Horizontal gene transfer
Horizontal gene transfer enables bacteria to exchange DNA. The simplest mechanism for gene transfer is called transformation. Transformation is the import and inheritable integration of DNA from the environment. In other words, bacteria take up DNA from their environment. Subsequently, the newly acquired DNA either integrates into the chromosome or forms self-replicating plasmids.
From a physicist's point of view, the import of DNA into the cell is a very interesting problem. The DNA molecule has a length of several micrometers and forms a random coil in solution. The size of the pore in the cell envelope has a diameter of nanometers. While the DNA threads into the pore, the number of possible conformations of the DNA is reduced and the conformational entropy decreases. Hence, there has to be work done on the molecule to get it into a state associated with smaller entropy. To ensure directed transport of DNA into the cell, the bacterium must invest energy. We are investigating how chemical energy (e.g. binding energy, ATP, proton motive force) drives import of DNA.
From an evolutionary point of view, it is still unclear how the benefit of transformation outweighs its multiple costs. In general, this comes down to the question how recombination / sex speeds up adaptive evolution. One obvious advantage of gene transfer is that bacteria can rapidly acquire adaptive alleles such as genes encoding for antibiotic resistance. Moreover, gene transfer can reduce clonal interference and maladaptation. On the other hand, bacteria must invest energy to synthesize sophisticated machines in order to import DNA. Under certain conditions, gene transfer can slow down adaptive evolution. We are interested in how bacteria optimize the probability of gene transfer for speeding up adaptation.