Bacterial resistance ATPases: primary pumps for exporting toxic cations and anions

Global diversity of enterococci and description of 18 novel species

Enterococci are commensal gut microbes of most land animals. They diversified over hundreds of millions of years adapting to evolving hosts and host diets. Of over 60 known enterococcal species, Enterococcus faecalis and E. faecium uniquely emerged in the antibiotic era among leading causes of multidrug resistant hospital-associated infection. The basis for the association of particular enterococcal species with a host is largely unknown. To begin deciphering enterococcal species traits that drive host association, and to assess the pool of Enterococcus-adapted genes from which known facile gene exchangers such as E. faecalis and E. faecium may draw, we collected 886 enterococcal strains from nearly 1,000 specimens representing widely diverse hosts, ecologies and geographies. This provided data on the global occurrence and host associations of known species, identifying 18 new species in the process expanding genus diversity by >25%. The novel species harbor diverse genes associated with toxins, detoxification, and resource acquisition. E. faecalis and E. faecium were isolated from a wide diversity of hosts highlighting their generalist properties, whereas most other species exhibited more restricted distributions indicative of specialized host associations. The expanded species diversity permitted the Enterococcus genus phylogeny to be viewed with unprecedented resolution, allowing features to be identified that distinguish its four deeply rooted clades as well as genes associated with range expansion, such as B-vitamin biosynthesis and flagellar motility. Collectively, this work provides an unprecedentedly broad and deep view of the genus Enterococcus, potential threats to human health, and new insights into its evolution.

Phytoremediation: A Novel Approach of Bast Fiber Plants (Hemp, Kenaf, Jute and Flax) for Heavy Metals Decontamination in Soil-Review

Heavy metal pollution in the environment is a major concern for humans as it is non-biodegradable and can have a lot of effects on the environment, humans as well as plants. At present, a solution to this problem is suggested in terms of a new, innovative and eco-friendly technology known as phytoremediation. Bast fiber plants are typically non-edible crops that have a short life cycle. It is one of the significant crops that has attracted interest for many industrial uses because of its constant fiber supply and ease of maintenance. Due to its low maintenance requirements with minimum economic investment, bast fiber plants have been widely used in phytoremediation. Nevertheless, these plants have the ability to extract metals from the soil through their deep roots, combined with their commercial prospects, making them an ideal candidate as a profit-yielding crop for phytoremediation purposes. Therefore, a comprehensive review is needed for a better understanding of the morphology and phytoremediation mechanism of four commonly bast fiber plants, such as hemp (Cannabis sativa), kenaf (Hibiscus cannabinus), jute (Corchorus olitorius) and Flax (Linum usitatissimum). This review article summarizes the existing research on the phytoremediation potential of these plants grown in different toxic pollutants such as Lead (Pb), Cadmium (Cd) and Zinc (Zn). This work also discusses several aids including natural and chemical amendments to improve phytoremediation. The role of these amendments in the bioavailability of contaminants, their uptake, translocation and bioaccumulation, as well as their effect on plant growth and development, has been highlighted in this paper. This paper helps in identifying, comparing and addressing the recent achievements of bast fiber plants for the phytoremediation of heavy metals in contaminated soil.

Research Progress of Soil Microorganisms in Response to Heavy Metals in Rice

Soil heavy-metal pollution leads to excessive heavy metals in rice and other food crops, which has caused serious impacts on the ecological environment and on human health. In recent years, environmental friendly treatment methods that reduce the bioavailability of heavy metals in soil by soil microorganisms improving the tolerance of heavy metals in rice and reducing the transfer of heavy metals from the roots to the above-ground parts of rice have attracted much attention. This paper reviews the role and mechanism of soil microorganisms in alleviating heavy-metal stress in rice at home and abroad in recent years. At present, microorganisms tolerant to heavy metals mainly include bacteria and fungi, and their mechanisms include the adsorption of heavy metals by microorganisms, the secretion of growth-promoting substances (growth hormone, ACC deaminase, IAA), changing the physical and chemical properties of the soil and the composition of the microbial community, changing the transport mode of heavy metals in soil, the improvement of the antioxidant capacity of rice, etc. Hence, soil microorganisms have good application value and prospects in rice and other crops. However, the vast majority of current research focuses on a single strain, the screening principles of strains are limited, the pathogenicities of the strains have not been evaluated, and there are still few field experiments under natural conditions. In the future, we should strengthen the action of soil microorganisms on rice in response to the above problems in heavy metals, to better promote the microbial remediation technology.

Cd(2+) extrusion by P-type Cd(2+)-ATPase of Staphylococcus aureus 17810R via energy-dependent Cd(2+)/H(+) exchange mechanism

Cd²⁺ is highly toxic to Staphylococcus aureus since it blocks dithiols in cytoplasmic 2-oxoglutarate dehydrogenase complex (ODHC) participating in energy conservation process. However, S. aureus 17810R is Cd²⁺-resistant due to possession of cadA-coded Cd²⁺ efflux system, recognized here as P-type Cd²⁺-ATPase. This Cd²⁺ pump utilizing cellular energy—ATP, ∆μ_H⁺ (electrochemical proton potential) and respiratory protons, extrudes Cd²⁺ from cytoplasm to protect dithiols in ODHC, but the mechanism of Cd²⁺ extrusion remains unknown. Here we propose that two Cd²⁺ taken up by strain 17810R via Mn²⁺ uniporter down membrane potential (∆ψ) generated during glutamate oxidation in 100 mM phosphate buffer (high P_iB) are trapped probably by high affinity sites in cytoplasmic domain of Cd²⁺-ATPase, forming SCdS. This stops Cd²⁺ transport towards dithiols in ODHC, allowing undisturbed NADH production, its oxidation and energy conservation, while ATP could change orientation of SCdS towards facing transmembrane channel. Now, increased number of P_i-dependent protons pumped electrogenically via respiratory chain and countertransported through the channel down ∆ψ, extrude two trapped cytoplasmic Cd²⁺, which move to low affinity sites, being then extruded into extracellular space via ∆ψ-dependent Cd²⁺/H⁺ exchange. In 1 mM phosphate buffer (low P_iB), external Cd²⁺ competing with decreased number of P_i-dependent protons, binds to ψ_s of Cd²⁺-ATPase channel, enters cytoplasm through the channel down ∆ψ via Cd²⁺/Cd²⁺ exchange and blocks dithiols in ODHC. However, Mg²⁺ pretreatment preventing external Cd²⁺ countertransport through the channel down ∆ψ, allowed undisturbed NADH production, its oxidation and extrusion of two cytoplasmic Cd²⁺ via Cd²⁺/H⁺ exchange, despite low P_iB.

Cation Diffusion Facilitator family: Structure and function

The Cation Diffusion Facilitators (CDFs) form a family of membrane-bound proteins capable of transporting zinc and other heavy metal ions. Involved in metal tolerance/resistance by efflux of ions, CDF proteins share a two-modular architecture consisting of a transmembrane domain (TMD) and C-terminal domain (CTD) that protrudes into the cytoplasm. Discovery of a Zn²⁺ and Cd²⁺ CDF transporter from a marine bacterium Maricaulis maris that does not possess the CTD questions current perceptions regarding this family of proteins. This article describes a new, CTD-lacking subfamily of CDFs and our current knowledge about this family of proteins in the view of these findings.

Bio-sensing of cadmium(II) ions using Staphylococcus aureus

Cadmium, as a hazardous pollutant commonly present in the living environment, represents an important risk to human health due to its undesirable effects (oxidative stress, changes in activities of many enzymes, interactions with biomolecules including DNA and RNA) and consequent potential risk, making its detection very important. New and unique technological and biotechnological approaches for solving this problems are intensely sought. In this study, we used the commonly occurring potential pathogenic microorganism Staphylococcus aureus for the determination of markers which could be used for sensing of cadmium(II) ions. We were focused on monitoring the effects of different cadmium(II) ion concentrations (0, 1.25, 2.5, 5, 10, 15, 25 and 50 μg mL(-1)) on the growth and energetic metabolism of Staphylococcus aureus. Highly significant changes have been detected in the metabolism of thiol compounds-specifically the protein metallothionein (0.79-26.82 mmol/mg of protein), the enzyme glutathione S-transferase (190-5,827 μmol/min/mg of protein), and sulfhydryl groups (9.6-274.3 μmol cysteine/mg of protein). The ratio of reduced and oxidized glutathione indicated marked oxidative stress. In addition, dramatic changes in urease activity, which is connected with resistance of bacteria, were determined. Further, the effects of cadmium(II) ions on the metabolic pathways of arginine, β-glucosidase, phosphatase, N-acetyl β-d-glucosamine, sucrose, trehalose, mannitol, maltose, lactose, fructose and total proteins were demonstrated. A metabolomic profile of Staphylococcus aureus under cadmium(II) ion treatment conditions was completed seeking data about the possibility of cadmium(II) ion accumulation in cells. The results demonstrate potential in the application of microorganisms as modern biosensor systems based on biological components.

Crystal structure of a copper-transporting PIB-type ATPase

Heavy-metal homeostasis and detoxification is crucial for cell viability. P-type ATPases of the class IB (PIB) are essential in these processes, actively extruding heavy metals from the cytoplasm of cells. Here we present the structure of a PIB-ATPase, a Legionella pneumophila CopA Cu(+)-ATPase, in a copper-free form, as determined by X-ray crystallography at 3.2 Å resolution. The structure indicates a three-stage copper transport pathway involving several conserved residues. A PIB-specific transmembrane helix kinks at a double-glycine motif displaying an amphipathic helix that lines a putative copper entry point at the intracellular interface. Comparisons to Ca(2+)-ATPase suggest an ATPase-coupled copper release mechanism from the binding sites in the membrane via an extracellular exit site. The structure also provides a framework to analyse missense mutations in the human ATP7A and ATP7B proteins associated with Menkes' and Wilson's diseases.

Kinetic consequences of replacing the internucleotide phosphorus atoms in DNA with arsenic

It was claimed in a recent publication that a strain of Halomonadacea bacteria (GFAJ-1) isolated from the arsenic-rich waters of Mono Lake, California is able to substitute arsenic for phosphorus in its macromolecules and small molecule metabolites. In this short Perspective, we consider chemical and biochemical issues surrounding the central claim that Halomonadacea GFAJ-1 is able to survive while incorporating kinetically labile arsenodiester linkages into the backbone of its DNA. Chemical precedents suggest that arsenodiester linkages in the putative arsenic-containing DNA of GFAJ-1 would undergo very rapid hydrolytic cleavage in water at 25 °C with an estimated half-life of 0.06 s. In contrast, the phosphodiester linkages of native DNA undergo spontaneous hydrolysis with a half-life of approximately 30,000,000 y at 25 °C. Overcoming such dramatic kinetic instability in its genetic material would present serious challenges to Halomonadacea GFAJ-1.

Computer Simulation of the Interaction of Cu(I) with Cys Residues at the Binding Site of the Yeast Metallochaperone Cu(I)−Atx1

The copper binding site and electronic structure of the metallochaperone protein Atx1 were investigated using the combination of quantum mechanics methods and molecular mechanics methods in the ONIOM(QM:MM) scheme at the density functional theory (DFT) B3LYP/ 6-31G(d):AMBER level. The residues in the binding site, -Met13-Thr14-Cys15-Cu(I)-Cys18-Gly17-Ser16-, were modeled with QM and the rest of the residues with MM. Our results indicate that the structure for Cu(I)-Atx1 has the copper atom coordinated to two sulfur atoms from Cys15 (2.110 A) and Cys18 (2.141 A) with an angle S-Cu(I) -S of 166 degrees . The potential energy surface of the copper atom is used to estimate its binding energy and the force field for the copper ligands. The potential surface is shallow for the bending mode S-Cu-S, which explains the origin of the disorder observed in crystallographic and nuclear magnetic resonance studies. Using molecular dynamics for Cu(I)-Atx1 in a box of water molecules and in vacuum, with the force field derived in this work, we observed a correlated motion between the side chains of Thr14 and of Lys65 which enhances distortions in the S-Cu-S geometry. The results are compared with recent experiments and the previous models. The vibrational spectra for the copper ligands and for the residues in the binding site were computed. The localized modes for the copper ligands and the amide bands were assigned. The presence of the copper atom affects the amide bands' frequencies of the residues Cys15 and Cys18, giving resolved bands that can be used to sense changes in the binding site upon translocation of copper atom or interaction with target proteins. Furthermore, the EXAFS (extended X-ray absorption fine structure) spectrum of the proposed structure for Cu(I)-Atx1 was calculated and reproduced the experiments fairly well.

Intracellular sequestration of manganese and phosphorus in a metal-resistant fungus Cladosporium cladosporioides from deep-sea sediment

A heavy metal resistant fungus was isolated from the sediment of Pacific Ocean, and identified to be Cladosporium cladosporioides. It grew normally in a medium containing 60 mM Mn(2+) and could endure 1,200 mM as the highest concentration tested. Quantification analysis confirmed a high accumulation of Mn which was 58 mg/g in dried biomass. Under transmission electron microscope, many intracellular crystals were observed in the cytoplasm of the hypha cells grown in a Mn-rich medium, and varied from a few nanometers to 200 nm in length. Energy dispersive X-ray (EDX) analysis showed that the crystals were composed of manganese and phosphorus in atomic ratio of 1.6:1 (Mn/P). Further, factors which might influence the resistance of this fungus were investigated. As a result, its high resistance to Mn(2+) was found dependent on the presence of Mg(2+), and could be further enhanced by phosphate. However, the effect of phosphate was not observed without the presence of Mg(2+). In addition, the resistance was also influenced by pH of the medium, which was lost above pH 8. This is the first report on a fungus which showed a hyper resistance to manganese by forming a large quantity of intracellular Mn/P crystals.

Metal-binding stoichiometry and selectivity of the copper chaperone CopZ from Enterococcus hirae

We studied the interaction of several metal ions with the copper chaperone from Enterococcus hirae (EhCopZ). We show that the stoichiometry of the protein-metal complex varies with the experimental conditions used. At high concentration of the protein in a noncoordinating buffer, a dimer, (EhCopZ)2-metal, was formed. The presence of a potentially coordinating molecule L in the solution leads to the formation of a monomeric ternary complex, EhCopZ-Cu-L, where L can be a buffer or a coordinating molecule (glutathione, tris(2-carboxyethyl)phosphine). This was demonstrated in the presence of glutathione by electrospray ionization MS. The presence of a tyrosine close to the metal-binding site allowed us to follow the binding of cadmium to EhCopZ by fluorescence spectroscopy and to determine the corresponding dissociation constant (Kd = 30 nm). Competition experiments were performed with mercury, copper and cobalt, and the corresponding dissociation constants were calculated. A high preference for copper was found, with an upper limit for the dissociation constant of 10-12 m. These results confirm the capacity of EhCopZ to bind copper at very low concentrations in living cells and may provide new clues in the determination of the mechanism of the uptake and transport of copper by the chaperone EhCopZ.

A Novel Cyanobacterial SmtB/ArsR Family Repressor Regulates the Expression of a CPx-ATPase and a Metallothionein in Response to Both Cu(I)/Ag(I) and Zn(II)/Cd(II)

A novel SmtB/ArsR family metalloregulator, denoted BxmR, has been identified and characterized from the cyanobacterium Oscillatoria brevis. Genetic and biochemical evidence reveals that BxmR represses the expression of both bxa1, encoding a CPx-ATPase metal transporter, as well as a divergently transcribed operon encoding bxmR and bmtA, a heavy metal sequestering metallothionein. Derepression of the expression of all three genes is mediated by both monovalent (Ag(I) and Cu(I)) and divalent (Zn(II) and Cd(II)) heavy metal ions, a novel property among SmtB/ArsR metal sensors. Electrophoretic gel mobility shift experiments reveal that apoBxmR forms multiple resolvable complexes with oligonucleotides containing a single 12-2-12 inverted repeat derived from one of the two operator/promoter regions with similar apparent affinities. Preincubation with either monovalent or divalent metal ions induces disassembly of both the BxmR-bxa1 and BxmR-bxmR/bmtA operator/promoter complexes. Interestingly, the temporal regulation of expression of bxa1 and bmtA mRNAs is different in O. brevis with bxa1 induced first upon heavy metal treatment, followed by bmtA/bxmR. A dynamic interplay among Bxa1, BmtA, and BxmR is proposed that maintains metal homeostasis in O. brevis by balancing the relative rates of metal storage and efflux of multiple heavy metal ions.

Zn(II) metabolism in prokaryotes

It is difficult to over-state the importance of Zn(II) in biology. It is a ubiquitous essential metal ion and plays a role in catalysis, protein structure and perhaps as a signal molecule, in organisms from all three kingdoms. Of necessity, organisms have evolved to optimise the intracellular availability of Zn(II) despite the extracellular milieu. To this end, prokaryotes contain a range of Zn(II) import, Zn(II) export and/or binding proteins, some of which utilise either ATP or the chemiosmotic potential to drive the movement of Zn(II) across the cytosolic membrane, together with proteins that facilitate the diffusion of this ion across either the outer or inner membranes of prokaryotes. This review seeks to give an overview of the systems currently classified as altering Zn(II) availability in prokaryotes.

Conjugative plasmid mediated inducible nickel resistance in Hafnia alvei 5-5

Hafnia alvei 5-5, isolated from a soil-litter mixture underneath the canopy of the nickel-hyperaccumulating tree Sebertia acuminata (Sapotaceae) in New Caledonia, was found to be resistant to 30 mM Ni(2+) or 2 mM Co(2+). The 70-kb plasmid, pEJH 501, was transferred by conjugation to Escherichia coli, Serratia marcescens, and Klebsiella oxytoca. Transconjugant strains expressed inducible nickel resistance to between 5 and 17 mM Ni(2+), and cobalt resistance to 2 mM Co(2+). A 4.8-kb Sal- EcoRI fragment containing the nickel resistance determinant was subcloned, and the hybrid plasmid was found to confer a moderate level of resistance to nickel (7 mM Ni(2+)) even to E. coli. The expression of nickel resistance was inducible by exposure to nickel chloride at a concentration as low as 0.5 mM Ni(2+). By random Tn phoA'-1 insertion mutagenesis, the fragment was shown to have structural genes as well as regulatory regions for nickel resistance. Southern hybridization studies showed that the nickel-resistance determinant from pEJH501 of H. alvei 5-5 was homologous to that of pTOM9 from Alcaligenes xylosoxydans 31A.

Structural and functional insights of Wilson disease copper-transporting ATPase

Wilson disease is an autosomal recessive disorder of copper metabolism. The gene for this disorder has been cloned and identified to encode a copper-transporting ATPase (ATP7B), a member of a large family of cation transporters, the P-type ATPases. In addition to the core elements common to all P-type ATPases, the Wilson copper-transporting ATPase has a large cytoplasmic N-terminus comprised six heavy metal associated (HMA) domains, each of which contains the copper-binding sequence motif GMT/HCXXC. Extensive studies addressing the functional, regulatory, and structural aspects of heavy metal transport by heavy metal transporters in general, have offered great insights into copper transport by Wilson copper-transporting ATPase. The findings from these studies have been used together with homology modeling of the Wilson disease copper-transporting ATPases based on the X-ray structure of the sarcoplasmic reticulum (SR) calcium-ATPase, to present a hypothetical model of the mechanism of copper transport by copper-transporting ATPases.

Structural biology of metal-binding sequences

NMR spectroscopy and X-ray crystallography in conjunction with extended X-ray absorption fine structure spectroscopy, have contributed to the elucidation of the structural biology of protein-mediated mechanisms of heavy metal homeostasis. Among the most striking aspects of these investigations are the remarkable similarity of metal-ion-transport and sequestering systems across different species, and the need to continue the research to confirm hypotheses for the molecular mechanisms of transfers of metal ions between proteins.

Metallochaperones and metal-transporting ATPases: a comparative analysis of sequences and structures

A comparative structural genomic analysis of a new class of metal-trafficking proteins can provide insights into the intracellular chemistry of reactive cofactors such as copper and zinc. Starting from the sequences of the metallochaperone Atx1 and from the first soluble domain of the copper-transporting ATPase Ccc2, both from yeast, a search on the available genomes was performed using a homology criterion and a metal-binding motif x'-x"-C-x'''-x''''-C. By limiting ourselves to 20% identity with any of the proteins found, several soluble copper-transport proteins were identified, as well as soluble domains of membrane-bound ATPases. Structural models were calculated using high-resolution solution structures as templates, and the models were validated using statistical and energy criteria. Residue conservation and substitution have been interpreted and discussed in terms of structure-function relationship. The potential energy surfaces have been analyzed in terms of protein-protein interactions. We find that metallochaperones and their physiological partner ATPases from several phylogenetic kingdoms recognize one another, via an interplay of electrostatics, hydrogen bonding, and hydrophobic interactions, in a manner that precisely orients the metal-binding side chains for rapid metal transfer between otherwise tight binding sites. Finally, other putative metal-transport proteins are mentioned that have low homology and/or a different metal-binding consensus motif and that appear to use similar structures for recognition and transfer. This analysis highlights the wealth and the complexity of the field.

Detection and analysis of chromosomal arsenic resistance in Pseudomonas fluorescens strain MSP3

Pseudomonas fluorescens MSP3 isolated from sea water was resistant to arsenate. This bacterium harbored no plasmids, indicating that arsenic resistance was chromosomally encoded. The chromosomal DNA from MSP3 when transformed onto Escherichia coli DH5alpha using pBluescript exhibited resistance to sodium arsenate and sodium arsenite. Three clones MSA1, MSA2, and MSI3 containing the ars genes were obtained and further subcloning resulted in three fragments of size 2.2, 2.6, and 2.1 kb for pMSA11, pMSA12, and pMSI13, respectively, which contained the genes arsRBC of the arsenic operon. An efflux mechanism of detoxification was observed which was ATP dependent. The resistance mechanism was encoded from a single operon which consisted of an arsenite inducible repressor that regulates the expression of arsenate reductase (ars C) and inner membrane associated arsenite export system encoded by ars B. The chromosomal operon was cloned, sequenced, and found to consist of three cistrons, named as ars R, ars B, and ars C. Southern hybridization and mating experiments confirmed the functioning of the ars genes in the operon, thereby conferring increased resistance to sodium arsenate and sodium arsenite.

Purification and functional analysis of the copper ATPase CopA of Enterococcus hirae

The Enterococcus hirae ATPase CopA is a member of the recently discovered heavy metal ATPases and shares 43% sequence identity with the human Menkes and Wilson copper ATPases. To study CopA biochemically, it was overexpressed in E. coli with an N-terminal histidine tag and purified to homogeneity by nickel affinity chromatography. The purified CopA catalyzed ATP hydrolysis with a V(max) of 0.15 micromol/min/mg and a K(m) for ATP of 0.2 mM and had an optimum pH of 6.25. The activity was 3- to 4-fold stimulated by reconstitution into proteoliposomes. The enzyme formed an acylphosphate intermediate. Its kinetics of formation and the effects of inhibitors and metal ions upon it support a function of CopA in copper transport. Purification and functional reconstitution of CopA provides the basis to study copper transport in vitro.

Microbial resistance to metals in the environment

Many microorganisms demonstrate resistance to metals in water, soil and industrial waste. Genes located on chromosomes, plasmids, or transposons encode specific resistance to a variety of metal ions. Some metals, such as cobalt, copper, nickel, serve as micronutrients and are used for redox processes, to stabilize molecules through electrostatic interactions, as components of various enzymes, and for regulation of osmotic pressure. Most metals are nonessential, have no nutrient value, and are potentially toxic to microorganisms. These toxic metals interact with essential cellular components through covalent and ionic bonding. At high levels, both essential and nonessential metals can damage cell membranes, alter enzyme specificity, disrupt cellular functions, and damage the structure of DNA. Microorganisms have adapted to the presence of both nutrient and nonessential metals by developing a variety of resistance mechanisms. Six metal resistance mechanisms exist: exclusion by permeability barrier, intra- and extra-cellular sequestration, active transport efflux pumps, enzymatic detoxification, and reduction in the sensitivity of cellular targets to metal ions. The understanding of how microorganisms resist metals can provide insight into strategies for their detoxification or removal from the environment.

Do biocides select for antibiotic resistance?

Some similarities exist between bacterial resistance to antibiotics and to biocides, and gram-negative bacteria that have developed resistance to cationic biocides may also be insusceptible to some antibiotics. Outer membrane changes are believed to be responsible for this non-specific increase in resistance. Efflux, another important resistance mechanism, is associated with the qacA/B gene system in staphylococci that confers low-level resistance to cationic agents including chlorhexidine salts and quaternary ammonium compounds. It has been proposed that the introduction into clinical practice of chlorhexidine and quaternary ammonium compounds has resulted in the selection of staphylococci containing qacA genes on multiresistance plasmids. A linkage between low-level resistance to triclosan and to antibiotics has recently been claimed to occur in Escherichia coli, with the bisphenol selecting for chromosomally-mediated antibiotic resistance. A key issue in many studies has been the use of biocides at concentrations significantly below those used clinically. It remains to be determined how an increase to low-level resistance to cationic biocides can be held responsible for the selection of antibiotic-resistant bacteria.

Cloning, expression, and characterization of cadmium and manganese uptake genes from Lactobacillus plantarum

An Mn(2+) and Cd(2+) uptake gene, mntA, was cloned from Lactobacillus plantarum ATCC 14917 into Escherichia coli. Its expression conferred on E. coli cells increased Cd(2+) sensitivity as well as energy-dependent Cd(2+) uptake activity. Both transcription and translation of mntA were induced by Mn(2+) starvation in L. plantarum, as indicated by reverse transcriptase PCR and immunoblotting. Two Cd(2+) uptake systems have been identified in L. plantarum: one is a high-affinity Mn(2+) and Cd(2+) uptake system that is expressed in Mn(2+)-starved cells, and the other is a nonsaturable Cd(2+) uptake system that is expressed in Cd(2+)-sufficient cells (Z. Hao, H. R. Reiske, and D. B. Wilson, Appl. Environ. Microbiol. 65:592-99, 1999). MntA was not detected in an Mn(2+)-dependent mutant of L. plantarum which had lost high-affinity Mn(2+) and Cd(2+) uptake activity. The results suggest that mntA is the gene encoding the high-affinity Mn(2+) and Cd(2+) transporter. On the basis of its predicted amino acid sequence, MntA belongs to the family of P-type cation-translocating ATPases. The topology and potential Mn(2+)- and Cd(2+)-binding sites of MntA are discussed. A second clone containing a low-affinity Cd(2+) transport system was also isolated.

Cloning and expression of cadD, a new cadmium resistance gene of Staphylococcus aureus

A cadmium resistance gene, designated cadD, has been identified in and cloned from the Staphylococcus aureus plasmid pRW001. The gene is part of a two-component operon which contains the resistance gene cadD and an inactive regulatory gene, cadX*. A high degree of sequence similarity was observed between cadD and the cadB-like gene from S. lugdunensis, but no significant similarity was found with either cadA or cadB from the S. aureus plasmids pI258 and pII147. The positive regulatory gene cadX* is identical to cadX from pLUG10 over a stretch of 78 codons beginning at the N terminus, but it is truncated at this point and inactive. Sequence analysis showed that the cadmium resistance operon resides on a 3,972-bp element that is flanked by direct repeats of IS257. The expression of cadD in S. aureus and Bacillus subtilis resulted in low-level resistance to cadmium; in contrast, cadA and cadB from S. aureus induced higher level resistance. However, when the truncated version of cadX contained in pRW001 is complemented in trans with cadX from plasmid pLUG10, resistance increased approximately 10-fold suggesting that the cadmium resistance operons from pRW001 and pLUG10 are evolutionarily related. Moreover, the truncated version of cadX contained in pRW001 is nonfunctional and may have been generated by deletion during recombination to acquire the cadmium resistance element.

A novel pineal night-specific ATPase encoded by the Wilson disease gene

We have identified a pineal night-specific ATPase (PINA), a novel splice variant of the ATP7B gene disrupted in Wilson disease (WD). PINA expression exhibits a dramatic diurnal rhythm in both pineal gland and retina with 100-fold greater expression at night than at day. PINA is expressed in pinealocytes and a subset of photoreceptors in adult rats and is transiently expressed in the retinal pigment epithelium and the ciliary body during retinal development. Nocturnal pineal expression of PINA is under the control of a suprachiasmatic nucleus clock mediated by superior cervical ganglion innervation of the pineal. In vitro, PINA expression in pineal cells can be stimulated by agents activating the cAMP signal transduction pathway. PINA is able to restore copper transport activity in Saccharomyces cerevisiae deficient in the homologous copper-transporting ATPase CCC2, suggesting that this protein may function as a copper transporter in rat pinealocytes. These studies suggest a potential role of rhythmic copper metabolism in pineal and/or retina circadian function.

Antiseptics and disinfectants: activity, action, and resistance

Antiseptics and disinfectants are extensively used in hospitals and other health care settings for a variety of topical and hard-surface applications. A wide variety of active chemical agents (biocides) are found in these products, many of which have been used for hundreds of years, including alcohols, phenols, iodine, and chlorine. Most of these active agents demonstrate broad-spectrum antimicrobial activity; however, little is known about the mode of action of these agents in comparison to antibiotics. This review considers what is known about the mode of action and spectrum of activity of antiseptics and disinfectants. The widespread use of these products has prompted some speculation on the development of microbial resistance, in particular whether antibiotic resistance is induced by antiseptics or disinfectants. Known mechanisms of microbial resistance (both intrinsic and acquired) to biocides are reviewed, with emphasis on the clinical implications of these reports.

Inorganic cation transport and energy transduction in Enterococcus hirae and other streptococci

Energy metabolism by bacteria is well understood from the chemiosmotic viewpoint. We know that bacteria extrude protons across the plasma membrane, establishing an electrochemical potential that provides the driving force for various kinds of physiological work. Among these are the uptake of sugars, amino acids, and other nutrients with the aid of secondary porters and the regulation of the cytoplasmic pH and of the cytoplasmic concentration of potassium and other ions. Bacteria live in diverse habitats and are often exposed to severe conditions. In some circumstances, a proton circulation cannot satisfy their requirements and must be supplemented with a complement of primary transport systems. This review is concerned with cation transport in the fermentative streptococci, particularly Enterococcus hirae. Streptococci lack respiratory chains, relying on glycolysis or arginine fermentation for the production of ATP. One of the major findings with E. hirae and other streptococci is that ATP plays a much more important role in transmembrane transport than it does in nonfermentative organisms, probably due to the inability of this organism to generate a large proton potential. The movements of cations in streptococci illustrate the interplay between a variety of primary and secondary modes of transport.

The Sge1 protein of Saccharomyces cerevisiae is a membrane-associated multidrug transporter

In this study, we report the further characterization of the Saccharomyces cerevisiae crystal violet-resistance protein Sge1. Sge1 is a highly hydrophobic 59 kDa protein with 14 predicted membrane-spanning domains. It shares homologies with several drug-resistance proteins and sugar transporters of the major facilitator superfamily. Here, we have demonstrated that Sge1 is not only a crystal violet-resistance protein, but that it also confers resistance to ethidium bromide and methylmethane sulfonate. Disruption of SGE1 leads to increased sensitivity towards all three compounds, thus designating Sge1 as a multiple drug-resistance protein. Subcellular fractionation as well as immunolocalization on whole yeast cells demonstrated that Sge1 was tightly associated with the yeast plasma membrane. Furthermore, Sge1 was highly enriched in preparations of yeast plasma membranes. In analogy to other multidrug-resistance proteins, we suggest that Sge1 functions as a drug export permease.

Solution structure of the fourth metal-binding domain from the Menkes copper-transporting ATPase

Menkes disease is an X-linked disorder in copper transport that results in death during early childhood. The solution structures of both apo and Ag(I)-bound forms of the fourth metal-binding domain (mbd4) from the Menkes copper-transporting ATPase have been solved. The 72-residue mbd4 has a ferredoxin-like beta alpha beta beta alpha beta fold. Structural differences between the two forms are limited to the metal-binding loop, which is disordered in the apo structure but well ordered in the Ag(I)-bound structure. Ag(I) binds in a linear bicoordinate manner to the two Cys residues of the conserved GMTCxxC motif; Cu(I) likely coordinates in a similar manner. Menkes mbd4 is thus the first bicoordinate copper-binding protein to be characterized structurally. Sequence comparisons with other heavy-metal-binding domains reveal a conserved hydrophobic core and metal-binding motif.

Properties of the P-type ATPases encoded by the copAP operons of Helicobacter pylori and Helicobacter felis

The cop operons of Helicobacter pylori and Helicobacter felis were cloned by gene library screening. Both operons contain open reading frames for a P-type ion pump (CopA) with homology to Cd2+ and Cu2+ ATPases and a putative ion binding protein (CopP), the latter representing a CopZ homolog of the copYZAB operon of Enterococcus hirae. The predicted CopA ATPases contained an N-terminal GMXCXXC ion binding motif and a membrane-associated CPC sequence. A synthetic N-terminal peptide of the H. pylori CopA ATPase bound to Cu2+ specifically, and gene disruption mutagenesis of CopA resulted in an enhanced growth sensitivity of H. pylori to Cu2+ but not to other divalent cations. As determined experimentally, H. pylori CopA contains four pairs of transmembrane segments (H1 to H8), with the ATP binding and phosphorylation domains lying between H6 and H7, as found for another putative transition metal pump of H. pylori (K. Melchers, T. Weitzenegger, A. Buhmann, W. Steinhilber, G. Sachs, and K. P. Schäfer, J. Biol. Chem. 271:446-457, 1996). The corresponding transmembrane segments of the H. felis CopA pump were identified by hydrophobicity analysis and via sequence similarity. To define functional domains, similarly oriented regions of the two enzymes were examined for sequence identity. Regions with high degrees of identity included the N-terminal Cu2+ binding domain, the regions of ATP binding and phosphorylation in the energy transduction domain, and a transport domain consisting of the last six transmembrane segments with conserved cysteines in H4, H6, and H7. The data suggest that H. pylori and H. felis employ conserved mechanisms of ATPase-dependent copper resistance.

Expression, purification, and metal binding properties of the N-terminal domain from the wilson disease putative copper-transporting ATPase (ATP7B)

The putative copper binding domain from the copper-transporting ATPase implicated in Wilson disease (ATP7B) has been expressed and purified as a fusion to glutathione S-transferase. Immobilized metal ion affinity chromatography revealed that the fusion protein is able to bind to columns charged with different transition metals with varying affinities as follows: Cu(II)>>Zn(II)>Ni(II)>Co(II). The fusion protein did not bind to columns charged with Fe(II) or Fe(III). 65Zinc(II) blotting analysis showed that the domain is able to bind Zn(II) over a range of pH values from 6.5 to 9.0. Competition 65Zn(II) blotting showed that Cd(II), Hg(II), Au(III), and Fe(III) can successfully compete with Zn(II), at comparable concentrations, for binding to the domain. In contrast, the domain had little or no affinity for Ca(II), Mg(II), Mn(II), and Ni(II) relative to copper. Neutron activation analysis of the copper bound to the domain showed a copper:protein ratio of 6.5-7.3:1. Both Cu(II) and Cu(I) were found to have a higher affinity for the domain relative to Zn(II). In addition, a sharp, reproducible transition was only observed in competition experiments with copper, which may suggest that copper binding has some degree of cooperativity.

Genetic analysis of regions involved in replication and cadmium resistance of the plasmid pND302 from Lactococcus lactis

The 8.8-kb Lactococcus lactis plasmid pND302 encodes resistance to cadmium (CdR). Regions of pND302 involved in replication and CdR were subcloned and sequenced. The replication region is localized on a 1.5-kb region and consists of an open reading frame (repB) preceded by a noncoding AT-rich sequence (ori) which is highly homologous to lactococcal theta-type replicons. The CdR determinant is localized on a 2.9-kb region and encodes putative proteins similar to the Cd(2+)-specific P-type efflux ATPase (CadA) and the transcriptional regulatory repressor (CadC) identified in Staphylococcus aureus, Bacillus firmus, and Listeria monocytogenes. Similar CdR determinants were also detected by PCR in other CdR plasmids isolated from different L. lactis strains.

The mottled mouse as a model for human Menkes disease: identification of mutations in the Atp7a gene

Mutations in the Atp7a gene, the mouse homologue of the MNK (ATP7A) gene, have been suggested to be responsible for the mottled phenotype. To date, despite considerable effort, changes associated with the mottled mutations have been detected in only two such mutants. In this study, we identify changes in the level of Atp7a transcript and mutations which could explain the mottled phenotype in nine out of the 10 mutants analysed. The fluorescence-assisted mismatch analysis method used here has proved particularly well suited for mRNA scanning of heterozygous carrier animals, because of its ability to detect mutations even in the presence of an excess of wild-type mRNA. The three new underlying mutations identified at the Atp7a locus include a splice mutation and two missense mutations. While the spectrum of mutations detected in the Atp7a murine gene provides an explanation for at least part of the wide phenotypic variation observed in mottled mutant mice, there is a singular absence of deletions which are associated with a sizeable fraction of human Menkes syndrome cases.

Enzymatic methylation of arsenic species and other new approaches to arsenic toxicity

Arsenic metabolism has typically been studied by administering arsenate or arsenite into animals and humans and then studying the metabolites excreted in the urine. Although such studies have yielded information about the beginning and the end of the metabolic pathways for the metabolism of inorganic arsenic compounds, any statements as to the molecular mechanisms of these reactions have had to be highly speculative. Now that the rabbit and the rhesus monkey liver enzymes that transfer methyl groups from S-adenosylmethionine to arsenite and monomethlyarsonic acid have been purified and the reactions characterized, meaningful investigations of species diversity and polymorphism of these enzymes have become possible. New World animals studied thus far appear to be deficient in or totally lacking these enzymes. Old World animals, with the exception of the chimpanzee, have ample amounts of arsenite and monomethylarsonic acid methyltransferases. A hypothesis that the lack of arsenite methyltransferases may have had an evolutionary advantage for certain species is proposed.

CPx-type ATPases: a class of P-type ATPases that pump heavy metals

ATP-driven heavy metal pumps represent a newly defined class of proteins that translocate toxic and essential metals across biological membranes. These transporters form a separate evolutionary branch of the ion-transporting P-type ATPases. We propose to call these enzymes CPx-type ATPases, based on the common novel feature of a conserved intramembranous cysteine-proline-cysteine or cysteine-proline-histidine motif.

Cloning and sequence analysis of a novel member of the ATP-binding cassette (ABC) protein gene family from Plasmodium falciparum

We have employed oligonucleotide primers directed against the Walker A and B ATP-binding consensus motifs in a PCR-approach to clone a novel member of the eukaryotic ABC protein family of genes from Plasmodium falciparum. The novel gene is predicted to encode a 95.5-kDa protein with two ATP-binding folds each containing a Walker A and B consensus motif and an ABC protein signature sequence. The predicted protein is highly hydrophilic and contains numerous phosphorylation consensus sites but does not contain any potential membrane spanning domains. The gene is present on chromosome 11 and is expressed as a 3.3-kb transcript. The closest homologue with known function to the plasmodial gene is the yeast GCN20 gene which is part of the translation initiation pathway in amino acid starved yeast cells. We have therefore tentatively named the gene Plasmodium falciparum GCN20 homologue (pfgcn20). The pfgcn20 encoded Pfgcn20 protein is also highly homologous to a number of ATP-binding subunits of prokaryotic ABC transporters. We speculate that Pfgcn20 may be an example of a eukaryotic ATP-binding cytosolic subunit of a multipeptide ABC transporter.

Cloning and membrane topology of a P type ATPase from Helicobacter pylori

Southern blot screening of a genomic Helicobacter pylori library was employed to find a P type ATPase using a mixture of 16 DNA oligonucleotides coding for the DKTGT(I/L)T consensus sequence specific for the phosphorylation site of this family of ATPases. A positive clone, pRH439, was isolated and sequenced. The inserted 3.4-kb H. pylori DNA contained an intact open reading frame encoding a protein of 686 amino acids carrying the consensus sites for phosphorylation and ATP binding. The amino acid sequence exhibits a 25-30% identity with bacterial Cd2+ and Cu2+ ATPases. Genomic Southern blot analysis showed that this ATPase was present in all H. pylori strains examined, whereas it was not detectable in Campylobacter jejuni and other bacteria. The membrane topology of this ATPase was investigated using in vitro transcription/translation of fusion vectors to find signal anchor and/or stop transfer sequences. Eight regions of the H. pylori ATPase acted as signal anchor and/or stop transfer sequences and were ordered pairwise along the polypeptide chain placing the N and C-terminal amino acids in the cytoplasm. These transmembrane segments are contained between positions 73 and 92 (H1), 98 and 125 (H2), 128 and 148 (H3), 149 and 176 (H4), 309 and 327 (H5), 337 and 371 (H6), 637 and 658 (H7), and 659 and 685 (H8). The membrane domain of the ATPase, therefore, consists of at least four pairs of transmembrane segments with the phosphorylation site and ATP binding domain located in the large cytoplasmic loop between H6 and H7. The cytoplasmic domain contains several histidines and cysteines, perhaps indicative of divalent cation binding sites. There are several charged amino acids (3 Lys, 2 Glu, 2 Asp), predicted to be in the membrane domain mainly in H2, H3, and H4 and a Cys-Pro-Cys putative metal ion site in H6. The extracytoplasmic domain also has several charged amino acids (5 Glu, 1 Asp, 1 Lys, 1 Arg). It is likely that this novel protein is a heavy metal cation transporting ATPase and belongs to a family of P type ATPases containing eight transmembrane segments.

CadC, the transcriptional regulatory protein of the cadmium resistance system of Staphylococcus aureus plasmid pI258

The CadC protein from the cadA cadmium resistance operon of Staphylococcus aureus plasmid pI258 regulates transcription of this system in vitro. The CadC protein was overproduced in Escherichia coli cells and partially purified. Gel shift assays of the proposed cadA operator/promoter region DNA showed specific association with the CadC protein. Control arsenic resistance operator/promoter DNA from the same plasmid was not shifted by the CadC protein. Cd2+, Bi3+, and Pb2+ caused the release of CadC from DNA in gel retardation assays. DNase I footprinting measurements showed that the CadC protein specifically associated with and protected a region of operator/promoter DNA from nucleotide positions -7 to +14 relative to the start point of mRNA synthesis. Runoff transcription assays with the operator/promoter region of DNA (plus the first 69 nucleotides of the cadC gene) and purified E. coli RNA polymerase gave an mRNA product of the predicted size. Added CadC protein inhibited transcription in vitro.