Microbial biofilms and catabolic plasmid harbouring degradative fluorescent pseu-domonads in Scots pine mycorrhizospheres developed on petroleum contaminated soil. FEMS Microbiol Ecol

Department of Biosciences, Division of General Microbiology, Viikki Biocenter, P.O. Box 56 (Viikinkaari 9), FIN-00014, University of Helsinki, Helsinki, Finland
FEMS Microbiology Ecology (Impact Factor: 3.57). 01/1998; 27(2):115 - 126. DOI: 10.1111/j.1574-6941.1998.tb00529.x

ABSTRACT Cellular interactions and catabolic activities of mycorrhizal root associated non-sporulating bacteria were investigated in a simplified phytoremediation simulation involving a woody plant species. Mycorrhizal Scots pine (Pinus sylvestris) seedlings pre-colonised by Suillus bovinus or Paxillus involutus were grown in forest humus containing microcosms amended with petroleum hydrocarbon (PHC) contaminated soil. Fungal hyphae of both species, emanating from mycorrhizal roots, colonised the PHC contaminated soil over a 16-week period and dense long-lived patches of S. bovinus hyphae formed on the PHC contaminated soil. Transmission electron microscopy revealed a microbial biofilm at the PHC soil-fungal interface composed of differentiated pseudoparenchymous patch hyphae supporting a morphologically diverse bacterial population. Certain non-sporulating bacterial isolates closely associated with the S. bovinus patch hyphae or P. involutus‘web’ hyphae from the PHC soil harboured similar sized mega-plasmids (approx. 150 kb). Isolates of Pseudomonas fluorescens from the ‘patch’ mycorrhizospheres represented different biovars, displayed similar REP-PCR genomic fingerprints, grew on e.g. m-toluate and m-xylene as sole carbon sources, cleaved catechol, and harboured plasmid-borne catabolic marker genes, xylE and xylMA, involved in degradation of mono-aromatics. The plasmids were transmissible in vitro, and Pseudomonas putida transconjugants retained a similar catabolic profile. The identification of microbial biofilms containing catabolic bacteria in the external mycorrhizosphere is discussed in relation to both phytoremediation mechanisms and normal efficient nutrient mobilisation from highly lignin-rich forest soils.

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Available from: Robin Sen, May 20, 2015
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    • "nC16+) fractions occurred in only pine and birch systems provides indirect evidence for a stimulatory role of ECMs in the biodegradation process. The extensive extraradical mycelia of ECM fungi provide colonization surfaces and C substrates that enhance bacterial metabolism (Sarand et al., 1998; 2000; Heinonsalo et al., 2000) and secrete oxidative enzymes that open aromatic ring structures (Burke and Cairney, 2002). In our study, establishment of diverse ECM communities on the fine roots of pine and birch likely limited competition for reduced C by free-living soil fungi in the rhizosphere (Lindahl et al., 2007). "
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    ABSTRACT: Petroleum hydrocarbon (PHC) contamination is becoming more common in boreal forest soils. However, linkages between PHC biodegradation and microbial community dynamics in the mycorrhizosphere of boreal forest soils are poorly understood. Seedlings (lodgepole pine, paper birch, lingonberry) were established in reconstructed soil systems, consisting of an organic layer (mor humus, coarse woody debris, or previously oil-contaminated mor humus) overlying mineral (Ae, Bf) horizons. Light crude oil was applied to the soil surface after 4 months; systems were destructively sampled at 1 and 16 weeks following treatment. Soil concentrations of four PHC fractions were determined using acetone–hexane extraction followed by gas chromatography – flame ionization detection analysis. Genotypic profiles of root-associated bacterial communities were generated using length heterogeneity-PCR of 16S rDNA. Most plant–soil treatments showed significant loss in the smaller fraction PHCs indicating an inherent capacity for biodegradation. Concentrations of total PHCs declined significantly only in planted (pine-woody debris and birch-humus) systems (averaging 59% and 82% loss between 1 and 16 weeks respectively), reinforcing the importance of the mycorrhizosphere for enhancing microbial catabolism. Bacterial community structure was correlated more with mycorrhizosphere type and complexity than with PHC contamination. However, results suggest that communities in PHC-contaminated and pristine soils may become distinct over time.
    Environmental Microbiology Reports 07/2010; 2(4):587 - 593. DOI:10.1111/j.1758-2229.2010.00153.x · 3.29 Impact Factor
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    • "Recent work has demonstrated that metal-resistant PGPR inoculates containing ACCdeaminase-producing bacteria protected Brassica napus and B. campestris against metal toxicity and stimulated plant growth (Burd et al. 1998; Belimov et al. 2001). Ectomycorrhizal associations can display considerable resistance against toxicity in soil polluted with metals (Leyval et al. 1997; Meharg and Cairney 2000) and organic compounds such as m-toluate (Sarand et al. 1999), petroleum (Sarand et al. 1998), or polycyclic aromatic hydrocarbons (Leyval and Binet 1998). Densely packed mycorrhizal sheaths and phenolic inter-hyphal material can protect plant roots from direct contact with the pollutant (Ashford et al. 1988), while the large surface and cation exchange capacity of extramatrical mycelia may reduce bioavailable pollutant concentrations, at least for some metals, through their substantial adsorption capacities (Colpaert and Asche, 1993; Marschner et al. 1998). "
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    ABSTRACT: Plant-assisted bioremediation or phytoremediation holds promise for in situ treatment of polluted soils. Enhancement of phytoremediation processes requires a sound understanding of the complex interactions in the rhizosphere. Evaluation of the current literature suggests that pollutant bioavailability in the rhizosphere of phytoremediation crops is decisive for designing phytoremediation technologies with improved, predictable remedial success. For phytoextraction, emphasis should be put on improved characterisation of the bioavailable metal pools and the kinetics of resupply from less available fractions to support decision making on the applicability of this technology to a given site. Limited pollutant bioavailability may be overcome by the design of plant–microbial consortia that are capable of mobilising metals/metalloids by modification of rhizosphere pH (e.g. by using Alnus sp. as co-cropping component) and ligand exudation, or enhancing bioavailability of organic pollutants by the release of biosurfactants. Apart from limited pollutant bioavailability, the lack of competitiveness of inoculated microbial strains (in particular degraders) in field conditions appears to be another major obstacle. Selecting/engineering of plant–microbial pairs where the competitiveness of the microbial partner is enhanced through a “nutritional bias” caused by exudates exclusively or primarily available to this partner (as known from the “opine concept”) may open new horizons for rhizodegradation of organically polluted soils. The complexity and heterogeneity of multiply polluted “real world” soils will require the design of integrated approaches of rhizosphere management, e.g. by combining co-cropping of phytoextraction and rhizodegradation crops, inoculation of microorganisms and soil management. An improved understanding of the rhizosphere will help to translate the results of simplified bench scale and pot experiments to the full complexity and heterogeneity of field applications.
    Plant and Soil 08/2009; 321(1):385-408. DOI:10.1007/s11104-008-9686-1 · 2.95 Impact Factor
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    • "Attempts to introduce micro-organisms with biocontrol or bioremediation properties often fail because the inoculants fail to establish themselves. Mycorrhizal hyphae may facilitate the establishment of some bacteria and Sarand et al. (1998) suggested that mycorrhizal hyphae were able to support microbial biofilms of catabolic plasmid (Tol + ) harbouring bacteria which could be active in bioremediation of petroleum-contaminated soil. In further experiments, these authors (Sarand et al., 2000) demonstrated that the number of Tol + bacteria was higher in mycorrhizospheric soil compared with bulk soil, and inoculation with bacteria had a positive effect on plant and fungal development. "
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    ABSTRACT: Different symbiotic mycorrhizal associations between plants and fungi occur, almost ubiquitously, in a wide range of terrestrial ecosystems. Historically, these have mainly been considered within the rather narrow perspective of their effects on the uptake of dissolved mineral nutrients by individual plants. More recent research has placed emphasis on a wider, multifunctional perspective, including the effects of mycorrhizal symbiosis on plant and microbial communities, and on ecosystem processes. This includes mobilization of N and P from organic polymers, release of nutrients from mineral particles or rock surfaces via weathering, effects on carbon cycling, interactions with myco-heterotrophic plants, mediation of plant responses to stress factors such as drought, soil acidification, toxic metals, and plant pathogens, as well as a range of possible interactions with groups of other soil micro-organisms. Mycorrhizal fungi connect their plant hosts to the heterogeneously distributed nutrients required for their growth, enabling the flow of energy-rich compounds required for nutrient mobilization whilst simultaneously providing conduits for the translocation of mobilized products back to their hosts. In addition to increasing the nutrient absorptive surface area of their host plant root systems, the extraradical mycelium of mycorrhizal fungi provides a direct pathway for translocation of photosynthetically derived carbon to microsites in the soil and a large surface area for interaction with other micro-organisms. The detailed functioning and regulation of these mycorrhizosphere processes is still poorly understood but recent progress is reviewed and potential benefits of improved understanding of mycorrhizosphere interactions are discussed.
    Journal of Experimental Botany 02/2008; 59(5):1115-26. DOI:10.1093/jxb/ern059 · 5.53 Impact Factor
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