Biomedical subjects

Willy Verstraete

Publications and source records attributed to Willy Verstraete.

At least 19 recordsLinked to original sources

PubMed2007

Reactivation of aerobic and anaerobic ammonium oxidizers in OLAND biomass after long-term storage.

The biomass of an oxygen-limited autotrophic nitrification/denitrification (OLAND) biofilm reactor was preserved in various ways to find a storage method for both aerobic and anaerobic ammonium-oxidizing bacteria (AerAOB and AnAOB). Storage occurred at -20 degrees C with and without glycerol as cryoprotectant and at 4 and 20 degrees C with and without nitrate as redox buffer. After 2 and 5 months, reactivation of AerAOB and AnAOB was achieved with the biomass stored at 4 degrees C with and without nitrate and at 20 degrees C with nitrate. Moreover, the presence of the AerAOB and AnAOB was confirmed with fluorescent in situ hybridization (FISH). Preservation in a nitrate environment resulted in a lag phase for the AnAOB reactivation. The supplied nitrate was denitrified during storage, and a real-time polymerase chain reaction with nitrifying and denitrifying genes allowed to estimate that at least 1.0 to 6.0% of the OLAND biofilm consisted of denitrifiers. It was concluded that reactivation after long-term storage is possible and that preservation at 4 degrees C without nitrate addition is the recommended storage technique. The possibility to store OLAND biomass will facilitate research on AnAOB and can overcome larger-scale start-up and inhibition problems of novel nitrogen processes involving AnAOB.

Bacteria, Aerobic↗

PubMed2007

The bacterial storage compound poly-beta-hydroxybutyrate protects Artemia franciscana from pathogenic Vibrio campbellii.

Infections caused by antibiotic-resistant luminescent Vibrios can cause dramatic losses in aquaculture. In this study, the short-chain fatty acid beta-hydroxybutyrate and its polymer poly-beta-hydroxybutyrate were investigated as possible new biocontrol agents. beta-Hydroxybutyrate was shown to completely inhibit the growth of pathogenic Vibrio campbelli at 100 mM. Moreover, the addition of 100 mM of this fatty acid to the culture water of Artemia nauplii infected with the V. campbelli strain significantly increased the survival of the nauplii. As Artemia is a non-selective and particle filter feeder, we also investigated whether poly-beta-hydroxybutyrate particles could be used to protect Artemia from the pathogenic V. campbellii. The addition of 100 mg l(-1) poly-beta-hydroxybutyrate or more to the Artemia culture water offered a preventive and curative protection from the pathogen as a significantly enhanced survival was noticed. If added as a preventive treatment, a complete protection of infected nauplii (no significant mortality compared with uninfected nauplii) was observed at 1000 mg l(-1) poly-beta-hydroxybutyrate. Our data indicate that the use of poly-beta-hydroxybutyrate might constitute an ecologically and economically sustainable alternative strategy to fight infections in aquaculture.

3-Hydroxybutyric Acid↗

PubMed2006

Biological control of the size and reactivity of catalytic Pd(0) produced by Shewanella oneidensis.

The interaction between Shewanella oneidensis MR-1 and the soluble metal Pd(II) during the reductive precipitation of Pd(0) determined the size and properties of the precipitated Pd(0) nanoparticles. Assessment of cell viability indicated that the bioreduction of Pd(II) was a detoxification mechanism depending on the Pd(II) concentration and on the presence and properties of the electron donor. The addition of H(2) in the headspace allowed S. oneidensis to resist the toxic effects of Pd(II). Interestingly, 25 mM formate was a less effective electron donor for bioreductive detoxification of Pd(II), since there was a 2 log reduction of culturable cells and a 20% decrease of viable cells within 60 min, followed by a slow recovery. When the ratio of Pd:cell dry weight (CDW) was below 5:2 at a concentration of 50 mg l(-1) Pd(II), most of the cells remained viable. These viable cells precipitated Pd(0) crystals over a relatively larger bacterial surface area and had a particle area that was up to 100 times smaller when compared to Pd(0) crystals formed on non-viable biomass (Pd:CDW ratio of 5:2). The relatively large and densely covering Pd(0) crystals on non-viable biomass exhibited high catalytic reactivity towards hydrophobic molecules such as polychlorinated biphenyls, while the smaller and more dispersed nanocrystals on a viable bacterial carrier exhibited high catalytic reactivity towards the reductive degradation of the anionic pollutant perchlorate.

Biodegradation, Environmental↗

PubMed2006

Microbial fuel cells for sulfide removal.

Thus far, microbial fuel cells (MFCs) have been used to convert carbon-based substrates to electricity. However, sulfur compounds are ubiquitously present in organic waste and wastewater. In this study, a MFC with a hexacyanoferrate cathodic electrolyte was used to convert dissolved sulfide to elemental sulfur. Two types of MFCs were used, a square type closed to the air and a tubular type in which the cathode compartment was open to the air. The square-type MFCs demonstrated a potential-dependent conversion of sulfide to sulfur. In the tubular system, up to 514 mg sulfide L(-1) net anodic compartment (NAC) day(-1) (241 mg L(-1) day(-1) total anodic compartment, TAC) was removed. The sulfide oxidation in the anodic compartment resulted in electricity generation with power outputs up to 101 mW L(-1) NAC (47 W m(-3) TAC). Microbial fuel cells were coupled to an anaerobic upflow anaerobic sludge blanket reactor, providing total removals of up to 98% and 46% of the sulfide and acetate, respectively. The MFCs were capable of simultaneously removing sulfate via sulfide. This demonstrates that digester effluents can be polished by a MFC for both residual carbon and sulfur compounds. The recovery of electrons from sulfides implies a recovery of energy otherwise lost in the methane digester.

Anaerobiosis↗

PubMed2006

Microbial fuel cells: methodology and technology.

Microbial fuel cell (MFC) research is a rapidly evolving field that lacks established terminology and methods for the analysis of system performance. This makes it difficult for researchers to compare devices on an equivalent basis. The construction and analysis of MFCs requires knowledge of different scientific and engineering fields, ranging from microbiology and electrochemistry to materials and environmental engineering. Describing MFC systems therefore involves an understanding of these different scientific and engineering principles. In this paper, we provide a review of the different materials and methods used to construct MFCs, techniques used to analyze system performance, and recommendations on what information to include in MFC studies and the most useful ways to present results.

Bacteria↗

PubMed2006

Transport and activity of Desulfitobacterium dichloroeliminans strain DCA1 during bioaugmentation of 1,2-DCA-contaminated groundwater.

The transport and activity of Desulfitobacterium dichloroeliminans strain DCA1 in 1,2-dichloroethane (1,2-DCA)-contaminated groundwater have been evaluated through an in situ bioaugmentation test at an industrial site (Belgium). The migration of strain DCA1 was monitored from an injection well toward a monitoring well, and the effect of the imposed groundwater flow on its distribution was assessed by means of transport model MOCDENS3D. The results of the real-time PCR (16S rRNA gene) quantification downstream from the injection point were used to evaluate the bacterial distribution pattern simulated by MOCDENS3D. In the injection well, the 1,2-DCA concentration in the groundwater decreased from 939.8 to 0.9 microM in a 35 day time interval and in the presence of a sodium lactate solution. Moreover, analyses from the monitoring well showed that the cells were still active after transport through the aquifer, although biodegradation occurred to a lesser extent. This study showed that strain DCA1 can be successfully applied for the removal of 1,2-DCA under field conditions and that its limited retardation offers perspectives for large-scale cleanup processes of industrial sites.

Chromatography, Gas↗

PubMed2006

Experimental parameters affecting sensitivity and specificity of a yeast assay for estrogenic compounds: results of an interlaboratory validation exercise.

In vitro assays are considered as the first step in a tiered approach to compound screening for hormonal activity. Although many new assays have been developed in recent years, little attention has been paid towards assay validation. Our objective was to identify critical experimental parameters in a yeast estrogen screen (YES) that affect its sensitivity and specificity. We investigated the role of incubation time, solvent type, yeast inoculum growth stage and concentration on the outcome of the YES. Compounds tested included new and established agonists, antagonists and negative controls, and results were evaluated according to prefixed statistical criteria. In addition, we assessed the assay's performance in a blind interlaboratory validation exercise (IVE). An incubation time of five days was necessary to positively identify the estrogenic properties of all agonists tested, when dissolved in DMSO. Longer incubation times were required when using an ethanol protocol. Similar estrogenic activity was reported for benzyl butyl phthalate, bisphenol-A, methoxychlor, permethrin and genistein in the IVE. One out of the three laboratories did not classify alpha,beta-endosulfan, dissolved in DMSO, as an estrogen. The same was true for 4,4'-DDE and lindane, dissolved in ethanol, a result that might be attributable to an inappropriate yeast start concentration and/or growth stage. These validation experiments show that under appropriate experimental conditions the YES yields sensitive, specific and reliable results. Therefore it fulfills the requirements as a first step screening assay to evaluate the capacity of chemicals to interact with the estrogen receptor.

Chemistry Techniques, Analytical↗

PubMed2006

Biocatalytic dechlorination of lindane by nano-scale particles of Pd(0) deposited on Shewanella oneidensis.

A new approach for the removal of the pesticide lindane (gamma-hexachlorocyclohexane or gamma-HCH) makes use of catalytic reduction of HCH to benzene over a metal catalyst, namely Pd(0). Since specific surface area plays an important role in reactivity of catalysts, this study investigated the use of bioPd(0), i.e. nano-scale Pd(0) particles precipitated on the biomass of Shewanella oneidensis, for the removal of lindane. It was demonstrated that bioPd(0) has catalytic activity towards dechlorination of gamma-HCH, with the addition of formate as electron donor, and that dechlorination with bioPd(0) was more efficient than with commercial powdered Pd(0). The biodegradable compound benzene was formed as reaction product and other HCH isomers could also be dechlorinated. Subsequently bioPd(0) was implemented in a membrane reactor technology for the treatment of gamma-HCH polluted water. In a fed-batch process configuration with formate as electron donor, a removal percentage of 98% of gamma-HCH saturated water (10 mg l(-1)) was achieved within 24h. The measured chloride mass balance approached the theoretical value. The results of this work showed that a complete, efficient and fast removal of lindane was achieved by biocatalysis with bioPd(0).

Biodegradation, Environmental↗

PubMed2006

Real time PCR quantification in groundwater of the dehalorespiring Desulfitobacterium dichloroeliminans strain DCA1.

Quantifying microorganisms responsible for bioremediation can provide insight in their behavior and can help to obtain a better understanding of the physicochemical parameters monitored during bioremediation. A real time PCR (RTm PCR) assay based on the detection with SYBR Green I was optimized in order to quantify the 1,2-dichloroethane dehalorespiring Desulfitobacterium dichloroeliminans strain DCA1. A primer pair targeting unique regions of the 16 S rRNA gene was designed and tested in silico for its specificity. Selectivity was furthermore evaluated and a Limit of Quantification of 1.5 x 10(4) cells/microL DNA extract was obtained for spiked groundwater. Real time measurements of groundwater samples retrieved from a bioaugmented monitoring well and which had an average concentration lying in the range of the Limit of Quantification were evaluated positively with regards to reproducibility. Validation of the RTm PCR assay on groundwater samples originating from different sites confirmed the specificity of the designed primer pair. This RTm PCR assay can be used to survey the abundance and kinetics of strain DCA1 in in situ bioaugmentation field studies.

Benzothiazoles↗

PubMed2006

Continuous electricity generation at high voltages and currents using stacked microbial fuel cells.

Connecting several microbial fuel cell (MFC) units in series or parallel can increase voltage and current; the effect on the microbial electricity generation was as yet unknown. Six individual continuous MFC units in a stacked configuration produced a maximum hourly averaged power output of 258 W m(-3) using a hexacyanoferrate cathode. The connection of the 6 MFC units in series and parallel enabled an increase of the voltages (2.02 V at 228 W m(-3)) and the currents (255 mA at 248 W m(-3)), while retaining high power outputs. During the connection in series, the individual MFC voltages diverged due to microbial limitations at increasing currents. With time, the initial microbial community decreased in diversity and Gram-positive species became dominant. The shift of the microbial community accompanied a tripling of the short time power output of the individual MFCs from 73 W m(-3) to 275 W m(-3), a decrease of the mass transfer limitations and a lowering of the MFC internal resistance from 6.5 +/- 1.0 to 3.9 +/- 0.5 omega. This study demonstrates a clear relation between the electrochemical performance and the microbial composition of MFCs and further substantiates the potential to generate useful energy by means of MFCs.

Bacteria↗

PubMed2006

Metabolism of the food-associated carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine by human intestinal microbiota.

2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine is a putative human carcinogenic heterocyclic aromatic amine formed from meat and fish during cooking. Although the formation of hazardous PhIP metabolites by mammalian enzymes is well-documented, nothing is known about the PhIP transformation potency of human intestinal bacteria. In this study, the in vitro metabolism of PhIP by human fecal samples was investigated. Following anaerobic incubation of PhIP with stools freshly collected from six healthy volunteers, we found that PhIP was extensively transformed by the human intestinal bacteria. HPLC analysis showed that the six human fecal microbiota transformed PhIP with efficiencies from 47 to 95% after 72 h incubation, resulting in one major derivative. ESI-MS/MS, HRMS, 1D (1H, 13C, DEPT) and 2D (gCOSY, gTOCSY, gHMBC, gHSQC) NMR, and IC analysis elucidated the complete chemical identity of the microbial PhIP metabolite as 7-hydroxy-5-methyl-3-phenyl-6,7,8,9-tetrahydropyrido[3',2':4,5]imidazo[1,2-a]pyrimidin-5-ium chloride. At present, no information is available about the biological activity of this newly discovered bacterial PhIP metabolite. Our findings however suggest that bacteria derived from the human intestine play a key role in the activation or detoxification of PhIP, a digestive fate ignored so far in risk assessments. Moreover, the variation in transformation efficiency between the human microbiota indicates interindividual differences in the ability to convert PhIP. This may predict individual susceptibility to carcinogenic risk from this suspected dietary carcinogen.

Adult↗

PubMed2006

H2S degradation is reflected by both the activity and composition of the microbial community in a compost biofilter.

In this study, 16S rRNA- and rDNA-based denaturing gradient gel electrophoresis (DGGE) were used to study the temporal and spatial evolution of the microbial communities in a compost biofilter removing H(2)S and in a control biofilter without H(2)S loading. During the first 81 days of the experiment, the H(2)S removal efficiencies always exceeded 93% at loading rates between 4.1 and 30 g m(-3) h(-1). Afterwards, the H(2)S removal efficiency decreased to values between 44 and 71%. RNA-based DGGE analysis showed that H(2)S loading to the biofilter increased the stability of the active microbial community but decreased the activity-based diversity and evenness. The most intense band in both the RNA- and DNA-based DGGE patterns of the H(2)S-degrading biofilter represented the sulfur oxidizing bacterium Thiobacillus thioparus. This suggested that T. thioparus constituted a major part of the bacterial community and was an important primary degrader in the H(2)S-degrading biofilter. The decreasing H(2)S removal efficiencies near the end of the experiment were not accompanied by a substantial change of the DGGE patterns. Therefore, the decreased H(2)S removal was probably not caused by a failing microbiology but rather by a decrease of the mass transfer of substrates after agglutination of the compost particles.

Bioreactors↗

PubMed2006

Characterization of Escherichia coli isolates from different fecal sources by means of classification tree analysis of fatty acid methyl ester (FAME) profiles.

Microbial source tracking (MST) methods need to be rapid, inexpensive and accurate. Unfortunately, many MST methods provide a wealth of information that is difficult to interpret by the regulators who use this information to make decisions. This paper describes the use of classification tree analysis to interpret the results of a MST method based on fatty acid methyl ester (FAME) profiles of Escherichia coli isolates, and to present results in a format readily interpretable by water quality managers. Raw sewage E. coli isolates and animal E. coli isolates from cow, dog, gull, and horse were isolated and their FAME profiles collected. Correct classification rates determined with leaveone-out cross-validation resulted in an overall low correct classification rate of 61%. A higher overall correct classification rate of 85% was obtained when the animal isolates were pooled together and compared to the raw sewage isolates. Bootstrap aggregation or adaptive resampling and combining of the FAME profile data increased correct classification rates substantially. Other MST methods may be better suited to differentiate between different fecal sources but classification tree analysis has enabled us to distinguish raw sewage from animal E. coli isolates, which previously had not been possible with other multivariate methods such as principal component analysis and cluster analysis.

Animals↗

PubMed2006

Use of flow cytometry for analysis of phage-mediated killing of Enterobacter aerogenes.

In this study, the use of flow cytometry to analyze phage-mediated killing of Enterobacter aerogenes under varying conditions of temperature and nutrient availability was assessed. Bacteriophage UZ1, specific for an E. aerogenes strain, was applied at a multiplicity of infection (MOI) of 1 and 1000 to a Teflon surface, artificially infected with its host at a level of 4.5 log cells. After incubation for 20 h, bacteriophages were quantified using the soft agar layer method. For the quantification of bacterial cells, plate counting and flow cytometric analysis of live/dead stained cells were performed in parallel. At an MOI of 1, phage treatment was successful only after incubation under nutrient-rich conditions at 37 degrees C: E. aerogenes cells were not detected and a tenfold increase in phage UZ1 was observed. At a MOI of 1000, no E. aerogenes cells could be cultured after incubation at 37 and 4 degrees C. However, flow cytometric analysis revealed that lysis did not occur at 4 degrees C but was achieved during subsequent plate culture. In conclusion, the use of flow cytometry enabled identification of culture-based bias during plate culture. The flow cytometric assay used in this study proved to be rapid, as this culture-independent method does not require lengthy incubation periods post-sampling. The bacteriophage-mediated killing of E. aerogenes cells on Teflon surfaces indicated that disinfection of E. aerogenes with bacteriophage UZ1 can be successful when high MOIs are achieved, while at low multiplicities of infection conditions favorable for phage replication are required.

Bacteriolysis↗

PubMed2006

Bio-deposition of a calcium carbonate layer on degraded limestone by Bacillus species.

To obtain a restoring and protective calcite layer on degraded limestone, five different strains of the Bacillus sphaericus group and one strain of Bacillus lentus were tested for their ureolytic driven calcium carbonate precipitation. Although all the Bacillus strains were capable of depositing calcium carbonate, differences occurred in the amount of precipitated calcium carbonate on agar plate colonies. Seven parameters involved in the process were examined: calcite deposition on limestone cubes, pH increase, urea degrading capacity, extracellular polymeric substances (EPS)-production, biofilm formation, zeta-potential and deposition of dense crystal layers. The strain selection for optimal deposition of a dense CaCO(3) layer on limestone, was based on decrease in water absorption rate by treated limestone. Not all of the bacterial strains were effective in the restoration of deteriorated Euville limestone. The best calcite precipitating strains were characterised by high ureolytic efficiency, homogeneous calcite deposition on limestone cubes and a very negative zeta-potential.

Absorption↗

PubMed2006

Administration of equol-producing bacteria alters the equol production status in the Simulator of the Gastrointestinal Microbial Ecosystem (SHIME).

The intestinal microbial transformation of daidzein, one of the principal isoflavones from soy, into the isoflavan equol is subjected to a high interindividual variability. The latter compound is considered to have a higher biological activity than its precursor; hence, there is interest in dietary applications that modulate this important biotransformation. In 2 separate experiments, we administered a mixed microbial culture (EPC4), which we had isolated previously and which efficiently transforms daidzein into equol, to the Simulator of the Human Intestinal Microbial Ecosystem (SHIME). The SHIME was fed soy germ powder and inoculated with fecal samples from two nonequol-producing individuals. Equol production was induced in the distal colon compartments in both experiments, 5-6 d after the start of the treatment; 2 wk after interrupting the addition of EPC4, equol was still produced in high amounts. There are large interregional differences in daidzein metabolism in the simulated colon. Furthermore, no major shifts in the composition and activity of the microbial communities were caused by the supplementation with the microbial consortium. Although further confirmation in in vivo studies is required, these results validate the concept that administering EPC4 could constitute a novel means for converting a nonequol-producer into a producer.

Bacteria↗

PubMed2006

The prenylflavonoid isoxanthohumol from hops (Humulus lupulus L.) is activated into the potent phytoestrogen 8-prenylnaringenin in vitro and in the human intestine.

Hops, an essential beer ingredient, are a source of prenylflavonoids, including 8-prenylnaringenin (8-PN), one of the most potent phytoestrogens. Because 8-PN concentrations in beers are generally low, its health effects after moderate beer consumption were considered negligible. However, human intestinal microbiota may activate up to 4 mg/L isoxanthohumol (IX) in beer into 8-PN. Depending on interindividual differences in the intestinal transformation potential, this conversion could easily increase the 8-PN exposure 10-fold upon beer consumption. Here, we present a further investigation of the process both in vitro and in vivo. In vitro experiments with the dynamic SHIME model showed that hop prenylflavonoids pass unaltered through the stomach and small intestine and that activation of IX into 8-PN (up to 80% conversion) occurs only in the distal colon. In vitro incubations of 51 fecal samples from female volunteers with IX enabled us to separate the fecal microbiota into high (8 of 51), moderate (11 of 51) and slow (32 of 51) 8-PN producers, clearly illustrating an interindividual variability. Three women, selected from the respective groups, received a daily dose of 5.59 mg IX for 4 d. Intestinal IX activation and urinary 8-PN excretion were correlated (R(2) = 0.6417, P < 0.01). These data show that intestinal conversion of IX upon moderate beer consumption can lead to 8-PN exposure values that might fall within the range of human biological activity.

Adult↗

PubMed2006

AggA is required for aggregation and increased biofilm formation of a hyper-aggregating mutant of Shewanella oneidensis MR-1.

Shewanella oneidensis COAG, a hyper-aggregating mutant of MR-1, was isolated from a rifampicin-challenged culture. Compared to the wild-type, COAG exhibited increased biofilm formation on glass carrier material. The role of surface-located proteins in the process of COAG auto-aggregation was confirmed by different proteolytic treatments of the aggregates. All of the tested proteolytic enzymes resulted in deflocculation within 3 h of incubation. In order to examine the altered expression of outer-membrane proteins in COAG, membrane-enriched cell preparations were analysed by proteomics and the protein pattern was compared to that of MR-1. From the proteomics results, it was hypothesized that the agglutination protein AggA, associated with the secretion of a putative RTX protein, was involved in the hyper-aggregating phenotype. These results were confirmed with a DNA microarray study of COAG versus MR-1. An insertional mutation in the S. oneidensis COAG aggA locus resulted in loss of the hyper-aggregating properties and the increased biofilm-forming capability. The insertional mutation resulted in strongly decreased attachment during the initial stage of biofilm formation. By complementing this mutation with the vector pCM62, expressing the aggA gene, this effect could be nullified and biofilm formation was restored to at least the level of the MR-1 wild-type.

Bacterial Adhesion↗