Fate of invading bacteria in soil and survival of transformants after simulated uptake of transgenes, as evaluated by a model system based on lindane degradation
Résumé
Emergence of bacteria carrying new traits resulting from mutations, gene synthesis by gene-shuffling or acquisition of exogenous DNA underpins the need to better understand factors influencing their spread and establishment. Studies of soils may be difficult, since the gene of interest is often already present in high numbers. The gene linA, responsible for the first dechlorination steps during degradation of lindane (gamma-hexachlorocyclohexane), has low background levels in soil and is simple to detect. Development of transgenic plants containing linA and newly proposed approaches to bioremediation by in situ electrotransformation after addition of a vector carrying this gene call for documentation on the fate of bacteria that incorporate it. We inserted linA into the broad-host-range conjugative RP4-plasmid and transferred it to different soil bacteria which were inoculated into soil microcosms in the presence/absence of lindane. Similar experiments were performed using Sphingobium francense Sp+, which carries all genes for complete lindane degradation. This strain increased in numbers during lindane mineralization, but other bacteria increased more, resulting in a modified bacterial community structure. The engineered strains decreased below the detection limit, but rose in numbers after nutrient addition, demonstrating that new invading bacteria may persist in soil in the form of small populations over extended time periods. (C) 2012 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.