Cyclic nitramine explosives, RDX, HMX, and CL-20 are hydrophobic pollutants with very little aqueous solubility. In sediment and soil environments, they are often attached to solid surfaces and/or trapped in pores and distribute heterogeneously in aqueous environments. For efficient bioremediation of these explosives, the micro organism(s) must access them by chemotaxis ability. In the present study, we isolated an obligate anaerobic bacterium Clostridium sp. strain EDB2 from a marine sediment. Strain EDB2, motile with numerous peritrichous flagella, demonstrated chemotactic response towards RDX, HMX, CL-20, and NO2-. The three explosives were biotransformed by strain EDB2 via N-denitration with concomitant release of NO2-. Biotransformation rates of RDX, HMX, and CL-20 by the resting cells of strain ED132 were 1.8 +/- 0.2, 1.1 +/- 0.1, and 2.6 +/- 0.2 nmol h(-1) mg wet biomass(-1) (mean +/- SD; n = 3), respectively. We found that commonly seen RDX metabolites such as TNX, methylenedinitramine, and 4-nitro-2,4-diazabutanal neither produced NO2- during reaction with strain EDB2 nor they elicited chemotaxis response in strain EDB2. The above data suggested that NO2- released from explosives during their biotransformation might have elicited chemotaxis response in the bacterium. Biodegradation and chemotactic ability of strain EDB2 renders it useful in accelerating the bioremediation of explosives under in situ conditions. (C) 2004 Elsevier Inc. All rights reserved.