Bacteria associated with the extraradical mycelium of an arbuscular mycorrhizal fungus in an As/Cu polluted soil

Synergistic interactions between bacteria and arbuscular mycorrhizal fungi (AMF) occur under natural soil conditions; however, in polluted soils there is little information regarding these relationships. Microscopy was used to study the interaction between the hyphae of an AM fungus (Glomus claroideum BEG134 from an As/Cu polluted soil) and bacteria in polluted soil cultures. BacLight (TM) staining showed viable bacteria mainly in the runner hyphae of the fungus associated with plants (Holcus lanatus L.) growing in polluted soils. Transmission electron microscopy revealed that a morphologically different bacterial population was intimately associated with the extraradical mycelium (ERM). Bacteria were embedded in the mucilaginous outer layer, encrusted at the outer layer, between hyphal wall layers, and inside hyphae. Crystals, comprising precipitated metal, were observed outside the ERM. The ecological relevance of this bacteria-AMF interaction is discussed.