# | Rank | Similarity | Title + Abs. | Year | PMID |
|---|---|---|---|---|---|
| 0 | 1 | 2 | 3 | 4 | 5 |
| 507 | 0 | 0.9339 | Tellurite resistance and reduction by obligately aerobic photosynthetic bacteria. Seven species of obligately aerobic photosynthetic bacteria of the genera Erythromicrobium, Erythrobacter, and Roseococcus demonstrated high-level resistance to tellurite and accumulation of metallic tellurium crystals. High-level resistance without tellurite reduction was observed for Roseococcus thiosulfatophilus and Erythromicrobium ezovicum grown with certain organic carbon sources, implying that tellurite reduction is not essential to confer tellurite resistance. | 1996 | 16535446 |
| 523 | 1 | 0.9283 | Sulfide-carbonate-mineralized functional bacterial consortium for cadmium removal in flue gas. Sulfide-carbonate-mineralized functional bacterial consortium was constructed for flue gas cadmium biomineralization. A membrane biofilm reactor (MBfR) using the bacterial consortium containing sulfate reducing bacteria (SRB) and denitrifying bacteria (DNB) was investigated for flue gas cadmium (Cd) removal. Cadmium removal efficiency achieved 90%. The bacterial consortium containing Citrobacter, Desulfocurvus and Stappia were dominated for cadmium resistance-nitrate-sulfate reduction. Under flue gas cadmium stress, ten cadmium resistance genes (czcA, czcB, czcC, czcD, cadA, cadB, cadC, cueR, copZ, zntA), and seven genes related to sulfate reduction, increased in abundance; whereas others, nine genes related to denitrification, decreased, indicating that cadmium stress was advantageous to sulfate reduction in the competition with denitrification. A bacterial consortium could capable of simultaneously cadmium resistance, sulfate reduction and denitrification. Microbial induced carbonate precipitation (MICP) and biological adsorption process would gradually yield to sulfide-mineralized process. Flue gas cadmium could transform to Cd-EPS, cadmium carbonate (CdCO(3)) and cadmium sulfide (CdS) bioprecipitate. The functional bacterial consortium was an efficient and eco-friendly bifunctional bacterial consortium for sulfide-carbonate-mineralized of cadmium. This provides a green and low-carbon advanced treatment technology using sulfide-carbonate-mineralized functional bacterial consortium for the removal of cadmium or other hazardous heavy metal contaminants in flue gas. | 2024 | 39019186 |
| 504 | 2 | 0.9280 | Activation of Dithiolopyrrolone Antibiotics by Cellular Reductants. Dithiolopyrrolone (DTP) natural products are broad-spectrum antimicrobial and anticancer prodrugs. The DTP structure contains a unique bicyclic ene-disulfide that once reduced in the cell, chelates metal ions and disrupts metal homeostasis. In this work we investigate the intracellular activation of the DTPs and their resistance mechanisms in bacteria. We show that the prototypical DTP holomycin is reduced by several bacterial reductases and small-molecule thiols in vitro. To understand how bacteria develop resistance to the DTPs, we generate Staphylococcus aureus mutants that exhibit increased resistance to the hybrid DTP antibiotic thiomarinol. From these mutants we identify loss-of-function mutations in redox genes that are involved in DTP activation. This work advances the understanding of how DTPs are activated and informs development of bioreductive disulfide prodrugs. | 2025 | 39665630 |
| 505 | 3 | 0.9265 | Production of phytoalexins in peanut (Arachis hypogaea) seed elicited by selected microorganisms. Under favorable conditions, the peanut plant demonstrates appreciable resistance to fungal invasion by producing and accumulating phytoalexins, antimicrobial stilbenoids. This mechanism for resistance is little understood, yet it is crucial for breeding and genetically modifying peanut plants to develop new cultivars with fungal resistance. The dynamics of phytoalexin production in peanut seeds and embryos challenged by selected important fungi and bacteria was investigated. Different biotic agents selectively elicited production of major peanut stilbenoids, resveratrol, arachidin-1, arachidin-3, and SB-1. Aspergillis species, compared to other biotic agents, were more potent elicitors of stilbenoids. Embryos demonstrated significantly higher production of stilbenoids compared to cotyledons and may serve as a convenient source of genetic material in isolating genes for peanut plant defense enhancement. | 2013 | 23387286 |
| 581 | 4 | 0.9261 | Inorganic polyphosphates and heavy metal resistance in microorganisms. The mechanisms of heavy metal resistance in microbial cells involve multiple pathways. They include the formation of complexes with specific proteins and other compounds, the excretion from the cells via plasma membrane transporters in case of procaryotes, and the compartmentalization of toxic ions in vacuoles, cell wall and other organelles in case of eukaryotes. The relationship between heavy metal tolerance and inorganic polyphosphate metabolism was demonstrated both in prokaryotic and eukaryotic microorganisms. Polyphosphates, being polyanions, are involved in detoxification of heavy metals through complex formation and compartmentalization. The bacteria and fungi cultivated in the presence of some heavy metal cations contain the enhanced levels of polyphosphate. In bacteria, polyphosphate sequesters heavy metals; some of metal cations stimulate an exopolyphosphatase activity, which releases phosphate from polyphosphates, and MeHPO(4)(-) ions are then transported out of the cells. In fungi, the overcoming of heavy metal stresses is associated with the accumulation of polyphosphates in cytoplasmic inclusions, vacuoles and cell wall and the formation of cation/polyphosphate complexes. The effects of knockout mutations and overexpression of the genes encoding polyphosphate-metabolizing enzymes on heavy metal resistance are discussed. | 2018 | 30151754 |
| 580 | 5 | 0.9259 | Acid-tolerant bacteria and prospects in industrial and environmental applications. Acid-tolerant bacteria such as Streptococcus mutans, Acidobacterium capsulatum, Escherichia coli, and Propionibacterium acidipropionici have developed several survival mechanisms to sustain themselves in various acid stress conditions. Some bacteria survive by minor changes in the environmental pH. In contrast, few others adapt different acid tolerance mechanisms, including amino acid decarboxylase acid resistance systems, mainly glutamate-dependent acid resistance (GDAR) and arginine-dependent acid resistance (ADAR) systems. The cellular mechanisms of acid tolerance include cell membrane alteration in Acidithiobacillus thioxidans, proton elimination by F(1)-F(0)-ATPase in Streptococcus pyogenes, biofilm formation in Pseudomonas aeruginosa, cytoplasmic urease activity in Streptococcus mutans, synthesis of the protective cloud of ammonia, and protection or repair of macromolecules in Bacillus caldontenax. Apart from cellular mechanisms, there are several acid-tolerant genes such as gadA, gadB, adiA, adiC, cadA, cadB, cadC, speF, and potE that help the bacteria to tolerate the acidic environment. This acid tolerance behavior provides new and broad prospects for different industrial applications and the bioremediation of environmental pollutants. The development of engineered strains with acid-tolerant genes may improve the efficiency of the transgenic bacteria in the treatment of acidic industrial effluents. KEY POINTS: • Bacteria tolerate the acidic stress by methylating unsaturated phospholipid tail • The activity of decarboxylase systems for acid tolerance depends on pH • Genetic manipulation of acid-tolerant genes improves acid tolerance by the bacteria. | 2023 | 37093306 |
| 123 | 6 | 0.9258 | Genes for all metals--a bacterial view of the periodic table. The 1996 Thom Award Lecture. Bacterial chromosomes have genes for transport proteins for inorganic nutrient cations and oxyanions, such as NH4+, K+, Mg2+, Co2+, Fe3+, Mn2+, Zn2+ and other trace cations, and PO4(3-), SO4(2-) and less abundant oxyanions. Together these account for perhaps a few hundred genes in many bacteria. Bacterial plasmids encode resistance systems for toxic metal and metalloid ions including Ag+, AsO2-, AsO4(3-), Cd2+, Co2+, CrO4(2-), Cu2+, Hg2+, Ni2+, Pb2+, TeO3(2-), Tl+ and Zn2+. Most resistance systems function by energy-dependent efflux of toxic ions. A few involve enzymatic (mostly redox) transformations. Some of the efflux resistance systems are ATPases and others are chemiosmotic ion/proton exchangers. The Cd(2+)-resistance cation pump of Gram-positive bacteria is membrane P-type ATPase, which has been labeled with 32P from [gamma-32P]ATP and drives ATP-dependent Cd2+ (and Zn2+) transport by membrane vesicles. The genes defective in the human hereditary diseases of copper metabolism, Menkes syndrome and Wilson's disease, encode P-type ATPases that are similar to bacterial cadmium ATPases. The arsenic resistance system transports arsenite [As(III)], alternatively with the ArsB polypeptide functioning as a chemiosmotic efflux transporter or with two polypeptides, ArsB and ArsA, functioning as an ATPase. The third protein of the arsenic resistance system is an enzyme that reduces intracellular arsenate [As(V)] to arsenite [As(III)], the substrate of the efflux system. In Gram-negative cells, a three polypeptide complex functions as a chemiosmotic cation/protein exchanger to efflux Cd2+, Zn2+ and Co2+. This pump consists of an inner membrane (CzcA), an outer membrane (CzcC) and a membrane-spanning (CzcB) protein that function together. | 1998 | 9523453 |
| 502 | 7 | 0.9258 | A highly specialized flavin mononucleotide riboswitch responds differently to similar ligands and confers roseoflavin resistance to Streptomyces davawensis. Streptomyces davawensis is the only organism known to synthesize the antibiotic roseoflavin, a riboflavin (vitamin B2) analog. Roseoflavin is converted to roseoflavin mononucleotide (RoFMN) and roseoflavin adenine dinucleotide in the cytoplasm of target cells. (Ribo-)Flavin mononucleotide (FMN) riboswitches are genetic elements, which in many bacteria control genes responsible for the biosynthesis and transport of riboflavin. Streptomyces davawensis is roseoflavin resistant, and the closely related bacterium Streptomyces coelicolor is roseoflavin sensitive. The two bacteria served as models to investigate roseoflavin resistance of S. davawensis and to analyze the mode of action of roseoflavin in S. coelicolor. Our experiments demonstrate that the ribB FMN riboswitch of S. davawensis (in contrast to the corresponding riboswitch of S. coelicolor) is able to discriminate between the two very similar flavins FMN and RoFMN and shows opposite responses to the latter ligands. | 2012 | 22740651 |
| 124 | 8 | 0.9256 | A bacterial view of the periodic table: genes and proteins for toxic inorganic ions. Essentially all bacteria have genes for toxic metal ion resistances and these include those for Ag+, AsO2-, AsO4(3-), Cd2+ Co2+, CrO4(2-), Cu2+, Hg2+, Ni2+, Pb2+, TeO3(2-), Tl+ and Zn2+. The largest group of resistance systems functions by energy-dependent efflux of toxic ions. Fewer involve enzymatic transformations (oxidation, reduction, methylation, and demethylation) or metal-binding proteins (for example, metallothionein SmtA, chaperone CopZ and periplasmic silver binding protein SilE). Some of the efflux resistance systems are ATPases and others are chemiosmotic ion/proton exchangers. For example, Cd2+-efflux pumps of bacteria are either inner membrane P-type ATPases or three polypeptide RND chemiosmotic complexes consisting of an inner membrane pump, a periplasmic-bridging protein and an outer membrane channel. In addition to the best studied three-polypeptide chemiosmotic system, Czc (Cd2+, Zn2+, and Co2), others are known that efflux Ag+, Cu+, Ni2+, and Zn2+. Resistance to inorganic mercury, Hg2+ (and to organomercurials, such as CH3Hg+ and phenylmercury) involve a series of metal-binding and membrane transport proteins as well as the enzymes mercuric reductase and organomercurial lyase, which overall convert more toxic to less toxic forms. Arsenic resistance and metabolizing systems occur in three patterns, the widely-found ars operon that is present in most bacterial genomes and many plasmids, the more recently recognized arr genes for the periplasmic arsenate reductase that functions in anaerobic respiration as a terminal electron acceptor, and the aso genes for the periplasmic arsenite oxidase that functions as an initial electron donor in aerobic resistance to arsenite. | 2005 | 16133099 |
| 8543 | 9 | 0.9250 | Soil bacteria, genes, and metabolites stimulated during sulfur cycling and cadmium mobilization under sodium sulfate stress. Sodium sulfate stress is known to improve cadmium (Cd) mobilization in soil and microbial sulfur oxidation, Cd resistance, and the accumulation of stress tolerance-associated metabolites has been correlated with increased soil Cd availability and toxicity. In this study, aerobic soil microcosms with Cd-contamination were stimulated with sodium sulfate to investigate its effects on soil microbial community structure, functional genes, and associated metabolite profiles. Metagenomic analysis revealed that sulfur oxidizing and Cd-resistant bacteria carried gene clusters encoding sox, dsr, and sqr genes, and znt, czc, and cad genes, respectively. Exposure to sodium sulfate resulted in the reprogram of soil metabolites. In particular, intensification of sulfur metabolism triggered an up-regulation in the tricarboxylic acid (TCA) cycle, which promoted the secretion of carboxylic acids and their precursors by soil bacteria. The accumulation of organic acids induced in response to high sodium sulfate dosages potentially drove an observed increase in Cd mobility. Pseudomonas and Erythrobacter spp. exhibited a high capacity for adaptation to heavy metal- or sulfur-induced stress, evident by an increased abundance of genes and metabolites for sulfur cycling and Cd resistance. These results provide valuable insights towards understanding the microbial mechanisms of sulfur transformation and Cd dissolution under saline stress. | 2021 | 34214562 |
| 8716 | 10 | 0.9244 | Organophosphorus mineralizing-Streptomyces species underpins uranate immobilization and phosphorus availability in uranium tailings. Phosphate-solubilizing bacteria (PSB) are important but often overlooked regulators of uranium (U) cycling in soil. However, the impact of PSB on uranate fixation coupled with the decomposition of recalcitrant phosphorus (P) in mining land remains poorly understood. Here, we combined gene amplicon sequencing, metagenome and metatranscriptome sequencing analysis and strain isolation to explore the effects of PSB on the stabilization of uranate and P availability in U mining areas. We found that the content of available phosphorus (AP), carbonate-U and Fe-Mn-U oxides in tailings was significantly (P < 0.05) higher than their adjacent soils. Also, organic phosphate mineralizing (PhoD) bacteria (e.g., Streptomyces) and inorganic phosphate solubilizing (gcd) bacteria (e.g., Rhodococcus) were enriched in tailings and soils, but only organic phosphate mineralizing-bacteria substantially contributed to the AP. Notably, most genes involved in organophosphorus mineralization and uranate resistance were widely present in tailings rather than soil. Comparative genomics analyses supported that organophosphorus mineralizing-Streptomyces species could increase soil AP content and immobilize U(VI) through organophosphorus mineralization (e.g., PhoD, ugpBAEC) and U resistance related genes (e.g., petA). We further demonstrated that the isolated Streptomyces sp. PSBY1 could enhance the U(VI) immobilization mediated by the NADH-dependent ubiquinol-cytochrome c reductase (petA) through decomposing organophosphorous compounds. This study advances our understanding of the roles of PSB in regulating the fixation of uranate and P availability in U tailings. | 2024 | 38908177 |
| 524 | 11 | 0.9242 | Sulfamethoxazole degradation by Pseudomonas silesiensis F6a isolated from bioelectrochemical technology-integrated constructed wetlands. The antibiotic-degrading ability and mechanism of the bacteria in the novel and ecological bioelectrochemical technology-integrated constructed wetlands (BICW) remain unknown. In this study, the sulfamethoxazole (SMX) degrading strain Pseudomonas silesiensis F6a (F6a), which had high degradation efficiency, was firstly isolated from a substrate sample in BICW. The SMX degradation process of F6a follows pseudo first order kinetics. Four metabolic pathways and twelve degradation products were identified. Based on genomics and proteomics analysis, six key SMX-degrading genes, Gene4641 deoC, Gene0552 narI, Gene0546 luxS, Gene1753 nuoH, Gene0655 and Gene4650, were identified, which were mainly participated in C-S cleavage, S-N hydrolysis and isoxazole ring cleavage. Interestingly, we found the corresponding sulfonamides resistance genes were not detected in F6a, which may provide an evidence for low abundance of the sulfonamides resistance genes in BICW system. These findings would contribute to a better understanding of biotransformation of antibiotic in the BICW. | 2022 | 35636241 |
| 522 | 12 | 0.9238 | Detoxification of ars genotypes by arsenite-oxidizing bacteria through arsenic biotransformation. The detoxification process of transforming arsenite (As(III)) to arsenate (As(V)) through bacterial oxidation presents a potent approach for bioremediation of arsenic-polluted soils in abandoned mines. In this study, twelve indigenous arsenic-oxidizing bacteria (AOB) were isolated from arsenic-contaminated soils. Among these, Paenibacillus xylanexedens EBC-SK As2 (MF928871) and Ochrobactrum anthropi EBC-SK As11 (MF928880) were identified as the most effective arsenic-oxidizing isolates. Evaluations for bacterial arsenic resistance demonstrated that P. xylanexedens EBC-SK As2 (MF928871) could resist As(III) up to 40 mM, while O. anthropi EBC-SK As11 (MF928880) could resist As(III) up to 25 mM. From these bacterial strains, genotypes of arsenic resistance system (ars) were detected, encompassing ars leader genes (arsR and arsD), membrane genes (arsB and arsJ), and aox genes known to be crucial for arsenic detoxification. These ars genotypes in the isolated AOBs might play an instrumental role in arsenic-contaminated soils with potential to reduce arsenic contamination. | 2024 | 39382695 |
| 508 | 13 | 0.9237 | Insights into the chaotropic tolerance of the desert cyanobacterium Chroococcidiopsis sp. 029 (Chroococcidiopsales, Cyanobacteria). The mechanism of perchlorate resistance of the desert cyanobacterium Chroococcidiopsis sp. CCMEE 029 was investigated by assessing whether the pathways associated with its desiccation tolerance might play a role against the destabilizing effects of this chaotropic agent. During 3 weeks of growth in the presence of 2.4 mM perchlorate, an upregulation of trehalose and sucrose biosynthetic pathways was detected. This suggested that in response to the water stress triggered by perchlorate salts, these two compatible solutes play a role in the stabilization of macromolecules and membranes as they do in response to dehydration. During the perchlorate exposure, the production of oxidizing species was observed by using an oxidant-sensing fluorochrome and determining the expression of the antioxidant defense genes, namely superoxide dismutases and catalases, while the presence of oxidative DNA damage was highlighted by the over-expression of genes of the base excision repair. The involvement of desiccation-tolerance mechanisms in the perchlorate resistance of this desert cyanobacterium is interesting since, so far, chaotropic-tolerant bacteria have been identified among halophiles. Hence, it is anticipated that desert microorganisms might possess an unrevealed capability of adapting to perchlorate concentrations exceeding those naturally occurring in dry environments. Furthermore, in the endeavor of supporting future human outposts on Mars, the identified mechanisms might contribute to enhance the perchlorate resistance of microorganisms relevant for biologically driven utilization of the perchlorate-rich soil of the red planet. | 2024 | 38156502 |
| 8832 | 14 | 0.9233 | Pharyngeal Pumping and Tissue-Specific Transgenic P-Glycoprotein Expression Influence Macrocyclic Lactone Susceptibility in Caenorhabditis elegans. Macrocyclic lactones (MLs) are widely used drugs to treat and prevent parasitic nematode infections. In many nematode species including a major pathogen of foals, Parascaris univalens, resistance against MLs is widespread, but the underlying resistance mechanisms and ML penetration routes into nematodes remain unknown. Here, we examined how the P-glycoprotein efflux pumps, candidate genes for ML resistance, can modulate drug susceptibility and investigated the role of active drug ingestion for ML susceptibility in the model nematode Caenorhabditis elegans. Wildtype or transgenic worms, modified to overexpress P. univalens PGP-9 (Pun-PGP-9) at the intestine or epidermis, were incubated with ivermectin or moxidectin in the presence (bacteria or serotonin) or absence (no specific stimulus) of pharyngeal pumping (PP). Active drug ingestion by PP was identified as an important factor for ivermectin susceptibility, while moxidectin susceptibility was only moderately affected. Intestinal Pun-PGP-9 expression elicited a protective effect against ivermectin and moxidectin only in the presence of PP stimulation. Conversely, epidermal Pun-PGP-9 expression protected against moxidectin regardless of PP and against ivermectin only in the absence of active drug ingestion. Our results demonstrate the role of active drug ingestion by nematodes for susceptibility and provide functional evidence for the contribution of P-glycoproteins to ML resistance in a tissue-specific manner. | 2021 | 33668460 |
| 328 | 15 | 0.9231 | Multiresistance genes of Rhizobium etli CFN42. Multidrug efflux pumps of bacteria are involved in the resistance to various antibiotics and toxic compounds. In Rhizobium etli, a mutualistic symbiont of Phaseolus vulgaris (bean), genes resembling multidrug efflux pump genes were identified and designated rmrA and rmrB. rmrA was obtained after the screening of transposon-generated fusions that are inducible by bean-root released flavonoids. The predicted gene products of rmrAB shared significant homology to membrane fusion and major facilitator proteins, respectively. Mutants of rmrA formed on average 40% less nodules in bean, while mutants of rmrA and rmrB had enhanced sensitivity to phytoalexins, flavonoids, and salicylic acid, compared with the wild-type strain. Multidrug resistance genes emrAB from Escherichia coli complemented an rmrA mutant from R. etli for resistance to high concentrations of naringenin. | 2000 | 10796024 |
| 512 | 16 | 0.9230 | An alternate pathway of antimonite [Sb(III)] resistance in Ensifer adhaerens mediated by ArsZ'. Trivalent arsenicals, such as arsenite [As(III)] and methylarsenite [MAs(III)], are highly toxic and commonly found in anoxic environments. Similarly, antimony (Sb), a toxic metalloid present in the environment, triggers the activation of numerous genes in microorganisms to resist, transform, and efflux it. This study focuses on the arsZ' gene from the trivalent metalloids-resistant Ensifer adhaerens strain ST2 and its role in mitigating antimonite [Sb(III)] toxicity. The introduction of arsZ' into Escherichia coli AW3110 provided resistance to Sb(III) but not MAs(III). Crucial cysteine residues, Cys95 and Cys109 in ArsZ', were found to be essential for Sb(III) resistance. The disruption of arsZ' in E. adhaerens resulted in decreased tolerance to Sb(III) but not As(III). Exposure to Sb(III) in the ΔarsZ' mutant strain ST2(Δars'Z) led to a significant rise in reactive oxygen species production and a decline in catalase activity, indicating oxidative stress. Particularly, Sb(III) induced glutathione reductase activity. These discoveries shed light on a novel detoxification pathway for Sb(III) in bacteria and underscore the potential of soil bacteria like strain ST2 in mitigating Sb(III) toxicity for future bioremediation endeavors. | 2025 | 40682878 |
| 139 | 17 | 0.9230 | The strategy of arsenic metabolism in an arsenic-resistant bacterium Stenotrophomonas maltophilia SCSIOOM isolated from fish gut. Bacteria are candidates for the biotransformation of environmental arsenic (As), while As metabolism in bacteria is not yet fully understood. In this study, we sequenced the genome of an As-resistant bacterium strain Stenotrophomonas maltophilia SCSIOOM isolated from the fish gut. After arsenate (As(V)) exposure, S. maltophilia transformed As(V) to organoarsenicals, along with the significant change of the expression of 40 genes, including the upregulation of arsH, arsRBC and betIBA. The heterogeneous expression of arsH and arsRBC increased As resistance of E. coli AW3110 by increasing As efflux and transformation. E. coli AW3110 (pET-betIBA) could transform inorganic As into dimethylarsinate (DMA) and nontoxic arsenobetaine (AsB), which suggested that AsB could be synthesized through the synthetic pathway of its analog-glycine betaine. In addition, the existence of arsRBC, betIBA and arsH reduced the reactive oxygen species (ROS) induced by As exposure. In total, these results demonstrated that S. maltophilia adopted an As metabolism strategy by reducing As accumulation and synthesizing less toxic As species. We first reported the production and potential synthetic pathway of AsB in bacteria, which improved our knowledge of As toxicology in microorganisms. | 2022 | 36058313 |
| 528 | 18 | 0.9228 | Effect of dimethyl sulphoxide on the expression of nitrogen fixation in bacteria. Storage in dimethyl sulphoxide (DMSO) of Escherichia coli K12 hybrids carrying nif+ genes from Klebsiella pneumoniae can result in selection of a defective nitrogen-fixing phenotype. Similar results are obtained with E. coli K12 hybrids containing the nitrogen-fixing capacity from Rhizobium trifolii. DMSO appears to affect particular inner membrane proteins associated with energy metabolism in E. coli K12 and four chromosomal regions (chlD, chlG, his and unc) are associated with resistance to DMSO. | 1977 | 332135 |
| 137 | 19 | 0.9226 | Bacterial transformations of and resistances to heavy metals. Bacteria carry out chemical transformations of heavy metals. These transformations (including oxidation, reduction, methylation, and demethylation) are sometimes byproducts of normal metabolism and confer no known advantage upon the organism responsible. Sometimes, however, the transformations constitute a mechanism of resistance. Many species of bacteria have genes that control resistances to specific toxic heavy metals. These resistances often are determined by extrachromosomal DNA molecules (plasmids). The same mechanisms of resistance occur in bacteria from soil, water, industrial waste, and clinical sources. The mechanism of mercury and organomercurial resistance is the enzymatic detoxification of the mercurials into volatile species (methane, ethane, metallic HgO) which are rapidly lost from the environment. Cadmium and arsenate resistances are due to reduced net accumulation of these toxic materials. Efficient efflux pumps cause the rapid excretion of Cd2+ and AsO4(3-). The mechanisms of arsenite and of antimony resistance, usually found associated with arsenate resistance, are not known. Silver resistance is due to lowered affinity of the cells for Ag+, which can be complexed with extracellular halides, thiols, or organic compounds. Sensitivity is due to binding of Ag+ more effectively to cells than to Cl-. | 1984 | 6367730 |