Degradation of dichlorodiphenyltrichloroethane (DDT) by bacterial isolates from cultivated and uncultivated soil

The re-introduction of dichlorodiphenyltrichloroethane (DDT) to control mosquitos was recommended by the World Health Organization in 2007. In this study, the potential for biodegradation of DDT by soil microorganisms through enrichment and isolation of DDT biodegraders from soils without a history of prior exposure to DDT was done. Microorganisms from cultivated and uncultivated soils grew in minimal media with DDT (100 ppm) as the only carbon source. Six bacteria coded as isolates 101, 102, 103, 104, 105 and 110 degraded DDT to l, l-dichloro-2, 2-bis (p-chlorophenyl) ethane (DDD). None of the isolates degraded DDT into l, l-dichloro-2,2-bis (p-chlorophenyl) ethylene (DDE). Degradation by the mixed culture of the six isolates was higher (82.63%) than that of any individual isolates whose range was 28.48 - 58.08%. The identity of the isolates was determined through biochemical, morphological, physiological and molecular techniques. Isolate 101 was a member of the genus Bacillus; isolates 102 and 110 belonged to the genus Staphylococcus while isolates 103, 104 and 105 clustered with members of the genus Stenotrophomonas. This study showed that there are microorganisms in the soil that can degrade DDT and that the rate of degradation is dependent on the presence and numbers of microbes in the soil with the required degradative ability, environmental factors and access of the microbes to DDT.