Bdellovibrio is a Gram negative bacterium preying on other bacteria such as E. coli . It has a life cycle with two distinct growth phases: an extracellular attack phase, and a growth phase within the periplasm of its prey. During the growth phase the Bdellovibrio feeds on host macromolecules, including RNA and DNA. It is possible that as this process is taking place, gene transfer from prey to predator occurs. One way to analyze whether gene transfer has occurred during evolutionary time is to analyze the types of small mobile DNA sequences (IS elements) found in Bdellovibrio and compare them to those of E.coli . If the IS elements of Bdellovibrio resemble those characteristic of E. coli , it would be evidence of such a gene transfer event. The Bdellovibrio strain 109J-KAIRf was conjugally mated with the E.coli strain S17-1/pJK13. The pJK13 plasmid contains the sacB gene, expression of which is lethal in the presence of sucrose. The sacB gene can become inactivated when an IS element inserts itself into the gene, making a cell carrying that mutation sucrose resistant and thus identifiable. pJK13 was successfully conjugated into Bdellovibrio , and the resultant strain was shown to be sucrose sensitive. Sucrose resistant colonies have been isolated, and are under investigation at present. Analysis of plasmid DNA isolated from the sucrose resistant strains will hopefully lead to isolation of Bdellovibrio -specific IS elements and subsequent comparison to IS elements found in E.coli .