Showing papers by "Alfons J. M. Stams published in 1995"

Enhanced biodegradation of aromatic pollutants in cocultures of anaerobic and aerobic bacterial consortia

Abstract: Toxic aromatic pollutants, concentrated in industrial wastes and contaminated sites, can potentially be eliminated by low cost bioremediation systems. Most commonly, the goal of these treatment systems is directed at providing optimum environmental conditions for the mineralization of the pollutants by naturally occurring microflora. Electrophilic aromatic pollutants with multiple chloro, nitro and azo groups have proven to be persistent to biodegradation by aerobic bacteria. These compounds are readily reduced by anaerobic consortia to lower chlorinated aromatics or aromatic amines but are not mineralized further. The reduction increases the susceptibility of the aromatic molecule for oxygenolytic attack. Sequencing anaerobic and aerobic biotreatment steps provide enhanced mineralization of many electrophilic aromatic pollutants. The combined activity of anaerobic and aerobic bacteria can also be obtained in a single treatment step if the bacteria are immobilized in particulate matrices (e.g. biofilm, soil aggregate, etc.). Due to the rapid uptake of oxygen by aerobes and facultative bacteria compared to the slow diffusion of oxygen, oxygen penetration into active biofilms seldom exceeds several hundred micrometers. The anaerobic microniches established inside the biofilms can be applied to the reduction of electron withdrawing functional groups in order to prepare recalcitrant aromatic compounds for further mineralization in the aerobic outer layer of the biofilm. Aside from mineralization, polyhydroxylated and chlorinated phenols as well as nitroaromatics and aromatic amines are susceptible to polymerization in aerobic environments. Consequently, an alternative approach for bioremediation systems can be directed towards incorporating these aromatic pollutants into detoxified humic-like substances. The activation of aromatic pollutants for polymerization can potentially be encouraged by an anaerobic pretreatment step prior to oxidation. Anaerobic bacteria can modify aromatic pollutants by demethylating methoxy groups and reducing nitro groups. The resulting phenols and aromatic amines are readily polymerized in a subsequent aerobic step.

Desulforhabdus amnigenus gen. nov. sp. nov., a sulfate reducer isolated from anaerobic granular sludge

Abstract: From granular sludge of an upflow anaerobic sludge bed (UASB) reactor treating paper-mill wastewater, a sulfate-reducing bacterium (strain ASRB1) was isolated with acetate as sole carbon and energy source. The bacterium was rod-shaped, (1.4–1.9 × 2.5–3.4 μm), non-motile, and gram-negative. Optimum growth with acetate occurred around 37° C in freshwater medium (doubling time: 3.5–5.0 days). The bacterium grew on a range of organic acids, such as acetate, propionate, and butyrate, and on alcohols, and grew autotrophically with H2, CO2, and sulfate. Fastest growth occurred with formate, propionate, and ethanol (doubling time: approx. 1.5 days). Strain ASRB1 clusters with the delta subdivision of Proteobacteria and is closely related to Syntrophobacter wolinii, a syntrophic propionate oxidizer. Strain ASRB1 was characterized as a new genus and species: Desulforhabdus amnigenus.

The effect of sulfate and nitrate on methane formation in a freshwater sediment.

Abstract: A freshwater sediment from a ditch of a peat grassland near Zegveld (Province of Utrecht, The Netherlands) was investigated for its potential methanogenic and syntrophic activity and the influence of sulfate and nitrate on these potential activities. Methanogenesis started after a 10 days lagphase. After 35-40 days aceticlastic methanogens were sufficiently enriched to cause a net decrease of acetate. In the presence of sulfate methane formation was only slightly affected. The addition of nitrate led to an outcompetition of aceticlastic methanogens by nitrate reducers. When inorganic electron acceptors were absent, substrates like propionate and butyrate were converted by syntrophic methanogenic consortia. Addition of inorganic electron acceptors resulted in an outcompetition of the syntrophic propionate and butyrate degrading consortia by the sulfate and nitrate reducers.

Role of formate and hydrogen in the degradation of propionate and butyrate by defined suspended cocultures of acetogenic and methanogenic bacteria

Abstract: The butyrate-degradingSyntrophospora bryantii degrades butyrate and a propionate-degrading strain (MPOB) degrades propionate in coculture with the hydrogen- and formate-utilizingMethanospirillum hungatii orMethanobacterium formicicum. However, the substrates are not degraded in constructed cocultures with twoMethanobrevibacter arboriphilus strains which are only able to consume hydrogen. Pure cultures of the acetogenic bacteria form both hydrogen and formate during butyrate oxidation with pentenoate as electron acceptor and during propionate oxidation with fumarate as electron acceptor. Using the highest hydrogen and formate levels which can be reached by the acetogens and the lowest hydrogen and formate levels which can be maintained by the methanogens it appeared that the calculated formate diffusion rates are about 100 times higher than the calculated hydrogen diffusion rates.

Sulfate reduction by a syntrophic propionate-oxidizing bacterium.

Abstract: The syntrophic propionate-oxidizing bacterium MPOB was able to grow in the absence of methanogens by coupling the oxidation of propionate to the reduction of sulfate. Growth on propionate plus sulfate was very slow (μ=0.024 day−1). An average growth yield was found of 1.5 g (dry weight) per mol of propionate. MPOB grew even slower than other sulfate-reducing syntrophic propionate-oxidizing bacteria. The growth rates and yields of strict sulfate-reducing bacteria (Desulfobulbus sp.) grown on propionate plus sulfate are considerably higher.

Localization of the enzymes involved in H2 and formate metabolism in Syntrophospora bryantii.

Abstract: Cell-free extracts of crotonate-grown cells of the syntrophic butyrate-oxidizing bacteriumSyntrophospora bryantii contained high hydrogenase activities (8.5–75.8 µmol · min−1 mg−1 protein) and relatively low formate dehydrogenase activities (0.04–0.07 µmol · min−1 mg−1 protein). The KM value and threshold value of the hydrogenase for H2 were 0.21 mM and 18 µM, respectively, whereas the KM value and threshold value of the formate dehydrogenase for formate were 0.22 mM and 10 µM, respectively. Hydrogenase, butyryl-CoA dehydrogenase and 3-OH-butyryl-CoA dehydrogenase were detected in the cytoplasmic fraction. Formate dehydrogenase and CO2 reductase were membrane-bound, likely located at the outer aspect of the cytoplasmic membrane. Results suggest that during syntrophic butyrate oxidation H2 is formed intracellularly while formate is formed at the outside of the cell.

Removal of tetrachloromethane by granular methanogenic sludge.

Abstract: Granular sludge grown on sucrose, methanol, or a volatile fatty acid mixture was found to readily degrade tetrachloromethane without any prior adaptation to this compound. Preliminary experiments showed that degradation rates were comparable for the three different sludges. Tetrachloromethane was degraded by granular sludge grown on methanol, forming chloroform as a transient intermediate which was rapidly degraded to dichloromethane and methyl chloride. Degradation by autoclaved controls indicated the involvement of biologically generated abiotic cofactors such as vitamin B{sub 12} and cofactor F{sub 430}. The dechlorination by the autoclaved sludge was inhibited by addition of 1-iodopropane, a selective inhibitor of vitamin B{sub 12}. Degradation by autoclaved granular sludge was also severely inhibited by addition of H{sub 2}O{sub 2} to the medium, which oxidized all reducing equivalents.

Assessment report on NRP subtheme “gGeenhouse Gases”: Sources and sinks of CO2CH4 and N2O, databases and socio-economic causes

Abstract: The aim of the subtheme Greenhouse gases of the Dutch National Research programme on (NRP) is to quantify the sources and sinks of the major greenhouse gases to enable estimates of the future atmospheric concentration. The major part of the projects in this theme is focused on the Dutch situation, but the results can be extrapolated countries or regions. The information gained will be used for Dutch policy decisions regarding abatement of greenhouse gases. Section 1 deals with the aim and organization of Causes of climate change, and relates the scope to increased awareness of uncertainties in sources and sinks of greenhouse gases: at the start of the National Research Programme the general consensus of the scientific community was that these uncertainties were not extreme large, it is nowadays accepted that these uncertainties are larger than assumed before. The aim the Cluster CO 2 ( Section 2 ) was devoted to study the exchange between terrestrial ecosystems and the atmosphere to gain more knowledge of the “fertilization” flux. The research was mainly focused on the development of a CO 2 exchange model for grassland describing diurnal and seasonal fluxes, and on the validation of this local scale model on a regional and national scale. In both the clusters CH 4 and N 2 O (respectively Section 3 and Section 4 ) anthropogenic and biogenic sources were studied. Major criteria to study sources were the source strength, but also the uncertainty in the source estimate and the potential emission reduction, all projected on the Dutch situation. Exception were the projects on CH 4 emission from rice fields, and the sea/air exchange of N 2 O in oceans; expertise was available in The Netherlands to carry out these studies. As in the sub-theme CO 2 the study of processes in grasslands was given a high priority in the sub themes CH 4 and N 2 O in order to quantify emission the mentioned greenhouse gases. Moreover, in the CH 4 -sub theme projects were performed to evaluate and validate the strength of various sources. The two remaining clusters (limited in extend) were aimed at the development of emission databases and geographic quantification of soil processes controlling greenhouse gas fluxes (cluster Database Development, Section 5 ), and on national inventories (cluster Socio-economic Causes, Section 6 ). In the framework of the first cluster two databases were developed, one was the World Inventory of Soil Emission potentials (WISE), a global gridded database of the primary soil factors controlling soil greenhouse gas emissions, and the other was Emission Database for Global Atmospheric Research (EDGAR) aimed to describe the processes as land use, energy consumption etc, which control the emissions of greenhouse gases and other air pollutants. The goal of the other sub theme was to develop and apply methodologies to compile national inventories of greenhouse gas emissions in The Netherlands, focused on the compounds CH 4 and N 2 O.