PARENT SESSION
32 - Survival and Behavior of Genetically Modified Organisms
2:10 PM to 5:20 PM, Tuesday, 14 May 2002
Session Chair: Gaugitsch, Helmut ¹, Tebbe, Christoph ², ^{1 2} .
Stolz B

(32-01) Field and soil microcosm studies on conjugal transfer of atrazine degradation genes between Pseudomonas species.

LaBossiere, Danielle¹, Germida, James^*,1, ¹ University of Saskatchewan, Saskatoon, Saskatchewan

ABSTRACT- Atrazine is an s-triazine herbicide used extensively for the control of broad-leaved weeds. The persistence of the herbicide and its widespread usage have contributed to the contamination of ground and surface water. The prevalence of atrazine in the environment has stimulated investigations into the use of bacteria for the in situ degradation of this environmental pollutant. Plasmid-encoded pathways such as atrazine degradation are advantageous because they can potentially lead to the dispersion of the degradation genes to other soil bacteria. This study assessed the survival of a genetically engineered Pseudomonas putida strain CR30RNS (pADPTel) in the field and in soil microcosms, and its ability to transfer genes for atrazine degradation and tellurite resistance to indigenous soil bacteria. The P. putida strain survived for up to seven weeks in soil microcosms at approximately 10⁵ cfu per g dry soil, whereas the population in the field soil declined to undetectable levels by the fourth week. The P. putida strain survived longer in the rhizosphere of canola plants in the field and microcosm soils, whereas the presence of atrazine had no effect on its persistence. Indigenous soil bacteria were capable of receiving the plasmid from this P. putida strain under optimized laboratory conditions. However, no conjugal plasmid transfer to indigenous soil bacteria was detected in the field or microcosm soils regardless of the presence or absence of a canola rhizosphere. Our results show that the survival and population size of genetically engineered bacteria might be sufficient for degradation of environmental pollutants, but that plasmid transfer frequency was too low to cause dispersion of the beneficial phenotype under the conditions of this study.

Key words: gene transfer, herbicide, catabolic plasmid