Bacterial conjugation between Escherichia coli and Pseudomonas spp. donor and recipient cells in soil

Experiments conducted in microcosms containing loam soil samples inoculated with either E. coli or Pseudomonas spp. donor and recipient cells showed that bacterial cells survived and conjugated over a 24-h incubation period. E. coli transconjugants were detected 6 h after donor and recipient strains were introduced into sterile soil samples. In non-sterile soil samples, transconjugants were detected between 8 and 24 h incubation. Pseudomonas transconjugants were recovered from sterile soil samples between 6 and 12 h after their introduction and as early as 2 h in non-sterile soil. The results show that genetic interactions occur in non-sterile soil in relatively short periods of time at relatively high transfer frequencies (10(-3) to 10(-4]. Studies on genetic interactions in soil are becoming necessary in risk assessment/environmental impact studies prior to the release of genetically engineered or modified organisms into uncontained environments.