DISTRIBUTION OF A GENETICALLY-ENGINEERED ESCHERICHIA-COLI POPULATION INTRODUCED INTO SOIL

The spatial localization of the cells and the DNA of a genetically-eng ineered Escherichia coli population introduced into soil was investiga ted. Inoculated soils were size fractioned and bacterial numbers and E . coli EL1003 specific chromosomal DNA target sequences were enumerate d in each fraction using plate-counting and MPN-PCR, respectively. Dif ferent numbers of either indigenous or introduced bacteria were found in each fraction indicating that their distribution in the soil was no n-uniform. The distributions of the indigenous bacteria and the E. col i cells within the size fractions were significantly different: the E. coli population was mainly associated with the dispersible clay fract ion (79.0%) from which only 10.7% of the indigenous bacteria were reco vered. The distribution of the E. coli target DNA sequences was in agr eement with the location of the cells. The different distribution of t he two populations is likely to restrict genetic interactions. These r esults are relevant to potential interactions between native soil micr oflora and populations introduced into soil for competitive purposes.