Shuffling genes around in hot environments: the unique DNA transporter of Thermus thermophilus

Natural transformation permits the transport of DNA through bacterial membranes and represents a dominant mode for the transfer of genetic information between bacteria and between microorganisms of distant evolutionary lineages and even between members of different domains. This phenomenon, known as horizontal, or lateral, gene transfer, has been a major force for genome plasticity over evolutionary history, and is largely responsible for the spread of fitness-enhancing traits, including antibiotic resistance and virulence factors. In particular, for adaptation of prokaryotes to extreme environments, lateral gene transfer seems to have played a crucial role. Here, we present a survey of the natural transformation machinery of the thermophile Thermus thermophilus HB27. A tentative model of the transformation machinery comprising of components similar to proteins of type IV pili and type II secretion systems is presented. A comparative discussion of the subunits and the structure of the DNA translocator and the underlying mechanism of transfer of free DNA in T. thermophilus highlights conserved and unique features of the DNA translocator in T. thermophilus. We hypothesize that the extraordinary broad substrate specificity and the high efficiency of the T. thermophilus DNA uptake system is of major importance for thermoadaptation and interdomain DNA transfer in hot environments.