Type I nitroreductases in soil enterobacteria reduce TNT (2,4,6-trinitrotoluene) and RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine)

Many enteric bacteria express a type I oxygen-insensitive nitroreductase, w hich reduces nitro groups on many different nitroaromatic compounds under a erobic conditions. Enzymatic reduction of nitramines was also documented in enteric bacteria under anaerobic conditions. This study indicates that nit ramine reduction in enteric bacteria is carried out by the type I, or oxyge n-insensitive nitroreductase, rather than a type II enzyme. The enteric bac terium Morganella morganii strain B2 with documented hexahydro-1,3,5-trinit ro-1,3,5-triazine (RDX) nitroreductase activity, and Enterobacter cloacae s train 96-3 with documented 2,4,6-trinitrotoluene (TNT) nitroreductase activ ity, were used here to show that the explosives TNT and RDX were both reduc ed by a type I nitroreductase. Morganella morganii and E. cloacae exhibited RDX and TNT nitroreductase activities in whole cell assays. Type I nitrore ductase, purified from E. cloacae, oxidized NADPH with TNT or RDX as substr ate. When expression of the E. cloacae type I nitroreductase gene was induc ed in an Escherichia coli strain carrying a plasmid, a simultaneous increas e in TNT and RDX nitroreductase activities was observed. In addition, neith er TNT nor RDX nitroreductase activity was detected in nitrofurazone-resist ant mutants of M. morganii. We conclude that a type I nitroreductase presen t in these two enteric bacteria was responsible for the nitroreduction of b oth types of explosive.