Conjugative plasmids in anthropogenic soils

Abstract

Horizontal transfer of mobile genetic elements such as plasmids and bacteriophages and their associated hitchhiking elements such as transposons, integrative and conjugative elements and insertion sequences shapes bacterial chromosomes and enables their adaptation to changing environmental conditions. In soils, a diversity of conjugative plasmids involved in microbial metabolism, coping with stress factors or providing their carriers with traits outcompeting competitors in the ecological niche have been detected by classical and molecular techniques. The rhizosphere displays a hot spot for conjugative plasmid transfer in soil. Plasmid transfer has been studied in a variety of soil habitats from pristine to heavily polluted soils, such as heavy metal and radionuclide contaminated ones. In all of these environments, plasmid transfer has been demonstrated to contribute to the spread of genes that provide their recipients with ecological traits conferring adaptation to contaminant stress, to cope with the presence of toxic pharmaceuticals (e.g. antibiotics) or enable them to degrade xenobiotic compounds. Transconjugants harbouring the traits acquired by horizontal transfer were shown to survive in soil and to spread the acquired beneficial factors to both indigenous related and phylogenetically distant microorganisms. PCR screens have been developed to detect conjugative plasmids of different incompatibility groups and virulence/pathogenicity-encoded traits in a rapid, reliable and sensible way. This chapter summarizes the state of the art of mobile genetic elements and their transmission in soils.