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

Abstract

Abstract:Many enteric bacteria express a type I oxygen-insensitive nitroreductase, which reduces nitro groups on many different nitroaromatic compounds under aerobic conditions. Enzymatic reduction of nitramines was also docu mented in enteric bacteria under anaerobic conditions. This study indicates that nitramine reduction in enteric bacteria is carried out by the type I, or oxygen-insensitive nitroreductase, rather than a type II enzyme. The enteric bacterium Morganella morganii strain B2 with documented hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) nitroreductase activity, and Enterobacter cloacae strain 96-3 with documented 2,4,6-trinitrotoluene (TNT) nitroreductase activity, were used here to show that the explosives TNT and RDX were both reduced by a type I nitroreductase. Morganella morganii and E. cloacae exhibited RDX and TNT nitroreductase activities in whole cell assays. Type I nitroreductase, purified from E. cloacae, oxidized NADPH with TNT or RDX as substrate. When expression of the E. cloacae type I nitroreductase gene was induced in an Escherichia coli strain carrying a plasmid, a simultaneous increase in TNT and RDX nitroreductase activities was observed. In addition, neither TNT nor RDX nitroreductase activity was detected in nitrofurazone-resistant mutants of M. morganii. We conclude that a type I nitroreductase present in these two enteric bacteria was responsible for the nitroreduction of both types of explosive.Key words: nitroreductase, TNT, RDX, Enterobacter cloacae, Morganella morganii.Résumé : Différentes bactéries entériques produisent une nitroréductase de type I insensible à l'oxygène capable de ré duire les groupements nitro de divers composés nitroaromatiques dans des conditions anaérobies. La réduction enzyma tique des nitramines en anaérobiose est aussi connue chez les entérobactéries. La présente étude indique que la réduction des nitramines par les entérobactéries était catalysée par une nitroréductase de type I non sensible à l'oxygène plutôt que par une enzyme de type II. La souche B2 de Morganella morganii reconnue pour son activité hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) nitroréductase, et la souche 96-3 d'Enterobacter cloacae reconnue pour son activité 2,4,6 trinitrotoluène (TNT) nitroréductase, ont toutes deux servi à démontrer que les deux explosifs TNT et RDX étaient réduits par une nitroréductase de type I. Les RDX et TNT nitroréductases de M. morganii et d'E. cloacae ont été observées lors d'essais avec des bactéries entières. La nitroréductase de type I, purifiée de l'E. cloacae, oxydait le NADPH en présence de TNT ou de RDX comme substrat. L'induction de l'expression du gène de la nitroréductase de type I de l'E. cloacae chez une souche d'Escherichia coli porteuse d'un plasmide a causé une augmentation spon tanée de l'activité des TNT et RDX nitroréductases. Par contre aucune activité TNT ou RDX nitroréductase n'a été ob servée chez des mutants de M. morganii résistants au nitrofurazone. La présente étude permet de conclure que la nitroréductase de type I ret...

Effect of organic and inorganic nitrogenous compounds on RDX degradation and cytochrome P-450 expression in Rhodococcus strain YH1

“…This observation is unique and to the best of our knowledge, has never been reported for aerobic RDX-degrading strains. Although type 1 oxygen-insensitive nitroreductase from Morganella morganii strain B2 is known for its ability to reduce RDX (Kitts et al 2000), this is not the case with the YH1 culture because no RDX nitroso derivatives were detected.…”

Bioremediation of soils contaminated with explosives

“…A study using 14 C-labeled RDX in a laboratory compost system showed CO 2 (56%) as well as bound and soluble products (Sublette et al, 1992). Both the nitramine explosives are transformed anaerobically in mixed cultures (Boopathy et al, 1998;Freedman and Sutherland, 1998;Funk et al, 1993;Kitts et al, 1994Kitts et al, , 2000McCormick et al, 1981;Yang et al, 1986). Where products have been identified, the familiar nitro group reduction to form nitroso congeners has been found.…”

Metagenomic Insights into the RDX-Degrading Potential of the Ovine Rumen Microbiome

“…The gene encoding diaphorase, diaA , has been cloned [13]. In addition, oxygen-insensitive (type I) NADPH nitroreductases ( nsfI ) cloned from many bacteria, particularly enterobacteria, such as Enterobacter cloacae and Morganella morganii , are also able to degrade RDX [14]. Two flavin mononucleotide-containing oxidoreductases, or xenobiotic reductase, genes xenA and xenB , have been cloned from Pseudomonas putida and P. fluorescens , respectively [15].…”