Biomedical subjects

Willy Verstraete

Publications and source records attributed to Willy Verstraete.

At least 73 records · Page 4Linked to original sources

PubMed2004

Prebiotic effects of chicory inulin in the simulator of the human intestinal microbial ecosystem.

The prebiotic potential of native chicory inulin was assessed in the Simulator of the Human Intestinal Microbial Ecosystem (SHIME) by monitoring microbial community from the colon compartments, its metabolic activity and community structure. Inulin addition selected for a higher short chain fatty acid production with shifts towards propionic and butyric acid. Conventional culture-based techniques and PCR-denaturing gradient gel electrophoresis analysis showed no remarkable changes in the overall microbial community from the colon compartments of the SHIME, whereas selective effects were seen for lactic acid bacteria. Quantitative PCR with bifidobacteria-specific primers revealed a significant increase with more than 1 log CFU ml(-1) from the proximal to distal colon, in contrast to culture-based techniques, which only showed a minor bifidogenic effect in the ascending colon. Our results indicate that inulin purports prebiotic effects from the proximal to distal colon and that real-time PCR is a more precise technique to detect differences in bifidobacterial populations whereas conventional culturing techniques are much more variable.

Bifidobacterium↗

PubMed2004

Isolation and characterisation of an equol-producing mixed microbial culture from a human faecal sample and its activity under gastrointestinal conditions.

Only about one third of humans possess a microbiota capable of transforming the dietary isoflavone daidzein into equol. Little is known about the dietary and physiological factors determining this ecological feature. In this study, the in vitro metabolism of daidzein by faecal samples from four human individuals was investigated. One culture produced the metabolites dihydrodaidzein and O-desmethylangolensin, another produced dihydrodaidzein and equol. From the latter, a stable and transferable mixed culture transforming daidzein into equol was obtained. Molecular fingerprinting analysis (denaturing gradient gel electrophoresis) showed the presence of four bacterial species of which only the first three strains could be brought into pure culture. These strains were identified as Lactobacillus mucosae EPI2, Enterococcus faecium EPI1 and Finegoldia magna EPI3, and did not produce equol in pure culture. The fourth species was tentatively identified as Veillonella sp strain EP. It was found that hydrogen gas in particular, but also butyrate and propionate, which are all colonic fermentation products from poorly digestible carbohydrates, stimulated equol production by the mixed culture. However, when fructo-oligosaccharides were added, equol production was inhibited. Furthermore, the equol-producing capacity of the isolated culture was maintained upon its addition to a faecal culture originating from a non-equol-producing individual.

Bacteria↗

PubMed2004

Influence of the carbon/nitrogen/phosphorus ratio on polycyclic aromatic hydrocarbon degradation by Mycobacterium and Sphingomonas in soil.

Biodegradation of polycyclic aromatic hydrocarbons (PAHs) in the environment is often limited due to unfavorable nutrient conditions for the bacteria that use these PAHs as sole source of carbon and energy. Mycobacterium and Sphingomonas are 2 PAH-degrading specialists commonly present in PAH-polluted soil, but not much is known about their specific nutrient requirements. By adding different inorganic supplements of nitrogen (N) and phosphorus (P), affecting the overall carbon/nitrogen/phosphorus ratio of soil in soil slurry degradation tests, we investigated the impact of soil inorganic N and P nutrient conditions on PAH degradation by PAH-degrading Sphingomonas and Mycobacterium strains. The general theoretically calculated C/N/P ratio of 100/10/1 (expressed in moles) allowed rapid PAH metabolization by Sphingomonas and Mycobacterium strains without limitation. In addition, PAH-degradation rate and extent was not affected when ca. ten times lower concentrations of N and P were provided, indicating that Sphingomonas and Mycobacterium strains are capable of metabolizing PAHs under low nutrient conditions. Nor does PAH-degradation seem to be affected by excesses of N and P creating an imbalanced C/N/P ratio. However, supplements of N and P salts increased the salinity of soil slurry solutions and seriously limited or even completely blocked biodegradation.

Biodegradation, Environmental↗

PubMed2004

Elevated salinity selects for a less diverse ammonia-oxidizing population in aquarium biofilters.

The activity and changes in the structure of the community of the ammonia-oxidizing bacteria belonging to the Betaproteobacteria were monitored in freshwater and artificial seawater biofilters for two months after inoculation with a commercial nitrifying consortium. Both in freshwater and artificial seawater, ammonium oxidation proceeded immediately after addition of the inoculum, although initial activity in artificial seawater was lower than in freshwater. Denaturing gradient gel electrophoresis of the ammonia-oxidizing bacterial community of the inoculum and the freshwater and the artificial seawater aquaria as a function of time showed that initially only one dominant ammonia-oxidizer, closely related to Nitrosomonas marina, was detectable in all the systems. The fingerprint of the ammonia-oxidizing bacterial community in the artificial seawater biofilters continued to be dominated by this single band. In the freshwater aquaria, in contrast, the composition of the ammonia-oxidizer community became more diverse after one month, with 4-7 new bands appearing in the denaturing gradient gel fingerprint. Since the inoculum is cultivated at an average salinity of 11 gl(-1), it is argued that the elevated salinity selects for a less diverse ammonia-oxidizer community in the inoculum and the artificial seawater aquaria.

Ammonia↗

PubMed2004

Occurrence and origin of phosphine in landfill gas.

A landfill (Hooge Maey, Flanders, Belgium) was subjected to an in-depth study in order to explain the origin of phosphine detected in high amounts in landfill gas, in comparison with biogas from other sources, during a previous study. The spatial and temporal variability of the phosphine concentration in landfill gas was assessed. Twenty-four wells were monitored and differences in phosphine concentration up to one log unit were observed (3.2-32.4 microg/m(3)). The phosphine concentration in each well was constant in time over a period of 4 months. No correlation was found between the phosphine concentration and methane, carbon dioxide, hydrogen sulfide, ethene or ethane concentration. In a series of laboratory tests, it was shown that phosphine was emitted during batch fermentation tests inoculated with landfill leachate when Fe(0) or Al(0) specimens were added. Conditions favouring corrosion of iron gave rise to higher emissions of phosphine. The phosphine concentration in the headspace of a batch test rose to 1.43 mg/m(3) after 27 days of incubation. Weight loss of corroding steel coupons correlated with phosphine emission. Calculations showed that all phosphine emitted from the 0.005 km(3) landfill (160 g/year) could be attributed to corrosion of metals. No evidence of de novo synthesis could be established.

Aluminum↗

PubMed2004

Thermal wet oxidation improves anaerobic biodegradability of raw and digested biowaste.

Anaerobic digestion of solid biowaste generally results in relatively low methane yields of 50-60% of the theoretical maximum. Increased methane recovery from organic waste would lead to reduced handling of digested solids, lower methane emissions to the environment, and higher green energy profits. The objective of this research was to enhance the anaerobic biodegradability and methane yields from different biowastes (food waste, yard waste, and digested biowaste already treated in a full-scale biogas plant (DRANCO, Belgium)) by assessing thermal wet oxidation. The biodegradability of the waste was evaluated by using biochemical methane potential assays and continuous 3-L methane reactors. Wet oxidation temperature and oxygen pressure (T, 185-220 degrees C; O2 pressure, 0-12 bar; t, 15 min) were varied for their effect on total methane yield and digestion kinetics of digested biowaste. Measured methane yields for raw yard waste, wet oxidized yard waste, raw food waste, and wet oxidized food waste were 345, 685, 536, and 571 mL of CH/g of volatile suspended solids, respectively. Higher oxygen pressure during wet oxidation of digested biowaste considerably increased the total methane yield and digestion kinetics and permitted lignin utilization during a subsequent second digestion. The increase of the specific methane yield for the full-scale biogas plant by applying thermal wet oxidation was 35-40%, showing that there is still a considerable amount of methane that can be harvested from anaerobic digested biowaste.

Bacteria, Anaerobic↗

PubMed2004

Modeling and simulation of oxygen-limited partial nitritation in a membrane-assisted bioreactor (MBR).

Combination of a partial nitritation process and an anaerobic ammonium oxidation process for the treatment of sludge reject water has some general cost-efficient advantages compared to nitrification-denitrification. The integrated process features two-stage autotrophic conversion of ammonium via nitrite to dinitrogen gas with lower demand for oxygen and no external carbon requirement. A nitrifying membrane-assisted bioreactor (MBR) for the treatment of sludge reject water was operated under continuous aeration at low dissolved oxygen (DO) concentrations with the purpose of generating nitrite accumulation. Microfiltration was applied to allow a high sludge retention time (SRT), resulting in a stable partial nitritation process. During start-up of the MBR, oxygen-limited conditions were induced by increasing the ammonium loading rate and decreasing the oxygen transfer. At a loading rate of 0.9 kg N m(-3) d(-1) and an oxygen concentration below 0.1 mg DO L(-1), conversion to nitrite was close to 50% of the incoming ammonium, thereby yielding an optimal effluent within the stoichiometric requirements for subsequent anaerobic ammonium oxidation. A mathematical model for ammonium oxidation to nitrite and nitrite oxidation to nitrate was developed to describe the oxygen-limited partial nitritation process within the MBR. The model was calibrated with in situ determinations of kinetic parameters for microbial growth, reflecting the intrinsic characteristics of the ammonium oxidizing growth system at limited oxygen availability and high sludge age. The oxygen transfer coefficient (K(L)a) and the ammonium-loading rate were shown to be the appropriate operational variables to describe the experimental data accurately. The validated model was used for further steady state simulation under different operational conditions of hydraulic retention time (HRT), K(L)a, temperature and SRT, with the intention to support optimized process design. Simulation results indicated that stable nitrite production from sludge reject water was feasible with this process even at a relatively low temperature of 20 degrees C with HRT down to 0.25 days.

Bacteria, Anaerobic↗

PubMed2004

Start-up of autotrophic nitrogen removal reactors via sequential biocatalyst addition.

A procedure for start-up of oxygen-limited autotrophic nitrification-denitrification (OLAND) in a lab-scale rotating biological contactor (RBC) is presented. In this one-step process, NH4+ is directly converted to N2 without the need for an organic carbon source. The approach is based on a sequential addition of two types of easily available biocatalyst to the reactor during start-up: aerobic nitrifying and anaerobic, granular methanogenic sludge. The first is added as a source of aerobic ammonia-oxidizing bacteria (AAOB), the second as a possible source of planctomycetes including anaerobic ammonia-oxidizing bacteria (AnAOB). The initial nitrifying biofilm serves as a matrix for anaerobic cell incorporation. By subsequently imposing oxygen limitation, one can create an optimal environment for autotrophic N removal. In this way, N removal of about 250 mg of N L(-1) d(-1) was achieved after 100 d treating a synthetic NH4+-rich wastewater. By gradually imposing higher loads on the reactor, the N elimination could be increased to about 1.8 g of N L(-1) d(-1) at 250 d. The resulting microbial community was compared with that of the inocula using general bacterial and AAOB- and planctomycete-specific PCR primers. Subsequently, the RBC reactor was shown to treat a sludge digestor effluent under suboptimal and strongly varying conditions. The RBC biocatalyst was also submitted to complete absence of oxygen in a fixed-film bioreactor (FFBR) and proved able to remove NH4+ with NO2- as electron acceptor (maximal 434 mg of NH4+-N (g of VSS)(-1) d(-1) on day 136). DGGE and real-time PCR analysis demonstrated that the RBC biofilm was dominated by members of the genus Nitrosomonas and close relatives of Kuenenia stuttgartiensis, a known AnAOB. The latter was enriched during FFBR operation, but AAOB were still present and the ratio planctomycetes/AAOB rRNA gene copies was about 4.3 after 136 d of reactor operation. Whether this relates to an active role of AAOB in the anoxic N removal process remains to be solved.

Bacteria, Aerobic↗

PubMed2004

Toluene removal from waste air using a flat composite membrane bioreactor.

In this report, gaseous toluene biodegradation results in a flat composite membrane reactor inoculated with Pseudomonas putida TVA8 are presented. Preliminary abiotic experiments showed that transport of toluene through the membrane was linearly and negatively correlated with the gas residence time (tau). During a 339-day biofiltration experiment, the influence of gas residence time (2-24 sec) and mass loading rate (B(v); 10-483 g x m(-3) h(-1)) on the toluene elimination capacity was investigated. A maximum elimination capacity (EC(max)) of 397 g x m(-3) h(-1) was achieved at tau = 24 sec and B(v) = 473 g x m(-3) h(-1). Expressed per unit membrane area, the EC(m,max) was 0.793 g x m(-2) h(-1), which is five times higher than results obtained with other membrane bioreactor experiments in the same range of loading rates. At low gas residence times, reactor performance was limited by mass transfer. Toluene concentration profiles along the membrane were measured for several biotic and abiotic conditions. For inlet concentrations (C(in)) up to 1 g x m(-3), more than 90% was eliminated at 15 cm from the reactor inlet. For C(in) > 1.65 g x m(-3), longer membranes are necessary to obtain these high removal efficiencies.

Air Pollutants↗

PubMed2004

A quantitative in silico analysis calculates the angiotensin I converting enzyme (ACE) inhibitory activity in pea and whey protein digests.

Angiotensin I converting enzyme (ACE) inhibitory peptides can induce antihypertensive effects after oral administration. By means of an ACE inhibitory peptide database, containing about 500 reported sequences and their IC(50) values, the different proteins in pea and whey were quantitatively evaluated as precursors for ACE inhibitory peptides. This analysis was combined with experimental data from the evolution in ACE inhibitory activity and protein degradation during in vitro gastrointestinal digestion. Pea proteins produced similar in silico scores and were degraded early in the in vitro digestion. High ACE inhibitory activity was observed after the simulated stomach phase and augmented slightly in the simulated small intestine phase. The major whey protein beta-lactoglobulin obtained the highest in silico scores, which corresponded with the fact that degradation of this protein in vitro only occurred from the simulated small intestine phase on and resulted in a 10-fold increase in the ACE inhibitory activity. Whey protein obtained total in silico scores of about 124 ml/mg, compared to 46 ml/mg for pea protein, indicating that whey protein would be a richer source of ACE inhibitory peptides than pea protein. Although beta-lactoglobulin is only partially digested, a higher ACE inhibitory activity was indeed found in the whey (IC(50) = 0.048 mg/ml) compared to the pea digest (IC(50) = 0.076 mg/ml). In silico gastrointestinal digestion of the highest scoring proteins in pea and whey, vicilin and albumin PA2, and beta-lactoglobulin, respectively, directly released a number of potent ACE inhibitory peptides. Several other ACE inhibitory sequences resisted in silico digestion by gastrointestinal proteases. Briefly, the quantitative in silico analysis will facilitate the study of precursor proteins on a large scale and the specific release of bioactive peptides.

Amino Acid Sequence↗

PubMed2004

Sedimentological evolution in an UASB treating SYNTHES, a new representative synthetic sewage, at low loading rates.

The changes in the sedimentological attributes of the sludge bed in an upflow anaerobic sludge blanket (UASB) reactor fed with a low-strength wastewater mimicking raw domestic sewage were assessed in this study. The reactor was inoculated with 250 ml of granular sludge from a full-scale UASB reactor. The organic loading rate (OLR) varied from 1 to 2 g COD/ld. During the half-year long study, the reactor was operated at hydraulic retention times (HRTs) of 4.8 and 10 h, at 33 degrees C. Sludge sedimentology showed that the original granular sludge experienced serious instability and disintegration, leading to a much finer final grain assemblage, mainly due to substrate transfer limitation and cell starvation at the interior of larger granules. With time, the size uniformity tended to decrease, sphericity tended to increase, the skewness of the granule size distribution became negative, and the kurtosis became peaked and leptokurtic. In spite of the observed size reduction, reactor efficiency increased to a CODtotal removal of 96%. Biomass (sludge) yield was 0.012 g VS/g COD removed. The CH4 content of the biogas was high (up to 96%). This study thus highlights the treatment of a new type of wastewater with the deployment of the UASB reactor. It also reports the evolutionary trend of the biomass particle size distribution, making reference to a classic sedimentological appraisal.

Bacteria, Anaerobic↗

PubMed2004

Advanced water treatment with manganese oxide for the removal of 17alpha-ethynylestradiol (EE2).

Municipal wastewater is supposed to be one of the most important sources of endocrine-disrupting compounds (EDCs) in water. Therefore, advanced treatments and cost-efficient techniques should be developed to prevent the spread of this type of pollution into the environment. In this view, experiments were conducted in which the removal of 17alpha-ethynylestradiol (EE2), a synthetic and persistent estrogen, from water was monitored in three upstream bioreactors (UBRs), filled with, respectively, sand, granulated activated carbon (GAC) and MnO(2) granules. Tap water, spiked with 15,000ngEE2/L was filtered through the reactors with a hydraulic retention time of approximately 1h. The removal of EE2 in the sand, GAC and MnO(2) reactors was, respectively, 17.3%,>99.8% and 81.7%. The removal in the GAC reactor was mainly due to adsorption. The MnO(2) reactor, however, removed significantly more EE2 than could be predicted from its adsorption capacity, probably thanks to its catalytic properties. These catalytic properties could make it a cost-efficient technique for the removal of EE2, but further research at more environmentally relevant concentrations is needed.

Adsorption↗

PubMed2004

Removal of carbon and nutrients from domestic wastewater using a low investment, integrated treatment concept.

An integrated chemical-physical-biological treatment concept for the low-cost treatment of domestic wastewater is proposed. Domestic wastewater was subjected to a chemically enhanced primary treatment (CEPT), followed by treatment in an upflow anaerobic sludge blanket (UASB) reactor. In addition, a regenerable zeolite was used to remove NH4+, either after CEPT pretreatment or after biological treatment in the UASB reactor. The CEPT pretreatment consisted of the addition of a coagulant (FeCl3) and an anionic organic flocculant and removed on average 73% of the total chemical oxygen demand (COD(t)), 85% of the total suspended solids, and 80% of PO4(3-) present in the wastewater. The UASB system, which consequently received a low COD(t) input of approximately 140 mg/L, was operated using a volumetric loading rate of 0.4 g COD(t)/L. d (hydraulic retention time [HRT]=10 h) and 0.7 g COD(t)/L. d (HRT=5 h). For these conditions, the system removed about 55% of the COD(t) in its influent, thus producing an effluent with a low COD(t) of approximately 50 mg/L. The zeolite, when applied in batch mode before the UASB reactor, removed approximately 45% of the NH4+, whereas its application as a post-treatment cartridge resulted in almost 100% NH4+ removal. The simple design and relatively low operating costs, due to low costs of added chemicals and low energy input (estimated at Euro 0.07-0.1 per m3 wastewater treated), combined with excellent treatment performance, means that this system can be used as a novel domestic wastewater treatment system for developing countries. Therefore, the system is called a Low Investment Sewage Treatment (LIST) system.

Bioreactors↗

PubMed2004

Advanced anaerobic bioconversion of lignocellulosic waste for bioregenerative life support following thermal water treatment and biodegradation by Fibrobacter succinogenes.

The feasibility of nearly-complete conversion of lignocellulosic waste (70% food crops, 20% faecal matter and 10% green algae) into biogas was investigated in the context of a life support project. The treatment comprised a series of processes, i.e., a mesophilic laboratory scale CSTR (continuously stirred tank reactor), an upflow biofilm reactor, a fiber liquefaction reactor employing the rumen bacterium Fibrobacter succinogenes and a hydrothermolysis system in near-critical water. By the one-stage CSTR, a biogas yield of 75% with a specific biogas production of 0.37 l biogas g(-1) VSS (volatile suspended solids) added at a RT (hydraulic retention time) of 20-25 d was obtained. Biogas yields could not be increased considerably at higher RT, indicating the depletion of readily available substrate after 25 d. The solids present in the CSTR-effluent were subsequently treated in two ways. Hydrothermal treatment (T approximately 310-350 degrees C, p approximately 240 bar) resulted in effective carbon liquefaction (50-60% without and 83% with carbon dioxide saturation) and complete sanitation of the residue. Application of the cellulolytic Fibrobacter succinogenes converted remaining cellulose contained in the CSTR-effluent into acetate and propionate mainly. Subsequent anaerobic digestion of the hydrothermolysis and the Fibrobacter hydrolysates allowed conversion of 48-60% and 30%, respectively. Thus, the total process yielded biogas corresponding with conversions up to 90% of the original organic matter. It appears that particularly mesophilic digestion in conjunction with hydrothermolysis at near-critical conditions offers interesting features for (nearly) complete and hygienic carbon and energy recovery from human waste in a bioregenerative life support context.

Anaerobiosis↗

PubMed2004

Bioavailability of angiotensin I converting enzyme inhibitory peptides.

Hypertension or high blood pressure is a significant health problem worldwide. Bioactive peptides that inhibit angiotensin I converting enzyme (ACE) in the cardiovascular system can contribute to the prevention and treatment of hypertension. These ACE inhibitory peptides are derived from many food proteins, especially milk proteins. An ACE inhibitory activity in vitro does not always imply an antihypertensive effect in vivo. Even if it does, it is very difficult to establish a direct relationship between in vitro and in vivo activity. This is mainly due to the bioavailability of the ACE inhibitory peptides after oral administration and the fact that peptides may influence blood pressure by mechanisms other than ACE inhibition. To exert an antihypertensive effect after oral ingestion, ACE inhibitory peptides have to reach the cardiovascular system in an active form. Therefore, they need to remain active during digestion by human proteases and be transported through the intestinal wall into the blood. The bioavailability of some ACE inhibitory peptides has been studied. It is also known that (hydroxy)proline-containing peptides are generally resistant to degradation by digestive enzymes. Peptides can be absorbed intact through the intestine by paracellular and transcellular routes, but the potency of the bioactivity after absorption is inversely correlated to chain length. In addition, some strategies are proposed to increase the bioavailability of ACE inhibitory peptides. Further research into the bioavailability of ACE inhibitory peptides will lead to the development of more effective ACE inhibitory peptides and foods.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed2004

Impact of agricultural practices on the Zea mays L. endophytic community.

Agricultural practices are known to alter bulk soil microbial communities, but little is known about the effect of such practices on the plant endophytic community. We assessed the influence of long-term applications (20 years) of herbicides and different fertilizer types on the endophytic community of maize plants grown in different field experiments. Nested PCR-denaturing gradient gel electrophoresis (DGGE) analyses targeting general bacteria, type I or II methanotrophs, actinomycetes, and general fungi were used to fingerprint the endophytic community in the roots of Zea mays L. Low intraplant variability (reproducible DGGE patterns) was observed for the bacterial, type I methanotroph, and fungal communities, whereas the patterns for endophytic actinomycetes exhibited high intraplant variability. No endophytic amplification product was obtained for type II methanotrophs. Cluster and stability analysis of the endophytic type I methanotroph patterns differentiated maize plants cultivated by using mineral fertilizer from plants cultivated by using organic fertilizer with a 100% success rate. In addition, lower methanotroph richness was observed for mineral-fertilized plants than for organically fertilized plants. The use of herbicides could not be traced by fingerprinting the endophytic type I methanotrophs or by evaluating any other endophytic microbial group. Our results indicate that the effect of agrochemicals is not limited to the bulk microbial community but also includes the root endophytic community. It is not clear if this effect is due to a direct effect on the root endophytic community or is due to changes in the bulk community, which are then reflected in the root endophytic community.

Agriculture↗

PubMed2004

Occurrence and phylogenetic diversity of Sphingomonas strains in soils contaminated with polycyclic aromatic hydrocarbons.

Bacterial strains of the genus Sphingomonas are often isolated from contaminated soils for their ability to use polycyclic aromatic hydrocarbons (PAH) as the sole source of carbon and energy. The direct detection of Sphingomonas strains in contaminated soils, either indigenous or inoculated, is, as such, of interest for bioremediation purposes. In this study, a culture-independent PCR-based detection method using specific primers targeting the Sphingomonas 16S rRNA gene combined with denaturing gradient gel electrophoresis (DGGE) was developed to assess Sphingomonas diversity in PAH-contaminated soils. PCR using the new primer pair on a set of template DNAs of different bacterial genera showed that the method was selective for bacteria belonging to the family Sphingomonadaceae.Single-band DGGE profiles were obtained for most Sphingomonas strains tested. Strains belonging to the same species had identical DGGE fingerprints, and in most cases, these fingerprints were typical for one species. Inoculated strains could be detected at a cell concentration of 10(4) CFU g of soil(-1). The analysis of Sphingomonas population structures of several PAH-contaminated soils by the new PCR-DGGE method revealed that soils containing the highest phenanthrene concentrations showed the lowest Sphingomonas diversity. Sequence analysis of cloned PCR products amplified from soil DNA revealed new 16S rRNA gene Sphingomonas sequences significantly different from sequences from known cultivated isolates (i.e., sequences from environmental clones grouped phylogenetically with other environmental clone sequences available on the web and that possibly originated from several potential new species). In conclusion, the newly designed Sphingomonas-specific PCR-DGGE detection technique successfully analyzed the Sphingomonas communities from polluted soils at the species level and revealed different Sphingomonas members not previously detected by culture-dependent detection techniques.

Base Sequence↗

PubMed2004

Biofuel cells select for microbial consortia that self-mediate electron transfer.

Microbial fuel cells hold great promise as a sustainable biotechnological solution to future energy needs. Current efforts to improve the efficiency of such fuel cells are limited by the lack of knowledge about the microbial ecology of these systems. The purposes of this study were (i) to elucidate whether a bacterial community, either suspended or attached to an electrode, can evolve in a microbial fuel cell to bring about higher power output, and (ii) to identify species responsible for the electricity generation. Enrichment by repeated transfer of a bacterial consortium harvested from the anode compartment of a biofuel cell in which glucose was used increased the output from an initial level of 0.6 W m(-2) of electrode surface to a maximal level of 4.31 W m(-2) (664 mV, 30.9 mA) when plain graphite electrodes were used. This result was obtained with an average loading rate of 1 g of glucose liter(-1) day(-1) and corresponded to 81% efficiency for electron transfer from glucose to electricity. Cyclic voltammetry indicated that the enhanced microbial consortium had either membrane-bound or excreted redox components that were not initially detected in the community. Dominant species of the enhanced culture were identified by denaturing gradient gel electrophoresis and culturing. The community consisted mainly of facultative anaerobic bacteria, such as Alcaligenes faecalis and Enterococcus gallinarum, which are capable of hydrogen production. Pseudomonas aeruginosa and other Pseudomonas species were also isolated. For several isolates, electrochemical activity was mainly due to excreted redox mediators, and one of these mediators, pyocyanin produced by P. aeruginosa, could be characterized. Overall, the enrichment procedure, irrespective of whether only attached or suspended bacteria were examined, selected for organisms capable of mediating the electron transfer either by direct bacterial transfer or by excretion of redox components.

Animals↗