| 1. |
- Langenheder, Silke, et al.
(author)
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Salinity as a structuring factor for the composition and performance of bacterioplankton degrading riverine DOC
- 2003
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In: FEMS Microbiology Ecology. - 0168-6496 .- 1574-6941. ; 45:2, s. 189-202
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Journal article (peer-reviewed)abstract
- The impact of salinity on the composition and functional performance (biomass production, growth efficiency and growth rates) of bacterial communities was investigated using batch cultures growing on dissolved organic carbon from a river draining into the Northern Baltic Sea. The cultures were adjusted to riverine or estuarine salinity levels and inoculated with bacteria from these two environments. Bacterial growth efficiencies differed in response to salinity and the origin of the inoculum. When salinity was adjusted to correspond to the salinity at the site where the inoculum was retrieved, growth efficiency was relatively high (11.5 +/- 2.6%). However, when bacteria were confronted with a shift in salinity, growth efficiency was lower (7.5 +/- 2.0%) and more of the utilized carbon was respired. In contrast, growth rates were higher when bacteria were exposed to a change in salinity. The composition of the bacterial communities developing in the batch cultures differed, as shown by 16S rDNA DGGE, depending on the origin of the inoculum and salinity. Reverse and direct DNA-DNA hybridization revealed salinity optima in the growth of specific bacterial strains as well as broader phylogenetic groups. Strains belonging to the alpha- and beta-Proteobacteria, Actinobacteria and gamma-Proteobacteria other than the genus Pseudomonas showed higher relative abundance under freshwater conditions, whereas strains of the genus Pseudomonas and the Cytophaga-Flavobacterium-Bacteroides group were favored by estuarine conditions. Generally, our results demonstrate functional changes associated with changes in community composition. We suggest that even moderate changes in salinity affect bacterial community composition, which subsequently leads to altered growth characteristics. (C) 2003 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.
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| 2. |
- Börjesson, Gunnar, et al.
(author)
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Microbial oxidation of CH4 at different temperatures in landfill cover soils
- 2004
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 0168-6496 .- 1574-6941. ; 48:3, s. 305-312
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Journal article (peer-reviewed)abstract
- Biological oxidation of CH4 is an important constraint on the emission of this gas from areas, such as landfills to the atmosphere. We studied the effect of temperature on methanotrophic bacteria in three different landfill cover soils, incubated in the laboratory. In samples of a young cover, consisting of wood chips and sewage sludge, the phospholipid fatty acids (PLFAs), regarded as biomarkers for type I methanotrophs (16:1?5t, 16:1?6c, 16:1?8c), primarily increased at low temperatures (5-10°C). On the other hand, the PLFA marker for type II methanotrophs (18:1?8c) was highly elevated only at 20°C. These results suggest that temperature can determine the selection of methanotroph populations. © 2004 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.
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| 3. |
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| 4. |
- Eriksson, M., et al.
(author)
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Bacterial growth and biofilm production on pyrene
- 2002
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 0168-6496 .- 1574-6941. ; 40:1, s. 21-27
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Journal article (peer-reviewed)abstract
- Enrichment cultures inoculated with Arctic soil yielded a biofilm that grew on pyrene and phenanthrene. In a 60-day period, the biofilm degraded 20 mug ml(-1) pyrene or 39 mug ml(-1) phenanthrene. Single colonized pyrene crystals (approximately 1.5 x 0.75 X 0.35 mm) yielded 10(11) culturable heterotrophs and 10(5) biofilm propagules. Analysis of ribosomal intergenic spacers identified six phylotypes in a clone library from the pyrene biofilm. Analysis of 16S rRNA gene sequences indicated that the phylotypes. in order of decreasing abundance, are most closely related to members of the genera Polaromonas, Sphingomonas, Alcaligenes, Caulobacter and Variovorax. Two isolates capable of growth on pyrene. both Pseudomonas spp., were obtained from the pyrene enrichment culture. Growth of microbial biofilms on polycyclic aromatic hydrocarbons has not been reported previously, and this mode of growth may have important effects on substrate uptake.
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| 5. |
- Germain, K, et al.
(author)
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Colonisation of poplar trees by gfp-expressing bacterial endophytes
- 2004
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In: FEMS Microbiology Ecology. - 0168-6496. ; 48:1, s. 109-118
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Journal article (peer-reviewed)abstract
- With the exception of nitrogen fixing bacteria, there is little known about the colonisation patterns or population sizes of bacterial endophytes in deciduous trees. This study describes the isolation, identification, construction and re-colonisation patterns of three green fluorescent protein(gfp):kanamycinR labelled bacterial endophytes when re-introduced into poplar trees, their original host plant. Two of these endophytes showed considerable colonisation in the roots and stems of inoculated plants. gfp expressing cells of all three strains were observed to colonise the xylem tissue of the root. All three strains proved to be efficient rhizosphere colonisers, supporting the theory that the rhizosphere can serve as a source of bacterial endophytes.
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| 6. |
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| 7. |
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| 8. |
- Jernberg, Cecilia, et al.
(author)
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Impact of 4-chlorophenol contamination and/or inoculation with the 4-chlorophenol-degrading strain, Arthrobacter chlorophenolicus A6L, on soil bacterial community structure
- 2002
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 0168-6496 .- 1574-6941. ; 42:3, s. 387-97
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Journal article (peer-reviewed)abstract
- The 4-chlorophenol-degrading strain, Arthrobacter chlorophenolicus A6L (chromosomally tagged with the firefly luciferase gene, luc) was inoculated into 4-chlorophenol-contaminated soil to assess the impact of bioaugmentation with a biodegrading strain on the indigenous microbiota. Simultaneously, the impact of 4-chlorophenol alone, or inoculation with A. chlorophenolicus into non-contaminated soil, was addressed. Using terminal restriction fragment length polymorphism (T-RFLP) several significant changes were detected in community fingerprint patterns obtained from soil microcosms treated under the different conditions. The relative abundances of some populations, as judged by the relative intensity of terminal restriction fragments, were significantly impacted by either 4-chlorophenol, A. chlorophenolicus inoculation, or by a combination of both inoculation and 4-chlorophenol contamination. Some populations were significantly stimulated and others were significantly repressed when compared to control soil with no additions. For several peaks, the positive or negative impact imposed by the treatments increased over the 13-day incubation period. Some members of the bacterial community were specifically sensitive to A. chlorophenolicus inoculation or to 4-chlorophenol contamination, whereas other populations remained relatively unaffected by any of the treatments. The A. chlorophenolicus inoculum was also monitored by T-RFLP and was found to have a significantly higher relative abundance in soil contaminated with 4-chlorophenol. These results were substantiated by a high correlation to luciferase activity measurements and the number of colony forming units of the inoculum. Therefore, the A. chlorophenolicus A6L population was positively stimulated by the presence of the 4-chlorophenol substrate (180 microg g(-1) soil) that it catabolized during the first 8 days of the incubation period as a carbon and energy source. Together, these results demonstrate that specific populations in the soil bacterial community rapidly fluctuated in response to specific disturbances and the resulting shifts in the community may therefore represent an adjustment in community structure favoring those populations best capable of responding to novel stress scenarios.
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| 9. |
- Maraha, Ninwe, et al.
(author)
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Monitoring physiological status of GFP-tagged Pseudomonas fluorescens SBW25 under different nutrient conditions and in soil by flow cytometry
- 2004
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 0168-6496 .- 1574-6941. ; 51:1, s. 123-132
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Journal article (peer-reviewed)abstract
- Pseudomonas fluorescens SBW25, a plant growth promoting bacterium. has been widely studied due to its potential as an inoculum for improving crop yields. Environmental inoculants are usually applied oil seeds or directly to soil and to effectively promote plant growth they need to be viable and active. However, it is difficult to study the physiological status of specific microorganisms in complex environments, such as soil. In this study, our aim was to use molecular tools to specifically monitor the physiological status of P. fluorescens SBW25 in soil and ill pure cultures incubated under different nutritional conditions. The cells were previously tagged with marker genes (encoding green fluorescent protein and bacterial luciferase) to specifically track the cells in environmental samples. The physiological status of the cells was determined using the viability stains 5-cyano-2,3-ditolyl-tetrazolium chloride (CTC) and propidium iodide (PI), which stain active and dead cells, respectively. Luciferase activity was used to monitor the metabolic activity of the population. Most of the cells died after incubation for nine days in nutrient rich medium. By contrast when incubated under starvation conditions, most of the population was not stained with CTC or PI (i.e. intact but inactive cells), indicating that most of the cells were presumably dormant. In soil, a large fraction of the SBW25 cell population became inactive and died, as determined by a decline in luciferase activity and CTC-stained cells, an increase in PI-stained cells, and an inability of the cells to be cultured oil agar medium. However, approximately 60% of the population was unstained, presumably indicating that the cells entered a state of dormancy in soil similar to that observed under starvation conditions in pure cultures. These results demonstrate the applicability of this approach for monitoring the physiological status of specific cells under stress conditions, such as those experienced by environmental inoculants in soil.
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| 10. |
- Oquist, M. G., et al.
(author)
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Nitrous oxide production in a forest soil at low temperatures - processes and environmental controls
- 2004
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In: Fems Microbiology Ecology. - : Oxford University Press (OUP). - 0168-6496 .- 1574-6941. ; 49:3, s. 371-378
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Journal article (peer-reviewed)abstract
- Recent investigations have highlighted the relative importance of the winter season for emissions of N2O from boreal soils. However, our understanding of the processes and environmental controls regulating these emissions is fragmentary. Therefore, we investigated the potential for, and relative importance of, N2O formation at temperatures below 0 degreesC in laboratory experiments involving incubations of a Swedish boreal forest soil. Our results show that frozen soils have a high potential for N2O formation and subsequent emission. Net N2O production rates at -4 degreesC equaled those observed at +10 to +15 degreesC at moisture contents >60% of the soil's water-holding capacity. The source of this N2O was found to be denitrification occurring in anoxic microsites in the frozen soil and temperature per se did not control the denitrification rates at temperatures around 0 degreesC. Furthermore, both net nitrogen-mineralisation and nitrification were observed in the frozen soil samples. Based on these findings we propose a conceptual model for the temperature response of N2O formation in soils at low temperatures. (C) 2004 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.
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