Survival, plasmid transfer and impact of pseudomonas fluorescens introduced into soil

Abstract

The survival of donor, recipient and transconjugant strains of Pseudomonas fluo‐rescens, transfer of plasmid RP4 from donor to recipient, and impact of the introduced strains on indigenous microflora was determined in a sandy‐loam soil. The introduced donor and recipient strains survived significantly better in sterile than in non‐sterile soil where a progressive decline in their numbers with time was observed. In both soils, conjugation and plasmid RP4 transfer from donor to recipient cells was observed during the first 3 days. The transconjugant survived significantly better when it was the only strain inoculated into the soil. When introduced into soil pre‐colonized by the recipient strain, the transconjugant was undetectable. The introduced strains caused stimulation of total number of indigenous heterotrophic bacteria and selected physiological groups such as proteolytic, amylolytic and am monifying bacteria, but had no effect on the number of indigenous fungi. These results confirm the fact of limited survival of genetically modified pseudomonads introduced into soil. However, their potential for conjugation and impact on soil microflora are noteworthy from the aspect of ecological risk assessment.

Key words:

• indigenous microflora
• plasmid transfer
• pseudomonads
• survival