Cullum, Bennett & Lenski
Department of Biology
Evolutionary Adaptation to Temperature. IX. Preadaptation to Novel Stressful Environments of Escherichia coli Adapted to High Temperature.
Alistair J. Cullum
Department of Biology, Creighton University, 2500 California Plaza, Omaha, Nebraska 68178-0103 E-mail: email@example.com
Albert F. Bennett
Department of Ecology and Evolutionary Biology, University of California, Irvine, California 92697-2525 E-mail: firstname.lastname@example.org
Richard E. Lenski
Center for Microbial Ecology, Michigan State University, East Lansing, Michigan 48824-1325 E-mail: email@example.com
Evolution 55(11):2194–2202 (2001)
Abstract - Stressful environments may be considered as those that reduce fitness, sometimes due in part to the increased metabolic expenditure required to sustain life. Direct adaptation to a stressor is expected to increase fitness and reduce maintenance metabolism, with the latter leading to increased biomass production. In this study, we test the general hypothesis that such adaptation to one stressor can preadapt organisms to novel stressful environments. Six lines of Escherichia coli propagated for 2000 generations at 41–42°C (42 group), a stressful temperature, were compared to six control lines propagated for 2000 generations at 37°C (37 group) and to the common ancestor of both groups. We assayed biovolume yield (a measure of growth efficiency) and competitive fitness in the 42 group's selective high temperature environment as well as five novel stressful environments—acid, alkali, ethanol, high osmolarity and peroxide. As previously reported, at high temperature the 42 group had both higher yield and fitness than the 37 group and ancestor. In the novel environments, the 42 group generally produced yields higher than the 37 group (and marginally higher than the ancestor), but we found no differences in competitive fitness among the 37 and 42 groups and the ancestor. We also found that the performance of lines within groups was not correlated across stressful environments for either yield or relative fitness. Because previous adaptation to one stressor did not improve our measure of Darwinian fitness in novel stressful environments, we conclude that the 42 group shows no useful preadaptation, or cross-tolerance, to these types of environments.