ON THE TRACK OF NATURAL TRANSFORMATION IN SOIL

The understanding of microbial gene transfer including how bacteria ac quire and disseminate genes in natural environments wilt provide data on the role of horizontal transfer in evolution. This understanding ha s been stimulated in recent years by concern about the impact of genet ically engineered microorganisms on natural environments. This prospec t has increased interest in determining the regulatory mechanisms of i ndigenous microbial populations as well as detecting genetic interacti ons between bacteria introduced into soil and the indigenous microflor a. This paper will review the strategies developed to demonstrate whet her the different steps required by natural bacterial transformation ( the uptake of naked DNA by competent bacteria) could actually occur in soil. This will include a review on the release of DNA from microbial cells by passive or active mechanisms, its persistence by adsorption of extracellular DNA onto major soil components such as sand or clay m inerals and the uptake of DNA by competent bacteria.