Bacterial and fungal contributions to chlorothalonil degradation in soil

The contributions of bacteria and fungi to the degradation of a chloroaromatic fungicide, chlorothalonil, in soil were evaluated quantitatively by a selective inhibition method. A mixture of ampicillin, chloramphenicol, and tetracycline was used to estimate the bacterial capacity, and cycloheximide to estimate the fungal capacity, A mixture of nutrient broth and yeast extract (NB + YE) was added to the soil to minimize the partial sterilization effect by antibiotics. The degradation of chlorothalonil was measured for a period of 6 h when the degradation rate and the carbon dioxide evolution rate were constant. The contribution rates estimated with the addition of NB+YE showed the same trend as the estimates with the addition of the dried powders of chlorothalonil-susceptible microorganisms, indicating the validity of NE + YE as a substrate for the chlorothalonil-degrading microorganisms. The contribution of the degrading fungi increased in the soils receiving farmyard manure (FYM). It was suggested that the accelerated biodegradation of chlorothalonil in FYM-amended soils was due to the activation of the degrading fungi.