Hydrolysis of benzonitrile herbicides by soil actinobacteria and metabolite toxicity.

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.

Biodegradation of brominated aromatics by cultures and laccase of Trametes versicolor.

2-Bromophenol (1), 4-bromophenol (2), 2,4-dibromophenol (3), 2,6-dibromophenol (4), 2,4,6-tribromophenol (5) and tetrabromobisphenol A (6) (1 mM each) added to growing submerged cultures of Trametes versicolor CCBAS 612 were eliminated by 65-85% from the culture medium within 4d. Extracellular laccase activity in the culture medium was influenced by the type of brominated compound added. Maximum level of laccase (63 U L(-1)) was found in the culture with 2-bromophenol. Tetrabromobisphenol A was degraded by a commercial laccase from Trametes versicolor in absence of any oxidation mediator, hydroxylated dibrominated compounds being detected as soluble reaction products by LC/MS. A significant degradation of brominated phenols by laccase was achieved only in the presence of ABTS structural characterization of major products suggesting reaction between bromophenol and ABTS radicals.

Mild hydrolysis of nitriles by Fusarium solani strain O1.

High levels of an aromatic nitrilase (about 37 microkat/L culture) were induced in Fusarium solani O1 after transfer of the mycelium from a rich medium into a medium with 20 mmol/L picolinonitrile. The mycelium was entrapped in lense-shaped particles consisting of a polyvinyl alcohol/polyethylene glycol copolymer (LentiKats). The cell-free extract was immobilized by hydrophobic binding onto a Butyl Sepharose column. The enzyme was useful for the mild hydrolysis of nicotinonitrile, isonicotinonitrile and benzonitrile.