Benzonitriles, soil degradation

Fig. 35.5. Soil degradation (DT50) of (a) benzonitriles (8-10) and (b) BPUs (33, 34) - the effect of halogen substituents, (c) Relative orientations of the 2,6-dichloro- and 2,6-difluoro-benzoyl moieties in 33 and 34, respectively.

The NHase/amidase in R. erythropolis A4, a strain used to hydrolyze a wide spectrum of nitriles [16], was recently applied to the biotransformation of benzonitrile analogs used as herbicides (Figure 11.4) and the products and parent compounds were compared in terms of their acute toxicides [17]. In other rhodococcal strains, the same compounds, apart from dichlobenil, can also be hydrolyzed in a direct pathway catalyzed by a nitrilase [18,19]. It was demonstrated that the hydrolysis of the nitriles cannot itself be considered a detoxification. The two-step transformation may be especially important in the natural degradation of these compounds because unlike nitrilases, NHases and amidases are often constitutive enzymes, and their producer strains form the typical constituents of soil microflora [17, 20]. 

Holtze, M.S., Sorensen, S.R., Sorensen, J., and Aamand, J. (2008) Microbial degradation of the benzonitrile herbicides dichlobenil, bromoxynil and ioxynil in soil and subsurface environments - insights into degradation... 

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