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J. Bacteriol., 08 1995, 4417-4426, Vol 177, No. 15
C Schleper, I Holz, D Janekovic, J Murphy and W Zillig
A plasmid of 45 kb, designated pNOB8, was found in high copy number in a
new heterotrophic Sulfolobus isolate, NOB8H2, from Japan. Dissemination of
the plasmid occurred in six cultures of nine different Sulfolobus strains
when small amounts of the donor were added. These mixed cultures exhibited
a high average copy number of the plasmid, between 20 and 40 per
chromosome, and showed a marked growth retardation. Horizontal transfer of
pNOB8 was proved by isolating transcipients from mating mixtures via single
colonies. In these isolates, the copy number of the plasmid appeared to be
subject to a control mechanism. Cell-free filtrates of donor cultures did
not transmit the plasmid, and plating of the donor on lawns of recipients
did not result in plaque formation, suggesting that the transfer was not
mediated by a virus. Rapid formation of cell-to-cell contacts between
differently stained donor and recipient partners was demonstrated after the
two strains were mixed. Electron microscopic analysis of mating mixtures
revealed many cell aggregates made up of 2 to 30 cells and intercellular
cytoplasmic bridges connecting two or more cells. Cells that had been
transformed with purified plasmid DNA as well as transcipients isolated
from mating mixtures were shown to serve as donors for further transmission
of pNOB8. The plasmid undergoes extensive genetic variations, since
deletions and insertions were frequently observed in plasmid preparations
from the donor strain and from mating mixtures.
Copyright © 1995, American Society for Microbiology
A multicopy plasmid of the extremely thermophilic archaeon Sulfolobus effects its transfer to recipients by mating
Max-Planck-Institut fur Biochemie, Martinsried, Germany.
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