Abstract
Nitramines are key constituents of most of the explosives in current use and consequently contaminate soil and groundwater at many military facilities around the world. Toxicity from nitramine contamination poses a health risk to plants and animals, thus understanding how nitramines are biodegraded is critical to environmental remediation. The biodegradation of synthetic nitramine compounds such as hexahydro-1,3,5-trinitro-1,3,5- triazine (RDX) has been studied for decades, but little is known about the catabolism of naturally produced nitramine compounds. In this study, we report the isolation of a soil bacterium Variovorax sp. JS1663, that degrades N-nitroglycine (NNG), a naturally produced nitramine, and the key enzyme involved in its catabolism. Variovorax sp. JS1663 is a Gram-negative, non-spore-forming, motile bacterium, isolated from activated sludge based on its ability to use NNG as a sole growth substrate under aerobic conditions. A single gene (nnlA) encodes an iron-dependent enzyme that releases nitrite from NNG through a proposed β-elimination reaction. Bioinformatics analysis of the amino acid sequence of NNG lyase identified a PAS (Per Arnt Sim) domain. PAS domains are typically associated with heme cofactors and function as signal sensors in signaling proteins. This is the first instance of a PAS domain present in denitration enzymes. The NNG biodegradation pathway should provide the basis for identification of other enzymes that cleave the N-N bond and facilitate the development of enzymes to cleave similar bonds in RDX, nitroguanidine, and other nitramine explosives.
