Microbial transformations of metals.
01 Jan 1978-Annual Review of Microbiology (Annual Reviews 4139 El Camino Way, P.O. Box 10139, Palo Alto, CA 94303-0139, USA)-Vol. 32, Iss: 1, pp 637-672
TL;DR: The mercury cycle in the biosphere and biological methylation of mercury and microbial resistance to mercury and organomercurials are studied.
Abstract: BIOTRANSFORMA nONS OF TOXIC MET AL CAnONS . Mercury . The mercury cycle in the biosphere .. Biological methylation of mercury . Microbial resistance to mercury and organomercurials .
TL;DR: The current state of knowledge on the physicochemical behavior of mercury in the aquatic environment, and in particular the environmental factors influencing its transformation into highly toxic methylated forms is examined in this paper.
Abstract: Mercury is one of the most hazardous contaminants that may be present in the aquatic environment, but its ecological and toxicological effects are strongly dependent on the chemical species present. Species distribution and transformation processes in natural aquatic systems are controlled by various physical, chemical, and biological factors. Depending on the prevailing environmental conditions, inorganic mercury species may be converted to many times more toxic methylated forms such as methylmercury, a potent neurotoxin that is readily accumulated by aquatic biota. Despite a considerable amount of literature on the subject, the behavior of mercury and many of the transformation and distribution mechanisms operating in the natural aquatic environment are still poorly understood. This review examines the current state of knowledge on the physicochemical behavior of mercury in the aquatic environment, and in particular the environmental factors influencing its transformation into highly toxic methylated forms.
TL;DR: This work focuses on the hypothesis that sulfate-reducing bacteria are important mediators of metal methylation in aquatic systems and, moreover, that sulfATE-deposition may stimulate methylmercury production by enhancing the activity of sulfate, reducing bacteria in sediments.
Abstract: Recently, it has been noted that fish in acidified lakes may contain elevated levels of mercury. While there is correlation among lakes between depressed pH and high mercury concentrations in fish, the cause of this problem is unknown. A number of hypotheses have been advanced in explanation, including increased mercury deposition, changes in mercury mobility due to acidification, pH dependent changes in mercury uptake by biota, and alterations in population size and/or structure which result in increased bioaccumulation in fish. Because fish accumulate mercury mainly in an organic form, methylmercury, changes in the biogeochemical cycling of this compound might account for elevated bioaccumulation. Mercury methylation is predominantly a microbial process which occurs in situ in lakes. This review focuses on microbiological and biogeochemical changes that may lead to increased levels of methylmercury in fresh waters impacted by acid-deposition. In particular, we focus on the hypothesis that sulfate-reducing bacteria are important mediators of metal methylation in aquatic systems and, moreover, that sulfate-deposition may stimulate methylmercury production by enhancing the activity of sulfate-reducing bacteria in sediments.
TL;DR: This work has shown clear trends in the emergence of multiresislant S. aureus-related resistance as well as in the development of novel mechanisms for this resistance.
Abstract: INTRODUCTION................................................................................................................. 89 Emergence of Multiresislant S. aureus.................................................................................... 89 Genetic Nature of Antimicrobial Resistance ...——....——......—.—......—..—..—.——.—..—.—...—. 90 TRANSFER OF RESISTANCE GENES IN STAPHYLOCOCCI..................................................... 91 Slaphylococcal Bacteriophages and Transduction ................................................................... 92
TL;DR: As described in this review, many microorganisms (bacteria, fungi, and yeasts) and animals are now known to biomethylate arsenic, forming both volatile and nonvolatile compounds, including methylarsines and trimethylstibine.
Abstract: A significant 19th century public health problem was that the inhabitants of many houses containing wallpaper decorated with green arsenical pigments experienced illness and death. The problem was caused by certain fungi that grew in the presence of inorganic arsenic to form a toxic, garlic-odored gas. The garlic odor was actually put to use in a very delicate microbiological test for arsenic. In 1933, the gas was shown to be trimethylarsine. It was not until 1971 that arsenic methylation by bacteria was demonstrated. Further research in biomethylation has been facilitated by the development of delicate techniques for the determination of arsenic species. As described in this review, many microorganisms (bacteria, fungi, and yeasts) and animals are now known to biomethylate arsenic, forming both volatile (e.g., methylarsines) and nonvolatile (e.g., methylarsonic acid and dimethylarsinic acid) compounds. The enzymatic mechanisms for this biomethylation are discussed. The microbial conversion of sodium arsenate to trimethylarsine proceeds by alternate reduction and methylation steps, with S-adenosylmethionine as the usual methyl donor. Thiols have important roles in the reductions. In anaerobic bacteria, methylcobalamin may be the donor. The other metalloid elements of the periodic table group 15, antimony and bismuth, also undergo biomethylation to some extent. Trimethylstibine formation by microorganisms is now well established, but this process apparently does not occur in animals. Formation of trimethylbismuth by microorganisms has been reported in a few cases. Microbial methylation plays important roles in the biogeochemical cycling of these metalloid elements and possibly in their detoxification. The wheel has come full circle, and public health considerations are again important.
TL;DR: Aerobic anoxygenic phototrophic bacteria are classified in two marine and six freshwater genera and phylogenetically belong to the α-1, α-3, and α-4 subclasses of the class Proteobacteria.
Abstract: The aerobic anoxygenic phototrophic bacteria are a relatively recently discovered bacterial group. Although taxonomically and phylogenetically heterogeneous, these bacteria share the following distinguishing features: the presence of bacteriochlorophyll a incorporated into reaction center and light-harvesting complexes, low levels of the photosynthetic unit in cells, an abundance of carotenoids, a strong inhibition by light of bacteriochlorophyll synthesis, and the inability to grow photosynthetically under anaerobic conditions. Aerobic anoxygenic phototrophic bacteria are classified in two marine (Erythrobacter and Roseobacter) and six freshwater (Acidiphilium, Erythromicrobium, Erythromonas, Porphyrobacter, Roseococcus, and Sandaracinobacter) genera, which phylogenetically belong to the α-1, α-3, and α-4 subclasses of the class Proteobacteria. Despite this phylogenetic information, the evolution and ancestry of their photosynthetic properties are unclear. We discuss several current proposals for the evolutionary origin of aerobic phototrophic bacteria. The closest phylogenetic relatives of aerobic phototrophic bacteria include facultatively anaerobic purple nonsulfur phototrophic bacteria. Since these two bacterial groups share many properties, yet have significant differences, we compare and contrast their physiology, with an emphasis on morphology and photosynthetic and other metabolic processes.
01 Jan 1999
TL;DR: Cotton and Wilkinson's Advanced Inorganic Chemistry (AIC) as discussed by the authors is one of the most widely used inorganic chemistry books and has been used for more than a quarter century.
Abstract: For more than a quarter century, Cotton and Wilkinson's Advanced Inorganic Chemistry has been the source that students and professional chemists have turned to for the background needed to understand current research literature in inorganic chemistry and aspects of organometallic chemistry. Like its predecessors, this updated Sixth Edition is organized around the periodic table of elements and provides a systematic treatment of the chemistry of all chemical elements and their compounds. It incorporates important recent developments with an emphasis on advances in the interpretation of structure, bonding, and reactivity.From the reviews of the Fifth Edition:* "The first place to go when seeking general information about the chemistry of a particular element, especially when up-to-date, authoritative information is desired." -Journal of the American Chemical Society.* "Every student with a serious interest in inorganic chemistry should have [this book]." -Journal of Chemical Education.* "A mine of information . . . an invaluable guide." -Nature.* "The standard by which all other inorganic chemistry books are judged."-Nouveau Journal de Chimie.* "A masterly overview of the chemistry of the elements."-The Times of London Higher Education Supplement.* "A bonanza of information on important results and developments which could otherwise easily be overlooked in the general deluge of publications." -Angewandte Chemie.
01 Jan 1975
TL;DR: The problem of mercury pollution came to focus when a recent Cana dian report indicated the presence of high concentrations of mercury residues in the fish taken from Lake St. Clair as mentioned in this paper.
Abstract: The problem of mercury pollution came to focus when a recent Cana dian report indicated the presence of high concentrations of mercury residues in the fish taken from Lake St. Clair. Later in vestigations in this country revealed that mercury pollution of the environment was widespread. Prompted into action by these findings, regulatory agencies sud denly prohibited the sale of fish containing undesirable amounts of mercury. Reportedly, more than 80,000 tons (72, 600 metric tons ) of mercury was consumed in the U. S. in the last century.1 The ma jor contributor of mercury to the environ ment is the chlorine-alkali industry, the largest commercial user of the metal in this country. Losses of mercury of up to 0.2 lb/ton (0.1 kg/metric ton) of chlorine produced have been reported.2 The sec ond largest consumptive use of mercury is in the manufacture of electrical apparatus.3 Mercury is also used extensively in the pro duction of fungicides, plastics, petrochemi cals, and photographic chemicals. It is conceivable that many of these in dustries are currently treating their wastes separately, discharging treated effluents into receiving bodies of water, or contem
TL;DR: No significant increase in mercuric ion-resistant strains of staphylococci or Escherichia coli were detected in exposed populations as compared to control groups, and the possible reasons for this result are discussed.
Abstract: Staphylococci were isolated from rural and urban populations in Iraq, which were not known to be exposed to either heavy metals or antibiotics. The antibiotic and heavy metal resistance patterns of these strains were analyzed in both mannitol-fermenting and nonfermenting strains. Over 90% of the strains were resistant to at least one of the following antibiotics: penicillin, chloramphenicol, erythromycin, tetracycline, cephalothin, lincomycin, or methicillin. In general, mannitol-fermenting strains were resistant to penicillin and cupric ions. Mannitol-negative strains were more frequently associated with mercuric ion and tetracycline resistance. Although resistance to penicillin and tetracycline can coexist, the combination of penicillin resistance and tetracycline resistance usually occurred in mannitol-negative strains. The possibility of selection of heavy metal-resistant strains due to exposure to toxic levels of methylmercury was examined. No significant increase in mercuric ion-resistant strains of staphylococci or Escherichia coli were detected in exposed populations as compared to control groups. The possible reasons for this result are discussed.