A pink-pigmented symbiotic bacterium was isolated from hybrid poplar tissues ( Populus deltoides × 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- ¹⁴ C]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 ¹⁴ CO ₂ was recorded from [ ¹⁴ C]TNT. In addition, the isolated methylotroph was shown to transform [U- ¹⁴ C]RDX (20 mg liter ⁻¹ ) and [U- ¹⁴ C]HMX (2.5 mg liter ⁻¹ ) in less than 40 days. After 55 days of incubation, 58.0% of initial [ ¹⁴ C]RDX and 61.4% of initial [ ¹⁴ C]HMX were mineralized into ¹⁴ CO ₂ . The radioactivity remaining in solution accounted for 12.8 and 12.7% of initial [ ¹⁴ C]RDX and [ ¹⁴ C]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.

A pink-pigmented, aerobic, facultatively methylotrophic bacterium, strain BJ001^T, was isolated from internal poplar tissues (Populus deltoides×nigraDN34) and identified as a member of the genusMethylobacterium. Phylogenetic analyses showed that strain BJ001^Tis related toMethylobacterium thiocyanatum,Methylobacterium extorquens,Methylobacterium zatmaniiandMethylobacterium rhodesianum. However, strain BJ001^Tdiffered from these species in its carbon-source utilization pattern, particularly its use of methane as the sole source of carbon and energy, an ability that is shared with only one other member of the genus,Methylobacterium organophilum. In addition, strain BJ001^Tis the only member of the genusMethylobacteriumto be described as an endophyte of poplar trees. On the basis of its physiological, genotypic and ecological properties, the isolate is proposed as a member of a novel species of the genusMethylobacterium,Methylobacterium populisp. nov. (type strain, BJ001^T=ATCC BAA-705^T=NCIMB 13946^T).