LEACHING OF GENETICALLY-MODIFIED PSEUDOMONAS-FLUORESCENS THROUGH INTACT SOIL MICROCOSMS - INFLUENCE OF SOIL TYPE

The leaching of a genetically modified Pseudomonas fluorescens through soil was investigated using intact (undisturbed) soil microcosms over a 2-month period. The microcosms comprised large cylindrical cores of three contrasting soil types (a loamy sand, a sandy loam, and a clay loam) supporting a grass/clover sward. Late log-phase cells of Pseudom onas fluorescens containing lux genes encoding for bioluminescence wer e applied to the surface of the soil cores. Eighteen hours after appli cation of the inocula, the microcosms were subjected to simulated rain events (9 mm per event) at 3-day intervals and leachates were analyse d for the concentration of genetically modified bacteria. The lux-modi fied pseudomonads were detected immediately in leachate from the clay looam with a steady decline in the concentration of cells with time. L eaching of pseudomonads from the sandy loam and loamy sand only occurr ed over a few rain events and total recoveries from the leachate were lower than from the clay loam. Leaching patterns are discussed in rela tion to differences in structure of top-soil and subsoil, which determ ine the pathways of water flow, and to the matric potential at inocula tion, which determines the pore-size classes into which cells were fir st introduced.