Hydrolysis of benzonitrile herbicides by soil actinobacteria and metabolite toxicity

Abstract

The soil actinobacteria Rhodococcus rhodochrous PA-34, Rhodococcus sp. NDB 1165 and Nocardia globerula NHB-2 grown in the presence of isobutyronitrile exhibited nitrilase activities towards benzonitrile (approx. 1.1-1.9 U mg(-1) dry cell weight). The resting cell suspensions eliminated benzonitrile and the benzonitrile analogues chloroxynil (3,5-dichloro-4-hydroxybenzonitrile), bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) and ioxynil (3,5-diiodo-4-hydroxybenzonitrile) (0.5 mM each) from reaction mixtures at 30 degrees C and pH 8.0. The products were isolated and identified as the corresponding substituted benzoic acids. The reaction rates decreased in the order benzonitrile >> chloroxynil > bromoxynil > ioxynil in all strains. Depending on the strain, 92-100, 70-90 and 30-51% of chloroxynil, bromoxynil and ioxynil, respectively, was hydrolyzed after 5 h. After a 20-h incubation, almost full conversion of chloroxynil and bromoxynil was observed in all strains, while only about 60% of the added ioxynil was converted into carboxylic acid. The product of ioxynil was not metabolized any further, and those of the other two herbicides very slowly. None of the nitrilase-producing strains hydrolyzed dichlobenil (2,6-dichlorobenzonitrile). 3,5-Dibromo-4-hydroxybenzoic acid exhibited less inhibitory effect than bromoxynil both on luminescent bacteria and germinating seeds of Lactuca sativa. 3,5-Diiodo-4-hydroxybenzoic acid only exhibited lower toxicity than ioxynil in the latter test.

Nitrilases in nitrile biocatalysis: recent progress and forthcoming research

“…Although most nitriles are highly toxic, mutagenic, and carcinogenic due to their cyano group, enzymatic hydrolysis of these compounds is a recognized method to avail a broad spectrum of useful amides, carboxylic acids, and so on [13,15]. Meanwhile, bioremediation with nitrile-converting enzymes is an efficient method for degrading highly toxic nitriles in environmental wastes and contaminants [16,17]. Nitrile catabolism comprises two distinct pathways [18]: (1) nitrilases (EC 3.5.5.1) directly convert nitriles to corresponding carboxylic acids and NH 3 ; and (2) nitrile hydratases (NHases; EC 4.2.1.84) catalyze the formation of corresponding amides from nitriles, and amidases (EC 3.5.1.4) subsequently hydrolyze amides to carboxylic acids and NH 3 .…”

“…The bioremediation potential of nitrilase has been illustrated in detail to degrade the compounds into harmless intermediates or, ultimately, carbon dioxide, as well as H 2 O. Several microorganisms are involved in the degradation of nitriles in literature [13,16,17,156]. Zhou et al reported that sodium alginate immobilized the microbial cells, which were isolated from acrylic fiber production wastewater and can degrade more than 80% of succinonitrile at the initial concentration of even 5,000 mg·L -1 after 24 h [156].…”

Characterization and genome functional analysis of a novel metamitron-degrading strain Rhodococcus sp. MET via both triazinone and phenyl rings cleavage

“…N1 in liquid medium also followed first-order kinetics, and the degradation rate decreased as the substrate concentrations increased from 50 mg/l to 100 mg/l10. Additionally, some researchers have reported that bacterial strains from the same genus Rhodococcus with the isolate MET used in this study could degrade other herbicides1718. Xiong et al 19.…”

Synthesis of novel cyano-cyclitols and their stereoselective biotransformation catalyzed by Rhodococcus erythropolis A4

“…NDB 1165 22b were grown in the presence of isobutyronitrile (nitrilase inducer) as described previously. 30 F. solani O1 was maintained at 4°C on a modified Czapek-Dox agar 31 and grown in the presence of 2-cyanopyridine (nitrilase inducer) as described previously. 32 …”