Microbial diversity in archived soils.
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Biodiversity↗
Biomedical subjects
J Dolfing
Publications and source records attributed to J Dolfing.
Potential for anaerobic conversion of xenobiotics.
This review covers the latest research on the anaerobic biodegradation of aromatic xenobiotic compounds, with emphasis on surfactants, polycyclic aromatic hydrocarbons, phthalate esters, polychlorinated biphenyls, halogenated phenols, and pesticides. The versatility of anaerobic reactor systems regarding the treatment of xenobiotics is shown with the focus on the UASB reactor, but the applicability of other reactor designs for treatment of hazardous waste is also included. Bioaugmentation has proved to be a viable technique to enhance a specific activity in anaerobic reactors and recent research on reactor and in situ bioaugmentation is reported.
Anaerobiosis↗
Soil phosphorus quantity-intensity relationships to predict increased soil phosphorus loss to overland and subsurface flow.
Soil phosphorus (P) quantity-intensity (q-i) relationships, based on common extraction methods, may potentially be used to estimate the risk of P loss in overland flow and subsurface drainage water. Some workers have used nonlinear q-i relationships to derive thresholds in soil test P (STP; a quantity factor) above which the risk of P loss increases, while others find linear relationships and no threshold. We present here a simple modelling exercise (based on Langmuir adsorption theory) along with data from literature to explain the behaviour of q-i relationships, and to give an explanation for this apparent discrepancy. The data indicate that q-i relationships are dependent upon the soil to solution ratio of the P intensity parameter, adsorption capacity (Qmax) and strength (K) of the soil, and the total range in STP. In turn, this affects the calculation of a threshold in STP. The q-i relationship tends towards linearity under conditions of a narrow total range of STP and/or when using a wide soil to solution ratio for estimating the P intensity parameter. Under such conditions, a threshold is difficult to detect, and uncertain. We conclude that the sensitivity of thresholds to experimental conditions and soils needs to be considered if thresholds are to be successful in environmental management to decrease P loss to surface waters.
Phosphorus↗
Effect of beringite on cadmium and zinc uptake by plants and earthworms: more than a liming effect?
Metal-contaminated soils are potentially harmful to plants, animals, and humans. Harmful effects are often related to the free-metal concentration in the soil solution. Immobilization is a potentially useful method to improve the quality of metal-contaminated soils by transforming free-metal ions into species that are less mobile and less toxic. The effect of many immobilizing products can be attributed to sorption on the surface of the material. Alkaline materials also enhance adsorption to soil particles by decreasing proton competition. Immobilization should preferably be evaluated independently of soil pH to discriminate between these processes. In this study, the immobilizing effect of beringite, an alkaline alumino silicate, was compared with that of lime. Plants (Swiss chard [Beta vulgaris L. var. cicla]) were grown on a soil contaminated with cadmium and zinc and treated with graded amounts of beringite or lime. Metal availability, as determined by a 0.01 M CaCl2 extraction, and metal uptake by plants strongly decreased in all treated soils. Beringite did not reduce metal availability more than liming when the obtained pH levels were similar. The effect of beringite can, therefore, be explained as a liming effect, at least for the duration of our experiment (10 weeks). The effect of beringite and lime on metal accumulation by earthworms (Eisenia veneta and Lumbricus rubellus) was small or not significant, although the CaCl2-extractable metal concentration in treated soils decreased by more than 90%. We conclude that immobilizing agents based on a liming effect can decrease metal uptake by plants, but they will hardly affect metal uptake by earthworms. Hence, these materials can reduce negative ecological effects of metal contamination on plants and herbivores, but not on earthworm predators.
Aluminum Silicates↗
Cadmium uptake by earthworms as related to the availability in the soil and the intestine.
The free metal concentration in the soil solution is often considered a key parameter for metal uptake by and toxicity to soft-bodied soil organisms. The equilibrium partitioning theory, which assumes a relationship between the contaminant concentration in pore water and the contaminant concentration in the body tissue, can be used to describe uptake by earthworms. This theory has proved useful for organic chemicals, but its applicability is less clear for metals. In this study, the Cd concentration in soil pore water (pw) was varied by increasing the soil pH by the addition of lime (Ca(OH)2) and by adding manganese oxide (MnO2), which has a high metal binding capacity. Both lime (0.135% w/w) and MnO2 (1% w/w) decreased [Cd2+]pw by a factor of 25, while Cdworm was reduced only by a factor of 1.3 in lime-treated soils and 2.5 in MnO2-treated soils. Cadmium uptake was weakly related to the free metal concentration (R2adj = 0.66). Adding pH as an explanatory variable increased R2adj to 0.89, indicating that Cd uptake from pore water is pH dependent, which might be attributed to competition of protons and Cd at the surface of the earthwororm body. However, previous earthworm experiments in reconstituted groundwater showed a conspicuously smaller pH dependency of Cd uptake. The differences in metal uptake between earthworms in lime- and MnO2-treated soils are therefore more likely to reflect the predominance of pH-independent intestinal uptake of Cd. Equilibrating the soil with a solution of 0.01 M CaCl2 and 0.1 M triethanolamine (buffered at pH 7.2), simulating the conditions prevailing in the worm intestine, yielded free Cd concentrations that were closely (R2adj = 0.83) and linearly related to the Cd concentration in the earthworm tissue.
Animals↗
Energetics of anaerobic degradation pathways of chlorinated aliphatic compounds.
This minireview explores the energetics of the (anaerobic) oxidative and fermentative degradation of halogenated ethenes and ethanes. It is shown that these pathways are viable alternatives to the traditional routes that start with one or more reductive dechlorination steps. In contrast to reductive dehalogenation, oxidative and fermentative degradation pathways do not require an external source of reducing equivalents. This suggests that organisms that use these pathways are most likely to be found at high redox potentials, i.e, under conditions where competition for reducing equivalents is great.
Journal Article↗
Halogenation of aromatic compounds: thermodynamic, mechanistic and ecological aspects.
Biological halogenation of aromatic compounds implies the generation of reducing equivalents in the form of e.g. NADH. Thermodynamic calculations show that coupling the halogenation step to a step in which the reducing equivalents are oxidized with a potent oxidant such as O2 or N2O makes the halogenation reaction thermodynamically feasible without the input of additional energy in the form of e.g. NADH. In a current model on the halogenation of tryptophan to 7-chloro-L-tryptophan NADH and O2 are proposed as co-substrates in a reaction in which the aromatic compound is oxidized via an epoxide as intermediate. The thermodynamic calculations thus indicate that such a route hinges on mechanistic insights but has no thermodynamic necessity. Furthermore the calculations suggest that halogenation of tryptophan and other aromatic compounds should be possible with N2O, and possibly even with nitrate replacing O2 as the oxidant.
Antifungal Agents↗
Degradation of Toluene and Trichloroethylene by Burkholderia cepacia G4 in Growth-Limited Fed-Batch Culture.
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)(sup-1) h(sup-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.
Journal Article↗
Degradation of halogenated aliphatic compounds: the role of adaptation.
A limited number of halogenated aliphatic compounds can serve as a growth substrate for aerobic microorganisms. Such cultures have (specifically) developed a variety of enzyme systems to degrade these compounds. Dehalogenations are of critical importance. Various heavily chlorinated compounds are not easily biodegraded, although there are no obvious biochemical or thermodynamic reasons why microorganisms should not be able to grow with any halogenated compound. The very diversity of catabolic enzymes present in cultures that degrade halogenated aliphatics and the occurrence of molecular mechanisms for genetic adaptation serve as good starting points for the evolution of catabolic pathways for compounds that are currently still resistant to biodegradation.
Adaptation, Physiological↗
Cometabolic degradation of trichloroethylene by Pseudomonas cepacia G4 in a chemostat with toluene as the primary substrate.
Pseudomonas cepacia G4 is capable of cometabolic degradation of trichloroethylene (TCE) if the organism is grown on certain aromatic compounds. To obtain more insight into the kinetics of TCE degradation and the effect of TCE transformation products, we have investigated the simultaneous conversion of toluene and TCE in steady-state continuous culture. The organism was grown in a chemostat with toluene as the carbon and energy source at a range of volumetric TCE loading rates, up to 330 mumol/liter/h. The specific TCE degradation activity of the cells and the volumetric activity increased, but the efficiency of TCE conversion dropped when the TCE loading was elevated from 7 to 330 mumol/liter/h. At TCE loading rates of up to 145 mumol/liter/h, the specific toluene conversion rate and the molar growth yield of the cells were not affected by the presence of TCE. The response of the system to varying TCE loading rates was accurately described by a mathematical model based on Michaelis-Menten kinetics and competitive inhibition. A high load of 3,400 mumol of TCE per liter per h for 12 h caused inhibition of toluene and TCE conversion, but reduction of the TCE load to the original nontoxic level resulted in complete recovery of the system within 2 days. These results show that P. cepacia can stably and continuously degrade toluene and TCE simultaneously in a single-reactor system without biomass retention and that the organism is more resistant to high concentrations and shock loadings of TCE than Methylosinus trichosporium OB3b.
Bacteriological Techniques↗
Influence of substituents on reductive dehalogenation of 3-chlorobenzoate analogs.
The biochemical effects of aryl substituents on the reductive dechlorination of 3-chlorobenzoate analogs were quantified with (i) a stable 3-chlorobenzoate-grown methanogenic sludge enrichment, (ii) Desulfomonile tiedjei DCB-1, isolated from this enrichment and able to catalyze the reductive dechlorination of 3-chlorobenzoate, and (iii) a defined 3-chlorobenzoate-degrading methanogenic consortium with D. tiedjei as the key dechlorinating organism. The addition of hydrogen stimulated the dechlorination rate in the consortium. The extent of this stimulation depended on the substituent. The data were evaluated with various sets of substituent constants compiled for the Hammett equation. None of the sets yielded a satisfactory correlation between experimental values and theoretical constants. This suggests that the microbially catalyzed reductive dechlorination of 3-chlorobenzoate cannot be described simply as either a nucleophilic or an electrophilic substitution reaction. Nevertheless, observations that the presence of a para-amino or -hydroxy group inhibited the rate of dechlorination suggest that the rate-limiting step in the reductive dechlorination of 3-chlorobenzoate is a nucleophilic attack on the negatively charged pi electron cloud around the benzene nucleus.
Journal Article↗
Reductive dechlorination of 3-chlorobenzoate is coupled to ATP production and growth in an anaerobic bacterium, strain DCB-1.
Thermodynamic data that the reductive dechlorination of 3-chlorobenzoate is exergonic have led to the hypothesis that this reaction yields biologically useful energy. This hypothesis was tested with strain DCB-1, a dehalogenating bacterium. The organism was grown under strictly anaerobic conditions in vitamin-amended mineral medium with formate plus acetate as electron donor and 3-chlorobenzoate as electron acceptor. The cell yield increased stoichiometrically to the amount of 3-chlorobenzoate dechlorinated. No growth was observed in the absence of 3-chlorobenzoate, or when 3-chlorobenzoate was replaced by benzoate. To obtain further evidence on that energy is derived from dechlorination, 3-chlorobenzoate was added to starved cells. This amendment resulted in an increase in the ATP level of the cells at 10 nmol per mg protein versus 3 nmol per mg protein in non-amended controls. These data indicate that the reductive dehalogenation of chlorinated aromatic compounds can be coupled to a novel type of chemotrophy.
Adenosine Triphosphate↗
Isolation and characterization of a bacterium that mineralizes toluene in the absence of molecular oxygen.
A bacterium tentatively identified as a Pseudomonas sp. was isolated from a laboratory aquifer column in which toluene was degraded under denitrifying conditions. The organism mineralized toluene in pure culture in the absence of molecular oxygen. In carbon balance studies using [ring-UL-14C]toluene, more than 50% of the radioactivity was recovered as 14CO2. Nitrate and nitrous oxide served as electron acceptors for toluene mineralization. The organism was also able to degrade m-xylene, benzoate, benzaldehyde, p-cresol, p-hydroxy-benzaldehyde, p-hydroxybenzoate and cyclohexanecarboxylic acid in the absence of molecular oxygen.
Anaerobiosis↗
Acetate inhibition of methanogenic, syntrophic benzoate degradation.
Acetate inhibited benzoate degradation by a syntrophic coculture of an anaerobic benzoate degrader (strain BZ-2) and Methanospirillum strain PM-1; the apparent K(i) for acetate was approximately 40 mM. The addition of acetate resulted in a decrease in the hydrogen concentration in the coculture, indicating that phenomena related to interspecies hydrogen transfer affected this value and that the effect of acetate on the benzoate-degrading partner was probably greater than the apparent K(i) for the coculture suggests.
Journal Article↗
Hopping ionic conductivity in Ce-doped SrF2. I. Ionic thermocurrent results.
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Journal Article↗
Growth yield increase linked to reductive dechlorination in a defined 3-chlorobenzoate degrading methanogenic coculture.
The microbially mediated reductive dehalogenation of aromatic compounds is potentially important in removal of chlorinated aromatic compounds from the environment. Thermodynamic data are presented which show that the reductive dechlorination of 3-chlorobenzoate to benzoate is exergonic, which led to the hypothesis that reductive elimination of chlorine from 3-chlorobenzoate yields biologically useful energy. In the present paper this hypothesis is tested. Experimental data were obtained with a defined 3-chlorobenzoate degrading methanogenic consortium. These data showed that (i) the molar growth yield of a defined 3-chlorobenzoate degrading consortium increased from 4.9 g protein per mol benzoate metabolized to 6.8 g protein per mol 3-chlorobenzoate when 3-chlorobenzoate replaced benzoate as energy source, and that (ii) the ATP level in starved consortium cells was twice as high when the cells were fed 3-chlorobenzoate than when fed benzoate. These observations show that the electrochemical potential between the redox partners of the H+/H2 (electron-donating) and 3-chlorobenzoate/benzoate (electron-accepting) couples is a potential source of energy and are consistent with the hypothesis that reductive dechlorination of aromatic compounds is coupled to a novel type of microbial chemotrophy.
Adenosine Triphosphate↗
Comparison of methane production rate and coenzyme f(420) content of methanogenic consortia in anaerobic granular sludge.
The coenzyme F(420) content of granular sludge grown on various substrates and substrate combinations was measured, and the potential of the sludge to form methane (maximum specific methane production rate) from hydrogen, formate, acetate, propionate, and ethanol was determined. The F(420) content varied between 55 nmol g of volatile suspended solids (VSS) for sludge grown on acetate and 796 nmol g of VSS for sludge grown on propionate. The best correlation was found between the F(420) content and the potential activity for methane formation from formate; almost no correlation, however, was found with acetate as the test substrate. The ratio between the potential methanogenic activities (qch(4)) of sludges grown on various substrates and their F(420) content was in general highest for formate (48.2 mumol of CH(4) mumol of F(420) min) and lowest for propionate (6.9 mumol of CH(4) mumol of F(420) min) as test substrates. However, acetate-grown granular sludge with acetate as test substrate showed the highest ratio, namely, 229 mumol of CH(4) mumol of F(420) min. The data presented indicate that the F(420) content of methanogenic consortia can be misleading for the assessment of their potential acetoclastic methanogenic activity.
Journal Article↗
Methanogenesis in an Upflow Anaerobic Sludge Blanket Reactor at pH 6 on an Acetate-Propionate Mixture.
High-rate anaerobic digestion can be applied in upflow anaerobic sludge blanket reactors for the treatment of various wastewaters. In upflow anaerobic sludge blanket reactors, sludge retention time is increased by a natural immobilization mechanism (viz. the formation of a granular type of sludge). When this sludge is cultivated on acid-containing wastewater, the granules mainly consist of an acetoclastic methanogen resembling Methanothrix soehngenii. This organism grows either in rods or in long filaments. Attempts to cultivate a stable sludge consisting predominantly of Methanosarcina sp. on an acetate-propionate mixture as substrate by lowering the pH from 7.5 during the start-up to approximately 6 failed. After 140 days of continuous operation of the reactor a filamentous organism resembling Methanothrix soehngenii prevailed in the sludge. The specific methanogenic activity of this sludge on acetate-propionate was optimal at pH 6.6 to 6.8 and 7.0 to 7.2, respectively.
Journal Article↗