ethylene response factor 115 (ERF115), which triggers cell replenishment. Here, we show that mutation of the gene encoding an MED18 subunit of the transcriptional MEDIATOR complex and chromate [Cr(VI)], an environmental pollutant, synergistically trigger a developmental program that enables the splitting of the meristem in vivo to produce twin roots. Expression of the quiescent centre gene marker WOX5, auxin-inducible DR5:GFP reporter and the ERF115 factor traced the changes in cell identity during the conversion of single primary root meristems into twin roots and were induced in an MED18 and chromate-dependent manner during the root twinning events, which also required auxin redistribution and signalling mediated by IAA14/SOLITARY ROOT (SLR1). Splitting of the root meristem allowed dichotomous root branching in Arabidopsis, a poorly understood process in which stem cells may act to enable whole organ regeneration.

Assuntos

Proteínas de Arabidopsis/genética , Arabidopsis/genética , Complexo Mediador/genética , Meristema/genética , Raízes de Plantas/genética , Arabidopsis/efeitos dos fármacos , Proteínas de Arabidopsis/metabolismo , Cromo/farmacologia , Regulação da Expressão Gênica de Plantas , Proteínas de Homeodomínio/genética , Ácidos Indolacéticos/metabolismo , Complexo Mediador/metabolismo , Meristema/efeitos dos fármacos , Mutação , Raízes de Plantas/efeitos dos fármacos , Raízes de Plantas/crescimento & desenvolvimento , Plantas Geneticamente Modificadas , Fatores de Transcrição/genética

RESUMO

The remotion of hexavalent chromium in the form of chromate in aqueous solution was done using the aquatic plant Salvinia sp as biosorbent. The chemical modification of the Salvinia surface was performed by organosolv adapted method. The untreated Salvinia and the modified were characterized by infrared spectroscopy, Boehm titration, scanning electron microscopy, energy dispersive system, point of zero charge, surface area analysis, and porosity. Batch adsorption experiments were performed to observe the effects of pH, contact time, initial concentration, and temperature on the metal removal process. The characterization results show the chemistry modifically changed the modified Salvinia structure compared with untreated Salvinia. The adsorption test results showed the maximum adsorption capacity of 26.03 mg g-1. The kinetic equilibrium was reached in about 3 h, and the better temperature and pH were 298 K and 7, respectively. The adsorption and kinetic models were Freundlich and pseud-second order, respectively. This study showed the Salvinia sp after the chemical treatment can be used with biosorbent for hexavalent chromate in the form of chromate, being a natural material with low cost and plentiful in the environment.

Assuntos

Cromo/isolamento & purificação , Traqueófitas/química , Poluentes Químicos da Água/isolamento & purificação , Adsorção , Brasil , Cromo/química , Concentração de Íons de Hidrogênio , Cinética , Microscopia Eletrônica de Varredura , Soluções , Espectrofotometria Infravermelho , Temperatura , Traqueófitas/metabolismo , Poluentes Químicos da Água/química , Purificação da Água/métodos

RESUMO

Old Yellow Enzymes play key roles in several cellular processes and have become an important family of enzymes with biotechnological potential. One of the major challenges of biotechnology consists of the bioremediation of co-polluted soils with organic and inorganic compounds. In co-contaminated areas, chromium normally exists in its more toxic and carcinogenic form Cr(VI). Microorganisms can reduce this metal to the insoluble and less toxic Cr(III). Streptomyces sp. M7 is a strain able to efficiently bioremediate polluted soils with γ-hexachlorocyclohexane and Cr(VI). The complete degradation pathway for γ-hexachlorocyclohexane was recently elucidated in this strain. In the present work, we confirmed the ability of Streptomyces sp. M7 to eliminate a high percentage of Cr(VI) from a synthetic culture medium. After a transcriptional study in the presence of Cr(VI), we also report the molecular cloning of a gene coding for an Old Yellow Enzyme with chromate reductase activity. Our results suggest that the elimination of Cr(VI) by Streptomyces sp. M7 is directly related to the activity of this Old Yellow Enzyme. The importance of our work is in identifying for the first time an Old Yellow Enzyme with chromate reductase activity in Streptomyces and Actinobacteria. Finding this enzyme helps understand chromium homeostasis in Streptomyces sp. M7, in addition to opening a new research window related to Old Yellow Enzymes from Actinobacteria.

Assuntos

Biodegradação Ambiental , Cromo/metabolismo , Meios de Cultura/química , NADPH Desidrogenase/metabolismo , Streptomyces/enzimologia , Redes e Vias Metabólicas , NADPH Desidrogenase/genética , Oxirredução , Oxirredutases/metabolismo , Microbiologia do Solo , Streptomyces/genética

RESUMO

Bacteria deploy global programs of gene expression, including components of the SOS response, to counteract the cytotoxic and genotoxic effects of environmental DNA-damaging factors. Here we report that genetic damage promoted by hexavalent chromium elicited the SOS response in Bacillus subtilis, as evidenced by the induction of transcriptional uvrA-lacZ, recA-lacZ, and P recA-gfp fusions. Accordingly, B. subtilis strains deficient in homologous recombination (RecA) and nucleotide excision repair (NER) (UvrA), components of the SOS response, were significantly more sensitive to Cr(VI) treatment than were cells of the wild-type strain. These results strongly suggest that Cr(VI) induces the formation in growing B. subtilis cells of cytotoxic and genotoxic bulky DNA lesions that are processed by RecA and/or the NER pathways. In agreement with this notion, Cr(VI) significantly increased the formation of DNA-protein cross-links (DPCs) and induced mutagenesis in recA- and uvrA-deficient B. subtilis strains, through a pathway that required YqjH/YqjW-mediated translesion synthesis. We conclude that Cr(VI) promotes mutagenesis and cell death in B. subtilis by a mechanism that involves the formation of DPCs and that such deleterious effects are counteracted by both the NER and homologous recombination pathways, belonging to the RecA-dependent SOS system.IMPORTANCE It has been shown that, following permeation of cell barriers, Cr(VI) kills B. subtilis cells following a mechanism of reactive oxygen species-promoted DNA damage, which is counteracted by the guanine oxidized repair system. Here we report a distinct mechanism of Cr(VI)-promoted DNA damage that involves production of DPCs capable of eliciting the bacterial SOS response. We also report that the NER and homologous recombination (RecA) repair pathways, as well as low-fidelity DNA polymerases, counteract this metal-induced mechanism of killing in B. subtilis Hence, our results contribute to an understanding of how environmental pollutants activate global programs of gene expression that allow bacteria to contend with the cytotoxic and genotoxic effects of heavy metals.

Assuntos

Bacillus subtilis/efeitos dos fármacos , Bacillus subtilis/enzimologia , Cromo/toxicidade , Dano ao DNA/efeitos dos fármacos , Reparo do DNA , Mutagênicos/toxicidade , Recombinases Rec A/metabolismo , Bacillus subtilis/metabolismo , Resposta SOS em Genética

RESUMO

Mobile plasmid-encoded elements are DNA segments that are transferred for horizontal gene transfer and that confer adaptive proprieties, as well as virulence and antibiotic and heavy metal resistance to bacteria. The conjugative plasmid pUM505, isolated from a clinical strain of Pseudomonas aeruginosa, possesses a putative 31.292 kb mobile element (denominated Mpe: Mobile plasmid- encoded element) that, in addition to possessing chr genes that confer chromate resistance to Pseudomonas, contains two putative mer operons that could confer mercury resistance. Moreover, the Mpe contains genes related previously with the virulence of both P. aeruginosa and Escherichia coli strains. In this work, we determined that Mpe from pUM505 was able to independently move to another DNA molecule, conferring chromate and mercury resistance to P. aeruginosa PAO1 and mercury resistance to E. coli JM101, suggesting that its transference might be beneficial to bacteria under certain environmental conditions. Additionally, the transference of Mpe increased the virulence of P. aeruginosa PAO1 against the nematode Caenorhabditis elegans, suggesting its contribution to the pathogenicity of P. aeruginosa. In this work, we describe a new mobile plasmid-encoded element that possesses the potential to be transferred by horizontal gene transference, which could provide bacteria with a wide variety of adaptive traits such as heavy metal resistance and virulence, which can be selective factors for the distribution and prevalence of this plasmid in diverse environments, including hospitals and heavy metal contaminated soils.

Assuntos

Caenorhabditis elegans/microbiologia , Farmacorresistência Bacteriana , Sequências Repetitivas Dispersas , Metais Pesados/toxicidade , Plasmídeos/genética , Infecções por Pseudomonas/microbiologia , Pseudomonas aeruginosa/genética , Animais , Caenorhabditis elegans/crescimento & desenvolvimento , DNA Bacteriano , Humanos , Infecções por Pseudomonas/tratamento farmacológico , Infecções por Pseudomonas/genética , Pseudomonas aeruginosa/patogenicidade , Fatores de Virulência/genética

RESUMO

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.

Assuntos

Bacillus/genética , Cromatos/química , Cromo/química , Metais Pesados/química , Fenol/química , Bacillus/química , Bactérias , Biodegradação Ambiental

RESUMO

An Gram negative strain of S. maltophilia, indigenous to environments contaminated by Cr(VI) and identified by biochemical methods and 16S rRNA gene analysis, reduced chromate by 100%, 98-99% and 92% at concentrations in the 10-70, 80-300, and 500 mg/L range, respectively at pH 7 and temperature 37 °C. Increasing concentrations of Cr(VI) in the medium lowered the growth rate but could not be directly correlated with the amount of Cr(VI) reduced. The strain also exhibited multiple resistance to antibiotics and tolerance and resistance to various heavy metals (Ni, Zn and Cu), with the exception of Hg. Hexavalent chromium reduction was mainly associated with the soluble fraction of the cell evaluated with crude cell-free extracts. A protein of molecular weight around 25 kDa was detected on SDS-PAGE gel depending on the concentration of hexavalent chromium in the medium (0, 100 and 500 mg/L). In silico analysis in this contribution, revealed the presence of the chromate reductase gene ChrR in S. maltophilia, evidenced through a fragment of around 468 bp obtained experimentally. High Cr(VI) concentration resistance and high Cr(VI) reducing ability of the strain make it a suitable candidate for bioremediation.

Assuntos

Proteínas de Bactérias/metabolismo , Cromo/metabolismo , Farmacorresistência Bacteriana Múltipla/genética , Oxirredutases/metabolismo , RNA Ribossômico 16S/genética , Stenotrophomonas maltophilia/efeitos dos fármacos , Antibacterianos/farmacologia , Proteínas de Bactérias/genética , Proteínas de Bactérias/isolamento & purificação , Biodegradação Ambiental , Cromo/farmacologia , Cobre/metabolismo , Cobre/farmacologia , Tolerância a Medicamentos , Expressão Gênica , Concentração de Íons de Hidrogênio , Testes de Sensibilidade Microbiana , Peso Molecular , Níquel/metabolismo , Níquel/farmacologia , Oxirredução , Oxirredutases/genética , Oxirredutases/isolamento & purificação , Filogenia , Stenotrophomonas maltophilia/classificação , Stenotrophomonas maltophilia/enzimologia , Stenotrophomonas maltophilia/genética , Temperatura , Zinco/metabolismo , Zinco/farmacologia

RESUMO

Stimulation of microbial reduction of Cr(VI) to the less toxic and less soluble Cr(III) through electron donor addition has been regarded as a promising approach for the remediation of chromium-contaminated soil and groundwater sites. However, each site presents different challenges; local physicochemical characteristics and indigenous microbial communities influence the effectiveness of the biostimulation processes. Here, we show microcosm assays stimulation of microbial reduction of Cr(VI) in highly alkaline and saline soil samples from a long-term contaminated site in Guanajuato, Mexico. Acetate was effective promoting anaerobic microbial reduction of 15 mM of Cr(VI) in 25 days accompanied by an increase in pH from 9 to 10. Our analyses showed the presence of Halomonas, Herbaspirillum, Nesterenkonia/Arthrobacter, and Bacillus species in the soil sample collected. Moreover, from biostimulated soil samples, it was possible to isolate Halomonas spp. strains able to grow at 32 mM of Cr(VI). Additionally, we found that polluted groundwater has bacterial species different to those found in soil samples with the ability to resist and reduce chromate using acetate and yeast extract as electron donors.

Assuntos

Ácido Acético/metabolismo , Bactérias/metabolismo , Cromo/metabolismo , Recuperação e Remediação Ambiental/métodos , Microbiologia do Solo , Poluentes do Solo/metabolismo , Ácido Acético/administração & dosagem , Anaerobiose , Bactérias/isolamento & purificação , Biodegradação Ambiental , Água Subterrânea/microbiologia , México , Oxirredução , Solo/química , Instalações de Eliminação de Resíduos

RESUMO

The chromate ion transporter (CHR) superfamily includes proteins that confer chromate resistance by extruding toxic chromate ions from cytoplasm. Burkholderia xenovorans strain LB400 encodes six CHR homologues in its multireplicon genome and has been reported as highly chromate-resistant. The objective of this work was to analyze the involvement of chr redundant genes in chromate resistance by LB400. It was found that B. xenovorans plant rhizosphere strains lacking the megaplasmid are chromate-sensitive, suggesting that the chr gene present in this replicon is responsible for the chromate-resistance phenotype of the LB400 strain. Transformation of a chromate-sensitive B. xenovorans strain with each of the six cloned LB400 chr genes showed that genes from 'adaptive replicons' (chrA1b and chr1NCb from chromosome 2 and chrA2 from the megaplasmid) conferred higher chromate resistance levels than chr genes from 'central' chromosome 1 (chrA1a, chrA6, and chr1NCa). An LB400 insertion mutant affected in the chrA2 gene displayed a chromate-sensitive phenotype, which was fully reverted by transferring the chrA2 wild-type gene, and partially reverted by chrA1b or chr1NCb genes. These data indicate that chr genes from adaptive replicons, mainly chrA2 from the megaplasmid, are responsible for the B. xenovorans LB400 chromate-resistance phenotype.

Assuntos

Burkholderia/efeitos dos fármacos , Burkholderia/genética , Cromatos/toxicidade , Proteínas de Membrana Transportadoras/genética , Proteínas de Membrana Transportadoras/metabolismo , Erros Inatos do Metabolismo , Clonagem Molecular , Mutagênese Insercional , Plasmídeos , Transformação Bacteriana

RESUMO

Microbiological analysis of overburden samples collected from chromite mining areas of Orissa, India revealed that they are rich in microbial density as well as diversity and dominated by Gram-negative (58%) bacteria. The phenotypically distinguishable bacterial isolates (130) showed wide degree of tolerance to chromium (2-8 mM) when tested in peptone yeast extract glucose agar medium. Isolates (92) tolerating 2 mM chromium exhibited different degrees of Cr(+6) reducing activity in chemically defined Vogel Bonner (VB) broth and complex KSC medium. Three potent isolates, two belonging to Arthrobacter spp. and one to Pseudomonas sp. were able to reduce more than 50 and 80% of 2 mM chromium in defined and complex media respectively. Along with Cr(+6) (MIC 8.6-17.8 mM), the isolates showed tolerance to Ni(+2), Fe(+3), Cu(+2) and Co(+2) but were extremely sensitive to Hg(+2) followed by Cd(+2), Mn(+2) and Zn(+2). In addition, they were resistant to antibiotics like penicillin, methicillin, ampicillin, neomycin and polymyxin B. During growth under shake-flask conditions, Arthrobacter SUK 1201 and SUK 1205 showed 100% reduction of 2 mM Cr(+6) in KSC medium with simultaneous formation of insoluble precipitates of chromium salts. Both the isolates were also equally capable of completely reducing the Cr(+6) present in mine seepage when grown in mine seepage supplemented with VB concentrate.

RESUMO

Microbiological analysis of overburden samples collected from chromite mining areas of Orissa, India revealed that they are rich in microbial density as well as diversity and dominated by Gramnegative (58%) bacteria. The phenotypically distinguishable bacterial isolates (130) showed wide degree of tolerance to chromium (2-8 mM) when tested in peptone yeast extract glucose agar medium. Isolates (92) tolerating 2 mM chromium exhibited different degrees of Cr+6 reducing activity in chemically defined Vogel Bonner (VB) broth and complex KSC medium. Three potent isolates, two belonging to Arthrobacter spp. and one to Pseudomonas sp. were able to reduce more than 50 and 80% of 2 mM chromium in defined and complex media respectively. Along with Cr+6 (MIC 8.6-17.8 mM), the isolates showed tolerance to Ni+2, Fe+3, Cu+2 and Co+2 but were extremely sensitive to Hg+2 followed by Cd+2, Mn+2 and Zn+2. In addition, they were resistant to antibiotics like penicillin, methicillin, ampicillin, neomycin and polymyxin B. During growth under shake-flask conditions, Arthrobacter SUK 1201 and SUK 1205 showed 100% reduction of 2 mM Cr+6 in KSC medium with simultaneous formation of insoluble precipitates of chromium salts. Both the isolates were also equally capable of completely reducing the Cr+6 present in mine seepage when grown in mine seepage supplemented with VB concentrate

Assuntos

Arthrobacter/isolamento & purificação , Biodiversidade , Carcinógenos Ambientais , Microbiologia Ambiental , Metais/análise , Resíduos de Alimentos , Pseudomonas/isolamento & purificação , Métodos , Minerais , Resíduos

RESUMO

Microbiological analysis of overburden samples collected from chromite mining areas of Orissa, India revealed that they are rich in microbial density as well as diversity and dominated by Gramnegative (58%) bacteria. The phenotypically distinguishable bacterial isolates (130) showed wide degree of tolerance to chromium (2-8 mM) when tested in peptone yeast extract glucose agar medium. Isolates (92) tolerating 2 mM chromium exhibited different degrees of Cr+6 reducing activity in chemically defined Vogel Bonner (VB) broth and complex KSC medium. Three potent isolates, two belonging to Arthrobacter spp. and one to Pseudomonas sp. were able to reduce more than 50 and 80% of 2 mM chromium in defined and complex media respectively. Along with Cr+6 (MIC 8.6-17.8 mM), the isolates showed tolerance to Ni+2, Fe+3, Cu+2 and Co+2 but were extremely sensitive to Hg+2 followed by Cd+2, Mn+2 and Zn+2. In addition, they were resistant to antibiotics like penicillin, methicillin, ampicillin, neomycin and polymyxin B. During growth under shake-flask conditions, Arthrobacter SUK 1201 and SUK 1205 showed 100% reduction of 2 mM Cr+6 in KSC medium with simultaneous formation of insoluble precipitates of chromium salts. Both the isolates were also equally capable of completely reducing the Cr+6 present in mine seepage when grown in mine seepage supplemented with VB concentrate.(AU)

Assuntos

Microbiologia/tendências , Pseudomonas/fisiologia , Bacteriologia , Minerais/análise