Tolerance and biodegradation of m-toluate by Scots pine, a mycorrhizal fungus and fluorescent pseudomonads individually and under associative conditions

The tolerance to, and degradation of m-toluate by Scots pine (Pinus sylvest ris), a symbiotic mycorrhizal fungus (Suillus bovinus) and Pseudomonas fluo rescens strains, with or without m-toluate-degrading capacity, was determin ed individually and in all symbiotic/associative plant-microbe combinations . Fungal survival on medium with m-toluate was increased in co-culture with the degradative bacterial strains on agar plates (up to 0.02%, w/v). When fungi were grown in mycorrhizal association with Scots pine seedlings in te st-tube microcosms containing expanded clay pellets and growth media, the f ungus was able to withstand m-toluate concentrations up to 2.0%, w/v in all treatments. The seedling tolerance remained unaltered regardless of the pr esence or absence of mycorrhizal fungi or biodegradative bacteria. Reductio n in m-toluate levels was only detected in treatments inoculated with bacte rial strains harbouring TOL catabolic plasmids. The plant and fungus, alone or in mycorrhizal symbiosis, were unable to cleave m-toluate. The presence of easily available plant-derived carbon sources did not impede m-toluate degradation by the bacteria in the mycorrhizosphere.