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ABSTRACT: Plasmids are important in evolution and adaptation of host bacteria, yet we lack a comprehensive picture of their own natural variation. We used replicon typing and RFLP analysis to assess diversity and distribution of plasmids in the ECOR, SARA, SARB and SARC reference collections of Escherichia coli and Salmonella. Plasmids, especially large (⩾30kb) plasmids, are abundant in these collections. Host species and genotype clearly impact plasmid prevalence; plasmids are more abundant in ECOR than SAR, but, within ECOR, subgroup B2 strains have the fewest large plasmids. The majority of large plasmids have unique RFLP patterns, suggesting high variation, even within dominant replicon families IncF and IncI1. We found only four conserved plasmid types within ECOR, none of which are widely distributed. Within SAR, conserved plasmid types are primarily serovar-specific, including a pSLT-like plasmid in 13 Typhimurium strains. Conservation of pSLT contrasts with variability of other plasmids, suggesting evolution of serovar-specific virulence plasmids is distinct from that of most enterobacterial plasmids. We sequenced a conserved serovar Heidelberg plasmid but did not detect virulence or antibiotic resistance genes. Our data illustrate the high degree of natural variation in large plasmids of E. coli and Salmonella, even among plasmids sharing backbone genes.
Plasmid 08/2012; · 1.52 Impact Factor
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Julia E S Shearer,
Joy Wireman,
Jessica Hostetler,
Heather Forberger,
Jon Borman,
John Gill,
Susan Sanchez,
Alexander Mankin,
Jacqueline Lamarre,
Jodi A Lindsay,
Kenneth Bayles,
Ainsley Nicholson,
Frances O'Brien,
Slade O Jensen,
Neville Firth,
Ronald A Skurray, Anne O Summers
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ABSTRACT: Staphylococci are increasingly aggressive human pathogens suggesting that active evolution is spreading novel virulence and resistance phenotypes. Large staphylococcal plasmids commonly carry antibiotic resistances and virulence loci, but relatively few have been completely sequenced. We determined the plasmid content of 280 staphylococci isolated in diverse geographical regions from the 1940s to the 2000s and found that 79% of strains carried at least one large plasmid >20 kb and that 75% of these large plasmids were 20-30 kb. Using restriction fragment length polymorphism (RFLP) analysis, we grouped 43% of all large plasmids into three major families, showing remarkably conserved intercontinental spread of multiresistant staphylococcal plasmids over seven decades. In total, we sequenced 93 complete and 57 partial staphylococcal plasmids ranging in size from 1.3 kb to 64.9 kb, tripling the number of complete sequences for staphylococcal plasmids >20 kb in the NCBI RefSeq database. These plasmids typically carried multiple antimicrobial and metal resistances and virulence genes, transposases and recombinases. Remarkably, plasmids within each of the three main families were >98% identical, apart from insertions and deletions, despite being isolated from strains decades apart and on different continents. This suggests enormous selective pressure has optimized the content of certain plasmids despite their large size and complex organization.
G3 (Bethesda, Md.). 12/2011; 1(7):581-91.
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ABSTRACT: The integrase IntI1 catalyses recombination of antibiotic-resistance gene cassettes in the integron, a widely found bacterial mobile element active in spreading antibiotic multi-resistance. We have previously shown that resistance cassette recombination rate and specificity depend on the amount of intracellular integrase. Here, we used in vivo and in vitro methods to examine convergent expression of the integrase promoter (P(int)) and of the cassette promoters (P(c) and P(2)) in the prototypical plasmid-borne class 1 integron, In2. Highly conserved P(int) has near consensus -10 and -35 hexamers for σ(70) RNA polymerase, but there are 11 naturally occurring arrangements of P(c) alone or combinations of the P(c)+P(2) cassette promoters (note that P(2) occurs with a 14 or 17 bp spacer). Using a bi-directional reporter vector, we found that P(int) is a strong promoter in vivo, but its expression is reduced by converging transcription from P(c) and P(2). In addition to cis-acting convergence control of integrase expression, the regulator site prediction program, prodoric 8.9, identified sites for global regulators FIS, LexA, IHF and H-NS in and near the integron promoters. In strains mutated in each global regulator, we found that: (1) FIS repressed integrase and cassette expression; (2) LexA repressed P(int) and P(2) with the 14 bp spacer version of P(2) and FIS was necessary for maximum LexA repression; (3) IHF activated P(int) when it faced the strong 17 bp spacer P(2) but did not elevate its expression versus LexA-repressed P(2) with the 14 bp spacer; and (4) H-NS repressed both P(int) and the 14 bp P(2) but activated the 17 bp P(2) cassette promoters. Mobility shift assays showed that FIS and IHF interact directly with the promoter regions and DNase I footprinting confirmed extensive protection by FIS of wild-type In2 integron promoter sequence. Thus, nucleoid-associated proteins, known to act directly in site-specific recombination, also control integron gene expression directly and possibly indirectly.
Microbiology 07/2011; 157(Pt 10):2841-53. · 3.06 Impact Factor
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ABSTRACT: The identification of peptides that result from post-translational modifications is critical for understanding normal pathways of cellular regulation as well as identifying damage from, or exposures to xenobiotics, i.e. the exposome. However, because of their low abundance in proteomes, effective detection of modified peptides by mass spectrometry (MS) typically requires enrichment to eliminate false identifications. We present a new method for confidently identifying peptides with mercury (Hg)-containing adducts that is based on the influence of mercury's seven stable isotopes on peptide isotope distributions detected by high-resolution MS. Using a pure protein and E. coli cultures exposed to phenyl mercuric acetate, we show the pattern of peak heights in isotope distributions from primary MS single scans efficiently identified Hg adducts in data from chromatographic separation coupled with tandem mass spectrometry with sensitivity and specificity greater than 90%. Isotope distributions are independent of peptide identifications based on peptide fragmentation (e.g. by SEQUEST), so both methods can be combined to eliminate false positives. Summing peptide isotope distributions across multiple scans improved specificity to 99.4% and sensitivity above 95%, affording identification of an unexpected Hg modification. We also illustrate the theoretical applicability of the method for detection of several less common elements including the essential element, selenium, as selenocysteine in peptides.
Molecular & Cellular Proteomics 04/2011; 10(8):M110.004853. · 7.40 Impact Factor
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ABSTRACT: USA300 methicillin-resistant Staphylococcus aureus (MRSA) isolates are usually resistant only to oxacillin, erythromycin, and, increasingly, levofloxacin. Of these, oxacillin and levofloxacin resistances are chromosomally encoded. Plasmid-mediated clindamycin, mupirocin, and/or tetracycline resistance has been observed among USA300 isolates, but these descriptions were limited to specific patient populations or isolated occurrences. We examined the antimicrobial susceptibilities of invasive MRSA isolates from a national surveillance population in order to identify USA300 isolates with unusual, possibly emerging, plasmid-mediated antimicrobial resistance. DNA from these isolates was assayed for the presence of resistance determinants and the presence of a pSK41-like conjugative plasmid. Of 823 USA300 isolates, 72 (9%) were tetracycline resistant; 69 of these were doxycycline susceptible and tetK positive, and 3 were doxycycline resistant and tetM positive. Fifty-one (6.2%) isolates were clindamycin resistant and ermC positive; 22 (2.7%) isolates were high-level mupirocin resistant (mupA positive); 5 (0.6%) isolates were trimethoprim-sulfamethoxazole (TMP-SMZ) resistant, of which 4 were dfrA positive; and 7 (0.9%) isolates were gentamicin resistant and aac6'-aph2'' positive. Isolates with pSK41-like plasmids (n = 24) were positive for mupA (n = 19), dfrA (n = 6), aac6'-aph2'' (n = 6), tetM (n = 2), and ermC (n = 8); 20 pSK41-positive isolates were positive for two or more resistance genes. Conjugative transfer of resistance was demonstrated between four gentamicin- and mupirocin-resistant and three gentamicin- and TMP-SMZ-resistant USA300 isolates; transconjugants harbored a single pSK41-like plasmid, which was PCR positive for aac6'-aph2'' and either mupA and/or dfrA. USA300 and USA100 isolates from the same state with identical resistance profiles contained pSK41-like plasmids with indistinguishable restriction and Southern blot profiles, suggesting horizontal plasmid transfer between USA100 and USA300 isolates.
Antimicrobial Agents and Chemotherapy 09/2010; 54(9):3804-11. · 4.84 Impact Factor
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ABSTRACT: The bacterial metalloregulator MerR is the index case of an eponymous family of regulatory proteins, which controls the transcription of a set of genes (the mer operon) conferring mercury resistance in many bacteria. Homodimeric MerR represses transcription in the absence of mercury and activates transcription upon Hg(II) binding. Here, the average structures of the apo and Hg(II)-bound forms of MerR in aqueous solution are examined using small-angle X-ray scattering, indicating an extended conformation of the metal-bound protein and revealing the existence of a novel compact conformation in the absence of Hg(II). Molecular dynamics (MD) simulations are performed to characterize the conformational dynamics of the Hg(II)-bound form. In both small-angle X-ray scattering and MD, the average torsional angle between DNA-binding domains is approximately 65 degrees. Furthermore, in MD, interdomain motions on a timescale of approximately 10 ns involving large-amplitude (approximately 20 A) domain opening-and-closing, coupled to approximately 40 degrees variations of interdomain torsional angle, are revealed. This correlated domain motion may propagate allosteric changes from the metal-binding site to the DNA-binding site while maintaining DNA contacts required to initiate DNA underwinding.
Journal of Molecular Biology 03/2010; 398(4):555-68. · 4.00 Impact Factor
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ABSTRACT: Demethylation is a key reaction in global mercury cycling. The bacterial organomercurial lyase, MerB, catalyzes the demethylation of a wide range of organomercurials via Hg-C protonolysis. Two strictly conserved cysteine residues in the active site are required for catalysis, but the source of the catalytic proton and the detailed reaction mechanism have not been determined. Here, the two major proposed reaction mechanisms of MerB are investigated and compared using hybrid density functional theory calculations. A model of the active site was constructed from an X-ray crystal structure of the Hg(II)-bound MerB product complex. Stationary point structures and energies characterized for the Hg-C protonolysis of methylmercury rule out the direct protonation mechanism in which a cysteine residue delivers the catalytic proton directly to the organic leaving group. Instead, the calculations support a two-step mechanism in which Cys96 or Cys159 first donates a proton to Asp99, enabling coordination of two thiolates with R-Hg(II). At the rate-limiting transition state, Asp99 protonates the nascent carbanion in a trigonal planar, bis thiol-ligated R-Hg(II) species to cleave the Hg-C bond and release the hydrocarbon product. Reactions with two other substrates, vinylmercury and cis-2-butenyl-2-mercury, were also modeled, and the computed activation barriers for all three organomercurial substrates reproduce the trend in the experimentally observed enzymatic reaction rates. Analysis of atomic charges in the rate-limiting transition state structure using Natural Population Analysis shows that MerB lowers the activation free energy in the Hg-C protonolysis reaction by redistributing electron density into the leaving group and away from the catalytic proton.
Journal of the American Chemical Society 10/2009; 131(37):13278-85. · 9.91 Impact Factor
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Anne O Summers
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ABSTRACT: Some elements are essential for life and others closely related to them are very toxic. In exploiting unique ecological niches many prokaryotes have evolved the means to defend themselves against and even to derive energy from deleterious elements. Toxic metal defense systems are related to those providing homeostasis of essential metals and metalloid elements. Expression of these multiprotein systems is costly but they must respond rapidly and, so, all are well controlled. Seven diverse families of metalloregulators are presently recognized for essential metal homeostasis in prokaryotes. Two of these, the ArsR and MerR families, figure more often than the others in controlling responses to toxic transition metals and metalloids. This review emphasizes recent advances in these two metalloregulator families and highlights emerging regulatory motifs of other types.
Current opinion in microbiology 04/2009; 12(2):138-44. · 7.87 Impact Factor
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ABSTRACT: IntI1 mediates the recombination of antibiotic-resistant gene cassettes between different integrons in the same cell, facilitating the persistence and dissemination of these genes. Historically, integrase activity has been measured by conjugating recombinant products from donor cells overexpressing integrase and quantifying them in recipient cells. Here we report the first measurements of the steady-state intracellular abundance of integrase-mediated recombination products in strains expressing natural or high IntI1 levels. Recombination products in both high and natural integrase strains increased markedly through late log phase and continued to rise in stationary phase in the high integrase strain, but declined in the natural expression strain. Simple acquisition of gene cassettes was seen only in strains expressing high integrase; in strains with natural integrase levels, only cointegrates between the two integron-bearing plasmids were detectable at all growth stages. Unexpectedly, more attIxattI than attCxattI recombination products were seen in log phase for both strains; however, in stationary phase, the high integrase strain increased attC recombination, consistent with earlier observations of integrase crossover site preferences. Thus, direct quantification of the steady-state concentration of recombination products reveals that the integrase's intracellular concentration affects the amount and type of recombination events in a growth-phase-dependent manner.
Journal of Molecular Biology 01/2009; 386(2):316-31. · 4.00 Impact Factor
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ABSTRACT: Metalloregulators of the MerR family activate transcription upon metal binding by underwinding the operator-promoter DNA to permit open complex formation by pre-bound RNA polymerase. Historically, MerR's allostery has been monitored only indirectly via nuclease sensitivity or by fluorescent nucleotide probes and was very specific for Hg(II), although purified MerR binds several thiophilic metals. To observe directly MerR's ligand-induced behavior we made 2-fluorotyrosine-substituted MerR and found similar, minor changes in (19)F chemical shifts of tyrosine residues in the free protein exposed to Hg(II), Cd(II) or Zn(II). However, DNA binding elicits large chemical shift changes in MerR's tyrosine residues and in DNA-bound MerR Hg(II) provokes changes very distinct from those of Cd(II) or Zn(II). These chemical shift changes and other biophysical and phenotypic properties of wild-type MerR and relevant mutants reveal elements of an allosteric network that enables the coordination state of the metal binding site to direct metal-specific movements in the distant DNA binding site and the DNA-bound state also to affect the metal binding domain.
Journal of Molecular Biology 09/2007; 371(1):79-92. · 4.00 Impact Factor
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ABSTRACT: Sequencing of the large (>50 kb), low-copy-number (<5 per cell) plasmids that mediate horizontal gene transfer has been hindered by the difficulty and expense of isolating DNA from individual plasmids of this class. We report here that a kit method previously devised for purification of bacterial artificial chromosomes (BACs) can be adapted for effective preparation of individual plasmids up to 220 kb from wild gram-negative and gram-positive bacteria. Individual plasmid DNA recovered from less than 10 ml of Escherichia coli, Staphylococcus, and Corynebacterium cultures was of sufficient quantity and quality for construction of high-coverage libraries, as shown by sequencing five native plasmids ranging in size from 30 kb to 94 kb. We also report recommendations for vector screening to optimize plasmid sequence assembly, preliminary annotation of novel plasmid genomes, and insights on mobile genetic element biology derived from these sequences. Adaptation of this BAC method for large plasmid isolation removes one major technical hurdle to expanding our knowledge of the natural plasmid gene pool.
Applied and Environmental Microbiology 08/2006; 72(7):4899-906. · 3.83 Impact Factor
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ABSTRACT: MerR, the metalloregulator of the bacterial mercury resistance (mer) operon, binds Hg(II) with high affinity. To study the mechanism of metal-induced activation, a small protein was previously engineered embodying in a single polypeptide the metal-binding domain (MBD) ordinarily formed between two monomers of MerR. Here the physiological and biochemical properties of MBD expressed on the cell surface or in the cytosol were examined, to better understand the environments in which specific metal binding can occur with this small derivative. Over 20 000 surface copies of MBD were expressed per Escherichia coli cell, with metal stoichiometries of approximately 1.0 Hg(II) per MBD monomer. Cells expressing MBD on their surface in rich medium bound 6.1-fold more Hg(II) than those not expressing MBD. Although in nature cells use the entire mer operon to detoxify mercury, it was interesting to note that cells expressing only MBD survived Hg(II) challenge and recovered more quickly than cells without MBD. Cell-surface-expressed MBD bound Hg(II) preferentially even in the presence of a 22-fold molar excess of Zn(II) and when exposed to equimolar Cd(II) in addition. MBD expressed in the cystosol also afforded improved survival from Hg(II) exposure for E. coli and for the completely unrelated bacterium Deinococcus radiodurans.
Microbiology 04/2006; 152(Pt 3):709-19. · 3.06 Impact Factor
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ABSTRACT: We used slot blot hybridization, quantitative polymerase chain reaction (qPCR), and flow cytometry microarrays to quantify specific 16S rDNAs in weekly fecal specimens from four monkeys housed in a research vivarium for periods ranging from five to 8 months. Even in these uniformly housed and fed animals the gut microbiota is idiosyncratic, very dynamic on short timescales, and shows significant positive and negative correlations among some bacteria as well as responses to heavy metal exposure. The relative quantification (fmol targets per total fmol bacterial 16S rDNA) afforded by flow cytometry microarrays agreed well with the absolute quantification (nanogram of target DNA per nanogram of fecal DNA) afforded by slot blots and qPCR. We also noted strengths and weaknesses in inter-method comparisons for DNA-based quantification of these complex bacterial communities.
Environmental Microbiology 04/2006; 8(3):490-503. · 5.84 Impact Factor
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Anne O Summers
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ABSTRACT: Bacteria carrying resistance genes for many antibiotics are moving beyond the clinic into the community, infecting otherwise healthy people with untreatable and frequently fatal infections. This state of affairs makes it increasingly important that we understand the sources of this problem in terms of bacterial biology and ecology and also that we find some new targets for drugs that will help control this growing epidemic. This brief and eclectic review takes the perspective that we have too long thought about the problem in terms of treatment with or resistance to a single antibiotic at a time, assuming that dissemination of the resistance gene was affected by simple vertical inheritance. In reality antibiotic resistance genes are readily transferred horizontally, even to and from distantly related bacteria. The common agents of bacterial gene transfer are described and also one of the processes whereby nonantibiotic chemicals, specifically toxic metals, in the environment can select for and enrich bacteria with antibiotic multiresistance. Lastly, some speculation is offered on broadening our perspective on this problem to include drugs directed at compromising the ability of the mobile elements themselves to replicate, transfer, and recombine, that is, the three "infrastructure" processes central to the movement of genes among bacteria.
Animal Biotechnology 02/2006; 17(2):125-35. · 0.93 Impact Factor
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ABSTRACT: The ligand binding and catalytic properties of heavy metal ions have led to the evolution of metal ion-specific pathways for control of their intracellular trafficking and/or elimination. Small MW proteins/domains containing a GMTCXXC metal binding motif in a betaalphabetabetaalphabeta fold are common among proteins controlling the mobility of soft metal ions such as Cu(1+), Zn(2+), and Hg(2+), and the functions of several have been established. In bacterial mercuric ion reductases (MerA), which catalyze reduction of Hg(2+) to Hg(0) as a means of detoxification, one or two repeats of sequences with this fold are highly conserved as N-terminal domains (NmerA) of uncertain function. To simplify functional analysis of NmerA, we cloned and expressed the domain and catalytic core of Tn501 MerA as separate proteins. In this paper, we show Tn501 NmerA to be a stable, soluble protein that binds 1 Hg(2+)/domain and delivers it to the catalytic core at kinetically competent rates. Comparison of steady-state data for full-length versus catalytic core MerA using Hg(glutathione)(2) or Hg(thioredoxin) as substrate demonstrates that the NmerA domain does participate in acquisition and delivery of Hg(2+) to the catalytic core during the reduction catalyzed by full-length MerA, particularly when Hg(2+) is bound to a protein. Finally, comparison of growth curves for glutathione-depleted Escherichia coli expressing either catalytic core, full-length, or a combination of core plus NmerA shows an increased protection of cells against Hg(2+) in the media when NmerA is present, providing the first evidence of a functional role for this highly conserved domain.
Biochemistry 09/2005; 44(34):11402-16. · 3.42 Impact Factor
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ABSTRACT: Mercury resistant bacteria have developed a system of two enzymes (MerA and MerB), which allows them to efficiently detoxify both ionic and organomercurial compounds. The organomercurial lyase (MerB) catalyzes the protonolysis of the carbon-mercury bond resulting in the formation of ionic mercury and a reduced hydrocarbon. The ionic mercury [Hg(II)] is subsequently reduced to the less reactive elemental mercury [Hg(0)] by a specific mercuric reductase (MerA). To better understand MerB's unique enzymatic activity, we used nuclear magnetic resonance (NMR) spectroscopy to determine the structure of the free enzyme. MerB is characterized by a novel protein fold consisting of three noninteracting antiparallel beta-sheets surrounded by six alpha-helices. By comparing the NMR data of free MerB and the MerB/Hg/DTT complex, we identified a set of residues that likely define a Hg/DTT binding site. These residues cluster around two cysteines (C(96) and C(159)) that are crucial to MerB's catalytic activity. A detailed analysis of the structure revealed the presence of an extensive hydrophobic groove adjacent to this Hg/DTT binding site. This extensive hydrophobic groove has the potential to interact with the hydrocarbon moiety of a wide variety of substrates and may explain the broad substrate specificity of MerB.
Biochemistry 08/2004; 43(26):8322-32. · 3.42 Impact Factor
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ABSTRACT: Reversing the spread of antibiotic multiresistant bacteria is hampered by ignorance of the natural history of resistance genes, the mobile elements carrying them, and the bacterial hosts harboring them. Using traditional cultivation and cultivation-independent molecular techniques, we quantified antibiotic resistance genes and mobile elements called integrons in poultry house litter from commercial poultry farms. Unexpectedly, the major reservoir for Class 1 integrons in poultry litter is not their previously identified hosts, Gram-negative Enterobacteriaceae such as Escherichia coli. Rather, integrons and associated resistance genes abound in several genera of Gram-positive bacteria that constitute >85% of the litter community compared with Enterobacteriaceae that comprise <2% of this ecosystem. This finding warrants reexamination of our assumptions about the persistence and spread of antibiotic resistance genes.
Proceedings of the National Academy of Sciences 05/2004; 101(18):7118-22. · 9.68 Impact Factor
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ABSTRACT: The repressor-activator MerR that controls transcription of the mercury resistance (mer) operon is unusual for its high sensitivity and specificity for Hg(II) in in vivo and in vitro transcriptional assays. The metal-recognition domain of MerR resides at the homodimer interface in a novel antiparallel arrangement of alpha-helix 5 that forms a coiled-coil motif. To facilitate the study of this novel metal binding motif, we assembled this antiparallel coiled coil into a single chain by directly fusing two copies of the 48-residue alpha-helix 5 of MerR. The resulting 107-residue polypeptide, called the metal binding domain (MBD), and wild-type MerR were overproduced and purified, and their metal-binding properties were determined in vivo and in vitro. In vitro MBD bound ca. 1.0 equivalent of Hg(II) per pair of binding sites, just as MerR does, and it showed only a slightly lower affinity for Hg(II) than did MerR. Extended X-ray absorption fine structure data showed that MBD has essentially the same Hg(II) coordination environment as MerR. In vivo, cells overexpressing MBD accumulated 70 to 100% more (203)Hg(II) than cells bearing the vector alone, without deleterious effects on cell growth. Both MerR and MBD variously bound other thiophilic metal ions, including Cd(II), Zn(II), Pb(II), and As(III), in vitro and in vivo. We conclude that (i) it is possible to simulate in a single polypeptide chain the in vitro and in vivo metal-binding ability of dimeric, full-length MerR and (ii) MerR's specificity in transcriptional activation does not reside solely in the metal-binding step.
Journal of Bacteriology 04/2004; 186(6):1861-8. · 3.83 Impact Factor
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ABSTRACT: Complex mixtures of nucleic acids occur in numerous systems, including environmental samples (e.g., groundwater, sediment),
skin, feces, and blood. Often, it is desirable to be able to identify and measure the amount of a particular analyte DNA in
a mixture. When there are multiple analyte DNAs of interest, multiplexing techniques can speed up the analysis.
12/2003: pages 51-74;
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ABSTRACT: Bacterial resistance to inorganic and organic mercury compounds (HgR) is one of the most widely observed phenotypes in eubacteria. Loci conferring HgR in Gram-positive or Gram-negative bacteria typically have at minimum a mercuric reductase enzyme (MerA) that reduces reactive ionic Hg(II) to volatile, relatively inert, monoatomic Hg(0) vapor and a membrane-bound protein (MerT) for uptake of Hg(II) arranged in an operon under control of MerR, a novel metal-responsive regulator. Many HgR loci encode an additional enzyme, MerB, that degrades organomercurials by protonolysis, and one or more additional proteins apparently involved in transport. Genes conferring HgR occur on chromosomes, plasmids, and transposons and their operon arrangements can be quite diverse, frequently involving duplications of the above noted structural genes, several of which are modular themselves. How this very mobile and plastic suite of proteins protects host cells from this pervasive toxic metal, what roles it has in the biogeochemical cycling of Hg, and how it has been employed in ameliorating environmental contamination are the subjects of this review.
FEMS Microbiology Reviews 07/2003; 27(2-3):355-84. · 10.96 Impact Factor
