The transfer of mobile genetic elements within populations and across species boundaries plays a vital role in the adaptation and evolution of bacteria. There are specific driving forces and constraints of gene transfer in different habitats, which thereby differ in transfer rates. The benefit of bacterial populations from permissiveness to gene acquisition may depend on the stability of their habitat. Plasmid-mediated genetic variation allowed rapid adaptive responses to challenges like irregular antibiotic or metal concentrations, or opportunities like the utilization of xenobiotic compounds. Cultivation-independent detection and capture of plasmids from soil bacteria, and complete sequencing provided new insights into their ecology. Broad-host-range plasmids like those belonging to IncP-1 transfer a wealth of accessory functions which are carried by similar plasmid backbones. Plasmids with a narrower host range can be more specifically adapted to particular species and often transfer genes which complement chromosomally encoded functions. For species, that frequently bear epidemic phytopathogenic strains, virulence factors may be acquired by horizontal gene transfer. Mobile genetic elements seem to be an ancient and successful strategy to ensure survival of a population in spatially and temporally heterogeneous conditions with various environmental stresses or opportunities, that occur irregularly or as a novel challenge.
The transfer of mobile genetic elements within populations and across species boundaries plays a vital role in the adaptation and evolution of bacteria. There are specific driving forces and constraints of gene transfer in different habitats, which thereby differ in transfer rates. The benefit of bacterial populations from permissiveness to gene acquisition may depend on the stability of their habitat. Plasmid-mediated genetic variation allowed rapid adaptive responses to challenges like irregular antibiotic or metal concentrations, or opportunities like the utilization of xenobiotic compounds. Cultivation-independent detection and capture of plasmids from soil bacteria, and complete sequencing provided new insights into their ecology. Broad-host-range plasmids like those belonging to IncP-1 transfer a wealth of accessory functions which are carried by similar plasmid backbones. Plasmids with a narrower host range can be more specifically adapted to particular species and often transfer genes which complement chromosomally encoded functions. For species, that frequently bear epidemic phytopathogenic strains, virulence factors may be acquired by horizontal gene transfer. Mobile genetic elements seem to be an ancient and successful strategy to ensure survival of a population in spatially and temporally heterogeneous conditions with various environmental stresses or opportunities, that occur irregularly or as a novel challenge.