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.
Veselá
A B
AB
Institute of Microbiology, Academy of Sciences of the Czech Republic, Vídenská , Praha, Czech Republic.
Franc
M
M
Pelantová
H
H
Kubác
D
D
Vejvoda
V
V
Sulc
M
M
Bhalla
T C
TC
Macková
M
M
Lovecká
P
P
Janů
P
P
Demnerová
K
K
Martínková
L
L
D039903:Actinobacteria / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D000577:Amides / Q000378:metabolism; D000581:Amidohydrolases / Q000378:metabolism; D000619:Aminohydrolases / Q000378:metabolism; D001673:Biodegradation, Environmental / Q000187:drug effects; D001711:Biotransformation / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid; D006540:Herbicides / Q000378:metabolism* / Q000633:toxicity*; D006868:Hydrolysis / Q000187:drug effects; D018545:Lactuca / Q000187:drug effects / Q000254:growth & development; D009570:Nitriles / Q000378:metabolism* / Q000633:toxicity*; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development; D012988:Soil Microbiology; D023382:Toxicity Tests, Acute
D000577:Amides; D006540:Herbicides; D009570:Nitriles; C014356:benzonitrile; D000581:Amidohydrolases; C019665:amidase; D000619:Aminohydrolases; C021867:nitrilase