| 1. |
- Székely, Anna J., et al.
(author)
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The importance of species sorting in bacterial communities differs between habitat generalists and specialists
- 2014
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 0168-6496 .- 1574-6941. ; 87:1, s. 102-112
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Journal article (peer-reviewed)abstract
- Recent studies have shown that the spatial turnover of bacterial communities, that is, beta-diversity, is determined by a combination of different assembly mechanisms, such as species sorting, that is, environmental filtering, and dispersal-related mechanisms. However, it is currently unclear to what extent the importance of the different mechanisms depends on community traits. Here, we implemented a study using a rock pool metacommunity to test whether habitat specialization of bacterial taxa and groups or their phylogenetic identity influenced by which mechanisms communities were assembled. Ingeneral, our results show that species sorting was the most important assembly mechanism. However, we found that a larger fraction of the variation in bacterial community composition between pools could be explained by environmental factors in case of habitat generalists, that is, taxa that were widespread and abundant in the metacommunity, compared with habitat specialists, that is, taxa that had a more restricted distribution range and tended to be rare. Differences in assembly mechanisms were observedbetween different major phyla and classes. However, also here, a larger fraction of the variation incommunity composition among pools could be explained for taxonomic groups that contained on average more habitat generalists. In summary, our results show that species sorting is stronger for themost common taxa, indicating that beta-diversity along environmental gradients can be adequately described without considering rare taxa.
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| 2. |
- Bengtson, Per, et al.
(author)
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Links between methanotroph community composition and CH(4) oxidation in a pine forest soil
- 2009
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 70:3, s. 356-366
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Journal article (peer-reviewed)abstract
- The main gap in our knowledge about what determines the rate of CH(4) oxidation in forest soils is the biology of the microorganisms involved, the identity of which remains unclear. In this study, we used stable-isotope probing (SIP) following (13)CH(4) incorporation into phospholipid fatty acids (PLFAs) and DNA/RNA, and sequencing of methane mono-oxygenase (pmoA) genes, to identify the influence of variation in community composition on CH(4) oxidation rates. The rates of (13)C incorporation into PLFAs differed between horizons, with low (13)C incorporation in the organic soil and relatively high (13)C incorporation into the two mineral horizons. The microbial community composition of the methanotrophs incorporating the (13)C label also differed between horizons, and statistical analyses suggested that the methanotroph community composition was a major cause of variation in CH(4) oxidation rates. Both PLFA and pmoA-based data indicated that CH(4) oxidizers in this soil belong to the uncultivated 'upland soil cluster alpha'. CH(4) oxidation potential exhibited the opposite pattern to (13)C incorporation, suggesting that CH(4) oxidation potential assays may correlate poorly with in situ oxidation rates. The DNA/RNA-SIP assay was not successful, most likely due to insufficient (13)C-incorporation into DNA/RNA. The limitations of the technique are briefly discussed.
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| 3. |
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| 4. |
- de Vries, Franciska T., et al.
(author)
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High turnover of fungal hyphae in incubation experiments
- 2009
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 67:3, s. 389-396
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Journal article (peer-reviewed)abstract
- Soil biological studies are often conducted on sieved soils without the presence of plants. However, soil fungi build delicate mycelial networks, often symbiotically associated with plant roots (mycorrhizal fungi). We hypothesized that as a result of sieving and incubating without plants, the total fungal biomass decreases. To test this, we conducted three incubation experiments. We expected total and arbuscular mycorrhizal (AM) fungal biomass to be higher in less fertilized soils than in fertilized soils, and thus to decrease more during incubation. Indeed, we found that fungal biomass decreased rapidly in the less fertilized soils. A shift towards thicker hyphae occurred, and the fraction of septate hyphae increased. However, analyses of phospholipid fatty acids (PLFAs) and neutral lipid fatty acids could not clarify which fungal groups were decreasing. We propose that in our soils, there was a fraction of fungal biomass that was sensitive to fertilization and disturbance (sieving, followed by incubation without plants) with a very high turnover (possibly composed of fine hyphae of AM and saprotrophic fungi), and a fraction that was much less vulnerable with a low turnover (composed of saprotrophic fungi and runner hyphae of AMF). Furthermore, PLFAs might not be as sensitive in detecting changes in fungal biomass as previously thought.
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| 5. |
- Fernandez-Calvino, David, et al.
(author)
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Growth response of the bacterial community to pH in soils differing in pH
- 2010
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 73:1, s. 149-156
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Journal article (peer-reviewed)abstract
- The effect of pH on the instantaneous growth of soil bacterial communities was studied in five soils with different pH (4.5-7.8) using leucine (Leu) and thymidine (TdR) incorporation. The pH dependency of bacterial growth was modelled using three different unimodal functions, and the pH(opt) for growth and the pH range in which growth was > 50% of the optimal growth were compared. Leu and TdR incorporation yielded very similar results. The best fits were obtained using a third-degree polynomial function and the cardinal pH model. However, a simple second-degree function was adequate in most cases, yielding very similar pH(opt) values to the other two models. Bacterial growth was highly influenced by pH, showing optimum growth at a pH related to the soil pH. The lowest pH(opt) was found in the most acidic soil and the highest pH(opt) in the soil with the highest pH. The pH(opt) for bacterial growth was close to the soil pH measured in water, but higher (0.7-2.1 units) than the pH measured with 0.1 M KCl. The pH range in which bacterial growth was > 50% of that at optimum was, on average, 1.7 units below and above the optimum pH.
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| 6. |
- Hallbeck, Lotta, 1957, et al.
(author)
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Culture-dependent comparison of microbial diversity in deep granitic groundwater from two sites considered for a Swedish final repository of spent nuclear fuel
- 2012
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 81:1, s. 66-77
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Journal article (peer-reviewed)abstract
- Site selection for a spent nuclear fuel (SNF) repository required analysis of microbial abundance and diversity at two Swedish sites, Forsmark and Laxemar-Simpevarp. Information about sulphate-reducing bacteria (SRB) was required, as sulphide could corrode copper SNF canisters. Total number of cells (TNC) and ATP were analysed, and plate counts and most probable number (MPN) analyses were conducted using eight media based on different electron donors and acceptors for specific microorganism physiological groups. Groundwater chemical composition and Eh were analysed; sampling depths were 112-978 m below sea level. TNC was 5.5 × 103 to 4.7 × 105 cells mL-1, correlating with ATP concentrations. Culturability in TNC percentage was 0.01-35.9, averaging 5.12. Culturable numbers varied greatly between sample positions and uncorrelated with depth. SRB were found in 29 samples and were below detection in three; the MPN of SRB correlated negatively with Eh, as did the MPN of acetogens. Data indicated that microbial sulphate reduction was ongoing in many sampled aquifers; published stable isotope data and modelling results supported this observation. The sites did not differ significantly, but the large data range suggested that analysis of more samples would enable detailed evaluation of microbial processes and their relationship with geochemical information. © 2011 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.
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| 7. |
- Hammer, Edith, et al.
(author)
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Tit for tat? A mycorrhizal fungus accumulates phosphorus under low plant carbon availability.
- 2011
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 76, s. 236-244
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Journal article (peer-reviewed)abstract
- The exchange of carbohydrates and mineral nutrients in the arbuscular mycorrhizal symbiosis must be controlled by both partners in order to sustain an evolutionarily stable mutualism. Plants down-regulate their carbon flow to the fungus when nutrient levels are sufficient, while the mechanism controlling fungal nutrient transfer is unknown. Here we show that the fungus accumulates nutrients when connected to a host that is of less benefit to the fungus, indicating a potential of the fungus to control the transfer of nutrients. We used a monoxenic in vitro model of root organ cultures associated with G. intraradices, in which we manipulated the carbon availability to the plant. We found that G. intraradices accumulated up to 7 times more nutrients in its spores, and up to 9 times more in its hyphae, when the carbon pool available to the associated roots was halved. The strongest effect was found for phosphorus, considered to be the most important nutrient in the arbuscular mycorrhizal symbiosis. Other elements such as potassium and chorine were also accumulated, but to a lesser extent, while no accumulation of iron or manganese was found. Our results suggest a functional linkage between carbon and phosphorus exchange.
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| 8. |
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| 9. |
- Iovieno, Paola, et al.
(author)
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Effect of drying and rewetting on bacterial growth rates in soil.
- 2008
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 65:3, s. 400-407
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Journal article (peer-reviewed)abstract
- The effect of soil moisture on bacterial growth was investigated, and the effects of rewetting were compared with glucose addition because both treatments increase substrate availability. Bacterial growth was estimated as thymidine and leucine incorporation, and was compared with respiration. Low growth rates were found in air-dried soil, increasing rapidly to high stable values in moist soils. Respiration and bacterial growth at different soil moisture contents were correlated. Rewetting air-dried soil resulted in a linear increase in bacterial growth with time, reaching the levels in moist soil (10 times higher) after about 7 h. Respiration rates increased within 1 h to a level >10 times higher than that in moist soil. After the initial flush, there was a gradual decrease in respiration rate, while bacterial growth increased to levels twice that of moist soil 24 h after rewetting, and decreased to levels similar to those in moist soil after 2 days. Adding glucose resulted in no positive effect on bacterial growth during the first 9 h, despite resulting in more than five times higher respiration. This indicated that the initial increase in bacterial growth after rewetting was not due to increased substrate availability.
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| 10. |
- Javelle, Arnaud, et al.
(author)
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Ammonium and methylamine transport by the ectomycorrhizal fungus Paxillus involutus and ectomycorrhizas
- 1999
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 30:4, s. 355-366
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Journal article (peer-reviewed)abstract
- Using [C-14]methylamine as an analogue of ammonium, the kinetics and the energetics of NH: transport were studied in the ectomycorrhizal fungus, Paxillus involutus (Batsch) Fr. The apparent half-saturation constant (K-m) and the maximum uptake rate (V-max) for the carrier-mediated transport derived from the Eadie-Hofstee transformation were 180 mu M and 380 nmol (mg dry wt)(-1) min(-1,) respectively. Both pH dependence and inhibition by protonophores indicate that methylamine transport in P. involutus was dependent on the electrochemical H+ gradient. Both long-term and short-term uptake experiments were consistent with regulation of ammonium/methylamine transport processes by the presence of an organic nitrogen source. Analysis of methylamine uptake by different P. involutus isolates revealed no obvious trend in the uptake capacities in relation to N deposition at the collection site. Kinetic parameters were determined in P. involutus/Betula pendula (Roth.) axenic association and in detached mycorrhizal roots isolated from forest sites. Enhanced methylamine uptake in the presence of the fungal symbiont was demonstrated. Homogeneous V-max values were found for axenic and detached mycorrhizas, whereas K-m values showed greater variations. (C) 1999 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.
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| 11. |
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| 12. |
- Kritzberg, Emma, et al.
(author)
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Influence of dissolved organic matter source on lake bacterioplankton structure and function - implications for seasonal dynamics of community composition
- 2006
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 56:3, s. 406-417
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Journal article (peer-reviewed)abstract
- It has been suggested that autochthonous (internally produced) organic carbon and allochthonous (externally produced) organic carbon are utilized by phylogenetically different bacterioplankton. We examined the relationship between the source of organic matter and the structure and function of lake bacterial communities. Differences and seasonal changes in bacterial community composition in two lakes differing in their source of organic matter were followed in relation to environmental variables. We also performed batch culture experiments with amendments of various organic substrates, namely fulvic acids, leachates from algae, and birch and maple leaves. Differences in bacterial community composition between the lakes, analysed by terminal restriction fragment length polymorphism, correlated with variables related to the relative loading of autochthonous and allochthonous carbon (water colour, dissolved organic carbon, nutrients, and pH). Seasonal changes correlated with temperature, chlorophyll and dissolved organic carbon in both lakes. The substrate amendments led to differences in both structure and function, i.e. production, respiration and growth yield, of the bacterial community. In conclusion, our results suggest that the source of organic matter influences community composition both within and among lakes and that there may be a coupling between the structure and function of the bacterial community.
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| 13. |
- Ladygina, Natalia, et al.
(author)
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Diversity of bacteria associated with grassland soil nematodes of different feeding groups.
- 2009
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 69:1, s. 53-61
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Journal article (peer-reviewed)abstract
- Abstract The bacterial diversity associated with soil nematodes and its relationship with their feeding habits are as yet poorly understood. In the present study the diversity and abundance of bacteria from nematodes and their surrounding soil were analysed and compared. The nematodes were collected from a grassland soil and sorted into bacterial, fungal, plant, predatory and omnivore feeding groups and assigned to taxonomic groups. Total DNA was extracted from the nematodes and partial bacterial 16S rRNA genes were PCR amplified, cloned and sequenced. The abundance and composition of bacterial taxa differed between and within feeding groups. The lowest bacterial diversity was found in the predatory nematodes Prionchulus sp., whereas the highest bacterial diversity was associated with the bacterial-feeding nematode Acrobeles sp. The soil had a more diverse bacterial community than the communities found in the nematode groups. The 16S rRNA gene sequences of bacteria associated with nematodes did not overlap with those detected in soil as determined using the cloning screening approach. However, bacterial sequences identified from nematodes could be detected in the soil with targeted PCR. Our data suggest that the nematodes do not feed on the most abundant bacteria present in soil. Furthermore, several nematodes contained suspected bacterial symbionts and parasites.
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| 14. |
- Lehr, N A, et al.
(author)
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Antiamoebins, myrocin B and the basis of antifungal antibiosis in the coprophilous fungus Stilbella erythrocephala(syn. S-fimetaria)
- 2006
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 55:1, s. 105-112
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Journal article (peer-reviewed)abstract
- Antiamoebins I, III and XVI as well as several others in minor amounts were produced by four strains of the coprophilous fungus Stilbella erythrocephala (syn. S. fimetaria) in its natural substrate and in liquid culture. The total antiamoebin concentration in dung was 126-624 mu g g(-1) fresh weight, with minimum inhibitory concentrations against most other coprophilous fungi being at or below 100 mu g mL(-1). Myrocin B, not previously described from S. erythrocephala, was also produced, but only at low, nonfungicidal levels (<5.3 mu g g(-1)). No other antifungal substances were detected. It is concluded that antiamoebins are responsible for antibiosis in dung colonized by S. erythrocephala.
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| 15. |
- Lekberg, Ylva, et al.
(author)
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Plants as resource islands and storage units - adopting the mycocentric view of arbuscular mycorrhizal networks
- 2010
-
In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 74:2, s. 336-345
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Journal article (peer-reviewed)abstract
- The majority of herbaceous plants are connected by arbuscular mycorrhizal (AM) fungi in complex networks, but how this affects carbon (C) and phosphorus (P) allocation among symbionts is poorly understood. We utilized a monoxenic AM system where hyphae from donor roots colonized two younger receiver roots of varying C status. AM fungal C allocation from donor to receiver compartments was followed by measuring the 13C contents in fungal- and plant-specific lipids, and P movement from a hyphal compartment was traced using 33P. Four times more 13C was translocated from donor to C-limited receiver roots, but C remained in fungal tissue. Root C status did not influence the overall AM colonization, but arbuscule density was twice as high in non-C-limited roots, and they received 10 times more 33P. The number of hyphal connections between compartments did not influence C and P allocation. Interestingly, there were more fungal storage lipids, but fewer structural lipids inside C-limited roots. Our results indicate that AM colonization may poorly reflect host quality as C can be supplied from neighboring roots. A mycocentric view of the symbiosis is proposed where C-delivering hosts are resource islands for the exchange of P for C, and C-limited hosts are storage units.
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| 16. |
- Nylund, Göran M., 1974, et al.
(author)
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The red alga Bonnemaisonia asparagoides regulates epiphytic bacterial abundance and community composition by chemical defence
- 2010
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 0168-6496 .- 1574-6941. ; 71:1, s. 84-93
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Journal article (peer-reviewed)abstract
- Ecological research on algal-derived metabolites with antimicrobial activity has recently received increased attention and is no longer only aimed at identifying novel natural compounds with potential use in applied perspectives. Despite this progress, few studies have so far demonstrated ecologically relevant antimicrobial roles of algal metabolites, and even fewer have utilized molecular tools to investigate the effects of these metabolites on the natural community composition of bacteria. In this study, we investigated whether the red alga Bonnemaisonia asparagoides is chemically defended against bacterial colonization of its surface by extracting surface-associated secondary metabolites and testing their antibacterial effects. Furthermore, we compared the associated bacterial abundance and community composition between B. asparagoides and two coexisting macroalgae. Surface extracts tested at natural concentrations had broad-spectrum effects on the growth of ecologically relevant bacteria, and consistent with this antibacterial activity, natural populations of B. asparagoides had significantly lower densities of epibacteria compared with the coexisting algae. Terminal restriction fragment length polymorphism analysis further showed that B. asparagoides harboured surface-associated bacteria with a community composition that was significantly different from those on coexisting macroalgae. Altogether, these findings demonstrate that B. asparagoides produces surface-bound antibacterial compounds with a significant impact on the abundance and composition of the associated bacterial community.
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| 17. |
- Olsson, Pål Axel, et al.
(author)
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Carbon dynamics in mycorrhizal symbioses is linked to carbon costs and phosphorus benefits
- 2010
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 72:1, s. 123-131
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Journal article (peer-reviewed)abstract
- Abstract The nutrient and carbon (C) allocation dynamics in mycorrhizal hyphal networks cause variation in costs and benefits for individual plants and fungi and influence the productivity, diversity and C cycling in ecosystems. We manipulated light and phosphorus (P) availability in a pot experiment with Trifolium subterraneum colonised by the arbuscular mycorrhizal (AM) fungus Glomus intraradices. Stable (13)C-labelling was used to trace assimilated CO(2) to the mycorrhizal fungus in roots and soil using compound-specific isotope ratio mass spectrometry. We used the neutral lipid fatty acid 16:1omega5 as a signature for AM fungal storage lipids. Both P and shading reduced the AM fungal lipid accumulation in the intraradical mycelium, while only P reduced the amount of lipids in the extraradical mycelium. Recently assimilated plant C was only allocated to the mycorrhizal fungus to a small extent when plant mycorrhizal benefit was reduced by P fertilization, while increasing the plant C cost by shading did not reduce the C flow to the fungus. These results are of importance for our conception of mycorrhizal dynamics during periods of shade in nature.
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| 18. |
- Olsson, Pål Axel, et al.
(author)
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Ectomycorrhizal mycelia reduce bacterial activity in a sandy soil
- 1996
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 21:2, s. 77-86
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Journal article (peer-reviewed)abstract
- Bacterial activity was studied in a growth system containing Pinus contorta seedlings inoculated with different mycorrhizal fungi. Nylon nets enabled separation of soil compartments with extramatrical mycorrhizal hyphae from soil compartments with roots and mycelium. In three separate experiments bacterial activity, estimated as thymidine incorporation, was reduced in soils with Paxillus involutus hyphae compared to controls without mycorrhizal hyphae. This effect was found irrespective of compartments with and without roots were compared. Laccaria bicolor only reduced the activity in one of these three experiments. Thelephora terrestris (tested in two experiments), Laccaria proxima, Suillus variegatus and Hebeloma crustuliniforme (one experiment), also reduced the thymidine and leucine incorporation rates of bacteria. The reduction for these fungi varied between 20% and 50% in all experiments. Numbers of viable bacteria appeared to be reduced by T. terrestris, L. proxima, S. variegatus and H. crustuliniforme in one experiment, while no effect was seen in the other experiments.
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| 19. |
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| 20. |
- Pedersen, Karsten, 1952
(author)
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Influence of H2 and O2 on sulphate-reducing activity of a subterranean community and the coupled response in redox potential
- 2012
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 82:3, s. 653-665
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Journal article (peer-reviewed)abstract
- Deep Fennoscandian groundwater is anaerobic, reducing in character and populated by a large diversity of obligate and facultative anaerobic microorganisms. Concentrations of H2 and carbon monoxide are often 0.01-1 μM and of dissolved organic carbon (DOC) and methane 0.01-1 mM. Microbial activity involving these electron and energy donors may help keep deep groundwater anaerobic and reduced. H2 was added in concentrations of 0.1-10 mM to a sulphate-reducing community attached to crushed rock in groundwater under a pressure of 2.0 MPa and in situ geochemical conditions. Experiments reported a threshold concentration of approximately 1 μM H2 at which sulphate reduction ceased, despite the presence of DOC and acetate, suggesting that H2 was needed for sulphate-reducing activity. δ13C values of acetate and DOC data suggested that organic material was degraded to acetate by means of a heterotrophic process. New pressure-resistant micro-sensors for measuring Eh indicated an H2-concentration-dependent decrease in Eh. The investigated community rapidly mitigated the increase in Eh caused by repeated additions of 0.1-0.2 mM pulses of O2 as long as H2 was available. The results imply that sulphate reduction to sulphide with H2 may dominate sulphate-rich groundwater, which may have implications for metallic underground constructions. © 2012 Federation of European Microbiological Societies.
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| 21. |
- Pedersen, Karsten, 1952
(author)
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Subterranean microbial populations metabolize hydrogen and acetate under in situ conditions in granitic groundwater at 450 m depth in the Äspö Hard Rock Laboratory, Sweden
- 2012
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 81:1, s. 217-229
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Journal article (peer-reviewed)abstract
- Pressure-resistant circulating systems were constructed to enable the investigation of attached and unattached microbial populations under in situ pressure (2.5 MPa), diversity, dissolved gas and chemistry conditions. Three parallel flow cell cabinets were configured to allow observation of the effect on microbial metabolic activity of adding 3 mM hydrogen or 2.4 mM acetate, compared with an untreated control. Hydrogen addition reduced the generation time fourfold to 2 weeks, doubled the sulphide production rate and increased acetate production by approximately 50%. The acetate addition induced acetate consumption. The studied subterranean microbial processes appeared to proceed very slowly in terms of volume and time, although the results suggest that individual cells could be very active. Lytic bacteriophages are hypothesized to have caused this contradictive observation. Phages may consequently significantly reduce the rates of subterranean microbial processes. Furthermore, the results suggest that hydrogen from corroding underground constructions could induce significant local microbial activity and that the low concentrations of hydrogen often observed in pristine subterranean environments may support slow but sustainable microbial activity in deep groundwater. © 2012 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.
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| 22. |
- Rousk, Johannes, et al.
(author)
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Examining the fungal and bacterial niche overlap using selective inhibitors in soil.
- 2008
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 63:3, s. 350-358
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Journal article (peer-reviewed)abstract
- It is important to know the contributions of bacteria and fungi to decomposition in connection with both the structure of the food web and the functioning of the ecosystem. However, the extent of the competition between these groups of organisms is largely unknown. The bacterial influence on fungal growth in a soil system was studied by applying three different bacterial inhibitors - bronopol, tylosin and oxytetracycline - in a series of increasing concentrations, and comparing the resulting bacterial and fungal growth rates measured using leucine and acetate-in-ergosterol incorporation, respectively. Direct measurements of growth showed that fungi increased after adding inhibitors; the level of increase in fungal growth corresponded to that of the decrease in bacterial growth, irrespective of the bacterial inhibitor used. Similar antagonistic effects of the bacteria on fungal growth were also found after adding the bacterial inhibitors together with additional substrate (alfalfa or straw plant material). The resulting responses in bacterial and fungal growth indirectly indicated that the negative interaction between fungi and bacteria was mostly attributable to exploitation competition. The results of this study also emphasize the increased sensitivity of using growth-related, instead of biomass-based, measurements when studying bacterial and fungal interactions in soil.
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| 23. |
- Rousk, Johannes, et al.
(author)
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Fungal and bacterial growth in soil with plantmaterials of different C/N ratios
- 2007
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 62:3, s. 258-267
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Journal article (peer-reviewed)abstract
- Fungal (acetate-in-ergosterol incorporation) and bacterial (leucine/thymidine incorporation) growth resulting from alfalfa (C/N = 15) and barley straw (C/N = 75) addition was studied in soil microcosms for 64 days. Nitrogen amendments were used to compensate for the C/N difference between the substrates. Fungal growth increased to a maximum after 3–7 days, at five to eight times the controls, following the addition of straw, and three to four times the controls following the addition of alfalfa. After 20–30 days, the fungal growth rate converged with the controls, resulting in a cumulative fungal growth two to three times the controls following straw addition and about 20% higher than the controls following alfalfa addition. The bacterial growth rate reached rates five times the controls following alfalfa addition and twice that of the controls following straw addition after 3–7 days. It remained elevated after 64 days. The cumulative bacterial growth was two and four times the controls following straw and alfalfa addition, respectively. A negative correlation was found between N addition and bacterial growth, while N stimulated fungal growth. Thus, the C/N ratio of the additions (substrate and extra N) could not entirely explain the different results regarding fungal and bacterial growths. Respiration was not always related to the combined growth of the microorganisms, emphasizing the requirement for a better understanding of growth efficiencies of fungi and bacteria.
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| 24. |
- Rousk, Johannes, et al.
(author)
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Fungal and bacterial growth responses to N fertilization and pH in the 150-year 'Park Grass' UK grassland experiment.
- 2011
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 76, s. 89-99
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Journal article (peer-reviewed)abstract
- The effects of nitrogen (N) fertilization (0-150 kg N ha(-1) year(-1) since 1865) and pH (3.3-7.4) on fungal and bacterial growth, biomass and phospholipid fatty acid (PLFA) composition were investigated in grassland soils from the 'Park Grass Experiment', Rothamsted Research, UK. Bacterial growth decreased and fungal growth increased with lower pH, resulting in a 50-fold increase in the relative importance of fungi between pH 7.4 and 3.3. The PLFA-based fungal : bacterial biomass ratio was unchanged between pH 4.5 and 7.4, and decreased only below pH 4.5. Respiration and substrate-induced respiration biomass both decreased three- to fourfold with lower pH, but biomass concentrations estimated using PLFAs were unaffected by pH. N fertilization did not affect bacterial growth and marginally affected fungal growth while PLFA biomass marker concentrations were all reduced by higher N additions. Respiration decreased with higher N application, suggesting a reduced quality of the soil organic carbon. The PLFA composition was strongly affected by both pH and N. A comparison with a pH gradient in arable soil allowed us to generalize the pH effect between systems. There are 30-50-fold increases in the relative importance of fungi between high (7.4-8.3) and low (3.3-4.5) pH with concomitant reductions of respiration by 30-70%.
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| 25. |
- Rousk, Johannes, et al.
(author)
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Growth of saprotrophic fungi and bacteria in soil.
- 2011
-
In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 78, s. 17-30
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Journal article (peer-reviewed)abstract
- Bacterial and fungal growth rate measurements are sensitive variables to detect changes in environmental conditions. However, while methods to assess the species composition and biomass of fungi and bacteria has made much progress, information about growth rates remains surprisingly rudimentary. We review the recent history of approaches to assess bacterial and fungal growth rates, leading up to current methods, especially focusing on leucine/thymidine incorporation to estimate bacterial growth and acetate incorporation into ergosterol to estimate fungal growth. We present underlying assumptions for these methods, compare estimates of turnover times for fungi and bacteria based on them, and discuss issues, including e.g. elusive conversion factors. We review what the application of fungal and bacterial growth rate methods has revealed regarding the influence of the environmental factors of temperature, moisture (including drying/rewetting), pH, as well as the influence of substrate additions, presence of plants and toxins. We highlight experiments exploring competitive and facilitative interaction between bacteria and fungi enabled using growth rate methods. Finally, we predict that growth methods will be an important complement to molecular approaches to elucidate fungal and bacterial ecology, and we identify methodological concerns and how they should be addressed.
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