The Study of Microbial Adaptation by Long-Term Experimental Evolution

Abstract

Experimental evolution, the research approach discussed in this chapter, permits study of the fundamental processes of adaptation that underlie microbial evolution under controlled laboratory conditions. Long-term evolution experiments with microbes have displayed numerous elements of the complexity of natural systems and have therefore permitted the study of fundamental questions in evolutionary biology, ecology, physiology, and genetics. This chapter focuses on a few long-term, open-ended studies as well as other relevant experiments that best illustrate specific problems. Despite many excellent studies using fungal and viral models, the chapter is focused primarily on bacterial systems with occasional mention of viral systems. Specific topics under consideration include the dynamics of adaptation, the genetic and physiological bases of fitness, causes of specialization and functional losses, evolution of mutation rates, and models of the evolution of virulence. At the end of the chapter, the author addresses prospects for future experiments to study the evolution of pathogens. The author refers repeatedly to two longterm experiments throughout this chapter. The first involves the long-term experimental evolution of 12 populations of Escherichia coli B, originally founded by Richard Lenski in 1988. The second experiment of this review was derived from this first one. The chapter discusses selected examples in which the mechanisms and consequences of genetic adaptation were discovered. The evidence that important steps in microbial evolution have been driven significantly, and perhaps mostly, by interspecies recombination continues to grow.