Studies on the degradation of an isoxazolone fungicide by pure cultures of soil bacteria

Abstract

Soils enriched with 4-(2-chlorophenylhydrazono)-3-methyl-5-isoxazolone (drazoxolon) yielded 70 bacterial isolates capable of degrading this fungicide. An Aerobacter cloacaelike organism and a non-fluorescent Pseudomonas sp. were found to degrade drazoxolon preferentially in neutral to alkaline media and were able to use the compound as a sole source of nitrogen giving rise to 2-(2-chlorophenylhydrazono)-acetoacetic acid (metabolite I) and o-chloraniline. The type of energy source influenced the degradation of both drazoxolon and metabolite I, glucose apparently repressing the extent and rate of degradation. Metabolite I was toxic to both organisms at a concentration of 4.14 × 10 −4 m but was degraded at half this concentration. Metabolite I was apparently incapable of acting as sole nitrogen source. Both organisms were capable of degrading the fungicide at concentrations ranging from 4.2 × 10 −4 mto 2.1 × 10 −2 m and both isolates were shown to degrade commercial formulations of the fungicide. Crude enzyme preparations were capable of degrading the pesticide to metabolite I only. It is thought that two discrete enzyme systems are responsible for the degradation to o-chloraniline via metabolite I. The sequence of degradation and the nature of all intermediates has not been fully elucidated.