Degradation of Anilide Herbicides by Propham-Adapted Microorganisms

Abstract

A mixture of microorganisms cultured under nonsterile conditions on propham (isopropyl carbanilate) herbicide as the sole carbon source was tested for its ability to degrade a number of chlorinated and nonchlorinated anilide compounds. In separate tests under pure-culture conditions, species of the microbial mixture reacted individually in a manner similar to the nonsterile whole. The microorganisms grew and respired rapidly on nonchlorinated anilides, but ring chlorination depressed respiration and inhibited growth. Studies on the dimethylphenylureas indicated that the two methyl groups were primarily responsible for the biological stability of these compounds. All other anilides were degraded by hydrolysis of the side chain followed by metabolic degradation of the ring. Appearance of aniline in the medium depended on the relative rates of production by side chain hydrolysis and disappearance by ring degradation. Acylanilides were hydrolyzed more rapidly than carbanilates and chlorinated rings were degraded much more slowly than unchlorinated rings. Chlorination affected rates of ring degradation and microbial respiration in the following order (most rapid to least rapid): 0 > 2,4 > 2,4,5 > 3 > 4 ≥ 3,4. It is proposed that this unexpected degradative sequence might be explained in terms of the degree of microbial toxicity in the system generated by the formation of chloroazobenzenes from chloroaniline intermediates.