Poster: Phytoremediation

Abs # 991: Phytoremediation of Toxic Explosives RDX and HMX by Poplar Tissue Cultures (Populus sp.): Implication of an Endosymbiotic Methylobacterium sp.

Presenter:	Van Aken, Benoit , bvanaken@engineering.uiowa.edu
Authors	Van Aken, Benoit  (A)   Schnoor, Jerald L (A)
Affiliations:	(A): The University of Iowa

Phytoremediation is a promising biotechnology for cleaning up sites contaminated by explosives, such as toxic nitramines RDX and HMX. Recently, an endosymbiotic pink-pigmented bacterium has been isolated from plant tissue cultures used for phytoremediation studies. The bacterium was identified by 16S rDNA analysis as a Methylobacterium sp. (strain BJ001). Members of the genus are frequently associated with plants, colonizing the rhizosphere, the phyllosphere, or internal tissues. The detection of a bacterial endosymbionte raised the question of its implication in the degradation of toxic nitramines. This research investigated the involvement of Methylobacterium sp. BJ001 in the phytoremediation of RDX and HMX by poplar tissues (Populus deltoides x nigra). Degradation experiments were conducted using tissue cultures, both contaminated by Methylobacterium sp. BJ001 and non-contaminated, i.e., treated with gentamycin (100 mg L^-1) and tetracyclin (5 mg L^-1). When incubated in the presence of ¹⁴C-RDX (20 mg L^-1) or ¹⁴C-HMX (2.5 mg L^-1), antibiotic-treated tissues showed a significantly lower mineralization to ¹⁴CO₂ (less than 5 %) than the infected cultures (15 – 20 %). On the other hand, Methylobacterium sp. BJ001 in pure culture was able to mineralize to ¹⁴CO₂ up to 60 % of ¹⁴C-RDX (20 mg L^-1) and ¹⁴C-HMX (2.5 mg L^-1). These results strongly suggest the implication of Methylobacterium sp. BJ001 in the degradation of RDX and HMX inside poplar tissues. Phytoremediation encompasses a range of processes, including rhizofiltration, phytotransformation, or rhizodegradation. While the implication of rhizobial microflora in phytoremediation of organic pollutants has received some attention, this is the first time that the potential role of endosymbiotic bacteria was investigated.