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PubMed2002

Anaerobic biotransformation of tetrabromobisphenol A, tetrachlorobisphenol A, and bisphenol A in estuarine sediments.

Biotransformation of the flame retardants tetrabromobisphenol A and tetrachlorobisphenol A, and their ultimate biodehalogenation product, bisphenol A, was examined in anoxic estuarine sediments. Dehalogenation of tetrabromobisphenol A and tetrachlorobisphenol A was examined under conditions promoting either methanogenesis or sulfate reduction as the primary terminal electron-accepting process. Complete dehalogenation of tetrabromobisphenol A to bisphenol A with no further degradation of bisphenol A, was observed under both methanogenic and sulfate-reducing conditions. Dehalogenation of tetrachlorobisphenol A under both methanogenic and sulfate-reducing conditions resulted in the accumulation of a persistent dichlorinated bisphenol A isomer, while no bisphenol A was formed. Co-amendment of sediment enrichments with either 2,6-dibromo- or 2,6-dichlorophenol did not affect the extent of dehalogenation as compared to sediments that were amended only with the flame retardants. Sediment cultures pre-acclimated on 2-bromophenol dehalogenated the flame retardants in a manner similar to that of fresh sediments. No loss of bisphenol A was observed in separate incubations within 162 days under conditions promoting either methanogenesis, sulfate-reduction, iron(III)-reduction, or nitrate-reduction. Furthermore, identical enrichments that readily degraded 4-hydroxybenzoate, a structural analogue of bisphenol A, did not exhibit bisphenol A degradation. The dehalogenation of tetrabromo- and tetrachlorobisphenol A and the potential for accumulation of bisphenol A in anoxic sediments is significant given the widespread use of these chemicals.

Bacteria, Anaerobic↗
PubMed2002

Anaerobic, sulfate-dependent degradation of polycyclic aromatic hydrocarbons in petroleum-contaminated harbor sediment.

It has previously been demonstrated that [14C]-labeled polycyclic aromatic hydrocarbons (PAHs) can be oxidized to 14CO2 in anoxic, PAH-contaminated, marine harbor sediments in which sulfate reduction is the terminal electron-accepting process. However, it has not previously been determined whether this degradation of [14C]-PAHs accurately reflects the degradation of the in situ pools of contaminant PAHs. In coal tar-contaminated sediments from Boston Harbor, [14C]-naphthalene was readily oxidized to 14CO2, but, after 95 d of incubation under anaerobic conditions, there was no significant decrease in the detectable pool of in situ naphthalene in these sediments. Therefore, to better evaluate the anaerobic biodegradation of the in situ PAH pools, the concentrations of these contaminants were monitored for ca. 1 year during which the sediments were incubated under conditions that mimicked those found in situ. There was loss of all of the PAHs that were monitored (2-5 ring congeners), including high molecular weight PAHs, such as benzo[a]pyrene, that have not previously been shown to be degraded under anaerobic conditions. There was no significant change in the PAH levels in the sediments amended with molybdate to inhibit sulfate-reducing bacteria or in sediments in which all microorganisms had been killed with glutaraldehyde. In some instances, over half of the detectable pools of in situ 2-3 ring PAHs were degraded. In general, the smaller PAHs were degraded more rapidly than the larger PAHs. A distinct exception in the Boston Harbor sediment was naphthalene which was degraded very slowly at a rate comparable to the larger PAHs. In a similar in situ-like study of fuel-contaminated sediments from Liepaja Harbor, Latvia, there was no decline in PAH levels in samples that were sulfate-depleted. However, when the Latvia sediments were supplemented with sufficient sodium sulfate or gypsum to elevate pore water levels of sulfate to approximately 14-25 mM there was a 90% decline in the naphthalene and a 60% decline in the 2-methylnaphthalene pool within 90 days. These studies demonstrate for the first time that degradation by anaerobic microorganisms can significantly impact the in situ pools of PAHs in petroleum-contaminated, anoxic, sulfate-reducing harbor sediments and suggest that the self-purification capacity of contaminated harbor sediments is greater than previously considered.

Bacteria, Anaerobic↗
PubMed2002

Fouling of microfiltration and ultrafiltration membranes by natural waters.

Membrane filtration (microfiltration and ultrafiltration) has become an accepted process for drinking water treatment, but membrane fouling remains a significant problem. The objective of this study was to systematically investigate the mechanisms and components in natural waters that contribute to fouling. Natural waters from five sources were filtered in a benchtop filtration system. A sequential filtration process was used in most experiments. The first filtration steps removed specific components from the water, and the latter filtration steps investigated membrane fouling by the remaining components. Particulate matter (larger than 0.45 microm) was relatively unimportant in fouling as compared to dissolved matter. Very small colloids, ranging from about 3-20 nm in diameter, appeared to be important membrane foulants based on this experimental protocol. The colloidal foulants included both inorganic and organic matter, but the greatest fraction of material was organic. When the colloidal fraction of material was removed, the remaining dissolved organic matter (DOM), which was smaller than about 3 nm and included about 85-90% of the total DOM, caused very little fouling. Thus, although other studies have identified DOM as a major foulant during filtration of natural waters, this work shows that a small fraction of DOM may be responsible for fouling. Adsorption was demonstrated to be an important mechanism for fouling by colloids.

Adsorption↗
PubMed2003

Microbial mercury transformation in anoxic freshwater sediments under iron-reducing and other electron-accepting conditions.

Potential rates of microbial methylation of inorganic mercury (added as HgCl2) and degradation of methyl mercury (MeHg) (added as CH3HgCl) were investigated in anoxic sediments from the Mobile Alabama River Basin (MARB) dominated by different terminal electron-accepting processes (TEAPs). Potential rates of methylation were comparable under methanogenic and sulfate-reducing conditions but suppressed under iron-reducing conditions, in slurries of freshwater wetland sediment In contrast, MeHg degradation rates were similar under all three TEAPs. Microbial Hg methylation and MeHg degradation were also investigated in surface sediment from three riverine sites, two of which had iron reduction and one sulfate reduction, as the dominant TEAP (as determined by 14C-acetate metabolism and other biogeochemical measurements). Methylation was active in sulfate-reducing sediments of a tributary creek and suppressed in iron-reducing, sandy sediments from the open river, whereas MeHg degradation was active at all three sites. Although iron-reducing conditions often suppressed methylation, some methylation activity was observed in two out of three replicates from iron-reducing sediments collected near a dam. Given that MeHg degradation was consistently observed under all TEAPs, our results suggest that the net flux of MeHg from iron-reducing surface sediments may be suppressed (due to inhibition of gross MeHg production) compared to sediments supporting other TEAPs.

Anaerobiosis↗
PubMed2005

Effects of progressive anoxia on the solubility of technetium in sediments.

Technetium is a significant radioactive contaminant from nuclear fuel cycle operations. It is highly mobile in its oxic form (as Tc(VII)O4-) but is scavenged to sediments in its reduced forms (predominantly Tc(IV)). Here we examine the behavior of Tc at low concentrations and as microbial anoxia develops in sediment microcosms. A cascade of stable-element terminal-electron-accepting processes developed in microcosms due to indigenous microbial activity. TcO4- removal from solution occurred during active microbial Fe(III) reduction, which generated Fe(II) in the sediments and was complete before sulfate reduction began. Microbial community analysis revealed a similar and complex microbial population at all three sample sites. At the intermediate salinity site, PauII, a broad range of NO3-, Mn(IV), Fe(III), and SO4(2-) reducers were present in sediments including microbes with the potential to reduce Fe(III) to Fe(II), although no differences in the microbial population were discerned as anoxia developed. When sterilized sediments were incubated with pure cultures of NO3(-)-, Fe(III)-, and sulfate-reducing bacteria, TcO4- removal occurred during active Fe(III) reduction. X-ray absorption spectroscopy confirmed that TcO4- removal was due to reduction to hydrous Tc(IV)O2 in Fe(III)- and sulfate-reducing estuarine sediments.

Bacteria↗
PubMed2000

Microbial consortia involved in the anaerobic degradation of hydrocarbons.

In this review, we examine the energetics of well-characterized biodegradation pathways and explore the possibilities for these to support growth of multiple organisms interacting in consortia. The relevant phenotypic and/or phylogenetic characteristics of isolates and consortia mediating hydrocarbon degradation coupled with different terminal electron-accepting processes (TEAP) are also reviewed. While the information on metabolic pathways has been gained from the analysis of individual isolates, the energetic framework presented here demonstrates that microbial consortia could be readily postulated for hydrocarbon degradation coupled to any TEAP. Several specialized reactions occur within these pathways, and the organisms mediating these are likely to play a key role in defining the hydrocarbon degradation characteristics of the community under a given TEAP. Comparing these processes within and between TEAPs reveals biological unity in that divergent phylotypes display similar degradation mechanisms and biological diversity in that hydrocarbon-degraders closely related as phylotypes differ in the type and variety of hydrocarbon degradation pathways they possess. Analysis of microcosms and of field samples suggests that we have only begun to reveal the diversity of organisms mediating anaerobic hydrocarbon degradation. Advancements in the understanding of how hydrocarbon-degrading communities function will be significantly affected by the extent to which organisms mediating specialized reactions can be identified, and tools developed to allow their study in situ.

Bacteria, Anaerobic↗
PubMed2000

Anaerobic benzene degradation.

Although many studies have indicated that benzene persists under anaerobic conditions in petroleum-contaminated environments, it has recently been documented that benzene can be anaerobically oxidized with most commonly considered electron acceptors for anaerobic respiration. These include: Fe(III), sulfate, nitrate, and possibly humic substances. Benzene can also be converted to methane and carbon dioxide under methanogenic conditions. There is evidence that benzene can be degraded under in situ conditions in petroleum-contaminated aquifers in which either Fe(III) reduction or methane production is the predominant terminal electron-accepting process. Furthermore, evidence from laboratory studies suggests that benzene may be anaerobically degraded in petroleum-contaminated marine sediments under sulfate-reducing conditions. Laboratory studies have suggested that within the Fe(III) reduction zone of petroleum-contaminated aquifers, benzene degradation can be stimulated with the addition of synthetic chelators which make Fe(III) more available for microbial reduction. The addition of humic substances and other compounds that contain quinone moieties can also stimulate anaerobic benzene degradation in laboratory incubations of Fe(III)-reducing aquifer sediments by providing an electron shuttle between Fe(III)-reducing microorganisms and insoluble Fe(III) oxides. Anaerobic benzene degradation in aquifer sediments can be stimulated with the addition of sulfate, but in some instances an inoculum of benzene-oxidizing, sulfate-reducing microorganisms must also be added. In a field trial, sulfate addition to the methanogenic zone of a petroleum-contaminated aquifer stimulated the growth and activity of sulfate-reducing microorganisms and enhanced benzene removal. Molecular phylogenetic studies have provided indications of what microorganisms might be involved in anaerobic benzene degradation in aquifers. The major factor limiting further understanding of anaerobic benzene degradation is the lack of a pure culture of an organism capable of anaerobic benzene degradation.

Bacteria, Anaerobic↗
PubMed2001

Anaerobic degradation and dehalogenation of chlorosalicylates and salicylate under four reducing conditions.

The anaerobic biodegradability and transformation of the mono-and dichlorinated salicylates (2-hydroxybenzoates) was examined under denitrifying, Fe (III) reducing, sulfate reducing and methanogenic conditions. 3,6-Dichlorosalicylate and 6-chlorosalicylate are anaerobic microbial metabolites of dicamba, a widely used herbicide. Anaerobic microcosms were established with dicamba treated soil from Wyoming, and golf course drainage stream sediments from New Jersey, which were each spiked with salicylate, 3,6-dichlorosalicylate or one of the four monochlorosalicylate isomers. Salicylate was degraded under denitrifying, sulfidogenic and methanogenic conditions. In methanogenic enrichments 5-chlorosalicylate and 3-chlorosalicylate were reductively dehalogenated to salicylate which was then utilized. Dehalogenation of monochlorinated salicylates to salicylate was also observed in denitrifying chlorosalicylate degrading cultures. The study revealed that the position of the chlorine substituent as well as the predominant electron accepting process affect the rate and extent of chlorosalicylate degradation in anoxic environments.

Anaerobiosis↗
PubMed2002

The role of microbial populations in the containment of aromatic hydrocarbons in the subsurface.

A survey of soil gases associated with gasoline stations on the Swan Coastal Plain of Western Australia has shown that 20% leak detectable amounts of petroleum. The fates of volatile hydrocarbons in the vadose zone at one contaminated site, and dissolved hydrocarbons in groundwater at another site were followed in a number of studies which are herein reviewed. Geochemical evidence from a plume of hydrocarbon-contaminated groundwater has shown that sulfate reduction rapidly developed as the terminal electron accepting process. Toluene degradation but not benzene degradation was linked to sulfate reduction. The sulfate-reducing bacteria isolated from the plume represented a new species, Desulfosporosinus meridiei. Strains of the species do not mineralise 14C-toluene in pure culture. The addition of large numbers of cells and sulfate to microcosms did stimulate toluene mineralisation but not benzene mineralisation. Attempts to follow populations of sulfate-reducing bacteria by phospholipid signatures, or Desulfosporosinus meridiei by FISH in the plume were unsuccessful, but fluorescently-labeled polyclonal antibodies were successfully used. In the vadose zone at a different site, volatile hydrocarbons were consumed in the top 0.5 m of the soil profile. The fastest measured rate of mineralisation of 14C-benzene in soils collected from the most active zone (6.5 mg kg(-1) day(-1)) could account for the majority of the flux of hydrocarbon vapourtowards the surface. The studies concluded that intrinsic remediation by subsurface microbial populations in groundwater on the Swan Coastal Plain can control transport of aromatic hydrocarbon contamination, except for the transport of benzene in groundwater. In the vadose zone, intrinsic remediation by the microbial populations in the soil profile can contain the transport of aromatic hydrocarbons, provided the physical transport of gases, in particular oxygen from the atmosphere, is not impeded by structures.

Biodegradation, Environmental↗
PubMed2004

Modeling natural attenuation of chlorinated ethenes under spatially varying redox conditions.

A three-dimensional model for the transport and reductive dechlorination of chlorinated ethenes in ground-water systems with variable redox conditions is demonstrated and applied to a pilot test for accelerated natural attenuation of trichloroethene (TCE). The rate and extent of biotransformation of TCE and chlorinated progeny is controlled by the dominant terminal electron accepting process (TEAP) that is simulated over space and time. The solute transport code, Sequential Electron Acceptor Model, 3D-transport, (SEAM3D) which simulates aerobic and sequential anaerobic biodegradation of organic carbon, is modified to implement the equations. Results of a generic model for TCE transport in ground-water systems with different redox conditions demonstrate that the degree of chlorinated ethene attenuation is influenced by background concentrations of aqueous- and solid-phase electron acceptors, but that model results are sensitive to other input parameters (inhibition coefficients, maximum rate of reductive dechlorination, biomass concentrations, and ground-water velocity). Simulation results of enhanced in situ bioremediation using dissolved organic carbon as a reducing agent show that spatial and temporal changes in the dominant TEAP and the subsequent rate of reductive dechlorination are adequately represented with the model. Initial concentrations of Fe(III) and the dechlorinating microbial population influence the simulated time lag observed during the pilot test.

Biodegradation, Environmental↗
PubMed2003

Metabolism of organic compounds in anaerobic, hydrothermal sulphate-reducing marine sediments.

Previous studies of hot (>80 degrees C) microbial ecosystems have primarily relied on the study of pure cultures or analysis of 16S rDNA sequences. In order to gain more information on anaerobic metabolism by natural communities in hot environments, sediments were collected from a shallow marine hydrothermal vent system in Baia di Levante, Vulcano, Italy and incubated under strict anaerobic conditions at 90 degrees C. Sulphate reduction was the predominant terminal electron-accepting process in the sediments. The addition of molybdate inhibited sulphate reduction in the sediments and resulted in a linear accumulation of acetate and hydrogen over time. [U-14C]- acetate was completely oxidized to 14CO2, and the addition of molybdate inhibited 14CO2 production by 60%. [U-14C]-glucose was oxidized to 14CO2, and this was inhibited when molybdate was added. When the pool sizes of short-chain fatty acids were artificially increased, radiolabel from [U-14C]-glucose accumulated in the acetate pool. L-[U-14C]-glutamate, [ring-14C]-benzoate and [U-14C]-palmitate were also anaerobically oxidized to 14CO2 in the sediments, but molybdate had little effect on the oxidation of these compounds. These results demonstrate that natural microbial communities living in a hot, microbial ecosystem can oxidize acetate and a range of other organic electron donors under sulphate-reducing conditions and suggest that acetate is an important extracellular intermediate in the anaerobic degradation of organic matter in hot microbial ecosystems.

Acetates↗
PubMed1995

Human intestinal H+/peptide cotransporter. Cloning, functional expression, and chromosomal localization.

In mammalian small intestine, a H(+)-coupled peptide transporter is responsible for the absorption of small peptides arising from digestion of dietary proteins. Recently a cDNA clone encoding a H+/peptide cotransporter has been isolated from a rabbit intestinal cDNA library (Fei, Y.J., Kanai, Y., Nussberger, S., Ganapathy, V., Leibach, F.H., Romero, M.F., Singh, S.K., Boron, W. F., and Hediger, M. A. (1994) Nature 368, 563-566). Screening of a human intestinal cDNA library with a probe derived from the rabbit H+/peptide cotransporter cDNA resulted in the identification of a cDNA which when expressed in HeLa cells or in Xenopus laevis oocytes induced H(+)-dependent peptide transport activity. The predicted protein consists of 708 amino acids with 12 membrane-spanning domains and two putative sites for protein kinase C-dependent phosphorylation. The cDNA-induced transport process accepts dipeptides, tripeptides, and amino beta-lactam antibiotics but not free amino acids as substrates. The human H+/peptide cotransporter exhibits a high degree of homology (81% identity and 92% similarity) to the rabbit H+/peptide cotransporter. But surprisingly these transporters show only a weak homology to the H(+)-coupled peptide transport proteins present in bacteria and yeast. Chromosomal assignment studies with somatic cell hybrid analysis and in situ hybridization have located the gene encoding the cloned human H+/peptide cotransporter to chromosome 13 q33-->q34.

Amino Acid Sequence↗
PubMed1991

Practical strategies for CNS role implementation.

Methods of implementing the clinical nurse specialist (CNS) role can be approached in many ways. Providing the clinical specialist with concrete strategies to use during role implementation or expansion can aid in expediting the acceptance process for the CNS. Some authors have discussed phases the CNS encounters during role development. Time span of these phases vary greatly, dependent not only on the individual specialist, but also on the system for which they are employed. Kramer's four phases detailing the adjustment period of the newly practicing nurse may be used when discussing CNS role implementation. These four phases are: honeymoon, shock/rejection, recovery, and resolution. Practical suggestions to expedite role implementation can make progression through these phases easier and less overwhelming. Although obstacles will often be present, the CNS must then become a catalyst by using creative ideas and effective coping mechanisms to effect change and advance the role.

Adaptation, Psychological↗
PubMed2004

Spatial and temporal changes in microbial community structure associated with recharge-influenced chemical gradients in a contaminated aquifer.

In a contaminated water-table aquifer, we related microbial community structure on aquifer sediments to gradients in 24 geochemical and contaminant variables at five depths, under three recharge conditions. Community amplified ribsosomal DNA restriction analysis (ARDRA) using universal 16S rDNA primers and denaturing gradient gel electrophoresis (DGGE) using bacterial 16S rDNA primers indicated: (i). communities in the anoxic, contaminated central zone were similar regardless of recharge; (ii). after recharge, communities at greatest depth were similar to those in uncontaminated zones; and (iii). after extended lack of recharge, communities at upper and lower aquifer margins differed from communities at the same depths on other dates. General aquifer geochemistry was as important as contaminant or terminal electron accepting process (TEAP) chemistry in discriminant analysis of community groups. The Shannon index of diversity (H) and the evenness index (E), based on DGGE operational taxonomic units (OTUs), were statistically different across community groups and aquifer depths. Archaea or sulphate-reducing bacteria 16S rRNA abundance was not clearly correlated with TEAP chemistry indicative of methanogenesis or sulphate reduction. Eukarya rRNA abundance varied by depth and date from 0 to 13% of the microbial community. This contaminated aquifer is a dynamic ecosystem, with complex interactions between physical, chemical and biotic components, which should be considered in the interpretation of aquifer geochemistry and in the development of conceptual or predictive models for natural attenuation or remediation.

Archaea↗
PubMed1999

Repression of nitrogenase by ethanol in nitrogen-deprived cultures of Rhodovulum sulfidophilum.

Light-dependent H2 evolution did not occur in nitrogen-deprived cultures of Rhodovulum sulfidophilum in the presence of ethanol. When ethanol was added to cells which had been grown with ammonia, derepression of the nitrogen fixation genes (nifHD) was inhibited at an ethanol concentration of 1 mM. On the other hand, when cells had nitrogenase-catalyzed proton-reducing activity prior to ethanol addition, reduction of the nifHD transcript level did not occur after the addition. In cells grown with ammonia, concomitant addition of an auxiliary oxidant such as dimethylsulfoxide or sodium bicarbonate resulted in derepression of nitrogenase activity in the presence of ethanol. These results suggest that the electron-accepting process is necessary for derepression of nif genes in cultures which use ethanol as the electron donor.

Ammonia↗
PubMed1995

A novel comprehensive quality control instrument for medical accelerators.

A comprehensive quality control instrument for calibration of medical accelerators that use photon, electron, or proton beams in teleradiotherapy is described. It employs a fluorescence screen, mounted on a central stage with four degrees of freedom, monitored by a CCD camera. A single set-up of the instrument enables one to perform mechanical, light laser, and radiation tests, at arbitrary angles of the accelerator gantry. The new device provides for quantitative evaluation of the tests performed and provides for documentation of the test results in real time. The device provides significant time savings with concurrent improvement in accuracy for tests performed during installation and acceptance processes, and the implementation of quality control procedures for medical accelerators.

Electrons↗
PubMed1989

Requirement for a Microbial Consortium To Completely Oxidize Glucose in Fe(III)-Reducing Sediments.

In various sediments in which Fe(III) reduction was the terminal electron-accepting process, [C]glucose was fermented to C-fatty acids in a manner similar to that observed in methanogenic sediments. These results are consistent with the hypothesis that, in Fe(III)-reducing sediments, fermentable substrates are oxidized to carbon dioxide by the combined activity of fermentative bacteria and fatty acid-oxidizing, Fe(III)-reducing bacteria.

Journal Article↗
PubMed1999

Characterization of two subsurface H2-utilizing bacteria, Desulfomicrobium hypogeium sp. nov. and Acetobacterium psammolithicum sp. nov., and their ecological roles.

We examined the relative roles of acetogenic and sulfate-reducing bacteria in H2 consumption in a previously characterized subsurface sandstone ecosystem. Enrichment cultures originally inoculated with ground sandstone material obtained from a Cretaceous formation in central New Mexico were grown with hydrogen in a mineral medium supplemented with 0.02% yeast extract. Sulfate reduction and acetogenesis occurred in these cultures, and the two most abundant organisms carrying out the reactions were isolated. Based on 16S rRNA analysis data and on substrate utilization patterns, these organisms were named Desulfomicrobium hypogeium sp. nov. and Acetobacterium psammolithicum sp. nov. The steady-state H2 concentrations measured in sandstone-sediment slurries (threshold concentration, 5 nM), in pure cultures of sulfate reducers (threshold concentration, 2 nM), and in pure cultures of acetogens (threshold concentrations 195 to 414 nM) suggest that sulfate reduction is the dominant terminal electron-accepting process in the ecosystem examined. In an experiment in which direct competition for H2 between D. hypogeium and A. psammolithicum was examined, sulfate reduction was the dominant process.

DNA, Bacterial↗