Survival of free DNA encoding antibiotic resistance from transgenic maize and the transformation activity of DNA in ovine saliva, ovine rumen fluid and silage effluent

To assess the likelihood that the bla gene present in a transgenic maize li ne may transfer from plant material to the microflora associated with anima l feeds, we have examined the survival of fi ee DNA in maize silage effluen t, ovine rumen fluid and ovine saliva. Plasmid DNA that had previously been exposed to freshly sampled ovine saliva was capable of transforming compet ent Escherichia coli cells to ampicillin resistance even after 24 h, implyi ng that DNA released from the diet could provide a source of transforming D NA in the oral cavity of sheep. Although target DNA sequences could be ampl ified by polymerase chain reaction from plasmid DNA after a 30-min incubati on in silage effluent and rumen contents, only short term biological activi ty, lasting less than 1 min, was observed in these environments, as shown b y transformation to antibiotic resistance. These experiments were performed under in vitro conditions; therefore further studies are needed to elucida te the biological significance of free DNA in the rumen and ol al cavities of sheep and in silage effluent. (C) 2000 Federation of European Microbiolo gical Societies. Published by Elsevier Science B.V. All rights reserved.