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Journal of Bacteriology, December 1998, p. 6597-6606, Vol. 180, No. 24
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Stability of the Agrobacterium
tumefaciens VirB10 Protein Is Modulated by Growth Temperature
and Periplasmic Osmoadaption
Lois M.
Banta,1,*
Jutta
Bohne,2,
S. Dawn
Lovejoy,1 and
Kathleen
Dostal1
Department of Biology, Haverford College,
Haverford, Pennsylvania 19041,1 and
Plant Science Institute, Department of Biology, University
of Pennsylvania, Philadelphia, Pennsylvania 191042
Received 21 May 1998/Accepted 7 October 1998
Export of oncogenic T-DNA from the phytopathogen
Agrobacterium tumefaciens is mediated by the products of
the virB operon. It has recently been reported (K. J. Fullner and E. W. Nester, J. Bacteriol. 178:1498-1504, 1996) that
DNA transfer does not occur at elevated temperatures; these
observations correlate well with much earlier studies on the
temperature sensitivity of crown gall tumor development on plants. In
testing the hypothesis that this loss of DNA movement reflects a defect
in assembly or maintenance of a stable DNA transfer machinery at high
temperature, we have found that steady-state levels of VirB10 are
sensitive to growth temperature while levels of several other VirB
proteins are considerably less affected. This temperature-dependent
failure to accumulate VirB10 is exacerbated in an attachment-deficient
mutant strain (chvB) which exhibits pleiotropic defects in
periplasmic osmoadaption, and virulence of a chvB mutant
can be partially restored by lowering the temperature at which the
bacteria and the plant tissue are cocultivated. Furthermore, the
stability of VirB10 is diminished in cells lacking functional VirB9,
but only under conditions of low osmolarity. We propose that newly
synthesized VirB10 is inherently labile in the presence of a large
osmotic gradient across the inner membrane and is rapidly degraded
unless it is stabilized by VirB9-dependent assembly into oligomeric
complexes. The possibility that VirB10-containing complexes are not
assembled properly at elevated temperatures suggests an explanation for
the decades-old observation that tumor formation is exquisitely
sensitive to ambient temperature.
*
Corresponding author. Mailing address: Department of
Biology, Haverford College, Haverford, PA 19041. Phone: (610) 896-4907. Fax: (610) 896-4963. E-mail: lbanta{at}haverford.edu.

Present address: Microbiology Department, University of
Würzburg, D-97074 Würzburg,
Germany.
Journal of Bacteriology, December 1998, p. 6597-6606, Vol. 180, No. 24
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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