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Applied and Environmental Microbiology, June 2004, p. 3715-3723, Vol. 70, No. 6
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.6.3715-3723.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Use of Sinorhizobium meliloti as an Indicator for Specific Detection of Long-Chain N-Acyl Homoserine Lactones

Inmaculada Llamas, Neela Keshavan, and Juan E. González*

Department of Molecular and Cell Biology, University of Texas at Dallas, Richardson, Texas 75083-0688

Received 5 December 2003/ Accepted 20 February 2004

Population-density-dependent gene expression in gram-negative bacteria involves the production of signal molecules characterized as N-acyl homoserine lactones (AHLs). The synthesis of AHLs by numerous microorganisms has been identified by using biosensor strains based on the Agrobacterium tumefaciens and Chromobacterium violaceum quorum-sensing systems. The symbiotic nitrogen-fixing bacterium Sinorhizobium meliloti is rapidly becoming a model organism for the study of quorum sensing. This organism harbors at least three different quorum-sensing systems (Sin, Mel, and Tra), which play a role in its symbiotic relationship with its host plant, alfalfa. The Sin system is distinguished among them for the production of long-chain AHLs, including C18-HL, the longest AHL reported so far. In this work, we show that construction of a sinI::lacZ transcriptional fusion results in a strain that detects long-chain AHLs with exquisite sensitivity. Overexpression of the SinR regulator protein from a vector promoter increases its sensitivity without loss of specificity. We also show that the resulting indicator strain can recognize long-chain AHLs produced by unrelated bacteria such as Paracoccus denitrificans and Rhodobacter capsulatus. This S. meliloti indicator strain should serve as a tool for the specific detection of long-chain AHLs in new systems.


* Corresponding author. Mailing address: FO 3.1, Department of Molecular and Cell Biology, University of Texas at Dallas, Richardson, TX 75083-0688. Phone: (972) 883-2526. Fax: (630) 604-3093. E-mail: jgonzal{at}utdallas.edu.


Applied and Environmental Microbiology, June 2004, p. 3715-3723, Vol. 70, No. 6
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.6.3715-3723.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.




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