BACTERIAL-COLONIZATION PATTERNS OF INTACT PINUS-SYLVESTRIS MYCORRHIZOSPHERES IN DRY PINE FOREST SOIL - AN ELECTRON-MICROSCOPY STUDY

The bacterial populations associated with different plant and fungal h abitats of intact Pinus sylvestris - Suillus bovinus or Pinus sylvestr is - Paxillus involutus ectomycorrhizospheres grown in natural forest soil were examined by scanning and transmission electron microscopy. S urfaces of nonmycorrhizal Pinus sylvestris roots hosted large numbers of morphologically distinct bacteria. Bacteria were detected on the ma ntle surfaces and at inter-and intra-cellular locations in the mantle and Hartig net of Suillus bovinus mycorrhizas. The fungal strands were colonized by only a few bacteria unlike the outermost external fine h yphae on which extensive monolayers of bacteria were attached. The myc orrhizas of Paxillus involutus were mostly devoid of bacteria, but the intact external mycelium supported both bacterial colonies and solita ry bacteria. Intracellular bacteria were not present in Paxillus invol utus hyphae. In both mycorrhizal systems, bacterial aggregation and at tachment to hyphae were mediated with electron-dense or -translucent m aterial. Our study shows that the Pinus sylvestris mycorrhizospheres f ormed by two different ectomycorrhizal fungi are clearly dissimilar ha bitats for mycorrhizosphere-associated bacteria. Additionally, the spa tially and physiologically defined mycorrhizosphere habitats were show n to host distinct populations of bacteria.