Watching bacterial gene transfer

Bacteria multiply by division and thus the daughter cells are genetically identical to their mother cells. To exchange genetic information, bacteria have evolved various mechanisms called horizontal gene transfer. Gene transfer is thought to speed up adaptive evolution, and plays an important role in the development of multidrug resistance.

The simplest mechanism of horizontal gene transfer is called transformation and describes the process of import and inheritable integration of DNA from the environment. Transformation is a stochastic event and thus the fate of a new clone and its offspring in a population is unpredictable. At the population level, we directly visualize the fate individual transformants. At the molecular level, it is still unclear how the DNA is transported into the bacterium. Current evidence suggests that a DNA import machine binds DNA externally, transports it through the cell envelope, and directly hands it over to the chromosome for recombination. To understand the molecular mechanism of DNA import, we have developed an approach combining nanomanipulation with single cell fluorescence, and molecular genetics. We characterize the spatio-temporal dynamics, reversibility, and force generation of DNA import.