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Mild (unalloyed) steel electrodes were incubated in phosphate-buffered cultures of aerobic, biofilm-forming Rhodococcus sp. strain C125 and Pseudomonas putida mt2. A resulting surface reaction leading to the formation of a corrosion-inhibiting vivianite layer was accompanied by a characteristic electrochemical potential (E) curve. First, E increased slightly due to the interaction of phosphate with the iron oxides covering the steel surface. Subsequently, E decreased rapidly and after 1 day reached −510 mV, the potential of free iron, indicating the removal of the iron oxides. At this point, only scattered patches of bacteria covered the surface. A surface reaction, in which iron was released and vivianite precipitated, started. E remained at −510 mV for about 2 days, during which the vivianite layer grew steadily. Thereafter, E increased markedly to the initial value, and the release of iron stopped. Changes in E and formation of vivianite were results of bacterial activity, with oxygen consumption by the biofilm being the driving force. These findings indicate that biofilms may protect steel surfaces and might be used as an alternative method to combat corrosion.

Two different procedures were compared to isolate polycyclic aromatic hydrocarbon (PAH)-utilizing bacteria from PAH-contaminated soil and sludge samples, i.e., (i) shaken enrichment cultures in liquid mineral medium in which PAHs were supplied as crystals and (ii) a new method in which PAH degraders were enriched on and recovered from hydrophobic membranes containing sorbed PAHs. Both techniques were successful, but selected from the same source different bacterial strains able to grow on PAHs as the sole source of carbon and energy. The liquid enrichment mainly selected for Sphingomonas spp., whereas the membrane method exclusively led to the selection of Mycobacterium spp. Furthermore, in separate membrane enrichment set-ups with different membrane types, three repetitive extragenic palindromic PCR-related Mycobacterium strains were recovered. The new Mycobacterium isolates were strongly hydrophobic and displayed the capacity to adhere strongly to different surfaces. One strain, Mycobacterium sp. LB501T, displayed an unusual combination of high adhesion efficiency and an extremely high negative charge. This strain may represent a new bacterial species as suggested by 16S rRNA gene sequence analysis. These results indicate that the provision of hydrophobic sorbents containing sorbed PAHs in the enrichment procedure discriminated in favor of certain bacterial characteristics. The new isolation method is appropriate to select for adherent PAH-degrading bacteria, which might be useful to biodegrade sorbed PAHs in soils and sludge.

The transport of a selected set of bacteria able to degrade polycyclic aromatic hydrocarbons (PAHs) was investigated in saturated column experiments, using as packing materials either a clay-containing soil or the isolated soil constituents montmorillonite clay, sand, or soil humic acid-clay complexes. The bacterial strains studied were able to grow on phenanthrene, anthracene, fluorene, fluoranthrene, and pyrene and were characterized for cell size, aspect ratio, hydrophobicity, and zeta potential. Removal of bacteria from the transport solution was quantified by calculating relative adhesion efficiencies (α(τ)) for all combinations of bacteria and packing materials. Transport through soil varied from strain to strain. However, no clear relationship was observed between the studied physicochemical characteristics of the bacteria and their transport. The relative differences between strains observed in soil were conserved in column experiments with isolated clay. Coating the clay surfaces with two different soil humic acid fractions drastically increased the transport of all bacteria tested. The nonionic surfactant Triton X-100 facilitated transport of hydrophobic cells at concentrations above its critical micelle concentration but had no effect on the transport of hydrophilic bacteria. We suggest that clay is the main retarding agent of PAH-degrading bacteria in soil. | The transport of a selected set of bacteria able to degrade polycyclic aromatic hydrocarbons (PAHs) was investigated in saturated column experiments, using as packing materials either a clay-containing soil or the isolated soil constituents montmorillonite clay, sand, or soil humic acid-clay complexes. The bacterial strains studied were able to grow on phenanthrene, anthracene, fluorene, fluoranthrene, and pyrene and were characterized for cell size, aspect ratio, hydrophobicity, and zeta potential. Removal of bacteria from the transport solution was quantified by calculating relative adhesion efficiencies (αt) for all combinations of bacteria and packing materials. Transport through soil varied from strain to strain. However, no clear relationship was observed between the studied physicochemical characteristics of the bacteria and their transport. The relative differences between strains observed in soil were conserved in column experiments with isolated clay. Coating the clay surfaces with two different soil humic acid fractions drastically increased the transport of all bacteria tested. The nonionic surfactant Triton X-100 facilitated transport of hydrophobic cells at concentrations above its critical micelle concentration but had no effect on the transport of hydrophilic bacteria. We suggest that clay is the main retarding agent of PAH-degrading bacteria in soil., Was supported by the CSICETH cooperation program. Support for this research was also provided by the European Union (contract BIO4-CT97- 2015) and Spanish CICYT (grant BIO97-1960-CE).

Bioremediation has gained a lot of support for the clean up of contaminated soils and sediments because of its elegance and cost-effectiveness compared to chemical and physical methods (for reviews, see (7, 30)). Bioremediation is based on the capaCity of many indigenous microorganisms to degrade polluting compounds (13, 39, 43), although many different factors determine the actual microbial activity in the environment (43). For example, (macro) physicochemical parameters (e.g., redox potential, pH, temperature, salinity, moisture content, availability of nutrients, the presence and nature of surfaces) modulate microbial activity. A key factor influencing the rates of biodegradation in the field is the extent to which a compound is accessible (bioavailable) to the microorganisms.

The availability of clay-sorbed 2,4-dinitrotoluene (2,4-DNT) for degradation by Burkholderia sp. strain DNT was investigated in column experiments. Artificial aggregates of montmorillonite glued to glass spheres served as the sorbent. Sorption isotherms and bacterial kinetic parameters were determined in batches. Sorption of 2,4-DNT to clay aggregates gave reasonable fit to the Langmuir equation. The degradative activity of Burkholderia sp. strain DNT followed Michaelis−Menten kinetics. This allowed inferring bioavailable concentrations in the presence of clay from degradation rates. It appeared that montmorillonite-sorbed 2,4-DNT was readily available to Burkholderia sp. strain DNT. However, despite the accumulation of biomass in the columns due to filtration, absolute degradation rates remained constant, and specific rates continuously decreased toward the end of the experiments. Removal of suspended cells by miscible displacement led to a drastically reduced degradation rate that was not due to decreasing desorption, as 2,4-DNT concentrations in column effluents increased simultaneously. Decreasing degradation could be explained fairly well assuming that the specific activity of suspended cells remained at the initial value of 0.93 nmol mg dw-1 min-1, whereas the specific activity of adhered bacteria steadily dropped to 0.12 nmol mg dw-1 min-1. A likely explanation is the prolonged exposure (up to 6 h) to 2,4-DNT and nitrite for adhered cells, compared with a maximum exposure for suspended cells of 19.5 min, i.e., their residence time in the column. According to the Michaelis−Menten equation, the initial activity corresponded to a bioavailable concentration that exceeded the aqueous equilibrium concentration in the absence of bacteria by a factor of roughly two. The most probable explanation is a shift of the sorption equilibrium in the presence of cells, as direct accessibility of sorbed 2,4-DNT for suspended cells can be excluded.

To study the bioavailability of pollutants in a direct way, whole-cell living biosensors can be used. These are genetically constructed microorganisms, which upon sensing (bioavailable) pollutant concentrations express an easy detectable signal and may or may not degrade the pollutant as well. Biosensors are constructed by combining a sensor element (the regulatory protein) with a reporter gene fused to an inducible promoter. The most suitable reporter genes for the usage in biosensors are those coding for bioluminescent or fluorescent proteins like the luciferase and the Green Fluorescent Protein. Biosensors which are used to determine the bioavailability of pollutants in the environment should be sensitive, respond in a quantitative manner and be selective. Bioreportes should not be considered as an alternative for traditional chemical analyses but regarded as a valuable extension to these well-established techniques. By using both techniques, a better control in bioremediation processes may be obtained.

Nowadays the most frequently offered explanation for the failure of biotechno-logical measures to remediate polluted environments is poor bioavailability. We generally regard microorganisms as potent cleaning agents which are hindered by environmental factors as they pursue their business. On the other hand, ready bioavailability of pollutants to plants, animals and humans is one of the main risks arising from polluted sites. This seems to be contradictory, so much the more as limited bioavailability for degradation and ready bioavailability for toxic effects often are seen as characteristics of the same contamination. It appears that bioavailability is a Janus-faced characteristic of environmental chemicals. A treatise regarding bioavailability therefore requires a clear-cut definition of what is meant by this term and how a given bioavailability should be rated.

Cytometric monitoring of microbial community dynamics can be used to estimate stability of technical microbial processes like biogas production by analysis of segregated cell abundance changes. In this study, structure variations of a biogas community were cytometrically recorded over 9 months and found to be of diagnostic value for process details. The reactor regime was intentionally disturbed with regard to substrate overload or H(2)S accumulation. A single-cell based approach called cytometric bar coding (CyBar) for fast identification of reactive subcommunities was used. Functionality of specific subcommunities was uncovered by processing CyBar data with abiotic reactor parameters using Spearman's correlation coefficient. Twenty subcommunities showed a discrete and divergent behavior. For example, a 4-fold substrate overload increased the cell number of two acidogenic index subcommunities to 176 and 193% within three days. Supplementary analyses were done using DNA fingerprinting, cloning, and sequencing. Bioreactor perturbations were shown to create cell abundance changes in subcommunities rather than variations in their phylogenetic composition. The used workflow and macros are ready-to-use tools and allow on-site monitoring and interpretation of variation in microbial community functions within a few hours.

Medical implants are often colonized by bacteria which may cause severe infections. The initial step in the colonization, the adhesion of bacteria to the artificial solid surface, is governed mainly by long-range van der Waals and electrostatic interactions between the solid surface and the bacterial cell. While van der Waals forces are generally attractive, the usually negative charge of bacteria and solid surfaces leads to electrostatic repulsion. We report here on the adhesion of a clinical isolate, Stenotrophomonas maltophilia 70401, which is, at physiological pH, positively charged. S. maltophilia has an electrophoretic mobility of +0.3 x 10(-8) m2 V-1 s-1 at pH 7 and an overall surface isoelectric point at pH 11. The positive charge probably originates from proteins located in the outer membrane. For this bacterium, both long-range forces involved in adhesion are attractive. Consequently, adhesion of S. maltophilia to negatively charged surfaces such as glass and Teflon is much favored compared with the negatively charged bacterium Pseudomonas putida mt2. While adhesion of negatively charged bacteria is impeded in media of low ionic strength because of a thick negatively charged diffuse layer, adhesion of S. maltophilia was particularly favored in dilute medium. The adhesion efficiencies of S. maltophilia at various ionic strengths could be explained in terms of calculated long-range interaction energies between S. maltophilia and glass or Teflon.

Targeting large area and low cost processing of highly efficient thin film solar modules an advanced stacked elemental layer process for Cu(InGa)Se2 (CIGS) thin films is presented. Key process steps are i) barrier coating of the soda lime glass substrate combined with the addition of a sodium compound to the elemental Cu/In/Ga/Se-precursor stack and ii) rapid thermal processing (RTP) to form the CIGS compound.By this strategy exact impurity control is achieved and the advantageous influence of sodium on device performance and on CIGS film formation is demonstrated unambiguously by means of electrical characterisation, XRD, SEM, TEM and SIMS. Sodium enriched and sodium free precursor stacks were heated to intermediate states (300°C–500°C) of the RTPreaction process. The experiment clearly reveals that on the reaction pathway to the chalcopyrite semiconductor increased amounts of copper-selenide are formed, if sodium is added to the precursor films. TEM-electron diffraction unambiguously identifies the CuSe-phase which is localised at the surface of the forming CIGS-film. These experimental findings propose a sodium assisted quasi liquid growth model for the CIS formation taking into account that sodium promotes the existence of CuSe at higher temperatures and its effect as a flux agent. The model contributes to a better understanding of the observed superior crystal qualitiy for sodium enriched in contrast to sodium free CIGS films.Application of these experimental findings in the technique of the optimized and controlled sodium incorporation significantly improves process reproducibility, CIGS film homogenity over larger substrate areas and shifts the average efficiency of cells and modules to a significantly higher level. This is demonstrated by a 12-cell integrated series connected minimodule with an aperture area of 51 cm2 and a confirmed efficiency of 11.75 %.

The metabolism of 11 substituted dibenzofurans by the dibenzofuran-degrading Sphingomonas sp. strain HH69 was investigated. Strain HH69 utilizes 2-, 3-, and 4-acetoxydibenzofuran as well as 2-, 3-, and 4-hydroxydibenzofuran as sole sources of carbon and energy. The degradation of acetoxydibenzofurans is initiated by hydrolysis of the ester bonds, yielding the corresponding hydroxydibenzofurans and acetate. Strain HH69 grew on 2-methoxydibenzofuran only after it was adapted to the utilization of 5-methoxysalicylic acid, whereas 3- and 4-methoxydibenzofuran as well as 2- and 3-nitrodibenzofuran were only cooxidized. During the breakdown of all eight hydroxy-, methoxy-, and nitrodibenzofurans studied here, the corresponding substituted salicylic acids accumulated in the culture broth. In the cases of 2- and 3-hydroxydibenzofuran as well as 2- and 3-nitrodibenzofuran, salicylic acid was also formed. Those four dibenzofurans which did not serve as carbon sources for strain HH69 were converted to a nonutilizable salicylic acid derivative. From turnover experiments with the mutant HH69/II, which is deficient in meta-cleavage, 2,2(prm1),3,4(prm1)-tetrahydroxybiphenyl, 2,2(prm1),3-trihydroxy-5(prm1)-methoxybiphenyl, 2,2(prm1),3-trihydroxy-5(prm1)-nitrobiphenyl, and 2,2(prm1),3-trihydroxy-4(prm1)-nitrobiphenyl were isolated as the main products formed from 3-hydroxydibenzofuran, 2-methoxydibenzofuran, and 2- and 3-nitrodibenzofuran, respectively. These results indicate significant regioselectivity for the dioxygenolytic cleavage of the ether bond of these monosubstituted dibenzofurans, with a preference for the nonsubstituted aromatic nucleus. Substituted trihydroxybiphenyls are converted further by meta-cleavage followed by the removal of the side chain of the resulting product. A stepwise degradation of this side chain was found to be involved in the metabolism of 2-hydroxydibenzofuran.

One of the main factors impeding the bioremediation of polluted soils, sediments, and aquifers is the low bioavailability of chemicals which are sorbed by organic matter. To obtain more insight into the factors that control the degradation of sorbed compounds, we used a defined model system in which 3-chlorodibenzofuran (3CDF) was the organic contaminant, porous Teflon granules were the sorbent, and Sphingomonas sp. strain HH19k was the test organism. The sorption of 3CDF to Teflon reached equilibrium within 150 min. The curved shape of the sorption isotherm, the extent of sorption, and the desorption kinetics suggested that there was a surface interaction (adsorption) between 3CDF and Teflon which took place mainly inside the pores of the granules. The kinetics of desorption could be ascribed to sorption-retarded radial diffusion inside the granules since the desorption rate not only was correlated with the sorbed-phase concentration, but also depended on the equilibration status of sorption, since (i) the high initial desorption rate sharply declined because of the depletion of 3CDF in the outermost parts of the granules, but high rates were observed again after the system had been given time to reequilibrate, and (ii) the initial desorption rate was higher when the preceding contact time between sorbate and sorbent was shorter (i.e., most 3CDF was still located in the exterior parts of the granules). These characteristics were observed irrespective of whether the desorption was driven by percolating water through the sorbent or by attaching active bacteria to the sorbent. 3CDF consumption by attached cells drove 3CDF desorption to a considerable extent. The attached cells were thus efficiently supplied with desorbing 3CDF. On the basis of our results, we propose that the rate at which a sorbed substrate becomes available for organisms is influenced by (i) the specific affinity of the degrading organisms (i.e., their ability to reduce the aqueous substrate concentration) and (ii) the tendency of the organisms to adhere to the sorbent.

Background Stable isotope probing (SIP) technique was developed to link function, structure and activity of microbial cultures metabolizing carbon and nitrogen containing substrates to synthesize their biomass. Currently, available methods are restricted solely to the estimation of fully saturated heavy stable isotope incorporation and convenient methods with sufficient accuracy are still missing. However in order to track carbon fluxes in microbial communities new methods are required that allow the calculation of partial incorporation into biomolecules. Results In this study, we use the characteristics of the so-called 'half decimal place rule' (HDPR) in order to accurately calculate the partial13C incorporation in peptides from enzymatic digested proteins. Due to the clade-crossing universality of proteins within bacteria, any available high-resolution mass spectrometry generated dataset consisting of tryptically-digested peptides can be used as reference. We used a freely available peptide mass dataset from Mycobacterium tuberculosis consisting of 315,579 entries. From this the error of estimated versus known heavy stable isotope incorporation from an increasing number of randomly drawn peptide sub-samples (100 times each; no repetition) was calculated. To acquire an estimated incorporation error of less than 5 atom %, about 100 peptide masses were needed. Finally, for testing the general applicability of our method, peptide masses of tryptically digested proteins from Pseudomonas putida ML2 grown on labeled substrate of various known concentrations were used and13C isotopic incorporation was successfully predicted. An easy-to-use script 1 was further developed to guide users through the calculation procedure for their own data series. Conclusion Our method is valuable for estimating13C incorporation into peptides/proteins accurately and with high sensitivity. Generally, our method holds promise for wider applications in qualitative and especially quantitative proteomics.

Dibenzo- p -dioxin was oxidatively cleaved by the dibenzofuran-degrading bacterium Pseudomonas sp. strain HH69 to produce minor amounts of 1-hydroxydibenzo- p -dioxin and catechol, while a 2-phenoxy derivative of muconic acid was formed as the major product. Upon acidic methylation, the latter yielded the dimethylester of cis, trans -2-(2-hydroxyphenoxy)-muconic acid.

A Pseudomonas sp. strain, HH69, and a mixed culture, designated HH27, were isolated by selective enrichment from soil samples. The pure strain and the mixed culture grew aerobically on dibenzofuran as the sole source of carbon and energy. Degradation proceeded via salicylic acid which was branched into the gentisic acid and the catechol pathway. Both salicylic acid and gentisic acid accumulated in the culture medium of strain HH69. The acids were slowly metabolized after growth ceased. The enzymes responsible for their metabolism showed relatively low activities. Besides the above-mentioned acids, 2-hydroxyacetophenone, benzopyran-4-one (chromone), several 2-substituted chroman-4-ones, and traces of the four isomeric monohydroxydiben-zofurans were identified in the culture medium. 2,2′,3-Trihydroxybiphenyl was isolated from the medium of a dibenzofuran-converting mutant derived from parent strain HH69, which can no longer grow on dibenzofuran. This gives evidence for a novel type of dioxygenases responsible for the attack on the biarylether structure of the dibenzofuran molecule. A meta -fission mechanism for cleavage of the dihydroxylated aromatic nucleus of 2,2′,3-trihydroxybiphenyl is suggested as the next enzymatic step in the degradative pathway.

Der Abbau von Dibenzofuran (DBF) durch den Bakterienstamm Pseudomonas sp. HH 69 bzw. durch ein Konsortium aus dem gleichfalls abbauaktiven Stamm Pseudomonas sp. NRM und dem begleitenden, Nocardia-ahnlichen Stamm NRH wurde in Flussigkulturen sowie in Mustern unterschiedlicher Boden zeitlich verfolgt und bilanziert.

The degradation of dibenzofurane (DBF), by the bacterial strain Pseudomonas sp. HH 69 and a consortium consisting of the DBF-degrading Pseudomonas strain NRM and an accompanying Nocardia — like strain NRH, was monitored both in liquid batch cultures and in samples of different types of soils. These were monitored as a function of time and a balance calculated.

Testing for arsenic pollution is commonly performed with chemical test kits of unsatisfying accuracy. Bacterial biosensors are an interesting alternative as they are easily produced, simple, and highly accurate devices. Here, we describe the development of a set of bacterial biosensors based on a nonpathogenic laboratory strain of Escherichia coli, the natural resistance mechanism of E. coli against arsenite and arsenate, and three reporter proteins: bacterial luciferase, beta-galactosidase and Green Fluorescent Protein (GFP). The biosensors were genetically optimized to reduce background expression in the absence of arsenic. In calibration experiments with the biosensors and arsenite-amended potable water, arsenite concentrations at 4 microg of As/L (0.05 microM) were routinely and accurately measured. The currently most quantitative system expressed the bacterial luciferase as reporter protein, responding proportional with a concentration range between 8 and 80 microg of As/L. Sensor cells could be stored as frozen batches, resuspended in plain media, and exposed to the aqueous test sample, and light emission was measured after 30-min incubation. Field testing for arsenite was achieved with a system that contained beta-galactosidase, producing a visible blue color at arsenite concentrations above 8 microg/L. For this sensor, a protocol was developed in which the sensor cells were dried on a paper strip and placed in the aqueous test solution for 30 min after which time color development was allowed to take place. The GFP sensor showed good potential for continuous rather than end point measurements. In all cases, growth of the biosensors and production of the strip test was achieved by very simple means with common growth media, and quality control of the sensors was performed by isolating the respective plasmids with the genetic constructs according to simple standard genetic technologies. Therefore, the biosensor cells and protocols may offer a realistic alternative for measuring arsenic contamination in potable water.

This work critically evaluates current practices in modeling the release of hydrophobic organic contaminants (HOCs) from complex matrices. Using well-constrained model polymer release systems (MPRS), we evaluate several empirical kinetic release models and one class of semi-empirical diffusion model; generally these models either do not describe release well, and are thus not useful, or they describe release well but are overparameterized, thus decreasing confidence in the fitting parameters. Results indicate that the n-phasic release often attributed to soil and sediment matrices is a non-mechanistic operational definition, arising from bias in the choice of empirical fitting expression. Further analysis illustrates pitfalls in common approaches to characterizing desorption from complex environmental matrices with respect to parameter interpretation, particularly effective diffusion coefficients. We also consider MPRS release in the context of other models and find that, though release occurs from these materials via a mechanism of anomalous (non-Fickian) diffusion, Fickian diffusion models nonetheless describe release well. This finding reconciles previous reports about anomalous release from environmental matrices with the hitherto success of Fickian diffusion models of desorption.

a-Si:H TFTs with SiNx as dielectric were fabricated for application as readout switches in a-Si:H linear image sensors. μFE=0.4....0.5cm2/Vs and Ron = 2..l.5Mω were achieved. The transfer of the signal from a photodiode through a TFT to a readout circuit was investigated and computer calculations for the transfer were made in order to analyze signal, timing, and switching noise.

Etude de la degradation du dibenzofurane, et du clivage de 2 des 3 cycles de la di-benzo-p-dioxine par une souche de Pseudomonas. Les produits obtenus sont purifies par chromatographie HPLC et identifies par spectroscopie RMN et spectrometrie de masse. L'elucidation des etapes metaboliques impliquees dans ce mecanisme permettront la construction de bacteries capables de degrader des composes toxiques

In this paper we report on the use of low-loss fused-silica-plastic optical fibers as magneto-optic current-measuring devices. The fiber is wound around a conductor, and linearly polarized laser light is launched into the fiber core. A current flowing through the conductor will generate a longitudinal magnetic field within the fiber, which in turn will rotate the direction of polarization of the guided light. This so- called Faraday rotation is measured opto- electronically at the fiber end and serves as a measure for the amount of current flow. A precondition for accurate current measurements is that the degree of polarization of the guided light be maintained over the entire fiber length.

The performance of a thin-film transistor (TFT) driven linear image sensor is analyzed. By experiment and computer simulation the charge trans-fer is investigated and the results are applied to interprete the performance of the conventional readout circuit. Its main disadvantage are the large number of crossovers between signal lines. Therefore, an alternative readout circuit with reduced number of crossovers is proposed.

Clay minerals, charcoal and metal oxides are essential parts of the soil matrix and strongly influence the formation of biogeochemical interfaces in soil. We investigated the role of these parental materials for the development of functional microbial guilds using the example of alkane-degrading bacteria harbouring the alkane monooxygenase gene (alkB) in artificial mixtures composed of different minerals and charcoal, sterile manure and a microbial inoculum extracted from an agricultural soil. We followed changes in abundance and community structure of alkane-degrading microbial communities after 3 and 12 months of soil maturation and in response to a subsequent 2-week plant litter addition. During maturation we observed an overall increasing divergence in community composition. The impact of metal oxides on alkane-degrading community structure increased during soil maturation, whereas the charcoal impact decreased from 3 to 12 months. Among the clay minerals illite influenced the community structure of alkB-harbouring bacteria significantly, but not montmorillonite. The litter application induced strong community shifts in soils, maturated for 12 months, towards functional guilds typical for younger maturation stages pointing to a resilience of the alkane-degradation function potentially fostered by an extant 'seed bank'.

FEMS Microbiology Ecology, 48 (2), ISSN:0168-6496, ISSN:1574-6941

Pseudomonas aeruginosa pneumonia is a life threatening complication in mechanically ventilated patients that requires the ability of the bacteria to adhere to, and colonize the endotracheal intubation device. New strategies to prevent or reduce these nosocomial infections are greatly needed. We report here the study of a set of P. aeruginosa clinical isolates, together with specific mutants, regarding their adhesion on native and chemically modified poly(vinyl chloride) (PVC) surfaces from endotracheal intubation devices. The adhesion of the different strains to untreated PVC varied widely, correlating with several physico-chemical characteristics known to influence the attachment of bacteria to inert surfaces. The adhesion patterns were compared to the calculations obtained with the DLVO theory of colloidal stability. These results illustrate the importance of testing different clinical isolates when investigating bacterial adhesion. Oxygen plasma treatment of the PVC pieces yielded a hydrophilic surface and reduced the number of adhering bacteria by as much as 70%. This reduction is however unlikely to be sufficient to prevent P. aeruginosa colonization of endotracheal intubation devices. (C) 2002 Elsevier Science Ltd. All rights reserved.

Peatlands are ecosystems of exceptional conservation value because of their beauty, biodiversity, importance in global geochemical cycles, and the paleoenvironmental records they preserve. Commercial extraction and drainage for forestry or agriculture have caused the destruction of many peatlands, especially in or close to urban areas of the northern temperate zone. Are these commercial and environmental interests irreconcilable? A close analysis suggests that limited peat extraction may actually increase biodiversity in some cases, and may be sustainable over the long term. As we learn more about how peatlands spontaneously regenerate following disturbance, and what conditions govern the re-establishment of a diverse community and the ability to sequester carbon, we increase our chances of being able to restore damaged peatlands. Preserving the chronological records hidden in the peat profile, the natural heritage value of peatlands, and the bulk of sequestered carbon, however, will remain incompatible with any form of exploitation.

A luminescent bacterial biosensor was used to quantify bioavailable arsenic in artificial groundwater. Its light production above the background emission was proportional to the arsenite concentration in the toxicologically relevant range of 0 to 0.5 mu M. Effects of the inorganic solutes phosphate, Fe(II) and silicate on the biosensor signal were studied. Phosphate at a concentration of 0.25 g L-1 phosphate slightly stimulated the light emission, but much less than toxicologically relevant concentrations of the much stronger inducer arsenite. No effect of phosphate was oberved in the presence of arsenite. Freshly prepared sodium silicate solution at a concentration of 10 g L-1 Si reduced the arsenite-induced light production by roughly 37%, which can be explained by transient polymerization leading to sequestration of some arsenic. After three days of incubation, silicate did not have this effect anymore, probably because depolymerization occurred. In the presence of 0.4 g L-1 Fe(II), the arsenite-induced light emission was reduced by up to 90%, probably due to iron oxidation followed by arsenite adsorption on the less soluble Fe(III) possibly along with some oxidation to the stronger adsorbing As(V). Addition of 100 mu M EDTA was capable of releasing all arsenic from the precipitate and to transform it into the biologically measurable, dissolved state. The biosensor also proved valuable for monitoring the effectiveness of an arsenic removal procedure based on water filtration through a mixture of sand and iron granules.

This paper describes the development of an analytical technique for arsenic analyses that is based on genetically-modified bioreporter bacteria bearing a gene encoding for the production of a green fluorescent protein (gfp). Upon exposure to arsenic (in the aqueous form of arsenite), the bioreporter production of the fluorescent reporter molecule is monitored spectroscopically. We compared the response measured as a function of time and concentration by steady-state fluorimetry (SSF) to that measured by epi-fluorescent microscopy (EFM). SSF is a bulk technique; as such it inherently yields less information, whereas EFM monitors the response of many individual cells simultaneously and data can be processed in terms of population averages or subpopulations. For the bioreporter strain used here, as well as for the literature we cite, the two techniques exhibit similar performance characteristics. The results presented here show that the EFM technique can compete with SSF and shows substantially more promise for future improvement; it is a matter of research interest to develop optimized methods of EFM image analysis and statistical data treatment. EFM is a conduit for understanding the dynamics of individual cell response vs. population response, which is not only a matter of research interest, but is also promising in the practical terms of developing micro-scale analysis.

We report here the oxygenolytic cleavage of the ether bond occurring as the initial enzymatic step of high regioselectivity in the course of the bacterial attack on such aromatic compounds. Their complete catabolism is achieved by subsequent cleavage of the aromatic rings and further known reactions

Whereas straight liquid-core optical fibers have the capability of transporting linearly polarized light with any incident polarization angle,bent fibers exhibit form birefringence with the principal axes fixed to the plane of curvature. The effect of this curvature-dependent birefringence can be compensated by either periodically altering the plane of curvature by 90 degrees or winding the fiber into a helix.

A laboratory setup of a magnetooptical current transformer was established. A ingle-mode fiber acts as both a measuring sensor and a transmission line. The overall measurement accuracy at room temperature within a primary current range 50-1200 A is better than 0.24%, the SNR at 1000 A is 85 dB. Current measurements of high accuracy were also performed in the -20-+ 45 degrees C temperature range.