Hypermutation and stress adaptation in bacteria |
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Authors: | Jayaraman R |
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Institution: | (1) Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48824, USA;(2) Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT 06520, USA |
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Abstract: | Hypermutability is a phenotype characterized by a moderate to high elevation of spontaneous mutation rates and could result
from DNA replication errors, defects in error correction mechanisms and many other causes. The elevated mutation rates are
helpful to organisms to adapt to sudden and unforeseen threats to survival. At the same time hypermutability also leads to
the generation of many deleterious mutations which offset its adaptive value and therefore disadvantageous. Nevertheless,
it is very common in nature, especially among clinical isolates of pathogens. Hypermutability is inherited by indirect (second
order) selection along with the beneficial mutations generated. At large population sizes and high mutation rates many cells
in the population could concurrently acquire beneficial mutations of varying adaptive (fitness) values. These lineages compete
with the ancestral cells and also among themselves for fixation. The one with the ‘fittest’ mutation gets fixed ultimately
while the others are lost. This has been called ‘clonal interference’ which puts a speed limit on adaptation. The original
clonal interference hypothesis has been modified recently. Nonheritable (transient) hypermtability conferring significant
adaptive benefits also occur during stress response although its molecular basis remains controversial. The adaptive benefits
of heritable hypermutability are discussed with emphasis on host–pathogen interactions. |
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