Competition between different mutants ofpseudomonas fluorescensintroduced into soil

Survival of introduced Psudomonas fluorescens strains having different genetic modification, and survival of Tn 5 mutant in the presence of wild‐type parent strain and nonparent nalidixic acid (Nx) resistant mutant, was compared in soil microcosms. Competition between the introduced strains was determined in the rhizosphere of bean seedlings and in the nonrhizosphere soil. In both habitats, no significant differences in the numbers of P. fluorescens modified by insertion of plasmid RP4 into the cell or transposon Tn 5 into the chromosome were found. The Tn 5 mutant showed decreased survival in both environments as compared with the wild‐type parent strain and the nonparent Nx‐resistant mutant. The results of this study indicate that genetic modification of bacterial cells may decrease their fitness in the environment but that there is no significant difference between the effects of either plasmid RP4 or transposon Tn 5 introduction into the cells.