Degradative Potential of Microorganisms from DDT-Contaminated Soils

Abstract

Four DDT-contaminated soils (designated BF, As9a, As20a and As41), varying in DDT concentration from 2–200 mg/kg, were screened for microorganisms with the ability to utilise a number of environmental pollutants. Bacterial inocula were obtained by shaking soils in 1/4-strength Ringer’s solution and suspension supernatants were used to inoculate a basal salts medium (BSM) containing 50 or 100 mg/1 of various environmental pollutants (PAHs, heterocyclic aromatic compounds, PCBs, PCP, DDT and DDT metabolites) as sole carbon and energy sources. After three successive enrichments in BSM containing the test compounds, growth was observed for all microbial communities on phenanthrene, 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane (DDD), 2,2-bis(p-chlorophenyl)-1,1-dichloroethylene (DDE), 2,2-bis(p-chlorophenyl)ethanol (DDOH) and dichlorobenzhydrol (DBH). The microbial community from BF soil was able to grow on a broad substrate range: growth was observed on the above mentioned compounds as well as pyrene, benzo[a]pyrene, dibenz[a,h]anthracene, carbazole, indole, biphenyl, Aroclor 1254, DDT, dichlorobenzhydrol (DBH), dichlorobenzophenone (DBP), dichlorodiphenylmethane (DPM) and diphenylmethane. No growth was observed for either of the communities when PCP was used as the carbon source. The microbial community from BF soil was used for the isolation of pure cultures. Pure cultures were isolated using a spray plate technique with the test compounds as the sole carbon and energy source. Six pure cultures (designated BF1-BF6) were isolated using phenanthrene as the carbon source, while two pure cultures (designated BF7 and BF8) were isolated using DDE as the carbon source. Substrate utilisation tests revealed the pure cultures had a limited substrate range compared to the mixed culture from where they were isolated.