Possible reasons for the failure of natural microbial community to degrade low concentration of 2,4-dichlorophenol.

Abstract

The rapid microbial degradation of 2, 4-dichlorophenol (DCP) at 1.0μg DCP-C/ml in a groundwater was observed when the density of responsible degraders, estimated by the most probable number (MPN) method, had increased to 105 cells/ml. However, no degradation of 0.1 or 0.03μg DCP-C/ml was observed even when the density of degraders had increased to 104-105 cells/ml. Rapid degradation of 0.1μg DCP-C/ml occured within a day in the qroundwater in which 1.0μg DCP-C/ml was degraded beforehand, but not in the groundwater which had been precultured with 0.1μg DCP-C/ml. Addition of mineral nutrients enhanced the degradation of 0.1μg DCP-C/ml, but not the growth of degraders. These results suggest that in the groundwater the failure of DCP degradation at low concentration may be attributable to the failure of degraders to express their DCP-degrading activity, such as induction of responsible enzyme(s), and not to the failure to grow or to increase their density.