Nitrilases herbicides

Stalker DM, KE McBride (1987) Cloning and expresssion in Escherichia coli of a Klebsiella ozaenae plasmid-borne gene encoding a nitrilase specific for the herbicide Bromoxynil. J Bacterial 169 ... 

Cotton Calgene/1994 Nitrilase Klebsiella OTjoenae Tolerance to the herbicide bromoxynU... 

Similarly, the selective herbicides, bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) and ioxynil (3,5-diiodo-4-hydroxybenzonitrile) are degraded by soil bacteria to their corresponding amide products 3,5-dibromo-4-hydroxybenzamide (BrAM) and 3,5-diiodo-4-hydroxybenzamide (IAM) but are not further degraded to the corresponding acids. The identification of amidases or nitrilases able to effect these transformations, in a soil bacterium, would be of value as a bioremediation agent [48],... 

Holtze, M.S., Sorensen, J., Christian, H. and Aamand, J. (2006) Transformation of the herbicide 2,6-dichlorobenzonitrile to the persistent metabolite 2,6-dichlorobenzamide (BAM) by soil bacteria known to harbor nitrile hydratase or nitrilase. Biodegradation, 17, 503—510. 

In basic chemicals, nitrile hydratase and nitrilases have been most successful. Acrylamide from acrylonitrile is now a 30 000 tpy process. In a product tree starting from the addition of HCN to butadiene, nicotinamide (from 3-cyanopyridine, for animal feed), 5-cyanovaleramide (from adiponitrile, for herbicide precursor), and 4-cyanopentanoic acid (from 2-methylglutaronitrile, for l,5-dimethyl-2-piperidone solvent) have been developed. Both the enantioselective addition of HCN to aldehydes with oxynitrilase and the dihydroxylation of substituted benzenes with toluene (or naphthalene) dioxygenase, which are far superior to chemical routes, open up pathways to amino and hydroxy acids, amino alcohols, and diamines in the first case and alkaloids, prostaglandins, and carbohydrate derivatives in the second case. 

Transgenic plants containing a nitrilase specific for the herbicide bromoxynil (= 3,5-dibromo-4-hydroxybenzonitrile)have also been developed [93] the Cal-gene company transformed tobacco plants with the bacterial Klebsiella ozaenae gene encoding nitrilase [94] that detoxifies the herbicide by hydrolysis (conversion of bromoxynil to 3,5-dibromo-4-hydroxybenzoic acid), resulting in the establishment of the herbicide-resistant transgenic plants. 

Stalker, D.M., Malyi, L.D., and McBride, K.E. 1998. Purification and properties of a nitrilase specific for the herbicide bromoxynil and corresponding nucleotide sequence analysis of the bxn gene. Journal of Biological Chemistry, 263 6310-4. 

This strategy has led to commercial development of herbicide resistance for glu-fosinate, glyphosate and bromoxynil. Glufosinate and glyphosate resistance will be discussed in detail in later sections of this chapter (see also Chapter 6.2). Bro-moxynil s herbicide activity is due to inhibition of electron transport in photosystem II. Crops engineered with bromoxynil nitrilase metabolize the herbicide to a non-phytotoxic compound [5]. 

The metabolism of Bromoxjmil has been studied in some microorganisms, revealing the presence of amide and acid products [3,152-154] (Figure 8). Klebsiella pneumoniae subsp. ozaenae was shown to transform completely the herbicide, with the involvement of a nitrilase enzyme to... 

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]. 

Another method of increasing resistance to a PSII herbicide is to promote the breakdown of the molecule within the plant before it reaches the active site. This has been achieved in an effective way in the case of bromoxynil resistance in tobacco. Bromoxynil is broken down by a nitrilase enzyme to ammonia and a herbicidally inactive benzoic acid moiety (Figure 1.6). A strain of Klebsiella pneumoniae has been isolated which uses bromoxynil as a primary nitrogen source by virtue of its nitrilase activity. The gene has been characterized and transferred into tobacco using conventional gene transfer techniques. The transgenic tobacco thus produced was able to tolerate more than 20 times the normally lethal dose of bromoxynil. ... 

Iminodiacetic acid has important applications in the chemical industry for the manufacture of chelating agents, herbicide, and surfactants, especially for the production of herbicide glyphosate, for which there is a huge demand in the field of agriculture. Bioconversion of iminodiacetonitrile using nitrilase is an attractive method for... 

Detzel C, Maas R, Tubeleviciute A, Jose J. Autodisplay of nitrilase from Klebsiella pneumoniae and whole-cell degradation of ox5mil herbicides and related compoimds [J]. Ap>pl Microbiol Biotechnol 2013, 97 (11) 4887-4896. 

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