Toluene : biological waste-gas treatment, toxicity and microbial adaptation

Due to the increasing stringent legislation concerning the emission of volatile organic compounds, there is nowadays a growing interest to apply biological waste-gas treatment techniques for the removal of higher concentrations of specific contaminants from waste gases. Fluctuations in the contaminant concentrations can strongly affect the performance of bioreactors used for the treatment of waste-gas streams. Temporary high concentrations can be toxic for the microorganisms in the reactor, resulting in inactivation of the system. Furthermore, for a reliable operation the design of the reactor should be based on the peak concentrations in the waste gas, which is not an economically favourable situation. Therefore, it would be desirable to buffer the fluctuations in the contaminant concentration by means of an adsorbent, so that a constant supply of contaminants to the bioreactor can be achieved. The buffer capacity of a number of activated carbons and other adsorbents was tested (Chapter 2). Using one selected type of activated carbon it was demonstrated that fluctuations between 0 and 1000 mg toluene per m 3could be transformed to an average value of about 300 mg/m 3, which was subsequently completely degraded in a biofilter. Without an activated-carbon column significant amounts of toluene were not degraded in the biofilter when the inlet concentration was 1000 mg/m3,A disadvantage of trickie-bed reactors for biological waste-gas treatment is the reduction in reactor performance which is sometimed observed due to the formation of an excessive amount of biomass resulting in clogging. By limiting the amount of nutrients available for biomass formation it was attempted to prevent clogging of the reactor (Chapter 3). As a consequence of this nutrient limitation a reduced removal rate of toluene was observed. However, when a fungal culture was used to inoculate the reactor, the toluene removal rate under nutrient limiting conditions was almost twice as high. Over a period of 375 days an average removal rate of 27 g-C/(m 3h) was obtained with this fungal culture. These results clearly show that, even under non-sterile conditions, inoculation of the reactor with a specific starter culture can influence the reactor performance over a prolonged period of time. From the carbon balance over the reactor and the nitrogen availability it was concluded that under these nutrient-limited conditions large amounts of carbohydrates are formed. Even under nutrientlimited conditions the biomass content (including extracellular polysaccharides and other polymers) of the reactor increased, which eventually can result in clogging of the reactor. In order to prevent clogging eventually biomass has to be removed regularly from the reactor. We therefore studied the application of a NaOH- wash to remove excess biomass. Using regular NaOH-washes an average toluene removal rate of 35 g-C/(m 3h) was obtained with a mixed culture of bacteria. After about 50 days there was no longer a net increase in the biomass content of the reactor. The amount of biomass which was formed in the reactor equalled the amount removed by the NaOH-wash Under these conditions it should be possible to maintain a high toluene removal rate without clogging of the reactor taking place for a long period of time.From a biofilter used for the removal of toluene from waste gases we have isolated the fungus, Cladosporium sphaerospermum, which is able to grow on toluene as the sole source of carbon and energy (Chapter 4). To our knowledge this is the first report of toluene catabolism by an eukaryotic microorganism. The oxygen-consumption rates as well as the measured enzyme activities of toluenegrown C.sphaerospermum indicate that toluene is degraded by an initial attack on the methyl group.The toxicity of various pollutants in a waste-gas stream for microorganisms could limit the application of biological waste-gas treatment techniques. Especially compounds, with a good solubility in water can be expected to accumulate in the water-phase of the reactor during the start-up period. This accumulation can result in the inactivation of the biomass in the reactor as the contaminant concentrations reach toxic levels. The toxicity of various volatile organic compounds frequently present as contaminants in waste gases has been determined (Chapter 5). For both the Gram-positive Rhodococcus S5 and the Gram-negative Pseudomonas S12 the toxicity was assessed as the concentration which reduced the growth rate of the bacterium with 50%. No significant differences were observed between the IC50% values for these two bacteria. A relationship between the toxicity and hydrophobicity of various substituted benzene compounds was observed.Surprisingly, one of the selected bacteria, Pseudomonas putida S12 was able to adapt to the presence of high concentrations of contaminants. This adaptation resulted in the capacity of this strain to grow in the presence of supersaturating amounts of toluene (Chapter 6).In general, the toxicity of organic solvents is caused by the accumulation of these lipophilic solvents in the membrane lipid bilayer, affecting structural and functional properties of the membrane. The accumulation of solvents in the cell membrane can affect both the membrane fluidity and the bilayer stability. The physico-chemical effects of alkanols, alkanes and other hydrocarbons on biomembranes are summarized in Chapter 8. Although organic solvents can be highly toxic for microorganisms, some microorganisms are able to grow in the presence of concentrations of these solvents which are generally toxic (Chapter 8).P. putida S12 and two other solvent tolerant P. putida strains reacted to toxic concentrations of toluene by accumulating trans unsaturated fatty acids in the membrane instead of the cis isomers. This higher trans / cis ratio of the unsaturated fatty acids in toluene-adapted cells resulted a higher lipid-ordering since the gel to liquid-crystalline transition temperature was about 7-9 °C higher compared to the non- adapted cells. This cis / trans isomerization of fatty acids is probably a mechanism to very quickly compensate for the increase in membrane fluidity, and destabilization of the bilayer structure caused by toluene accumulating in the membrane (Chapter 7 & 8). Apart from changes in the fatty acid composition also changes in the phospholipid composition were observed when the organism was grown in the presence of toluene. The decreased incorporation of phosphaticlylethanolamine and the increased incorporation of diphosphatidylethanolamine (cardiolipin) are expected to prevent the formation of non-bilayer phospholipids configurations which might be caused by toluene (Chapter 8).In Chapter 9 the results presented in this thesis are discussed in relation to biotechnological applications

Hard-core Yukawa model for two-dimensional charge stabilized colloids

The hyper-netted chain (HNC) and Percus-Yevick (PY) approximations are used to study the phase diagram of a simple hard-core Yukawa model of charge-stabilized colloidal particles in a two-dimensional system. We calculate the static structure factor and the pair distribution function over a wide range of parameters. Using the statics correlation functions we present an estimate for the liquid-solid phase diagram for the wide range of the parameters.Comment: 7 pages, 9figure

Rapid Colorimetric Detection of Pseudomonas aeruginosa in Clinical Isolates Using a Magnetic Nanoparticle Biosensor

A rapid, sensitive, and specific colorimetric biosensor based on the use of magnetic nanoparticles (MNPs) was designed for the detection of Pseudomonas aeruginosa in clinical samples. The biosensing platform was based on the measurement of P. aeruginosa proteolytic activity using a specific protease substrate. At the N-terminus, this substrate was covalently bound to MNPs and was linked to a gold sensor surface via cystine at the C-terminus of the substrates. The golden sensor appears black to naked eyes because of the coverage of the MNPs. However, upon proteolysis, the cleaved peptide-MNP moieties will be attracted by an external magnet, revealing the golden color of the sensor surface, which can be observed by the naked eye. In vitro, the biosensor was able to detect specifically and quantitatively the presence of P. aeruginosa with a detection limit of 102 cfu/mL in less than 1 min. The colorimetric biosensor was used to test its ability to detect in situ P. aeruginosa in clinical isolates from patients. This biochip is anticipated to be useful as a rapid point-of-care device for the diagnosis of P. aeruginosa-related infections

Large-scale zero-shot learning in the wild: classifying zoological illustrations

In this paper we analyse the classification of zoological illustrations. Historically, zoological illustrations were the modus operandi for the documentation of new species, and now serve as crucial sources for long-term ecological and biodiversity research. By employing computational methods for classification, the data can be made amenable to research. Automated species identification is challenging due to the long-tailed nature of the data, and the millions of possible classes in the species taxonomy. Success commonly depends on large training sets with many examples per class, but images from only a subset of classes are digitally available, and many images are unlabelled, since labelling requires domain expertise. We explore zero-shot learning to address the problem, where features are learned from classes with medium to large samples, which are then transferred to recognise classes with few or no training samples. We specifically explore how distributed, multi-modal background knowledge from data providers, such as the Global Biodiversity Information Facility (GBIF), iNaturalist, and the Biodiversity Heritage Library (BHL), can be used to share knowledge between classes for zero-shot learning. We train a prototypical network for zero-shot classification, and introduce fused prototypes (FP) and hierarchical prototype loss (HPL) to optimise the model. Finally, we analyse the performance of the model for use in real-world applications. The experimental results are encouraging, indicating potential for use of such models in an expert support system, but also express the difficulty of our task, showing a necessity for research into computer vision methods that are able to learn from small samples.Computer Systems, Imagery and Medi

Analysis of the FoodNet case-control study of sporadic Salmonella serotype Enteritidis infections using persons infected with other Salmonella serotypes as the comparison group

Use of well persons as the comparison group for laboratory-confirmed cases of sporadic salmonellosis may introduce ascertainment bias into case-control studies. Data from the 1996-1997 FoodNet case-control study of laboratory-confirmed Salmonella serogroups B and D infection were used to estimate the effect of specific behaviours and foods on infection with Salmonella serotype Enteritidis (SE). Persons with laboratory-confirmed Salmonella of other serotypes acted as the comparison group. The analysis included 173 SE cases and 268 non-SE controls. SE was associated with international travel, consumption of chicken prepared outside the home, and consumption of undercooked eggs prepared outside the home in the 5 days prior to diarrhoea onset. SE phage type 4 was associated with international travel and consumption of undercooked eggs prepared outside the home. The use of ill controls can be a useful tool in identifying risk factors for sporadic cases of Salmonella

Dependence of direct detection signals on the WIMP velocity distribution

The signals expected in WIMP direct detection experiments depend on the ultra-local dark matter distribution. Observations probe the local density, circular speed and escape speed, while simulations find velocity distributions that deviate significantly from the standard Maxwellian distribution. We calculate the energy, time and direction dependence of the event rate for a range of velocity distributions motivated by recent observations and simulations, and also investigate the uncertainty in the determination of WIMP parameters. The dominant uncertainties are the systematic error in the local circular speed and whether or not the MW has a high density dark disc. In both cases there are substantial changes in the mean differential event rate and the annual modulation signal, and hence exclusion limits and determinations of the WIMP mass. The uncertainty in the shape of the halo velocity distribution is less important, however it leads to a 5% systematic error in the WIMP mass. The detailed direction dependence of the event rate is sensitive to the velocity distribution. However the numbers of events required to detect anisotropy and confirm the median recoil direction do not change substantially.Comment: 21 pages, 7 figures, v2 version to appear in JCAP, minor change

Magnetization relaxation in (Ga,Mn)As ferromagnetic semiconductors

We describe a theory of Mn local-moment magnetization relaxation due to p-d kinetic-exchange coupling with the itinerant-spin subsystem in the ferromagnetic semiconductor (Ga,Mn)As alloy. The theoretical Gilbert damping coefficient implied by this mechanism is calculated as a function of Mn moment density, hole concentration, and quasiparticle lifetime. Comparison with experimental ferromagnetic resonance data suggests that in annealed strongly metallic samples, p-d coupling contributes significantly to the damping rate of the magnetization precession at low temperatures. By combining the theoretical Gilbert coefficient with the values of the magnetic anisotropy energy, we estimate that the typical critical current for spin-transfer magnetization switching in all-semiconductor trilayer devices can be as low as $\sim 10^{5} {\rm A cm}^{-2}$.Comment: 4 pages, 2 figures, submitted to Rapid Communication

Cultural effects on neurodevelopmental testing in children from six European countries: An analysis of NUTRIMENTHE Global Database

Cultural background is an important variable influencing neuropsychological performance. Multinational projects usually involve gathering data from participants from different countries and/or different cultures. Little is known about the influence of culture on neuropsychological testing results in children and especially in European children. The objectives of this study were to compare neuropsychological performance of children from six European countries (Belgium, Germany, Italy, The Netherlands, Poland and Spain) using a comprehensive neuropsychological battery and to apply a statistical procedure to reduce the influence of country/cultural differences in neuropsychological performance. As expected, the results demonstrated differences in neuropsychological performance among children of the six countries involved. Cultural differences remained after adjusting for other confounders related to neuropsychological execution, such as sex, type of delivery, maternal age, gestational age and maternal educational level. Differences between countries disappeared and influence of culture was considerably reduced when standardised scores by country and sex were used. These results highlight the need for developing specific procedures to compare neuropsychological performance among children from different cultures to be used in multicentre studies

Semantic annotation of natural history collections

Large collections of historical biodiversity expeditions are housed in natural history museums throughout the world. Potentially they can serve as rich sources of data for cultural historical and biodiversity research. However, they exist as only partially catalogued specimen repositories and images of unstructured, non-standardised, hand-written text and drawings. Although many archival collections have been digitised, disclosing their content is challenging. They refer to historical place names and outdated taxonomic classifications and are written in multiple languages. Efforts to transcribe the hand-written text can make the content accessible, but semantically describing and interlinking the content would further facilitate research. We propose a semantic model that serves to structure the named entities in natural history archival collections. In addition, we present an approach for the semantic annotation of these collections whilst documenting their provenance. This approach serves as an initial step for an adaptive learning approach for semi-automated extraction of named entities from natural history archival collections. The applicability of the semantic model and the annotation approach is demonstrated using image scans from a collection of 8, 000 field book pages gathered by the Committee for Natural History of the Netherlands Indies between 1820 and 1850, and evaluated together with domain experts from the field of natural and cultural history.Computer Systems, Imagery and Medi