Uranium and other heavy metal resistance and accumulation in bacteria isolated from uranium mine wastes. - Related Documents




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611401.0000Uranium and other heavy metal resistance and accumulation in bacteria isolated from uranium mine wastes. Ten bacterial strains isolated from uranium mine wastes were characterized in terms of their uranium and other metal resistance and accumulation. 16S rRNA gene sequence analysis identified the strains as members of genera Bacillus, Serratia, and Arthrobacter. Strains were able to utilize various carbon sources, particularly aromatic hydrocarbons, grow at broad pH and temperature ranges and produce non specific acid phosphatase relevant for metal phosphate precipitation in contaminated environment. The isolates exhibited high uranium and other heavy metals (Ni, Co, Cu and Cd) resistance and accumulation capacities. Particularly, Arthrobacter sp. J001 and Bacillus sp. J003 were superior in terms of U resistance at low pH (pH 4.0) along with metals and actinides (U and Th) removal with maximum cell loading of 1088 μmol U, 1293 μmol Th, 425 μmol Cu, 305 μmol Cd, 377 μmol Zn, 250 μmol Ni g(-1) cell dry wt. Genes encoding P(1B)-type ATPases (Cu-CPx and Zn-CPx) and ABC transporters (nik) as catalytic tools for maintaining cellular metal homeostasis were detected within several Bacillus spp., with possible incidence of horizontal gene transfer for the later gene showing phylogenetic lineage to α Proteobacteria members. The study provides evidence on intrinsic abilities of indigenous bacteria from U-mine suitable for survival and cleaning up of contaminated mine sites.201222375546
610810.9993Genes involved in arsenic transformation and resistance associated with different levels of arsenic-contaminated soils. BACKGROUND: Arsenic is known as a toxic metalloid, which primarily exists in inorganic form [As(III) and As(V)] and can be transformed by microbial redox processes in the natural environment. As(III) is much more toxic and mobile than As(V), hence microbial arsenic redox transformation has a major impact on arsenic toxicity and mobility which can greatly influence the human health. Our main purpose was to investigate the distribution and diversity of microbial arsenite-resistant species in three different arsenic-contaminated soils, and further study the As(III) resistance levels and related functional genes of these species. RESULTS: A total of 58 arsenite-resistant bacteria were identified from soils with three different arsenic-contaminated levels. Highly arsenite-resistant bacteria (MIC > 20 mM) were only isolated from the highly arsenic-contaminated site and belonged to Acinetobacter, Agrobacterium, Arthrobacter, Comamonas, Rhodococcus, Stenotrophomonas and Pseudomonas. Five arsenite-oxidizing bacteria that belonged to Achromobacter, Agrobacterium and Pseudomonas were identified and displayed a higher average arsenite resistance level than the non-arsenite oxidizers. 5 aoxB genes encoding arsenite oxidase and 51 arsenite transporter genes [18 arsB, 12 ACR3(1) and 21 ACR3(2)] were successfully amplified from these strains using PCR with degenerate primers. The aoxB genes were specific for the arsenite-oxidizing bacteria. Strains containing both an arsenite oxidase gene (aoxB) and an arsenite transporter gene (ACR3 or arsB) displayed a higher average arsenite resistance level than those possessing an arsenite transporter gene only. Horizontal transfer of ACR3(2) and arsB appeared to have occurred in strains that were primarily isolated from the highly arsenic-contaminated soil. CONCLUSION: Soils with long-term arsenic contamination may result in the evolution of highly diverse arsenite-resistant bacteria and such diversity was probably caused in part by horizontal gene transfer events. Bacteria capable of both arsenite oxidation and arsenite efflux mechanisms had an elevated arsenite resistance level.200919128515
610220.9993Isolation of highly copper-resistant bacteria from deep-sea hydrothermal fields and description of a novel species Marinobacter metalliresistant sp. nov. INTRODUCTION: Hydrothermal vents, rich in heavy metals, provided a unique niche for heavy metal resistant microbes. However, knowledge about copper resistant microbes in deep sea hydrothermal vents is still limited. METHODS: The copper-resistant bacteria were isolated from deep-sea hydrothermal vent samples and conducted thorough physical, phylogenetic, and genomic analyses to elucidate their copper resistance capability and related genes. RESULTS: Twelve highly copper-resistant bacteria (up to 6-10 mM) were isolated from deep sea hydrothermal fields They were affiliated with the Pseudoalteromonas (4), Marinobacter (3), Halomonas (2), Psychrobacter (1), and Pseudomonas (1) genus in the α-Proteobacteria, and the Sphingomonas (1) genus in the β-Proteobacteria. The presence of copper in the medium obviously induced the amount of polysaccharides and proteins in the crude extracellular polymeric substances (EPS) produced by Halomonas sp. CuT 3-1, Pseudoalteromonas sp. CuT 4-3 and Marinobacter metalliresistant CuT 6, which could absorb 40 to 50 mg•g(-1) copper. We further described a novel species, Marinobacter metalliresistant sp. nov. CuT 6(T), which exhibited a higher copper resistance and encoded more heavy metal resistance-related genes than other Marinobacter species. DISCUSSION: It revealed that the copper resistance capability exhibited by these strains in hydrothermal fields is likely attributed to the production of exopolymeric substances, such as polysaccharides and proteins, as well as active transport or efflux mechanisms for heavy metals.202439234539
610530.9993Genomic Characterization of a Mercury Resistant Arthrobacter sp. H-02-3 Reveals the Presence of Heavy Metal and Antibiotic Resistance Determinants. Nuclear production and industrial activities led to widespread contamination of the Department of Energy (DOE) managed Savannah River Site (SRS), located in South Carolina, United States. The H-02 wetland system was constructed in 2007 for the treatment of industrial and storm water runoff from the SRS Tritium Facility. Albeit at low levels, mercury (Hg) has been detected in the soils of the H-02 wetland ecosystem. In anoxic sediments, Hg is typically methylated by anaerobic microbiota, forming the highly neurotoxic methylmercury (MeHg), which biomagnifies across food webs. However, in surficial oxic wetland soils, microbially mediated demethylation and/or volatilization processes can transform Hg(2+) into the less toxic Hg(0) form which is released into the atmosphere, thus circumventing MeHg formation. To obtain a deeper understanding on bacterial Hg volatilization, a robust Hg-resistant (HgR) bacteria, called as strain H-02-3 was isolated from the H-02 soils. A draft genome sequence of this strain was obtained at a coverage of 700×, which assembled in 44 contigs with an N50 of 171,569 bp. The genomic size of the strain H-02-3 was 4,708,612 bp with a total number of 4,240 genes; phylogenomic analysis revealed the strain as an Arthrobacter species. Comparative genomics revealed the presence of 1100 unique genes in strain H-02-3, representing 26.7% of the total genome; many identified previously as metal resistance genes (MRGs). Specific to Hg-cycling, the presence of mercuric ion reductase (merA), the organomercurial lyase (merB), and the mercuric resistance operon regulatory protein, were identified. By inference, it can be proposed that the organomercurial lyase facilitates the demethylation of MeHg into Hg(2+) which is then reduced to Hg(0) by MerA in strain H-02-3. Furthermore, gene prediction using resistome analysis of strain H-02-3 revealed the presence of several antibiotic resistance genes (ARGs), that statistically correlated with the presence of metal resistant genes (MRGs), suggesting co-occurrence patterns of MRGs and ARGs in the strain. Overall, this study delineates environmentally beneficial traits that likely facilitates survival of Arthrobacter sp. H-02-3 within the H-02 wetland soil. Finally, this study also highlights the largely ignored public health risk associated with the co-development of ARGs and MRGs in bacteria native to historically contaminated soils.201932010097
610940.9992Studies on arsenic transforming groundwater bacteria and their role in arsenic release from subsurface sediment. Ten different Gram-negative arsenic (As)-resistant and As-transforming bacteria isolated from As-rich groundwater of West Bengal were characterized to assess their role in As mobilization. 16S rRNA gene analysis confirmed the affiliation of these bacteria to genera Achromobacter, Brevundimonas, Rhizobium, Ochrobactrum, and Pseudoxanthomonas. Along with superior As-resistance and As-transformation abilities, the isolates showed broad metabolic capacity in terms of utilizing a variety of electron donors and acceptors (including As) under aerobic and anaerobic conditions, respectively. Arsenic transformation studies performed under various conditions indicated highly efficient As(3+) oxidation or As(5+) reduction kinetics. Genes encoding As(3+) oxidase (aioA), cytosolic As(5+) reductase (arsC), and As(3+) efflux pump (arsB and acr3) were detected within the test isolates. Sequence analyses suggested that As homeostasis genes (particularly arsC, arsB, and acr3) were acquired by most of the bacteria through horizontal gene transfer. A strong correlation between As resistance phenotype and the presence of As(3+) transporter genes was observed. Microcosm study showed that bacterial strain having cytosolic As(5+) reductase property could play important role in mobilizing As (as As(3+)) from subsurface sediment.201424764001
610650.9992Genomic evidence reveals the extreme diversity and wide distribution of the arsenic-related genes in Burkholderiales. So far, numerous genes have been found to associate with various strategies to resist and transform the toxic metalloid arsenic (here, we denote these genes as "arsenic-related genes"). However, our knowledge of the distribution, redundancies and organization of these genes in bacteria is still limited. In this study, we analyzed the 188 Burkholderiales genomes and found that 95% genomes harbored arsenic-related genes, with an average of 6.6 genes per genome. The results indicated: a) compared to a low frequency of distribution for aio (arsenite oxidase) (12 strains), arr (arsenate respiratory reductase) (1 strain) and arsM (arsenite methytransferase)-like genes (4 strains), the ars (arsenic resistance system)-like genes were identified in 174 strains including 1,051 genes; b) 2/3 ars-like genes were clustered as ars operon and displayed a high diversity of gene organizations (68 forms) which may suggest the rapid movement and evolution for ars-like genes in bacterial genomes; c) the arsenite efflux system was dominant with ACR3 form rather than ArsB in Burkholderiales; d) only a few numbers of arsM and arrAB are found indicating neither As III biomethylation nor AsV respiration is the primary mechanism in Burkholderiales members; (e) the aio-like gene is mostly flanked with ars-like genes and phosphate transport system, implying the close functional relatedness between arsenic and phosphorus metabolisms. On average, the number of arsenic-related genes per genome of strains isolated from arsenic-rich environments is more than four times higher than the strains from other environments. Compared with human, plant and animal pathogens, the environmental strains possess a larger average number of arsenic-related genes, which indicates that habitat is likely a key driver for bacterial arsenic resistance.201424632831
610760.9992Metagenomic and genomic analysis of heavy metal-tolerant and -resistant bacteria in resource islands in a semi-arid zone of the Colombian Caribbean. Bacteria from resource islands can adapt to different extreme conditions in semi-arid regions. We aimed to determine the potential resistance and tolerance to heavy metals from the bacterial community under the canopy of three resource islands in a semi-arid zone of the Colombian Caribbean. Total DNA was extracted from soil and through a metagenomics approach, we identified genes related to heavy metal tolerance and resistance under the influence of drought and humidity conditions, as well as the presence or absence of vegetation. We characterized the genomes of bacterial isolates cultivated in the presence of four heavy metals. The abundances of genes related to heavy metal resistance and tolerance were favored by soil moisture and the presence of vegetation. We observed a high abundance of resistance genes (60.4%) for Cu, Zn, and Ni, while 39.6% represented tolerance. These genes positively correlated with clay and silt content, and negatively correlated with sand content. Resistance and tolerance were associated with detoxification mechanisms involving oxidoreductase enzymes, metalloproteases, and hydrolases, as well as transmembrane proteins involved in metal transport such as efflux pumps and ion transmembrane transporters. The Bacillus velezensis C3-3 and Cytobacillus gottheilii T106 isolates showed resistance to 5 mM of Cd, Co, Mn, and Ni through detoxification genes associated with ABC pumps, metal transport proteins, ion antiporter proteins, and import systems, among others. Overall, these findings highlight the potential of bacteria from resource islands in bioremediation processes of soils contaminated with heavy metals.202438127234
611370.9991Metal tolerance assisted antibiotic susceptibility profiling in Comamonas acidovorans. Metal ions are known selective agents for antibiotic resistance and frequently accumulate in natural environments due to the anthropogenic activities. However, the action of metals that cause the antibiotic resistance is not known for all bacteria. The present work is aimed to investigate the co-selection of metals and antibiotic resistance in Comamonas acidovorans. Tolerance profile of 16 metals revealed that the strain could tolerate high concentrations of toxic metals i.e., Cr (710 ppm), As (380 ppm), Cd (320 ppm), Pb (305 ppm) and Hg (205 ppm). Additionally, metal tolerant phenotypes were subjected to antibiotic resistance profiling; wherein several metal tolerant phenotypes (Cr 1.35-fold; Co-1.33 fold; Mn-1.29 fold) were resistant, while other metal tolerant phenotypes (Mg 1.32-fold; Hg 1.29-fold; Cu 1.28-fold) were susceptible than control phenotype. Metal accumulation may alter the metabolism of C. acidovorans that activates or inactivates the genes responsible for antibiotic resistance, resulting in the resistance and/or susceptibility pattern observed in metal resistant phenotypes.201829302860
609780.9991Genetic diversity and characterization of arsenic-resistant endophytic bacteria isolated from Pteris vittata, an arsenic hyperaccumulator. BACKGROUND: Alleviating arsenic (As) contamination is a high-priority environmental issue. Hyperaccumulator plants may harbor endophytic bacteria able to detoxify As. Therefore, we investigated the distribution, diversity, As (III) resistance levels, and resistance-related functional genes of arsenite-resistant bacterial endophytes in Pteris vittata L. growing in a lead-zinc mining area with different As contamination levels. RESULTS: A total of 116 arsenite-resistant bacteria were isolated from roots of P. vittata with different As concentrations. Based on the 16S rRNA gene sequence analysis of representative isolates, the isolates belonged to Proteobacteria, Actinobacteria, and Firmicutes. Major genera found were Agrobacterium, Stenotrophomonas, Pseudomonas, Rhodococcus, and Bacillus. The most highly arsenite-resistant bacteria (minimum inhibitory concentration > 45 mM) were isolated from P. vittata with high As concentrations and belonged to the genera Agrobacterium and Bacillus. The strains with high As tolerance also showed high levels of indole-3-acetic acid (IAA) production and carried arsB/ACR3(2) genes. The arsB and ACR3(2) were most likely horizontally transferred among the strains. CONCLUSION: The results of this study suggest that P. vittata plants with high As concentrations may select diverse arsenite-resistant bacteria; this diversity might, at least partly, be a result of horizontal gene transfer. These diverse endophytic bacteria are potential candidates to enhance phytoremediation techniques.201829739310
615590.9991MerP/MerT-mediated mechanism: A different approach to mercury resistance and bioaccumulation by marine bacteria. Currently, mechanism underlying mercury resistance and bioaccumulation of marine bacteria remains little understood. A marine bacterium Pseudomonas pseudoalcaligenes S1 is resistant to 120 mg/L Hg(2+) with bioaccumulation capacity of 133.33 mg/g. Accordingly, Hg(2+) resistance and bioaccumulation mechanism of S1 was investigated at molecular and cellular level. Annotation of S1 transcriptome reveals 772 differentially expressed genes, including Hg(2+)-relevant genes merT, merP and merA. Both merT and merP gene have three complete copies in S1 genome, while merA gene has only one. In order to evaluate the function of these Hg(2+)-relevant genes, three recombinant strains were constructed to express MerA (named as A), MerT/MerP (TP) and MerT/MerP/MerA (TPA), respectively. The results show that Hg(2+) resistance of strain TP, TPA, and A are improved with minimum inhibition concentration (MIC) being 60 mg/L, 40 mg/L, and 20 mg/L, respectively compared to 2 mg/L of host strain. Strain TP and TPA exhibit enhanced Hg(2+) bioaccumulation capacity, while strain A does not differ from the control. Their equilibrium Hg(2+) bioaccumulation capacities are 110.48 mg/g, 94.49 mg/g, 83.76 mg/g and 82.29 mg/g, respectively. Summarily, different from most microorganisms that exhibit Hg(2+) resistance by MerA-mediated mechanism, marine bacterium S1 achieves Hg(2+) resistance and bioaccumulation capability via MerT/MerP-mediated strategy.202031955028
6100100.9991Characterization of copper-resistant bacteria and bacterial communities from copper-polluted agricultural soils of central Chile. BACKGROUND: Copper mining has led to Cu pollution in agricultural soils. In this report, the effects of Cu pollution on bacterial communities of agricultural soils from Valparaiso region, central Chile, were studied. Denaturing gradient gel electrophoresis (DGGE) of the 16S rRNA genes was used for the characterization of bacterial communities from Cu-polluted and non-polluted soils. Cu-resistant bacterial strains were isolated from Cu-polluted soils and characterized. RESULTS: DGGE showed a similar high number of bands and banding pattern of the bacterial communities from Cu-polluted and non-polluted soils. The presence of copA genes encoding the multi-copper oxidase that confers Cu-resistance in bacteria was detected by PCR in metagenomic DNA from the three Cu-polluted soils, but not in the non-polluted soil. The number of Cu-tolerant heterotrophic cultivable bacteria was significantly higher in Cu-polluted soils than in the non-polluted soil. Ninety two Cu-resistant bacterial strains were isolated from three Cu-polluted agricultural soils. Five isolated strains showed high resistance to copper (MIC ranged from 3.1 to 4.7 mM) and also resistance to other heavy metals. 16S rRNA gene sequence analyses indicate that these isolates belong to the genera Sphingomonas, Stenotrophomonas and Arthrobacter. The Sphingomonas sp. strains O12, A32 and A55 and Stenotrophomonas sp. C21 possess plasmids containing the Cu-resistance copA genes. Arthrobacter sp. O4 possesses the copA gene, but plasmids were not detected in this strain. The amino acid sequences of CopA from Sphingomonas isolates (O12, A32 and A55), Stenotrophomonas strain (C21) and Arthrobacter strain (O4) are closely related to CopA from Sphingomonas, Stenotrophomonas and Arthrobacter strains, respectively. CONCLUSIONS: This study suggests that bacterial communities of agricultural soils from central Chile exposed to long-term Cu-pollution have been adapted by acquiring Cu genetic determinants. Five bacterial isolates showed high copper resistance and additional resistance to other heavy metals. Detection of copA gene in plasmids of four Cu-resistant isolates indicates that mobile genetic elements are involved in the spreading of Cu genetic determinants in polluted environments.201222950448
6156110.9991Diversity of arsenite transporter genes from arsenic-resistant soil bacteria. A PCR approach was developed to assess the occurrence and diversity of arsenite transporters in arsenic-resistant bacteria. For this purpose, three sets of degenerate primers were designed for the specific amplification of approximately 750bp fragments from arsB and two subsets of ACR3 (designated ACR3(1) and ACR3(2)) arsenite carrier gene families. These primers were used to screen a collection of 41 arsenic-resistant strains isolated from two soil samples with contrasting amounts of arsenic. PCR results showed that 70.7% of the isolates contained a gene related to arsB or ACR3, with three of them carrying both arsB and ACR3-like genes. Phylogenetic analysis of the protein sequences deduced from the amplicons indicated a prevalence of arsB in Firmicutes and Gammaproteobacteria, while ACR3(1) and ACR3(2) were mostly present in Actinobacteria and Alphaproteobacteria, respectively. In addition to validating the use of degenerate primers for the identification of arsenite transporter genes in a taxonomically wide range of bacteria, the study describes a novel collection of strains displaying interesting features of resistance to arsenate, arsenite and antimonite, and the ability to oxidize arsenite.200717258434
3712120.9991Enumeration and characterization of culturable arsenate resistant bacteria in a large estuary. Arsenic is a toxic element that exists in two major inorganic forms, arsenate and arsenite. A number of bacteria have been shown to resist arsenic exposure, and even more bacteria appear to possess the genes for arsenic resistance. In this study, the numbers of culturable arsenate-resistant bacteria present in water at three coastal sites in the Lake Pontchartrain estuary, Louisiana, was determined. Despite insignificant (less than 1.33 microM) levels of arsenic in this system, 20-50% of the viable count of bacteria showed appreciable arsenate resistance, suggesting that arsenic-resistant bacteria are common and widespread. A diverse array of arsenate-resistant isolates was obtained, with 16S rRNA sequence analysis indicating 37 different bacterial strains, representing six major bacterial groups. Many of these isolates were affiliated with groups of bacteria that have been poorly characterized in terms of arsenic resistance, such as the Betaproteobacteria or Flavobacteria. Some isolates were capable of tolerating very high (> 100 mM) levels of arsenate, although arsenite resistance was generally much lower. The results suggest that arsenic-resistant bacteria are common, even in environments with insignificant arsenic contamination, and that many different groups of aquatic bacteria show appreciable arsenic resistance.200516261862
3612130.9991Copper resistance in Desulfovibrio strain R2. A sulfate-reducing bacterium, designated as strain R2, was isolated from wastewater of a ball-bearing manufacturing facility in Tomsk, Western Siberia. This isolate was resistant up to 800 mg Cu/l in the growth medium. By comparison, Cu-resistance of reference cultures of sulfate-reducing bacteria ranged from 50 to 75 mg Cu/l. Growth experiments with strain R2 showed that Cu was an essential trace element and, on one hand, enhanced growth at concentrations up to 10 mg/l but, on the other hand, the growth rate decreased and lag-period extended at copper concentrations of >50 mg/l. Phenotypic characteristics and a 1078 bp nucleotide sequence of the 16S rDNA placed strain R2 within the genus Desulfovibrio. Desulfovibrio R2 carried at least one plasmid of approximately of 23.1 kbp. A 636 bp fragment of the pcoR gene of the pco operon that encodes Cu resistance was amplified by PCR from plasmid DNA of strain R2. The pco genes are involved in Cu-resistance in some enteric and aerobic soil bacteria. Desulfovibrio R2 is a prospective strain for bioremediation purposes and for developing a homologous system for transformation of Cu-resistance in sulfate-reducing bacteria.200312755486
6112140.9990Analysis of heavy metal tolerance and genomics in an indigenous Kurthia strain from Kulik River reveals multi-metal resistance and dominance of selection pressure on codon usage patterns. Heavy metal(loid) contamination poses significant risks to biological entities and the ecosystem. Many metal(loid)-resistant bacteria have been isolated from different environmental sites, but still no work has described multi-metal resistant Kurthia sp. In this study, an indigenous Kurthia strain isolated from the surface water of River Kulik was studied to determine its level of tolerance to various metal(loid)s. This study aimed to isolate, characterize and determine the growth kinetics and efficiency of Kurthia gibsonii strain M6 to remove and bioaccumulate As(V), Ni and Pb in vitro. This study also aimed to sequence the whole genome of the bacterium, identify metal resistance genes and analyze the codon usage patterns and factors that affect the codon usage bias of these genes. The bacterium showed elevated resistance to As(V), Pb, Ni and Zn. Under metal(loid) stressed conditions, live cells of Kurthia strain M6 bioaccumulated 212.74, 91.51 and 40.38 mg g(-1) of As(V), Pb and Ni, respectively. The removal efficiency was 97%, 69.15% and 25.88% for Pb, Ni and As(V), respectively. Genome analysis revealed the existence of different genes conferring heavy metal resistance. A comprehensive analysis of codon usage patterns for metal resistance genes depicted the predominance of selection pressure as a prime force influencing codon usage patterns. This is the first time a multi-metal resistant K. gibsonii strain has been systematically studied regarding its heavy metal resistance biology. These findings will provide insights into the metal resistance mechanisms of the genus Kurthia and assist in devising new strategies for the bioremediation of metal-polluted environments.202539945867
8684150.9990Multiple Transcriptional Mechanisms Collectively Mediate Copper Resistance in Cupriavidus gilardii CR3. Bacteria resist copper (Cu) stress by implementing several metabolic mechanisms. However, these mechanisms are not fully understood. We investigated the mechanism of Cu resistance in Cupriavidus gilardii CR3, a Cu-resistant bacterium with a fully sequenced, annotated genome. The growth of CR3 was inhibited by higher Cu concentrations (≥1.0 mM) but not by lower ones (≤0.5 mM). CR3 accumulated Cu intracellularly (ratios of intercellular to extracellular Cu were 11.6, 4.24, and 3.9 in 0.1, 0.5, and 1.5 mM Cu treatments, respectively). A comparative transcriptome analysis of CR3 respectively revealed 310 and 413 differentially expressed genes under 0.5 and 1.5 mM Cu stress, most of which were up-regulated under Cu treatment. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes functional enrichment analyses uncovered several genotype-specific biological processes related to Cu stress. Besides revealing known Cu resistance-related genes, our global transcriptomics approach indicated that sulfur metabolism, iron-sulfur cluster, and cell secretion systems are involved in mediating Cu resistance in strain CR3. These results suggest that bacteria collectively use multiple systems to cope with Cu stress. Our findings concerning the global transcriptome response to Cu stress in CR3 provide new information for understanding the intricate regulatory network of Cu homeostasis in prokaryotes.201930920814
164160.9990Plasmids for heavy metal resistance in Alcaligenes eutrophus CH34: mechanisms and applications. Alcaligenes eutrophus CH34 is the main representative of a group of strongly related strains (mostly facultative chemolithotrophs) that are well adapted to environments containing high levels of heavy metals. It harbors the megaplasmids pMOL28 and pMOL30 which carry resistance determinants to Co2+, Ni2+, CrO(4)2-, Hg2+, Tl+, Cd2+, Cu2+ and Zn2+. Among the best characterized determinants are the cnr operon (resistance to Co, Ni) on pMOL28 and the czc operon on pMOL30 (resistance to Co, Cd and Zn). Although the two systems reveal a significant degree of amino acid similarity in the structural genes, the regulation of the operons is different. The resistance mechanism in both cases is based on efflux. The efflux mechanism leads to a pH increase outside of the cytoplasmic membrane. Metals are sequestered from the external medium through the bioprecipitation of metal carbonates formed in the saturated zone around the cell. This latter phenomenon can be exploited in bioreactors designed to remove metals from effluents. The bacteria are immobilized on composite membranes in a continuous tubular membrane reactor (CTMR). The effluent continuously circulates through the intertubular space, while the external surface of the tubes is in contact with the growth medium. Metal crystals are eventually removed by the effluent stream and collected on a glass bead column. The system has been applied to effluents containing Cd, Zn, Co, Ni and Cu. By introducing catabolic plasmids involved in the aerobic degradation of PCBs and 2,4-D into metal-resistant A. eutrophus strains, the application range was widened to include effluents polluted with both organic and inorganic substances. Biosensors have been developed which are based on the fusion of genes induced by metals to a reporter system, the lux operon of Vibrio fischeri. Bacterial luciferases produce light through the oxidation of fatty aldehydes. The gene fusions are useful both for the study of regulatory genes and for the determination of heavy metal concentrations in the environment.19947917428
6099170.9990Culture-dependent and independent studies of microbial diversity in highly copper-contaminated Chilean marine sediments. Cultivation and molecular-based approaches were used to study microbial diversity in two Chilean marine sediments contaminated with high (835 ppm) and very high concentrations of copper (1,533 ppm). The diversity of cultivable bacteria resistant to copper was studied at oxic and anoxic conditions, focusing on sulfate-, thiosulfate-, and iron-reducing bacteria. For both sediments, the cultivable bacteria isolated at oxic conditions were mostly affiliated to the genus Bacillus, while at anoxic conditions the majority of the cultivable bacteria found were closely related to members of the genera Desulfovibrio, Sphingomonas, and Virgibacillus. Copper resistance was between 100 and 400 ppm, with the exception of a strain affiliated to members of the genus Desulfuromonas, which was resistant up to 1,000 ppm of copper. In parallel, cloning and sequencing of 16S rRNA was performed to study the total bacterial diversity in the sediments. A weak correlation was observed between the isolated strains and the 16S rRNA operational taxonomic units detected. The presence of copper resistance genes (copA, cusA, and pcoA) was tested for all the strains isolated; only copA was detected in a few isolates, suggesting that other copper resistance mechanisms could be used by the bacteria in those highly copper-contaminated sediments.201322976340
6103180.9990Culture-dependent study of arsenic-reducing bacteria in deep aquatic sediments of Bengal Delta. Biogeochemical release of soil-bound arsenic (As) governs mobilization of the toxic metalloid into the groundwater. The present study has examined As(V)-reduction ability of bacteria from anoxic aquatic sediments that might contribute to arsenic mobilization in the Bengal Delta. Arsenic-reducing bacteria from deep layers of pond sediment were enriched and isolated in anaerobic environments and As(V) reduction was assessed in culture medium. The pond sediment enrichments harboured As(V)-reducing bacteria belonging to the phyla Firmicutes and Proteobacteria with dominance of Paraclostridium benzoelyticum and P. bifermentans. Among total 17 isolates, the respiratory reductase genes were not detected by the most common primers and only 3 strains had arsenic reductase ArsC gene suggesting involvement of resistance and some unknown mechanisms in As(V) reduction. Presence of high levels of organic matter, As, and As-reducing bacteria might make deep aquatic sediments a hot spot of As mobilization and aquifer contamination.202134482463
6754190.9990Real-time PCR based analysis of metal resistance genes in metal resistant Pseudomonas aeruginosa strain J007. A uranium (U)-resistant and -accumulating Pseudomonas aeruginosa strain was characterized to assess the response of toxic metals toward its growth and expression of metal resistance determinants. The bacterium showed MIC (minimum inhibitory concentration) values of 6, 3, and 2 mM for Zn, Cu, and Cd, respectively; with resistance phenotype conferred by periplasmic Cu sequestering copA and RND type heavy metal efflux czcA genes. Real-time PCR-based expression analysis revealed significant upregulation of both these genes upon exposure to low concentrations of metals for short duration, whereas the global stress response gene sodA encoding superoxide dismutase enzyme was upregulated only at higher metal concentrations or longer exposure time. It could also be inferred that copA and czcA are involved in providing resistance only at low metal concentrations, whereas involvement of "global stress response" phenomenon (expression of sodA) at higher metal concentration or increased exposure was evident. This study provides significant understanding of the adaptive response of bacteria surviving in metal and radionuclide contaminated environments along with the development of real-time PCR-based quantification method of using metal resistance genes as biomarker for monitoring relevant bacteria in such habitats.201626662317