Adaptive mutation inEscherichia coli strain FC40 |
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Authors: | Patricia L Foster William A Rosche |
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Institution: | (1) Department of Environmental Health, Boston University School of Public Health, 02118 Boston, MA, USA |
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Abstract: | Mutations can arise in static populations of cells that are subjected to nonlethal selective pressure, a phenomenon that has
been called ‘adaptive mutation’. This phenomenon has been extensively studied in FC40, a strain ofEscherichia coli that cannot metabolize lactose (Lac−) but that reverts to lactose utilization (Lac+) when lactose is its sole energy and carbon source. The adaptive Lac+ mutations arise by two mutational processes: a recombination-dependent process that is highly active on the episome carrying
the Lac− allele, and an unknown process that affects the whole genome. Most of the Lac+ mutations are due to the first process, which also produces nonselected mutations on the F′ episome. However, about 10% of
the Lac+ mutations arise in a subpopulation of cells that experience a period of transient hypermutation. Although minor contributors
to any one type of mutation, the hypermutators account for nearly all cases of multiple mutations. The evolutionary implications
of these results are: (i) DNA synthesis associated with recombination may be an important source of spontaneous mutation,
particularly in cells that are not actively growing; (ii) the efficient mutational mechanism that occurs on the episome could
result in the horizontal transfer of new alleles among species that carry and exchange conjugal plasmids; and (iii) a subpopulation
of transient hypermutators could be a source of multiple mutations that would allow for rapid adaptive evolution under adverse
conditions. |
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Keywords: | spontaneous mutation directed mutation stationary-phase mutation starvation-induced mutation recombination DNA replication |
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