Effect of tree species choice and mineral capping in a woodland phytostabilisation system: A case-study for calcareous dredged sediment landfills with an oxidised topsoil

Foliar, wood and bark metal concentrations were evaluated 2 and 12 years after afforestation of 3 metal-polluted calcareous upland dredged sediment landfills with an oxidised topsoil. Two techniques for reducing the metal entry into the food web were compared in a field situation: choice of appropriate tree species aiming at reduced metal transfer to the environment, and application of a thin uncontaminated mineral capping layer on top of the polluted sediment aiming at a good topsoil quality. Foliar concentrations show that an appropriate choice of tree species is very important in controlling metal cycling. Common ash, sycamore maple, pedunculate oak, black alder and small-leaved lime had normal foliar metal concentrations, while hybrid poplar showed very high Cd and Zn concentrations. The absence of a thin uncontaminated covering layer resulted in a higher metal load of the litter through direct (surface soil adhesion) and indirect (raindrop splash) soil load of the litter layer. Mineral capping affected foliar concentrations in an element-specific and species-specific way. It is concluded that an uncontaminated covering layer on polluted soils before afforestation is a management option which is only efficient in case of an appropriate tree species choice.     

Large-scale recording of neurons by movable silicon probes in behaving rodents

A major challenge in neuroscience is linking behavior to the collective activity of neural assemblies. Understanding of input-output relationships of neurons and circuits requires methods with the spatial selectivity and temporal resolution appropriate for mechanistic analysis of neural ensembles in the behaving animal, i.e. recording of representatively large samples of isolated single neurons. Ensemble monitoring of neuronal activity has progressed remarkably in the past decade in both small and large-brained animals, including human subjects. Multiple-site recording with silicon-based devices are particularly effective because of their scalability, small volume and geometric design. Here, we describe methods for recording multiple single neurons and local field potential in behaving rodents, using commercially available micro-machined silicon probes with custom-made accessory components. There are two basic options for interfacing silicon probes to preamplifiers: printed circuit boards and flexible cables. Probe supplying companies (http://www.neuronexustech.com/; http://www.sbmicrosystems.com/; http://www.acreo.se/) usually provide the bonding service and deliver probes bonded to printed circuit boards or flexible cables. Here, we describe the implantation of a 4-shank, 32-site probe attached to flexible polyimide cable, and mounted on a movable microdrive. Each step of the probe preparation, microdrive construction and surgery is illustrated so that the end user can easily replicate the process.     

Charged-particle activation analysis of biological material

Charged-particle activation analysis offers a number of interesting possibilities for the determination of trace elements in biological material. It allows the determination of those elements that are difficult or impossible to determine by neutron activation, such as Li, B, Al, Si, V, Cr, Ni, Cd, Sn, Tl, and Pb. Up to now, protons have been successfully applied to samples of both vegetale and human origin. A number of difficulties have to be overcome, one of which is excessive heating of the samples owing to the limited range of the charged particles, thus giving rise to a high energy deposition in a small volume. Moreover, the sample composition has to be known to allow the calculation of the range of the particles. an interesting alternative has been proposed using an internal standard together with a standard additions procedure. Proton activation analysis was tested on a wide variety of reference materials, giving evidence that accurate results can be obtained for many trace elements, even when applying a purely instrumental method. Thus, the method can also be applied in the certification of reference materials, since nuclear methods are independent of chemical properties of the sample.     

Butyrate production in continuous culture of Clostridium tyrobutyricum: effect of end-product inhibition

Summary Production of butyrate has been studied in continuous cultures of Clostridium tyrobutyricum. Production of acids, gases and cell biomass were determined under conditions of glucose limitation by varying either the glucose input or the dilution rate. Addition of acetate or butyrate to the cultures was also tested. The results led to the proposition that inhibition by acids acting as incouplers of energy production could provide a physiological explanation for most of the phenomena observed. It readily accounted for the higher productivities but lower product concentrations obtained in continuous culture with respect to batch or fed-batch conditions. It also explained the decrease in the ratios of butyrate to total acids and in cell yield observed at higher glucose input as well as the behaviour of the cultures under conditions of excess glucose. It could also possibly account for the partial conversion of added acetate to butyrate observed at moderate growth rates. Offprint requests to: J. P. Vandecasteele     

Identification and production of a rhamnolipidic biosurfactant by a Pseudomonas species

 A glycolipid-producing bacterium, Pseudomonas aeruginosa GL1, was isolated from the soil contaminated with polycyclic aromatic hydrocarbons (PAH) from a manufactured gas plant. The glycolipid produced was characterized in detail by chromatographic procedures as a mixture of four rhamnolipids, consisting of different associations of rhamnose and hydroxy fatty acids: the main component was monorhamnosyl di-3-hydroxydecanoic acid. The rhamnolipid composition presented marked analogies with a defined part of P. aeruginosa outer membrane lipopolysaccharides (lipopolysaccharide band A). Rhamnolipid production was stimulated under conditions of nitrogen limitation. Glycerol yielded higher productions than did hydrophobic carbon sources. Cell hydrophobicity decreased during growth on glycerol and on n-hexadecane whereas glycolipid production increased. P. aeruginosa GL1 was found to be unable to grow on a variety of 2, 3 and 4 cycle PAH. However, it was shown to persist after at least 12 subcultures in a bacterial population growing on a mixture of pure PAH, suggesting a physiological role for rhamnolipid as a means to enhance PAH availability in a mutualistic PAH-degrading bacterial community. Received: 4 July 1995/Received revision: 7 September 1995/Accepted: 13 September 1995     

Physiological methods to study biofilm disinfection

This report reviews the development of a rapidin situ approach to study the physiological responses of bacteria within biofilms to disinfectants. One method utilized direct viable counts (DVC) to assess the disinfection efficacy when thin biofilms were exposed to chlorine or monochloramine. Results obtained using the DVC method were one log higher than plate count (PC) estimates of the surviving population after disinfection. Other methods incorporated the use of fluorogenic stains, a cryotomy technique to yield thin (5-m) sections of biofilm communities and examination by fluorescence microscopy. The fluorogenic stains used in this approach included 5-cyano-2,3-ditolyl tetrazolium chloride (CTC), which indicates cellular electron transport activity and Rhodamine 123, which responds specifically to proton motive force. The use of these stains allowed the microscopic discrimination of physiologically active bacteria as well as heterogeneities of active cells within thicker biofilms. The results of experiments using these techniques with pure culture and binary population biofilms on stainless steel coupons indicated biocidal activity of chlorine-based disinfectants occurred initially at the bulk-fluid interface of the communities and progressed toward the substratum. This approach provided a unique opportunity to describe the spatial response of bacteria within biofilms to antimicrobial agents and address mechanisms explaining their comparative resistance to disinfection in a way that has not been possible using traditional approaches. Results obtained using this alternative approach were also consistently higher than PC data following disinfection. These observations suggest that traditional methods involving biofilm removal and bacterial enumeration by colony formation overestimate biocide efficacy. Hence the alternative approach described here more accurately indicates the ability of bacteria surviving disinfection to recover and grow as well as demonstrate spatial heterogeneities in cellular physiological activities within biofilms.     

Characterization and physiological function of a soluble l-amino acid oxidase in Corynebacterium

A general l-amino acid oxidase (l-amino acid: oxygen oxidoreductase (deaminating), EC 1.4.3.2.) has been characterized in Corynebacterium. The enzyme is soluble (MW 130 000–140 000) and is active with most l-α-amino acids but not with aspartate, threonine, proline and glycine. It is subject to substrate inhibition. This amino acid oxidase is induced along with catalase by growth in the presence of amino acids as a nitrogen source and is repressed when ammonium ions are present in the medium. Its probable physiological function is to allow the utilization of amino acids as a nitrogen source.     

Conversion into acetone and butanol of lignocellulosic substrates pretreated by steam explosion

Summary Hydrolysates obtained by enzymatic saccharification of wheat straw or cornstover pretreated by steam explosion in classical or acidic conditions, were found non fermentable into acetone-butanol (ABE). A simple treatment involving heating the hydrolysates in the presence of calcium or magnesium compounds such as Ca(OH)₂ or MgCO₃ at neutral pH values restored normal fermentability to these hydrolysates. The detoxification treatment could be included in the standard neutralization and sterilization procedures performed before fermentation.     

A comparison of genetically improved strains of the cellulolytic fungus Trichoderma reesei

Summary Production of cellulases by three different genetically improved strains of Trichoderma reesei: MCG 77, RUT-C30 and CL-847, has been assessed on various fermentation media. The three strains produce high levels of enzymes when grown on purified cellulose as the main carbon energy source; when grown on lactose, decrease in enzyme yield and productivity, differs significantly from strain to strain.     

Enzymatic Synthesis of l-Carnitine by Reduction of an Achiral Precursor: the Problem of Reduced Nicotinamide Adenine Dinucleotide Recycling

Synthesis of l-carnitine has been carried out by the enzymatic reduction of the carbonyl group of the achiral precursor 3-dehydrocarnitine with the oxidized nicotinamide adenine dinucleotide-linked carnitine dehydrogenase. Various enzymatic or chemical systems have been tested to regenerate the reduced nicotinamide adenine dinucleotide oxidized in the reduction of 3-dehydrocarnitine. Because of the instability of this compound in aqueous solutions, it was added by continuous feeding as a rate-limiting constituent in the reaction mixture. Under these conditions, conversion yields of 95% were achieved with the glucose plus glucose dehydrogenase system. A total number of 530 reduced nicotinamide adenine dinucleotide recyclings was obtained with this system for a production of 45 g of l-carnitine per liter. The stabilities of the oxidized nicotinamide adenine dinucleotide and the reduced nicotinamide adenine dinucleotide have been determined at various pH values. In view of these results, several possible strategies for enzymatic syntheses with the reduced nicotinamide adenine dinucleotide as a regenerable coenzyme are discussed.