Transport of a genetically engineered Pseudomonas fluorescens strain through a soil microcosm

Abstract

Vertical soil microcosms flushed with groundwater were used to study the influence of water movement on survival and transport of a genetically engineered Pseudomonas fluorescens C5t strain through a loamy sand and a loam soil. Transport of cells introduced into the top 1 cm of the vertical soil microcosms was dependent on the flow rate of water and the number of times microcosms were flushed with groundwater. The presence of wheat roots growing downward in the microcosms contributed only slightly to the movement of P. fluorescens C5t cells to lower soil regions of the loamy sand microcosms, but enhanced downward transport in the loam microcosms. Furthermore, the introduced P. fluorescens C5t cells were detected in the effluent water samples even after three flushes of groundwater and 10 days of incubation. As evidenced by a comparison of counts from immunofluorescence and selective plating, nonculturable C5t cells occurred in day 10 soil and percolated water samples, primarily of the loamy sand microcosms. Vertical soil microcosms that use water movement may be useful in studying the survival and transport of genetically engineered bacteria in soil under a variety of conditions prior to field testing.

Pathogens in livestock waste, their potential for movement through soil and environmental pollution

“…Water flow rate, as governed by the intensity of rainfall, will also affect the rate and extent of translocation with faster flow rates increasing movement of both bacteria (Wollum and Cassel, 1978;Trevors et al, 1990;Huysman and Verstraete, 1993b) and viruses (Lance and Gerba, 1980;Lance et al, 1982). Field studies support these observations.…”

“…In addition to soil water content, percolating water, either in the form of irrigation or rainfall will affect translocation through the soil matrix. Trevors et al (1990) showed that in the absence of downward water flow, movement of a Pseudomonasfluorescens strain in soil columns was negligible, whereas following percolation the bacterium could be detected throughout the soil column and in the leachate. Similarly, Madsen and Alexander (1982) showed increased movement of both Rhizobium and Pseudomonas following percolation of soil cores.…”

“…The majority of information on this topic has been obtained from investigations of root colonization by biocontrol agents or plant growth promoting rhizobacteria, or from risk assessment studies of genetically engineered microorganisms. Root growth in general increases the translocation of bacteria through soil (Howie et al, 1987;Trevors et al, 1990;Van Elsas et al, 1991 ;Kemp et al, 1992) and the extent of the effect may be increased further with the presence of percolating water (Mawdsley and Burns, 1994).…”

“…Bitton et al (1974),Tan et al ( 1991 ),Huysman and Verstraete (1993a) Wong and Griffin (1976),Worrall and Roughley ( 1991 ) Wollum and Cassell (1978),Madsen and Alexander (1982),Trevors et al (1990), Huysman and Verstraete (1993b)Kemp et al (1992) Duboise et al (1976,Burge and Enkiri (1978),Kemp et al (1992) Ruddick and Williams (1972),Opperman et al (1987) Bitton (1975,Stenstrom (1989),Gannon et al ( 1991 ), Huysman and Verstraete (1993c)Howie et al (1987),Trevors et al (1990),Van Elsas et al ( 1991 ),Mawdsley and Bums (1994) Evans and Owens (1992),Patni et al (1985),Couillard and Li (1993) Baxter-Potter and Gilliland (1988),Patni et al (1985) Young et al (1980,Moore et al (1989),Walker et al (1990),Couillard and Li (1993) Khaleel et al (1980),Culley and Philips (1982), Baxter-Potter and GiUiland…”

Water flow induced transport of Pseudomonas fluorescens cells through soil columns as affected by inoculant treatment

“…In addition, possible effects of the vessel wall are more likely to occur in smaller systems. Both problems have been addressed in a previous paper [30], in which it was shown the experimental set-up used here did not suffer from a significant wall effect. In addition, repacked small soil columns do permit the study of particular factors under controlled environmental conditions.…”