Three R's of bacterial evolution: How replication, repair, and recombination frame the origin of species

The genetic diversity of bacteria results not only from errors in DNA repli cation and repair but from horizontal exchange and recombination of DNA seq uences from similar and disparate species as well. New individuals carrying adaptive changes are thus being spawned constantly among the population at large. When new selection pressures appear, these are the individuals that survive, at the expense of the general population, to forge new population s. Depending on the severity and uniqueness of the selection pressure, this could lead to new speciation. It is becoming more and more evident that, a s nucleotide sequences of numerous loci from many bacterial strains continu e to amass, horizontal transfer has played a key role in configuring the Es cherichia coli chromosome. Here, we examine views, both old and new, for th e role of recombination in the evolution of bacterial chromosomes. We prese nt novel phylogenetic evidence for horizontal transfer of three genes invol ved in DNA replication and repair (mutS, uvrD, and polA). These data reveal a prominent role for horizontal transfer in the evolution of genes known t o play a key role in the fidelity of DNA replication and, thus, ultimate su rvival of the organism. Our data underscore that recombination plays both a diversifying and a homogenizing role in defining the structure of the E. c oli genome. Published 2001 Wiley-Liss, Inc.