Conjugation-Mediated Gene Transfer in Bacterial Strains to Be Used for Bioremediation

Plasmid-mediated conjugation has been widely used to transfer catabolic genes, metal resistance genes and other markers of relevance for bioremediation or bioaugmentation into gram-negative bacteria of interest (see Notes 1 and 2 ). Also, some soil gram-positive bacteria are accessible to broad-host range conjugative plasmids and vectors (1 -18 ). Conjugation-based processes have also been used to tag strains with reporter genes (19 -22 ) (see Note 3 ) and to pick up or capture various plasmids from soil mixtures into well-known recipients (23 -25 ) (see Notes 4 and 5 ) Moreover, many bacteria contam interesting metal resistance and catabolic markers in the chromosome that may be difficult to exchange if they are not transposon-borne. Use of plasmids with chromosomemobilizing activity (Cma⁺ ) or of plasmids able to form plasmid primes and to pick up chromosomal markers to transfer them can be considered in these cases (14 ,17 ,26 -31 ) (see Note 6 ). The latter variations on the main conjugation procedure will be described in the Notes