Resistance of microbial populations in DDT-contaminated and uncontaminatedsoils

One DDT-contaminated soil and two uncontaminated soils were used to enumera te DDT-resistant microbes (bacteria, actinomycetes and fungi) by using soil dilution agar plates in media either with 150 mug DDT ml(-1) or without DD T at different temperatures (25, 37 and 55 degreesC). Microbial populations in this study were significantly (p<0.001) affected by DDT in the growth m edium. However, the numbers of microbes in long-term contaminated and uncon taminated soils were similar, presumably indicating that DDT-resistant micr obes had developed over a long time exposure. The tolerance of isolated soi l microbes to DDT varied in the order fungi>actinomycetes>bacteria. Bacteri a from contaminated soil were more resistant to DDT than bacteria from unco ntaminated soils. Microbes isolated at different temperatures also demonstr ated varying degrees of DDT resistance. For example, bacteria and actinomyc etes isolated at all incubation temperatures were sensitive to DDT. Convers ely fungi isolated at all temperatures were unaffected by DDT. (C) 2001 Els evier Science B.V. All rights reserved.