Biodegradation of nitro-substituted explosives 2,4,6-trinitrotoluene, hexahydro-1,3,5-trinitro-1,3,5-triazine, an octahydro-1,3,5,7-tetranitro-1,3,5-tetrazocine by a phytosymbiotic Methylobacterium sp associated with poplar tissues (Populus deltoides x nigra DN34)

A pink-pigmented symbiotic bacterium was isolated from hybrid poplar tissues, (Populus deltoides X nigra DN34). The bacterium was identified by 16S and 16S-23S intergenic spacer ribosomal DNA analysis as a Methylobacterium sp. (strain BJ001). The isolated bacterium was able to use methanol as the sole source of carbon, and energy, which is a specific attribute of the genus Methylobacterium. The bacterium in pure culture was shown to degrade the toxic explosives 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazene (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5-tetrazocine (HMX). [U-ring-C-14]TNT (25 mg liter(-1)) was fully transformed in less than 10 days. Metabolites included the reduction derivatives amino-dinitrotoluenes and diamino-nitrotoluenes. No significant release of (CO2)-C-14 was recorded from [C-14]TNT. In addition, the isolated methylotroph was shown to transform [U-C-14]RDX (20 mg liter(-1)) and [U-C-14]HMX (2.5 mg liter(-1)) in less than 40 days. After 55 days of incubation, 58.0% of initial [14C]RDX and,61.4% of initial [C-14]HMX were mineralized into (CO2)-C-14. The radioactivity. remaining in solution accounted for 12.8 and 12.7% of initial [C-14] RDX and [C-14]HMX, respectively. Metabolites detected from RDX transformation included a mononitroso RDX derivative and a polar compound tentatively identified as methylenedinitramine. Since members of the genus Methylobacterium are distributed in a wide diversity of natural environments and are very often associated with plants, Methylobacterium sp. strain BJ001 may be involved. in natural attenuation or in situ biodegradation (including phytoremediation) of explosive-contaminated sites.