| 1. |
- Izumi, Hironari, et al.
(författare)
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Bacteria associated with ectomycorrhizas of slash pine (Pinus elliottii) in south-eastern Queensland, Australia
- 2008
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Ingår i: Fems Microbiology Letters. - : Oxford University Press (OUP). - 0378-1097 .- 1574-6968. ; 282:2, s. 196-204
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Tidskriftsartikel (refereegranskat)abstract
- Bacterial communities associated with ectomycorrhizal and uncolonized roots of Pinus elliottii (slash pine) collected from a plantation in south-east Queensland, Australia, were investigated, using cultivation-dependent and -independent methods. Denaturing gradient gel electrophoresis (DGGE) analysis of 16S rRNA gene PCR products obtained using a cultivation-independent approach revealed that bacterial communities associated with ectomycorrhizal root tips differed significantly from those associated with roots uncolonized by ectomycorrhizal fungi. DGGE analysis of cultivable bacterial communities revealed no significant difference between ectomycorrhizal and uncolonized roots. Neither analytical approach revealed significant differences between the bacterial communities associated with ectomycorrhizal roots colonized by a Suillus sp. or an Atheliaceae taxon. Cloned bacterial 16S rRNA genes revealed sequence types closely related with that of Burkholderia phenazinium, common in both ectomycorrhizal-colonized and -uncolonized roots, while sequence types most similar to the potentially phyopathogenic bacteria Burkholderia andropogonis and Pantoea ananatis were only detected in ectomycorrhizal roots. These results highlight the possibility of global movement of microorganisms, including putative pathogens, as a result of the introduction of exotic pine plantations.
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| 2. |
- Izumi, Hironari
(författare)
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Contrasting responses of the bacterial communities in ectomycorrhizal roots and rhizosphere soils to defoliation or winter hardening
- 2018
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Ingår i: Rhizosphere. - : Elsevier BV. - 2452-2198. ; 8, s. 8-11
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Tidskriftsartikel (refereegranskat)abstract
- We examined the effects of photosynthetic activity of the host tree on the bacterial communities in ectomycorrhizal (ECM) roots and in rhizosphere soil. The seedlings of two host tree species, birch (Betula pendula) and pine (Pinus sylvestris), were subjected to winter hardening treatments for inducing total (birch) or partial (pine) restriction of the photosynthesis. Additionally, physical defoliation was performed to prevent both tree species from photosynthetic activity entirely. The bacterial communities were analyzed by RT-PCR of 16S rRNA followed by DGGE. After winter hardening, the bacterial communities in ECM roots of both host species shifted considerably while no consistent change was observed after physical defoliation. In contrast, no significant separation of the communities in rhizosphere soil was observed after winter hardening in either of the host species although the communities were significantly altered after physical defoliation compared to those of non-defoliated control in both tree species. It is therefore interesting and curious that the bacteria communities of ectomycorrhizal roots respond differently than the rhizosphere soil, to both defoliation and winter-hardening
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| 3. |
- Izumi, Hironari, et al.
(författare)
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Diversity and expression of nitrogenase genes (nifH) from ectomycorrhizas of Corsican pine (Pinus nigra).
- 2006
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Ingår i: Environmental microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 8:12, s. 2224-30
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Tidskriftsartikel (refereegranskat)abstract
- The diversity of bacterial nitrogenase genes (nifH) and their mRNA transcription in ectomycorrhizas of Corsican pine (Pinus nigra) were examined. DNA and RNA were extracted from surface-sterilized and non-sterilized Corsican pine roots colonized by the ectomycorrhizal (ECM) fungi, Suillus variegatus and Tomentellopsis submollis. DNA-derived nifH polymerase chain reaction (PCR) products were obtained from all samples, but only a few reverse transcription PCRs for nifH mRNA were successful, suggesting that nitrogenase genes were not always transcribed. Several different nifH sequences were detected and the bacteria actively transcribing nifH were different from those whose genes were detected through DNA-based PCR. Putative nitrogenase amino acid sequences revealed that more than half of the nifH products were derived from methylotrophic bacteria, such as Methylocella spp. The next most frequent sequence types were similar to those from Burkholderia.
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| 4. |
- Izumi, Hironari, et al.
(författare)
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Diversity of predominant endophytic bacteria in European deciduous and coniferous trees.
- 2008
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Ingår i: Canadian journal of microbiology. - : Canadian Science Publishing. - 0008-4166 .- 1480-3275. ; 54:3, s. 173-179
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Tidskriftsartikel (refereegranskat)abstract
- The diversity of endophytic bacteria residing in root, stem, and leaf tissues was examined in coniferous and deciduous tree species, Scots pine (Pinus sylvestris L.), silver birch (Betula pendula Roth), and rowan (Sorbus aucuparia L.). Using cultivation-dependent and -independent analyses, the bacterial communities were observed to be significantly different in the belowground (roots and rhizosphere) and aboveground (leaves and stems) samples of the respective host trees. No significant differences, with respect to the different tree species, were observed in the associated communities. Predominant cultivable endophytes isolated included bacteria closely related to Bacillus subtilis, Bacillus licheniformis, Paenibacillus spp., and Acinetobacter calcoaceticus. Comparisons of the most abundant cultivable bacteria in the rhizosphere and root samples suggested that root endophytic bacteria may be in residence through processes of selection or active colonization rather than by passive diffusion from the rhizosphere.
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| 5. |
- Izumi, Hironari, et al.
(författare)
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Ectomycorrhizal roots select distinctive bacterial and ascomycete communities in Swedish subarctic forests
- 2011
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Ingår i: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 13, s. 819-830
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Tidskriftsartikel (refereegranskat)abstract
- P>Ectomycorrhizal (ECM) roots represent important niches for interactions with bacteria and ascomycete fungi, since they have a large surface area and receive a direct supply of plant assimilates from their tree hosts. We tested the hypothesis that the roots colonized by specific ECM fungi harbour distinct bacteria/ascomycete communities. Roots were collected from two different locations in a subarctic shrub forest dominated by Betula pubescens. Bacterial and ascomycete communities were analysed by PCR-DGGE and sequencing, in roots colonized by five frequently observed ECM fungi, Leccinum variicolor, Piloderma fallax, Tomentellopsis submollis, Lactarius torminosus and Pseudotomentella tristis. The bacterial communities associated with P. fallax- or P. tristis-colonized roots were distinct from those associated with roots colonized by three other ECM fungi at both sampling locations. Bacterial communities associated with T. submollis-, L. torminosus- and L. variicolor-colonized roots were more similar to each other. Lactarius- and Pseudotomentella-colonized roots hosted distinct ascomycete communities at one site while only the community associated with Lactarius was distinct at the second location. The results thus suggest that while the community structure of bacteria colonizing ECM roots can be influenced by the local soil environment, there can also be a strong selective effect of particular fungal symbionts.
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| 6. |
- Izumi, Hironari, et al.
(författare)
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Suillus mycelia under elevated atmospheric CO2 support increased bacterial communities and scarce nifH gene activity in contrast to Hebeloma mycelia
- 2013
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Ingår i: Mycorrhiza. - : Springer Science and Business Media LLC. - 0940-6360 .- 1432-1890. ; 23, s. 155-165
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Tidskriftsartikel (refereegranskat)abstract
- Bacterial communities associated with mycorrhizal roots are likely to respond to rising atmospheric CO2 levels in terms of biomass, community composition and activity since they are supported by the carbon (C) flow outside the root tips, especially by exudation of low molecular weight organic compounds. We studied how general bacterial and diazotrophic communities associated with ectomycorrhizal (ECM) fungi respond to different belowground C supply conditions, mediated by elevated atmospheric CO2 concentration under nitrogen (N) limited conditions. Microcosm systems were constructed using forest soil and Scots pine seedlings, which were either pre-inoculated with one of the ECM fungal species Hebeloma velutipes or Suillus variegatus, or non-inoculated. These fungal species differ in C allocation and exudation patterns. Seedlings were maintained under ambient (380 ppm) or elevated (700 ppm) CO2 levels for 6 months. Quantitative polymerase chain reaction (PCR) showed a significant increase in 16S rRNA gene copy numbers for Suillus-inoculated microcosms under elevated CO2 compared to ambient CO2. The copy numbers of the nitrogenase reductase (nifH) gene were under the detection limit in all samples regardless the CO2 treatments. Denaturing gradient gel electrophoresis analysis of PCR-amplified nifH genes revealed simple and consistent communities in all samples throughout the incubation period. A nested reverse transcription PCR approach revealed that expression of nifH genes were detected in some microcosms. Our findings suggest that the effect of mycorrhizal fungi on soil bacteria may vary depending on C supply and fungal species.
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| 7. |
- Izumi, Hironari
(författare)
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Temporal and spacial dynamics of metabolically active bacteria associated with ectomycorrhizal roots of Betula pubescens
- 2019
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Ingår i: Biology and Fertility of Soils. - : Springer Science and Business Media LLC. - 0178-2762 .- 1432-0789. ; 55, s. 777-788
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Tidskriftsartikel (refereegranskat)abstract
- Bacteria, mycorrhizal fungi and their host plants are ubiquitous terrestrial associations but their interactions are poorly understood. To investigate the effects of seasonal change of host plant phenology on the bacterial communities in ectomycorrhizal (ECM) roots, bacterial communities in birch root tips with different ECM fungal species, those of non-mycorrhizal roots and those in bulk soil, were examined over a 15-month period, including two autumn seasons of 2008 and 2009, in field settings. Morphotyping and sequencing to identify the fungal species and RNA-based DGGE, cloning and sequencing were used to characterise the active bacterial communities. The most frequently observed fungus was Leccinum scabrum while other ECM fungi including Hebeloma velutipes, Russula versicolor and unidentified Cortinarius and Tomentella species were commonly found. ECM roots with L. scabrum hosted declining numbers of bacterial sequence types, observed as distinct bands on the DGGE profile, from spring to autumn in 2009. The numbers of sequence types associated with L. scabrum and non-mycorrhizal roots were reduced in autumn 2009 than in autumn 2008, but the numbers associated with other ECM roots and bulk soil were constant over the same period. Roots with L. scabrum harboured unique bacterial communities which were distinct from bulk soils, non-mycorrhizal roots and roots with other ECM fungi in 2008 but the differences were less clear in 2009. The results indicate that the metabolically active bacterial communities in ECM are influenced by fungal species, seasonal host plant phenology and show year to year variation.
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