| 1. |
- Bengtsson, Göran, et al.
(author)
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Contribution of suspended and sorbed groundwater bacteria to degradation of dissolved and sorbed aniline
- 2001
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In: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 1432-0614 .- 0175-7598. ; 57:1-2, s. 234-241
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Journal article (peer-reviewed)abstract
- The influence of sorption on the mineralisation of 50 mug aniline l(-1) was examined in an aquifer material under batch conditions. The study was designed to distinguish the rates and extent of biodegradation of the sorbed and the dissolved trace organic and the contribution of sorbed and suspended bacteria to the degradation. Four different mathematical models were developed with different assumptions about the partitioning of aniline degradation and bacterial activity between the solid and the aqueous phases. The models were developed by combining an expression for logistic growth of the degrading population with Michaelis-Menten kinetics for the transformation of aniline. It was tested by a series of laboratory experiments conducted with C-14-labelled aniline, aseptically treated aquifer sand and filter-sterilised groundwater in different proportions and bacteria isolated from pristine groundwater. Model evaluation of the experimental data suggested that the fate of aniline was mainly controlled by suspended bacteria degrading both the dissolved and sorbed fractions. The degradation was slow. with a first-order degradation rate equal to 10(-6) h(-1).
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| 2. |
- Bengtsson, Göran, et al.
(author)
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Degradation of dissolved and sorbed 2,4-dichlorophenol in soil columns by suspended and sorbed bacteria.
- 2001
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In: Biodegradation. - 0923-9820. ; 12:6, s. 32-419
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Journal article (peer-reviewed)abstract
- The influence of sorption of bacteria, as well as 2,4-dichlorophenol (2,4-DCP), on the mineralization of 100 microg l(-1) of the organic compound was examined in an aquifer material under advective flow conditions (column displacement technique). The study was designed to distinguish the rates and extent of biodegradation of the sorbed and the dissolved trace organic and the contribution of sorbed and suspended bacteria to the degradation. The degradation of dissolved 2,4-DCP was significantly faster than the degradation of the same compound sorbed to the solids, and suspended bacteria degraded the dissolved compound at a higher rate than sorbed bacteria, also on a per cell basis. The suspended bacteria degraded 8-12% of the added dissolved 2.4-DCP, while sorbed bacteria made a smaller contribution by degrading about 5% of sorbed 2,4-DCP. No degradation was seen with sorbed 2,4-DCP and suspended bacteria, and a marginal contribution was made by sorbed bacteria on the degradation of dissolved 2,4-DCP (<0.4%).
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| 3. |
- Bengtsson, Göran, et al.
(author)
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Dissolved organic carbon dynamics in the peat-streamwater interface
- 2004
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In: Biogeochemistry. - 1573-515X. ; 70:1, s. 93-116
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Journal article (peer-reviewed)abstract
- A series of experiments were conducted to address the fate of dissolved organic carbon (DOC) in the peat - stream interface zone linking a minerotrophic poor fen and an ombrotrophic mire with surrounding stream water in the drainage area of Lake Ortrasket in northern Sweden. Transport and mineralisation of DOC were quantified in peat - stream interface cores in response to variations in pore water velocity, DOC concentration and the molecular size and source of DOC. Mineralisation and CH4 production were positively correlated with pore water velocity at rates between 0.08 and 0.20 cm h(-1) and negatively correlated at rates between 0.20 and 0.40 cm h(-1). The DOC concentration of the effluent from the peat cores was independent of the pore water velocity but proportional to the DOC concentration of the source water. Higher concentrations of DOC were exported from than imported to the peat cores, and the cores exported DOC molecules of smaller average molecular size than received. Carbon mineralisation in the peat, assessed in a static system, was independent of the concentration of DOC. DOC with a nominal cutoff at 100 Da was mineralised faster by streamwater bacteria than DOC dialysed with a cutoff at 3500 Da, and their mineralisation rate was positively correlated with the DOC concentration. Streamwater bacteria mineralised streamwater DOC at a lower rate than the peat - stream interface zone pore water DOC. The pattern of velocity dependence of mineralisation was the same for both sources of peat DOC but the mineralisation rates, average molecular size, and bioavailability of DOC were different, emphasising the importance of the compositional heterogeneity of the peat - stream interface zone for the DOC budget of streamwater.
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| 4. |
- Bengtsson, Göran, et al.
(author)
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Effects of carbon substrate enrichment and DOC concentration on biodegradation of PAHs in soil
- 2003
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In: Journal of Applied Microbiology. - : Oxford University Press (OUP). - 1364-5072 .- 1365-2672. ; 94:4, s. 608-617
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Journal article (peer-reviewed)abstract
- Aims: Two common reasons to explain slow environmental biodegradation of polycyclic aromatic hydrocarbons (PAHs), namely lack of appropriate carbon sources for microbial growth and limited bioavailability of PAHs, were tested in a laboratory bioassay using a creosote-contaminated soil. Methods and Results: The soil, containing a total of 8 mg g(-1) of 16 PAHs, was sieved and incubated in bottles for 45 days. The first explanation was tested by enrichment with the analogue anthracene and the non-analogue myristic acid, and both failed to stimulate degradation of all PAHs except anthracene. The second explanation was tested by addition of different concentrations of dissolved organic carbon (DOC), with effects depending on the DOC concentration and the molecular size of the PAH. The degradation was enhanced from 10 to 35% for 12 PAHs when the soil was saturated. The degraded amounts of individual PAHs were proportional to their concentration in the soil. Conclusions: The slow in situ degradation of PAHs was enhanced by more than three times by adding water as a solvent. Addition of DOC facilitated the degradation of four- to six-ring PAHs. Significance and Impact of Study: Bioremediation of PAH-contaminated sites may be facilitated by creating water-saturated conditions but retarded by addition of other carbon substrates, such as analogue compounds.
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| 5. |
- Bengtsson, Göran, et al.
(author)
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Fate of N-15 labelled nitrate and ammonium in a fertilized forest soil
- 2000
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In: Soil Biology & Biochemistry. - 0038-0717. ; 32:4, s. 545-557
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Journal article (peer-reviewed)abstract
- The possibility that long-term atmospheric nitrogen pollution and fertilization of forest soil may serve as a basis for adaptation for enhanced transformation rates of NO3- and NH4+ in soil. bacteria was elucidated in a laboratory bioassay. Bacteria extracted from soils that had been fertilized at various rates for the last 30 yr were characterised with respect to their capability to reduce or oxidise different nitrogen sources. The same soils were used under oxic or anoxic conditions to quantify denitrification, dissimilatory nitrate reduction to ammonium (DNRA) and nitrification. (NO3-)-N-15 and (NH4+)-N-15 were added as tracers to the soils, which were incubated in bottles for 3 to 5 d. Concentrations of (N2O)-N-15 in headspace and (NO3-)-N-15 and (NH4+)-N-15 in soil extracts were determined by gas chromatography-mass spectrometry. Total numbers of bacteria were similar in all soils and ranged from 3 to 4 x 10(8) cells g(-1) d.wt. of soil. Between 50 and 70% of the isolated strains were capable of reducing nitrate and the majority of them reduced nitrate to ammonium. About 0.01 parts per thousand of all isolates were classified as nitrifiers. Both nitrate reducers and nitrifiers were more common in fertilized soils than in the unfertilized control soil. The foremost fate of added (NO3-)-N-15 and (NH4+)-N-15 in all soils was immobilisation. More than 85% was immobilised in anoxic soils and between 64 and 97% in the oxic soils, with the lowest quantities in fertilized soils. As regards the remaining, non-immobilised N, DNRA dominated over denitrification, as could be expected from the higher frequency of ammonifying bacteria compared with denitrifiers. There was no obvious relationship between NH4+ produced and the amount of fertilizer applied, whereas denitrification was negatively correlated with the amount of fertilizer applied. Nitrifying activity was low in all soils with no obvious relationship between NO3- produced and fertilizer applied. Hence, no correlation was found between the relative abundance of N transforming bacteria and the transformation activity. The N flux followed essentially the same pattern as that seen for product formation. The DNRA Aux was higher than that of both denitrification and nitrification. DNRA and denitrification fluxes were highest in the control soil, whereas the nitrification flux was low in all soils. The absence of evidence for adaptation to enhanced rates of transformation of NO3- and NH4+ in soil bacteria exposed to long-term N fertilization is reflected by the low concentration of extractable inorganic N in the fertilized soils. As a consequence of the quantitative importance of immobilization of added N, differences in physiological capacity evolved in soil bacteria to immobilize and mobilise N may determine the rates by which inorganic N is available for plant growth or lost to groundwater and air. (C) 2000 Elsevier Science Ltd. All rights reserved.
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| 6. |
- Bengtsson, Göran, et al.
(author)
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Gross nitrogen mineralization-, immobilization-, and nitrification rates as a function of soil C/N ratio and microbial activity
- 2003
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In: Soil Biology & Biochemistry. - 0038-0717. ; 35:1, s. 143-154
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Journal article (peer-reviewed)abstract
- A laboratory experiment was designed to challenge the idea that the ON ratio of forest soils may control gross N immobilization, mineralization, and nitrification rates. Soils were collected from three deciduous forests sites varying in C/N ratio between 15 and 27. They were air-dried and rewetted to induce a burst of microbial activity. The N transformation rates were calculated from an isotope dilution and enrichment procedure, in which (NH4Cl)-N-15 or (NaNO3)-N-15 was repeatedly added to the soils during 7 days of incubation. The experiments suggested that differences in gross nitrogen immobilization and mineralization rates between the soils were more related to the respiration rate and ATP content than to the C/N ratio. Peaks of respiration and ATP content were followed by high rates of mineralization and immobilization, with 1-2 days of delay. The gross immobilization of NH4+ was dependent on the gross mineralization and one to two orders of magnitude larger than the gross NO3- immobilization. The gross nitrification rates were negatively related to the ATP content and the C/N ratio and greatly exceeding the net nitrification rates. Taken together, the observations suggest that leaching of nitrate from forest soils may be largely dependent on the density and activity of the microbial community.
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| 7. |
- Bengtsson, Göran, et al.
(author)
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Irregular walks and loops combines in small-scale movement of a soil insect : implications for dispersal biology
- 2004
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In: Journal of Theoretical Biology. - : Elsevier BV. - 0022-5193 .- 1095-8541. ; 231:2, s. 299-306
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Journal article (peer-reviewed)abstract
- Analysis of small-scale movement patterns of animals we may help to understand and predict movement at a larger scale, such as dispersal, which is a key parameter in spatial population dynamics. We have chosen to study the movement of a soil-dwelling Collembola, Protaphorura armata, in an experimental system consisting of a clay surface with or without physical obstacles. A combination of video recordings, descriptive statistics, and walking simulations was used to evaluate the movement pattern. Individuals were found to link periods of irregular walk with those of looping in ahomogeneous environment as well as in one structured to heterogeneity by physical obstacles. The number of loops varied between 0 and 44 per hour from one individual to another and some individuals preferred to make loops by turning right and others by turning left. P. armata spent less time at the boundary of small obstacles compared to large, presumably because of a lower probability to track the steepness of the curvature as the individual walks along a highly curved surface. Food deprived P. armata had amore winding movement and made more circular loops than those that were well fed. The observed looping behaviour is interpreted in the context of systematic search strategies and compared with similar movement patterns found in other species.
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| 8. |
- Bengtsson, Göran, et al.
(author)
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Persistence of plasmid RP4 in Pseudomonas putida and loss of its expression of antibiotic resistance in a groundwater microcosm
- 2004
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In: Atmospheric Environment. - : Elsevier BV. - 1352-2310. ; 36:6, s. 999-1008
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Journal article (peer-reviewed)abstract
- We examined the stability of plasmid RN and its expression of antibiotic-resistance genes in suspended and sorbed Pseudomonas putida in aquifer microcosms. Test tubes containing different proportions of sterilized aquifer soil and groundwater were inoculated with bacteria and incubated for up to 26 d. Serial dilutions were made to agar plates with or without antibiotics, to quantify the functional stability of the plasmid. The structural integrity of RN was examined by plasmid extraction, digestion with restriction enzymes, and agarose gel electrophoresis. The plasmid-borne resistance gene expression disappeared in 80-90% of the cells during day 1 of incubation in aquifer soil and then remained at that frequency throughout the experiment. The RP4 plasmid was present in cells without antibiotic-resistance gene expression, indicating that the observed loss of plasmid-encoded activity was most likely due to a reduction in expression of the resistance genes. The increased growth rate in groundwater amended with glucose and phosphate had no significant influence on plasmid loss or antibiotic-resistance expression, suggesting that plasmid loss and antibiotic-resistance expression were independent of the growth rate. Most of the reduction of resistance gene expression was associated with the presence of soil particles, and 70% of the resistance expression was retained in bacteria incubated for 1 d in groundwater alone. Bacteria sorbed to the soil particles had a lower frequency of expression of resistance genes than suspended bacteria, but the difference was not caused by sorbed inorganic or organic chemicals. Resistance gene expression was partly recovered in suspended bacteria after in vitro exposure to the antibiotics and after first isolating on agar without antibiotics and then replica plating to agar containing the antibiotics.
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| 9. |
- Bengtsson, Göran, et al.
(author)
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Predicting sorption of groundwater bacteria from size distribution, surface area, and magnetic susceptibility of soil particles
- 2001
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In: Water Resources Research. - 0043-1397. ; 37:6, s. 1795-1812
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Journal article (peer-reviewed)abstract
- Spatial heterogeneity of hydraulic and sorptive processes may have a strong impact on the mobility of bacteria in porous soils. Whereas heterogeneity at the microscopic solid particle/interstitial pore scale has been conceptually addressed by dividing the porous material into two or more coexisting sorbing fractions, field-scale spatial variability has been approached by developing stochastic methodologies for coupling advective flow and sorption reactions. This calls for an elucidation of correlations between certain soil parameters and sorption of bacteria, with the purpose of substituting tedious and labourious sorption measurements with indirect methods allowing more rapid screening of field samples. Sorption of two H-3-labeled strains of groundwater bacteria was examined in test tubes with sandy aquifer material and filter sterilized groundwater from the same aquifer. The aquifer particles were sieved to different size fractions (0-63, 63-106, 106-212, 212-500, 500-1000, and 1000-1500 mum) and mixtures thereof, and their specific surface area, magnetic susceptibility, and mineral composition were determined. Columns filled with the sieved or original aquifer material were saturated with groundwater, and the breakthrough of the labeled bacteria at a flow rate of 0.2 mL min(-1) was measured by liquid scintillation. Cell sorption to soil particles in test tube experiments was controlled by magnetic susceptibility, which characterizes the mineral surfaces primarily according to their iron content. In contrast, there was a negative nonlinear regression between the sorption coefficient and the particle size and a positive linear regression with the specific surface area, each with an R-2 Of similar to0.85 in the column experiments. The work demonstrates that sorption of groundwater bacteria to aquifer material of low organic carbon content can be predicted from the particle size distribution or the specific surface area.
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| 10. |
- Bengtsson, Göran, et al.
(author)
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Reduced grazing rates in Daphnia pulex caused by contaminants: Implications for trophic cascades
- 2004
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In: Environmental Toxicology and Chemistry. - : Wiley. - 0730-7268 .- 1552-8618. ; 23:11, s. 2641-2648
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Journal article (peer-reviewed)abstract
- Ecotoxicological endpoints based on behavioral traits (e.g., predator avoidance, feeding, and locomotion) may be more sensitive and give more insights into patterns of sublethal toxicity than survivorship tests. In this study, the density-dependent grazing rate of Daphnia pulex pre-exposed to p,p'-dichlorodiphenyldichloroethylene (DDE) (insecticide metabolite) and glyphosate (herbicide), via water or a vector, Scenedesmus spp., was assayed in laboratory experiments. The phytoplankton biomass was estimated from the chlorophyll content, and the pesticide uptake and turnover pattern in Daphnia and Scenedestnus were determined from parallel experiments with a radiolabeled source. Scenedestnus spp. relative net growth rate was inversely and linearly related to the density of the grazer. Daphnia pulex exhibited significant reductions in grazing rate: 30% for those pre-exposed to p,p'DDE via water and 40% for D. pulex pre-exposed to glyphosate via Scenedesmus spp. Through the process of trophic cascading, this impaired grazing allowed Scenedesmus spp. to grow at higher rates, 70 and 60%, respectively. The reduced grazing efficiencies were associated with the treatments that gave the highest body burden of p,p'-DDE (70 mug/g dry wt) and the lowest of glyphosate (13 mg/g dry wt). The pattern of results suggests a toxic effect of p,p'-DDE on D. pulex and a growth enhancement of Scenedesmus spp. in response to nitrogen and phosphorus in glyphosate excreted by D. pulex.
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