A review of available systems to investigate transfer of DNA to indigenous soil bacteria.

The deliberate or accidental release of genetically engineered microorganisms (GEMs) in the environment has led to some questions concerning microbial survival, transfer of DNA to the indigenous microflora and environmental consequences. Amongst horizontal gene transfer mechanisms, conjugation is probably the most frequent in the environment. With the aim of evaluating risks associated with environmental release of GEMs and their engineered DNA, studies of conjugative gene transfer between a donor strain and indigenous microflora have been conducted. Such studies required the development of a donor counterselection system to prevent growth of donor cells on transconjugant selective plates. This review summarizes the known and potential donor counterselection systems.