Abstract

The horizontal spread of plasmids among natural bacterial populations serves as an evolutionary function for adaptation to the ups and downs in nature. Recent evolutionary challenges are the introduction of antibiotics and the creation of new environmental conditions in agriculture and medical care. As a consequence, surviving bacterial populations have acquired new genetic determinants which enable the colonisation and maintenance in distinct ecological niches. The acquisition of new genetic determinants can take place rather rapidly because of the plasmids' biology: their self-transferability and their ability to pick up genes. As an example of horizontal gene transfer, from an ecological and evolutionary viewpoint, the emergence of resistance to streptothricins (sat genes) is described.