DEVELOPMENT AND USE OF A MOLECULAR SIGNATURE TAGGED RECIPIENT BACTERIAL STRAIN TO IMPROVE DETERMINATION OF HORIZONTAL GENE TRANSFER FREQUENCY IN THE ENVIRONMENT

International audienceAccording to analysis and comparison of numerous complete prokaryotic genome sequences, a significant proportion of the open reading frames in most prokaryotic genomes could have been acquired from other bacterial species by horizontal gene transfer (HGT). HGT is recognized as the main mechanism that has contributed to microbial evolution and has led to bacterial adaptation to various environments. However; there is a clear discrepancy between HGT frequencies deduced from in silico analysis and those resulting from in situ experiments in which transduction, conjugation, and natural genetic transformation were studied. In addition, numerous questions remain about the role that natural environments play in the maintenance and dispersion of bacterial genes and about the frequency with which these genes are exchanged among indigenous bacteria and whether they can spread from commensal strains to bacteria from other environments including clinical isolates. When considering complex and heterogeneous environments such as soil, detection and quantification of HGT events occurring in situ are limited by the lack of method sensitivity and specificity. In addition, conventional techniques based on the plating of environmental suspensions on growth media supplemented with selective factors (usually antibiotics) are biased because of the problem in discriminating between independent transfer events and clonal multiplication of transformants, transductants or transconjugants. Our objectives were to develop a new approach to provide a better assessment of the actual frequency of gene transfer. This was done by tagging every cell of a recipient Acinetobacter baylyi strain by a specific molecular signature that would detect independent transfer events as colonies exhibiting different molecular signatures. We will present the tagging technology and preliminary in vitro and in situ (soil) conjugation results based on the use of donor strains containing a conjugative plasmid and the tagged A. baylyi strain as recipient