Populations and activity of carbofuran-degrading microorganisms in soil

Abstract

Kendaia clay loam contained more than 10⁵ microbial cells per g able to convert ¹⁴C-carbonyl-labelled carbofuran (2,3-dihydro-2,2-dimethylbenzofuran-7-yl methylcarbamate) to ¹⁴CO₂ but never more than 130 cells per g transforming ¹⁴C-ring-labelled carbofuran to CO₂. The sizes of the population rarely increased as a result of addition of the insecticide to soil. Mineralization of these compounds proceeded with little or no acclimation phase, and subsequent additions were usually etabolized more readily, except at 10 mg of carbofuran per kg or if subsequent additions of the pesticide were made long after the first. More than 60% of the ¹⁴C in the carbonyl but less of the ¹⁴C in the ring was microbiologically converted to ¹⁴CO₂ in this soil. Streptomycin and cycloheximide each inhibited conversion of the carbonyl or ring carbon to CO₂. Urea but not NH₄NO₃ markedly inhibited the conversion of the carbonyl-labelled insecticide to ¹⁴CO₂. The addition of glucose and succinate together with the insecticide did not enhance mineralization of ring- or carbonyl-labelled carbofuran. The data suggest that soils containing a large population of microorganisms able to convert the carbonyl carbon to CO₂ will not show a marked effect of prior treatment with the insecticide and that few organisms individually are able to mineralize the ring.