Isolation and degradation ability of the DDT-degrading bacterial strain KK

A 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT)-degrading bacterium was isolated from soil samples that had been enriched with DDT over a prolonged period of time; these samples were collected from the sewer sludge of a pesticide factory and from DDT-contaminated fields. This consortium was acclimated by repeated passage through a mineral salt medium containing increasing concentrations of DDT. We examined the effects of various factors such as the pH, temperature, concentration of DDT, and the presence of an additional carbon source on the degradation rate of DDT. Based on the analysis of the phenotype, physiological and biochemical characteristics, and 16S rDNA, the strain KK was identified to belong to the bacteria Alcaligenes. The results showed that at the end of 10 days, the rate of degradation of DDT by the strain KK was 66.5%. When the additional carbon source concentration, pH, concentration of DDT, and cultivation temperature is 0.5%, 6, 10 mg l⁻¹, and 30°C, respectively, the biodegradation rate peaks. The results also suggested that (1) bacterial growth increases positively with an increase in the carbon source concentration; (2) the appropriate pH is between 8.0 and 10.0; and (3) the optimal temperature and DDT concentration are 30°C and 10 mg l⁻¹, respectively.