Microbial biofilms and catabolic plasmid harbouring degradative fluorescent pseudomonads in Scots pine mycorrhizospheres developed on petroleum contaminated soil

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


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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    • "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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    • "This observation is in accordance with a previous hypothesis which proposed that, after inoculation, the population of BBc6R8 decreases in the soil but concentrates in target niches such as the fungal cell wall (Frey-Klett et al., 1999). Bacterial colonization of arbuscular mycorrhizal hyphae (Toljander et al., 2006) and biofilm formation on ectomycorrhizal hyphae (Nurmiaho- Lassila et al., 1997; Sarand et al., 1998) have already been reported. However, the MHB status of these bacteria has not yet been described. "
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