Monitoring field releases of genetically modified sugar beets for persistence of transgenic plant DNA and horizontal gene transfer

Field releases of transgenic rizomania-resistant sugar beet (Beta vulgaris) plants were accompanied by a study of the persistence of DNA from transgen ic sugar beet litter in soil and of horizontal gene transfer of plant DNA t o bacteria. The transgenic sugar beets contained the marker genes nptII and bar under the control of the bidirectional TR1/2 promoter conferring kanam ycin (Km) and glufosinate ammonium resistance to the plant. Primer systems targeting the construct allowed the specific and sensitive detection of the transgenic DNA in soil. Soil samples were analyzed by cultivation of bacte ria on nonselective and Km-selective media to determine the proportion of K m-resistant bacteria and to monitor the culturable fraction for incorporati on of transgenic plant DNA. To detect the presence of transgenic DNA indepe ndently from cultivation, total soil DNA was extracted and amplified by PCR with three different primer sets specific for the transgenic DNA. Longterm persistence of transgenic DNA could be shown under field conditions (up to 2 years) and also in soil microcosms with introduced transgenic plant DNA. No construct-specific sequences were detected by dot blot hybridizations o f bacterial isolates. The experimental limitations of detecting horizontal gene transfer from plants to bacteria under field conditions are discussed. (C) 1999 Federation of European Microbiological Societies. Published by El sevier Science B.V. All rights reserved.