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J. Bacteriol., 06 1996, 3037-3043, Vol 178, No. 11
JE Peters, IM Bartoszyk, S Dheer and SA Benson
F plasmids use surface exclusion to prevent the redundant entry of
additional F plasmids during active growth of the host cells. This
mechanism is relaxed during stationary phase and nonlethal selections,
allowing homosexual redundant plasmid transfer. Homosexual redundant
transfer occurs in stationary-phase liquid cultures, within nongrowing
populations on solid media, and on media lacking a carbon source. We
examined the relationship between homosexual redundant transfer, which
occurs between F+ hosts, and reversion of a plasmid-encoded lac mutant
allele, lacI33omegalacZ. Sodium dodecyl sulfate (SDS) and mutations that
prevent normal transfer to F- cells reduced redundant transfer and
selection-induced reversion of the lacI33omegalacZ allele. A recA null
mutation reduced redundant transfer and selection-induced reversion of the
lacI33omegalacZ mutation. Conversely, a recD null mutation increased
redundant transfer and selection-induced reversion of the lacI33omegalacZ
allele. These results suggest an explanation for why SDS and these
mutations affect reversion of the plasmid lacI33omegalacZ allele. However,
a direct causal relationship between transfer and reversion remains to be
established. These results suggest that Rec proteins play an active role in
redundant transfer and/or that redundant transfer is regulated with the
activation of recombination. Redundant homosexual plasmid transfer during a
period of stress may represent a genetic response that facilitates
evolution of plasmid- encoded functions through mutation, recombination,
reassortment, and dissemination of genetic elements present in the
populations.
Copyright © 1996, American Society for Microbiology
Redundant homosexual F transfer facilitates selection-induced reversion of plasmid mutations
Department of Microbiology, University of Maryland at College Park, 20742, USA.
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