Leaching of Pseudomonas aeruginosa, and transconjugants containing pR68.45 through unsaturated, intact soil columns

Abstract

Leaching of genetically engineered microbes (GEMs) through soil is a significant concern related to groundwater quality.The objective of this study was to examine the leaching, survival and gene transfer of a genetically engineered microbe and indigenous recipients of pR68.45 in nonsterile, undisturbed soil columns. Pseudomonas aeruginosa PAO25, containing the plasmid R68.45, was added to the surface of undisturbed soil columns (10 em diameter x 80 cm length). Unsaturated flow conditions were maintained by 100 ml daily additions of 2 mM CaCI2 for a period of 70 days. The population of the GEM exhibited a significant (P = 0.05) linear decline with time. The GEM leached only to a depth of 30-40 cm in 70 days. Transfer of pR68.45 was shown to occur from P. aeruginosa into the indigenous bacterial population although relatively low numbers of transconjugants were observed (log 2 cfu g-1 dry soil). The number of transconjugants also decreased with depth and time. Leaching of transconjugants, however, occurred more readily than that of the GEM, probably as a result of ptasmid transfer into smaller, more mobile bacteria. At 70 days incubation, no GEMs were detected in the columns, while transconjugants were observed at several depths. These results demonstrate the importance of examining both the survival and movement of GEMs and transconjugants in soil.

Dispersal of plasmid pJP4 in unsaturated and saturated 2,4-dichlorophenoxyacetic acid contaminated soil

“…However, these studies were generally conducted in batch microcosms with little work done to evaluate the transport, or dispersal, of introduced genes. Although a few studies have concurrently assessed plasmid transfer from an introduced donor to indigenous recipients in conjunction with plasmid fate within a soil [8,15], to our knowledge, this is the ¢rst study conducted under both unsaturated and saturated £ow conditions to assess plasmid dissemination through donor transport and transconjugant dispersal.…”

Dispersal of plasmid pJP4 in unsaturated and saturated 2,4-dichlorophenoxyacetic acid contaminated soil

“…However, these studies were generally conducted in batch microcosms with little work done to evaluate the transport, or dispersal, of introduced genes. Although a few studies have concurrently assessed plasmid transfer from an introduced donor to indigenous recipients in conjunction with plasmid fate within a soil [8,15], to our knowledge, this is the first study conducted under both unsaturated and saturated flow conditions to assess plasmid dissemination through donor transport and transconjugant dispersal.…”