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Journal of Bacteriology, July 2008, p. 4398-4407, Vol. 190, No. 13
0021-9193/08/$08.00+0     doi:10.1128/JB.01684-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Induction and Loss of Ti Plasmid Conjugative Competence in Response to the Acyl-Homoserine Lactone Quorum-Sensing Signal{triangledown}

Shengchang Su,{dagger} Sharik R. Khan, and Stephen K. Farrand*

Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801

Received 18 October 2007/ Accepted 8 January 2008

Conjugative transfer of the Ti plasmids of Agrobacterium tumefaciens is controlled by a quorum-sensing system composed of TraR and its signal N-(3-oxo-octanoyl)-L-homoserine lactone. This system is, in turn, controlled by the conjugative opines produced by crown gall tumors induced on plants by the bacteria. Using nonpolar traI mutants, we examined the kinetics of induction of conjugative transfer in response to exogenous acyl-homoserine lactone. In the absence of the antiactivator TraM, onset of induction of transfer requires about 30 min, 15 to 20 min of which is needed for expression and construction of the conjugative apparatus. TraM delays the onset of conjugation by 30 min. While the rate of development of conjugative competence was not significantly affected by levels of TraR, maximum efficiencies of transfer were correlated with amounts of the activator in the donors. Donors harboring Ti plasmids lacking TraM were fully induced by the quormone at concentrations as low as 100 pM. TraM raised the concentration of signal required for maximum activity to 1 nM. Donors grown in batch culture retained conjugative competence following signal removal, even when in stationary phase. However, donors kept in balanced growth rapidly lost transfer ability following signal removal. Loss of transfer was mirrored by a decrease in levels of active TraR. Decreases in TraR activity and conjugative competence could be accounted for by dilution associated with cell division, suggesting that while induction of Ti plasmid conjugation is an active process, the cells lack a mechanism for disassembling the conjugative apparatus when signals become limiting.

* Corresponding author. Mailing address: Department of Microbiology, University of Illinois at Urbana-Champaign, B103 CLSL, 601 South Goodwin Avenue, Urbana, IL 61801. Phone: (217) 333-1524. Fax: (217) 244-6697. E-mail: stephenf{at}uiuc.edu

{triangledown} Published ahead of print on 18 January 2008.

{dagger} Present address: Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati College of Medicine, Cincinnati, OH 45267.

Journal of Bacteriology, July 2008, p. 4398-4407, Vol. 190, No. 13
0021-9193/08/$08.00+0     doi:10.1128/JB.01684-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Khan, S. R., Farrand, S. K. (2009). The BlcC (AttM) Lactonase of Agrobacterium tumefaciens Does Not Quench the Quorum-Sensing System That Regulates Ti Plasmid Conjugative Transfer. J. Bacteriol. 191: 1320-1329 [Abstract] [Full Text]  
  • Khan, S. R., Gaines, J., Roop, R. M. II, Farrand, S. K. (2008). Broad-Host-Range Expression Vectors with Tightly Regulated Promoters and Their Use To Examine the Influence of TraR and TraM Expression on Ti Plasmid Quorum Sensing. Appl. Environ. Microbiol. 74: 5053-5062 [Abstract] [Full Text]  
  • Liu, Y., Gao, P., Banga, S., Luo, Z.-Q. (2008). An in vivo gene deletion system for determining temporal requirement of bacterial virulence factors. Proc. Natl. Acad. Sci. USA 105: 9385-9390 [Abstract] [Full Text]  


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