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Journal of Bacteriology, May 2009, p. 3375-3383, Vol. 191, No. 10
0021-9193/09/$08.00+0     doi:10.1128/JB.01608-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Transsexuality in the Rhizosphere: Quorum Sensing Reversibly Converts Agrobacterium tumefaciens from Phenotypically Female to Male{triangledown}

Hongbaek Cho,{dagger},{ddagger} Uelinton M. Pinto,{ddagger} and Stephen C. Winans*

Department of Microbiology, Cornell University, Ithaca, New York 14853

Received 12 November 2008/ Accepted 5 March 2009

Conjugative plasmids generally encode proteins that block the conjugative entry of identical or similar plasmids into the host cell, a phenomenon known as entry exclusion. Here, we demonstrate that two Ti plasmids of Agrobacterium tumefaciens encode robust entry exclusion functions. Two proteins, TrbJ and TrbK, can each mediate entry exclusion and act synergistically. The trbJ and trbK genes are included within the trb operon, which is tightly regulated by the quorum-sensing regulator TraR and the cognate acylhomoserine lactone. In the absence of quorum-sensing signals, these proteins are not significantly expressed, and cells lacking TrbJ and TrbK are efficient Ti plasmid recipients. In the presence of these signals, these strains block the entry of Ti plasmids and instead become efficient conjugal donors.

* Corresponding author. Mailing address: Department of Microbiology, 360A Wing Hall, Cornell University, Ithaca, NY 14853. Phone: (607) 279-3886. Fax: (607) 255-3904. E-mail: scw2{at}cornell.edu

{triangledown} Published ahead of print on 20 March 2009.

{dagger} Present address: Department of Microbiology and Molecular Genetics, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115.

{ddagger} These authors made equal contributions.

Journal of Bacteriology, May 2009, p. 3375-3383, Vol. 191, No. 10
0021-9193/09/$08.00+0     doi:10.1128/JB.01608-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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