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Systematics and Evolution |
Center for Microbial Ecology1, Department of Crop and Soil Science2 and Department of Microbiology3, Michigan State University, East Lansing, MI 48824, USA
Department of Biology, University of Idaho, Moscow, ID 83844, USA4
Author for correspondence: Terence L. Marsh. Tel: +1 517 432 1365. Fax: +1 517 432 3770. e-mail: marsht{at}pilot.msu.edu
Evolutionary pathways open to even relatively simple organisms, such as bacteria, may lead to complex and unpredictable phenotypic changes, both adaptive and non-adaptive. The evolutionary pathways taken by 18 populations of Ralstonia strain TFD41 while they evolved in defined environments for 1000 generations were examined. Twelve populations evolved in liquid media, while six others evolved on agar surfaces. Phenotypic analyses of these derived populations identified some changes that were consistent across all populations and others that differed among them. The evolved populations all exhibited morphological changes in their cell envelopes, including reductions of the capsule in each population and reduced prostheca-like surface structures in most populations. Mean cell length increased in most populations (in one case by more than fourfold), although a few populations evolved shorter cells. Carbon utilization profiles were variable among the evolved populations, but two distinct patterns were correlated with genetic markers introduced at the outset of the experiment. Fatty acid methyl ester composition was less variable across populations, but distinct patterns were correlated with the two physical environments. All 18 populations evolved greatly increased sensitivity to bile salts, and all but one had increased adhesion to sand; both patterns consistent with changes in the outer envelope. This phenotypic diversity contrasts with the fairly uniform increases in competitive fitness observed in all populations. This diversity may represent a set of equally probable adaptive solutions to the selective environment; it may also arise from the chance fixation of non-adaptive mutations that hitchhiked with a more limited set of beneficial mutations.
Keywords: Ralstonia, phenotypic radiation, diversity, mutation
Abbreviations: FAME, fatty acid methyl ester; SEM, scanning electron microscopy; TEM, transmission electron microscopy
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