Chapter 23 : Plasmid Detection, Characterization, and Ecology

Abstract:

Plasmid-mediated horizontal gene transfer is recognized as a major driving force for bacterial adaptation and diversification. Different environmental settings have distinct bacterial community compositions, which determine—possibly with the exception of broad host range plasmids—the type of dominant plasmids that can be found. It is assumed that only a fraction of a population carries plasmids, which ensures a rapid adaptation of the population to changing environmental conditions ( 1 ). Without a doubt, plasmid-mediated spread of antibiotic resistance genes among bacteria of different taxa is one of the most impressive examples of bacterial plasticity in response to various selective pressures ( 2 , 3 ). While the molecular biology of the plasmid-encoded replication, maintenance, and transfer processes of some plasmids has been studied for decades, little attention has been paid to their dissemination in the environment, their ecology, and the factors that drive their spread and diversification. In an overwhelming number of studies, the investigated plasmid-carrying strains originate from clinical specimens or diseased plant material, mostly human or plant pathogens. The reason for the lack of studies of the ecology of plasmids in natural settings was mainly the lack of tools to detect and quantify plasmids and to successfully culture their hosts.