An E. coli host with chromosomally encoded IncP1transfer genes containing a czc marked IncP1 plasmid (pDN705) proved an excellent vehicle for studying plasmid transfer in soil microcosms. Intergeneric transfer of heavy metal resistance genes was strongly stimulated in heavy metal polluted soil. With this system the positive effects of the czc cassette on bacterial growth and survival in heavy metal polluted soils was clearly demonstrated.
The recirculating stream microcosm proved to be an excellent laboratory model for examining plasmid transfer in river epilithon at a wide range of temperatures. This system will be a useful tool for predicting both the transfer of recombinant genes and survival of GEMs in rivers with organisms which cannot be released into the environment. Many natural, large, conjugative epilithic plasmids were capable of retro capturing a small recombinant plasmid. Thus retrotransfer is a probable mechanism for the capture of recombinant genes from GEMs by natural bacterial populations.
A restriction assay based on comparisons of plasmid transfer rates and stability of RP4 and a RP4::miniMu cointegrate proved very efficient at describing the restriction status of many natural soil and water bacterial isolates. The restriction status of many fluorescent pseudomonads was shown to affect the transfer proficiency of a natural epilithic plasmid in situ and in laboratory experiments. Surprisingly most natural P. putida were restriction negative.
The Mud(lac)-marker has proven to be very useful in ecological studies of survival and mobility with plant growth promoting pseudomonads.
Mutants of plant growth promoting pseudomonads with an impared survival were isolated (sss) and could be used as containment systems.