949 research outputs found

    Handwriting recognition and verification : a hidden Markov approach

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    Degradation of Toluene and Trichloroethylene by Burkholderia cepacia G4 in Growth-Limited Fed-Batch Culture

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    Burkholderia (Pseudomonas) cepacia G4 was cultivated in a fed-batch bioreactor on either toluene or toluene plus trichloroethylene (TCE). The culture was allowed to reach a constant cell density under conditions in which the amount of toluene supplied equals the maintenance energy demand of the culture. Compared with toluene only, the presence of TCE at a toluene/TCE ratio of 2.3 caused a fourfold increase in the specific maintenance requirement for toluene from 22 to 94 nmol mg of cells (dry weight)-1 h-1. During a period of 3 weeks, approximately 65% of the incoming TCE was stably converted to unidentified products from which all three chlorine atoms were liberated. When toluene was subsequently omitted from the culture feed while TCE addition continued, mutants which were no longer able to grow on toluene or to degrade TCE appeared. These mutants were also unable to grow on phenol or m- or o-cresol but were still able to grow on catechol and benzoate. Plasmid analysis showed that the mutants had lost the plasmid involved in toluene monooxygenase formation (pTOM). Thus, although strain G4 is much less sensitive to TCE toxicity than methanotrophs, deleterious effects may still occur, namely, an increased maintenance energy demand in the presence of toluene and plasmid loss when no toluene is added.

    Emergent behaviour in a chlorophenol-mineralising three-tiered microbial `food web'

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    Anaerobic digestion enables the water industry to treat wastewater as a resource for generating energy and recovering valuable by-products. The complexity of the anaerobic digestion process has motivated the development of complex models. However, this complexity makes it intractable to pin-point stability and emergent behaviour. Here, the widely used Anaerobic Digestion Model No. 1 (ADM1) has been reduced to its very backbone, a syntrophic two-tiered microbial food chain and a slightly more complex three-tiered microbial food web, with their stability analysed as function of the inflowing substrate concentration and dilution rate. Parameterised for phenol and chlorophenol degradation, steady-states were always stable and non-oscillatory. Low input concentrations of chlorophenol were sufficient to maintain chlorophenol- and phenol-degrading populations but resulted in poor conversion and a hydrogen flux that was too low to sustain hydrogenotrophic methanogens. The addition of hydrogen and phenol boosted the populations of all three organisms, resulting in the counterintuitive phenomena that (i) the phenol degraders were stimulated by adding hydrogen, even though hydrogen inhibits phenol degradation, and (ii) the dechlorinators indirectly benefitted from measures that stimulated their hydrogenotrophic competitors; both phenomena hint at emergent behaviour.Comment: 19 pages, 8 figure

    Method and timing of grassland renovation affects herbage yield, nitrate leaching, and nitrous oxide emission in intensively managed grasslands

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    Managed grasslands are occasionally ploughed up and reseeded in order to maintain or increase the sward productivity. It has been reported that this renovation of grassland is associated with a flush of soil organic nitrogen (N) mineralization and with a temporary increase in soil mineral N contents. Here, we report on the effects of method and time of grassland renovation on herbage yield, nitrate (NO3 -) leaching and nitrous oxide (N2O) emission. Field experiments were carried out at three sites (two sandy soils and a clay soil) in the Netherlands for three years. Renovation of grassland increased the percentage of Perennial ryegrass from 48–70% up to more than 90%. However, averaged over three years, dry matter yields were higher for the reference (not reseeded) swards (on average 13.6 Mg ha-1 for the highest N application rate) than for the renovated grasslands (12.2–13.1 Mg ha-1 dry matter). Grassland renovation in April did not increase N leaching in comparison to the reference. However, renovation in September increased the risk of leaching, because mineral N contents in the 0–90 cm were in November on average 46–77 kg N ha-1 higher than in the reference. Contents of dissolved organic N (DON) in the soil were not affected by renovation. Renovation increased N2O emissions by a factor of 1.8–3.0 relative to the reference grassland. Emissions of N2O were on average higher after renovation in April (8.2 kg N2O-N ha-1) than in September (5.8 kg N2O-N ha-1). Renovation without ploughing (i.e. only chemically destruction of the sward) resulted in a lower percentage of perennial ryegrass (60–84%) than with ploughing (>90%). Moreover, N2O emissions were higher after renovation without ploughing than with ploughing. Clearly, farmers need better recommendations and tools for determining when grassland renovation has beneficial agronomic effects. Losses of N via leaching and N2O emission after renovation can probably not be avoided, but renovation in spring in stead of autumn in combination with ploughing and proper timing of fertilizer application can minimize N losses

    Temperature, inocula and substrate: contrasting electroactive consortia, diversity and performance in microbial fuel cells

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    The factors that affect microbial community assembly and its effects on the performance of bioelectrochemical systems are poorly understood. Sixteen microbial fuel cell (MFC) reactors were set up to test the importance of inoculum, temperature and substrate: Arctic soil versus wastewater as inoculum; warm (26.5°C) versus cold (7.5°C) temperature; and acetate versus wastewater as substrate. Substrate was the dominant factor in determining performance and diversity: unexpectedly the simple electrogenic substrate delivered a higher diversity than a complex wastewater. Furthermore, in acetate fed reactors, diversity did not correlate with performance, yet in wastewater fed ones it did, with greater diversity sustaining higher power densities and coulombic efficiencies. Temperature had only a minor effect on power density, (Q10: 2 and 1.2 for acetate and wastewater respectively): this is surprising given the well-known temperature sensitivity of anaerobic bioreactors. Reactors were able to operate at low temperature with real wastewater without the need for specialised inocula; it is speculated that MFC biofilms may have a self-heating effect. Importantly, the warm acetate fed reactors in this study did not act as direct model for cold wastewater fed systems. Application of this technology will encompass use of real wastewater at ambient temperatures

    Syntrophic propionate-oxidizing bacteria in methanogenic systems

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    This review summarizes discoveries in syntrophic propionate degradation research and reveals intriguing metabolic capabilities, mechanisms of cooperation and environmentally driven kinetics by taxonomically distinct microorganisms that are important for biotechnological applications and biogenic methane emissions.The mutual nutritional cooperation underpinning syntrophic propionate degradation provides a scant amount of energy for the microorganisms involved, so propionate degradation often acts as a bottleneck in methanogenic systems. Understanding the ecology, physiology and metabolic capacities of syntrophic propionate-oxidizing bacteria (SPOB) is of interest in both engineered and natural ecosystems, as it offers prospects to guide further development of technologies for biogas production and biomass-derived chemicals, and is important in forecasting contributions by biogenic methane emissions to climate change. SPOB are distributed across different phyla. They can exhibit broad metabolic capabilities in addition to syntrophy (e.g. fermentative, sulfidogenic and acetogenic metabolism) and demonstrate variations in interplay with cooperating partners, indicating nuances in their syntrophic lifestyle. In this review, we discuss distinctions in gene repertoire and organization for the methylmalonyl-CoA pathway, hydrogenases and formate dehydrogenases, and emerging facets of (formate/hydrogen/direct) electron transfer mechanisms. We also use information from cultivations, thermodynamic calculations and omic analyses as the basis for identifying environmental conditions governing propionate oxidation in various ecosystems. Overall, this review improves basic and applied understanding of SPOB and highlights knowledge gaps, hopefully encouraging future research and engineering on propionate metabolism in biotechnological processes

    The effect of anode potential on current production from complex substrates in bioelectrochemical systems: a case study with glucose

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    Anode potential can affect the degradation pathway of complex substrates in bioelectrochemical systems (BESs), thereby influencing current production and coulombic efficiency. However, the intricacies behind this interplay are poorly understood. This study used glucose as a model substrate to comprehensively investigate the effect of different anode potentials (− 150 mV, 0 mV and + 200 mV) on the relationship between current production, the electrogenic pathway and the abundance of the electrogenic microorganisms involved in batch mode fed BESs. Current production in glucose-acclimatized reactors was a function of the abundance of Geobacteraceae and of the availability of acetate and formate produced by glucose degradation. Current production was increased by high anode potentials during acclimation (0 mV and + 200 mV), likely due to more Geobacteraceae developing. However, this effect was much weaker than a stimulus from an artificial high acetate supply: acetate was the rate-limiting intermediate in these systems. The supply of acetate could not be influenced by anode potential; altering the flow regime, batch time and management of the upstream fermentation processes may be a greater engineering tool in BES. However, these findings suggest that if high current production is the focus, it will be extremely difficult to achieve success with complex waste streams such as domestic wastewater
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