Soil-borne Penicillium spp. and other microfungi as efficient degraders of the explosive RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine)

Soil microfungi belonging to the genera Aspergillus, Coniothyrium, Paecilomyces, Penicillium and Trichoderma, as well as wood-and litter-decomposing basidiomycetes, were able to degrade the explosive RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) co-metabolically, but were unable to utilize it as a sole carbon or nitrogen source. The most efficient RDX-degrading microfungi were characterized morphologically and by analysis of the ITS region of the ribosomal RNA gene cluster as Penicillium janczewskii and an unidentifiable Penicillium sp. with uniseriate phialides. Both species catalysed 80–100 % disappearance of RDX in a liquid defined medium. RDX degradation was inhibited by the presence of 30 mM NH₄ ⁺ but not by 40 mM NO₃ ⁻. In basidiomycetes but not Penicillium spp., RDX degradation was greatly reduced when biomass pregrown at 23 °C was incubated with RDX at 15 °C. Because of their production of copious conidial inoculum, simple growth requirements and ability to degrade RDX at reduced temperature, Penicillium spp. show promise for the bioremediation of RDX-contaminated groundwater.