EFFECT OF SELECTED DISINFECTANTS ON THE PERSISTENCE AND MOVEMENT OF AGENETICALLY-ENGINEERED PSEUDOMONAS SP IN SOIL

The effects of disinfectants on survival and movement of Pseudomonas U G14Lr were studied in soil microcosms. Twenty ml bacterial suspension (1.5 x 10(7) CFU/ml) were added to the surface of l-kg soil in microco sms, simulating an accidental release, followed by treatment with 20 m l of 5.0% (w/v) calcium hypochlorite, 75% (v/v) ethanol or 5.0% (v/v) formaldehyde at either 2, 24 or 48 h after inoculation. Microcosms wer e sampled by removing a soil core which was analyzed at 3 depths for t he presence of Pseudomonas sp. UG14Lr as well as total viable and non- viable cells using Lilve/Dead BacLight (Molecular Probes Inc. Oregon, USA), a commercially available fluorescent stain. UG14Lr cells remaine d concentrated in the upper 3 cm layer of the soil microcosms while de creasing in numbers toward the lower soil layer. However, upon additio n of ethanol or formaldehyde, the introduced strain moved toward the m iddle and lower soil layers. This trend was even more pronounced when disinfectants were added 2 h after inoculation. Pseudomonas sp. UG14Lr cells left in soil for 24 or 48 h before treatment with ethanol or fo rmaldehyde were killed, with the exception of a small number present i n the lower soil layer of ethanol-treated microcosms. Calcium hypochlo rite did not affect Pseudomonas sp. UG14Lr cell numbers but resulted i n a greater concentration of the introduced bacteria in the middle lay er of soil microcosms. There were more non-viable cells present at the surfaces of disinfectant-treated soil microcosms compared to the midd le and lower layers. Viable cell numbers were slightly reduced at micr ocosm surfaces upon addition of disinfectants. In ethanol-treated micr ocosms, viable cell numbers returned to those similar to untreated con trols within 2 weeks. These data demonstrated that vertical movement o f bacteria may be enhanced upon addition of antimicrobial agents. Addi tionally, the rime of chemical treatment may be an important considera tion in the event of an accidental spill of genetically engineered mic roorganisms.