Accelerated degradation of thiocarbamate herbicides in Israeli soils following repeated use of vernolate

Accelerated degradation of metam-sodium in soil and consequences for root-disease management

We studied the development of accelerated degradation (AD) of methyl isothiocyanate (MITC) following repeated applications of its parent compound, metam-sodium (MS). Laboratory studies and four sets of field experiments were conducted during 2002-04 in three commercial fields in Israel. Repeated applications of MS to the three soils in the laboratory under controlled conditions demonstrated AD of MITC in some soils. In a peanut field, MS significantly reduced the incidence of Pythium pod rot and improved pod quality after a single application but its effectiveness was greatly reduced after two applications. In a second experiment, MS was significantly effective after a single application in controlling Verticillium wilt in potato but its efficacy diminished after three consecutive applications. In an additional experiment, fumigation with MS following single or double applications was more effective in reducing Verticillium wilt severity of potato compared with triple applications. Soils which did not develop AD of MITC were also recorded. Preplant MS fumigation of melon fields was effective at reducing sudden wilt following a single and two consecutive applications. Our study shows that development of AD of MITC might occur following repeated applications of MS in commercial fields. The data on MITC dissipation in soil following repeated MS applications under controlled conditions indicate the chemical's potential loss of activity under regular agricultural practices and the need for a management strategy to prevent such a development.

Isolation and characterization of a carbofuran-degrading strainNovosphingobiumsp. FND-3

A gram-negative Novosphingobium sp. strain FND-3 capable of degrading carbofuran was isolated and characterized. The carbofuran-degrading ability of strain FND-3 was investigated under various culture conditions. Strain FND-3 showed a high average carbofuran-degrading rate of 28.6 mg L(-1) h(-1) in mineral salts medium with 100 mg L(-1) carbofuran. GC/MS analysis pointed out the presence of several unknown metabolites. One hydrolyzate was identified as 2-hydroxy-3-(3-methypropan-2-ol) phenol via hydrolysis of carbofuran phenol. The appearance of another metabolite with M(+) of 180 m/z indicated that the hydroxylation of carbofuran occurred at the aromatic ring. One novel degrading product with M(+) of 239 m/z was identified as 2-hydroxy-3-(3-methylpropan-2-ol) benzene-N-methylcarbamate via hydrolyzing at the ether bond of furanyl ring of carbofuran. Strain FND-3 was also able to degrade other N-methylcarbamate pesticides.

Nucleotide sequence and genetic structure of a novel carbaryl hydrolase gene (cehA) from Rhizobium sp. strain AC100

Rhizobium sp. strain AC100, which is capable of degrading carbaryl (1-naphthyl-N-methylcarbamate), was isolated from soil treated with carbaryl. This bacterium hydrolyzed carbaryl to 1-naphthol and methylamine. Carbaryl hydrolase from the strain was purified to homogeneity, and its N-terminal sequence, molecular mass (82 kDa), and enzymatic properties were determined. The purified enzyme hydrolyzed 1-naphthyl acetate and 4-nitrophenyl acetate indicating that the enzyme is an esterase. We then cloned the carbaryl hydrolase gene (cehA) from the plasmid DNA of the strain and determined the nucleotide sequence of the 10-kb region containing cehA. No homologous sequences were found by a database homology search using the nucleotide and deduced amino acid sequences of the cehA gene. Six open reading frames including the cehA gene were found in the 10-kb region, and sequencing analysis shows that the cehA gene is flanked by two copies of insertion sequence-like sequence, suggesting that it makes part of a composite transposon.

Purification and Characterization of Carbaryl Hydrolase from Blastobacter sp. Strain M501

A bacterium capable of hydrolyzing carbaryl (1-naphthyl- N -methylcarbamate) was isolated from a soil enrichment. This bacterium was characterized taxonomically as a Blastobacter sp. and designated strain M501. A carbaryl hydrolase present in this strain was purified to homogeneity by protamine sulfate treatment, ammonium sulfate precipitation, and hydrophobic, anion-exchange, gel filtration, and hydroxylapatite chromatographies. The native enzyme had a molecular mass of 166,000 Da and was composed of two subunits with molecular masses of 84,000 Da. The optimum pH and temperature of the enzyme activity were 9.0 and 45°C, respectively. The enzyme was not stable at temperatures above 40°C. The purified enzyme hydrolyzed seven N -methylcarbamate insecticides and also exhibited activity against 1-naphthyl acetate and 4-nitrophenyl acetate.