Experimental Evolution of the Bacteriophage Group Leviviridae

University Of California-San Diego, La Jolla CA

Investigators

Abstract

The genetics of adaptation will be examined in the Leviviridae, a group of single stranded RNA phage. The phage will be selected for growth at high temperature. High temperature inhibits the growth of the wild-type phage. However, after propagating the phage at high temperature for several generations, phage fitness recovers. In this study, eight different phage species will be propagated (via serial transfer) at high temperature. The genetic changes associated with adaptation to fast growth at high temperature will be assayed by completely sequencing the evolved phage and comparing these sequences to the ancestral sequence for each species. The specific questions that will be addressed include: (1) what are the genetic changes associated with adaptation to high temperature, (2) what are the fitness effects of the genetic changes, (3) what is the distribution of fitness effects of mutations that are fixed during the course of adaptive evolution, (4) is the evolution repeatable within a phage species, (5) to what extent does the phylogeny of the species predict specific change associated with adaptation to growth at high temperature, and, (6) to what extent do changes in the RNA molecule increase the stability of important stem-loop structures at high temperature? The Leviviridae are unique in that they have a very high mutation rate and the function of much of the secondary structure of the RNA molecule has been worked out; hence, the functional significance of many adaptive changes can be understood. Moreover, because a well-supported phylogeny of the group exists, the genetic changes can be placed into a phylogenetic context.