Hexahydro-1,3,5-Trinitro-1,3,5-Triazine (anaerobic) Pathway Map

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This pathway was contributed by Jeff Roberts, BioC/MicE 5309, and Prasad Kotharu, University of Minnesota.

Hexahydro-1,3,5-trinitro-1,3,5-triazine, commonly known as RDX (Royal Demolition eXplosive), is a reduced symmetrical triazine ring compound rendered explosively unstable by the three N-nitro substituents. RDX is a synthetic product that does not occur naturally in the environment. RDX is also known as cyclonite and hexagen.

RDX is degraded both aerobically and anaerobically by microorganisms. The biodegradation of RDX in anaerobic sludge shows that at least two degradation routes are involved. In one route, RDX is reduced to give nitroso derivatives hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX) and hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine (DNX). In the second route, methylenedinitramine and bis(hydroxymethyl)nitramine are formed (Hawari et al., 2000).

Many microorganisms such as Morganella morganii B2, Enterobacter cloacae 96-3, Providencia rettgeri, Citrobacter freundii, Stenotrophomonas maltophilia PB1, Desulfovibrio spp. are known to anerobically degrade RDX, but it is often not known which pathway they use. A Type I nitroreductase present in enteric bacteria is responsible for the nitroreduction of explosives RDX and TNT (Kitts et al., 2000). Nitrate ester reductases that degrade explosives are related in sequence and structure to Old Yellow Enzyme (Williams et al., 2001).

The following is a text-format RDX degradation pathway map. Organisms which can initiate the pathway are given, but other organisms may also carry out later steps. Follow the links for more information on compounds or reactions.

[----------------Graphic (17k)-------------------][---------------------- Graphic (15k)-----------------------]

    Hexahydro-1,3,5-trinitro-1,3,5-triazine                  Hexahydro-1,3,5-trinitro-1,3,5-triazine
         Morganella morganii strain B2                                  anaerobic consortia
                      |                                                         |
                      | type I                                                  | A
                      | nitroreductase                          +---------------+----------------+
                      |                                         |                                | 
                      v                                         |                                |
           Hexahydro-1-nitroso-3,5-                             v                                v
            dinitro-1,3,5-triazine                     Methylenedinitramine         bis(Hydroxymethyl)nitramine
                      |                                         |                                |
                      | type I                                  |                                |
                      | nitroreductase                          | B                              | D
                      |                                         |                                | spontaneous
                      |                                         |                                |
                      v                                         v                                |
          Hexahydro-1,3-dinitroso-5-                  Hydroxymethylnitramine                     |
             nitro-1,3,5-triazine                               |                                |
                      |                                         | E                              | 
                      | type I                                  | spontaneous                    |
                      | nitroreductase                          |                                |
                      |                                         +---------------+----------------+
                      |                                                         |
                      v                                                         |
          Hexahydro-1,3,5-trinitroso-                                           |
                1,3,5-triazine                                                  |
                      |                                                         v 
                      |                                           Formaldehyde  +    Nitramine
                      v                                                 |                |
                      | C                                               |                | F
                      |                                                 |                | spontaneous
                      |                                                 |                |
                      v                                                 v                v
       Carbon Dioxide + Nitrous Oxide                                 to the       Nitrous oxide
                                                               C1 Metabolic Cycle

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Page Author(s): Jeff Roberts and Prasad Kotharu

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