Aerobic degradation of dichlorodiphenyltrichloroethane (DDT) by Serratia marcescens DT-1P

Abstract

Microbial degradation of 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT)-residues is one of the mechanisms for the removal of this compound from the environment. A DDT-degrading consortium was isolated by long term enrichment of soil samples collected from DDT-contaminated fields. This consortium was acclimated by repeated passages through a mineral salt medium containing increasing concentrations of DDT. This acclimated consortium could degrade 25 ppm of DDT in 144 h. The consortium consisted of four bacteria. Of these, Serratia marcescens DT-1P was used for further studies. Various factors such as inoculum size, concentration of DDT, pH, temperature, presence of co-substrates, the type of carbon source used influenced the degradation of DDT in shake flasks. Complete degradation was observed up to 15 ppm DDT, followed by inhibitory effects at higher concentrations showing a total loss of degradative ability at 50 ppm DDT. Effective degradation of DDT was obtained with the inoculum pre-exposed to DDT for 72 h. Degradation was inhibited in the presence of auxiliary carbon sources such as citrate, rice straw hydrolysate. However, the presence of yeast extract, peptone, glycerol and tryptone soya broth (TSB) showed complete disappearance of DDT. Mesophilic temperatures (26–30 °C) and near neutral pH (6.0–8.0) were most favourable for degradation. This microbial culture holds the potential for use in bioremediation of DDT-contaminated soils, waste deposits and water bodies.