Benomyl Pathway Map

Benomyl, methyl N-[1-(butylcarbamoyl)benzimidazol-2-yl]carbamate, and its conversion product, carbendazim, methyl benzimidazol-2-yl carbamate, are systemic fungicides. Carbendazim is quite stable in soil and water, and is a suspected mutagen, carcinogen, and endrocrine disruptor. Thus studies on its biodegradation are of interest (Pandey et al., 2010).

Several Pseudomonas species can use benomyl as the sole carbon source for growth. The initial step in the degradation of benomyl is hydrolysis of the butylcarbamoyl side chain to form carbendazim (MBC). The N-butylcarbamate formed is hydrolyzed to n-butylamine. The carbendazim is hydrolyzed to 2-aminobenzimidazole (2-AB). Only small amounts of these compounds are formed; n-butylamine may be the carbon source for growth (Fuchs and DeVries, 1978).

Rhodococcus jialingiae djl-6-2 is capable of using carbendazim as the sole carbon and nitrogen source for growth. It also hydrolyzes it to 2-aminobenzimidazole, which is converted to 2-hydroxybenzimidazole. This last compound is postulated to be dioxygenated, either by a dioxygenase or two consecutive monoxygenase reactions, to 2,6,7-trihydroxybenzimidazole. Extradiol cleavage forms (2Z)-3-(4-formyl-2-hydroxy-1H-imidazol-5-yl)-2-hydroxyprop-2-enoate. Benzimidazole is also produced in a side reaction, possibly by deamination of carbendazim (Wang et al., 2010).

Pseudomonas sp. CBW is capable of using carbendazim as the sole source of carbon and energy for growth. It follows the above pathway through 2-hydroxybenzimidazole. It can metabolize 2-hydroxybenzimidazole and 1,2-diaminobenzene. It is postulated to cleave the heteroring of 2-hydroxybenzimidazole to produce 1,2-diaminobenzene, which might be converted to catechol (Fang et al., 2010).

Nocardioides sp. SG-4G is capable of using carbendazim, 2-aminobenzimidazole, and 2-hydroxybenzimidazole as sole carbon and energy sources for growth. The pathway followed is the same as for the above two organisms, through 2-hydroxybenzimidazole. This last compound is completely assimilated, but the exact pathway has not been determined (Pandey et al., 2010).

The following is a text-format benomyl pathway map. An organism which can initiate the pathway is given, but other organisms may also carry out later steps. Follow the links for more information on compounds or reactions. This map is also available in graphic (10k) format.

 
                  Benomyl       
              Pseudomonas spp.              
                     |
                     |
                     | A
                     | non-enzymatic 
                     |                           N-butylcarbamate
                     v                              hydrolase  
                Carbendazim   +   N-Butylcarbamate  ----------> n-Butylamine      
       Rhodococcus jialingiae djl-6-2
           Pseudomonas sp. CBW
           Nocardioides sp. SG-4G
                     |
                     | carbendazim
                     | hydrolase 
                     | 
                     v 
            2-Aminobenzimidazole   +   Monomethyl carbonate
                     |
                     |
                     | 2-aminobenzimidazole
                     | deaminase
                     |
                     v                   C         not Rhodococcus
           2-Hydroxybenzimidazole  ------>-----> [1,2-Diaminobenzene]
                     |                                    |
                     |                                    |
                     v B                                  v D
                     |                                    |
                     |                                    |
                     v                                    v
      [2,6,7-Trihydroxybenzimidazole]                 [Catechol]
                     |                                    |
                     |                                    |
                     | catechol 2,3-dioxygenase           |
                     |                                    |
                     |                                    v
                     v                                  to the
(2Z)-3-(4-formyl-2-hydroxy-1H-imidazol-5-yl)-        Nitrobenzene
           2-hydroxyprop-2-enoate                      Pathway

Page Author(s): Lynda Ellis and Michael Turnbull

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