Chapter 9 - The Dynamics of Bacterial Genomes

Abstract

This chapter discusses the dynamics of bacterial genomes. It reveals that the availability of complete genome sequences for large numbers of microorganisms has catalyzed a paradigm shift on how evolutionary biologists view the bacterial chromosome. Two sets of processes that affect the character of microbial genomes, mutation and recombination, and their roles in microbial evolution are quite different. Mutational processes alter the sequences of existing genes. Ultimately, mutations produce all of the variation seen among extant organisms. Even when examining multiple species, only a small number of differences between any two forms of a gene may affect that gene's function or expression, if at all. Therefore, while mutational processes are ubiquitous, their impact in cellular evolution is necessarily smaller than their numbers suggest. Recombinational processes serve to reassort genes among genomes. Intraspecific recombination acts to distribute variant alleles—including, but not restricted to, those arising by mutational processes—among members of a bacterial species.