Agricultural Microbes Genome 2 Conference

Poster: Cellular Processes, Regulatory Networks
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MOLECULAR CHARACTERIZATION OF AN ESSENTIAL COMPONENT OF QUORUM SENSING REGULATORY NETWORKS IN Agrobacterium tumefaciens

¹ Institute of Molecular Agrobiology, 1 Research Link, The National University of Singapore, Singapore 117604

A diverse range of biological functions in single-celled bacteria, including bioluminescence, Ti plasmid conjugal transfer, bacterial pathogenicity, biofilm maturation, and swarming, have been found to be regulated via cell-cell communications. The phenomenon has been known as quorum sensing. Acyl-homosenrine lactones (AHL) is one family of the most widely conserved quorum sensing signal molecules. It is known that in most cases the AHL signal is required to form a complex with its cognate transcription factor for gene regulation, but how the external AHL signal is recognized and channeled to the cognate transcription factor is largely unknown. By using a Tn5 mutagenesis approach and a quantitative bioassay system, a gene responsible for channeling the AHL signal to the TraR transcription factor has been identified in Agrobacterium tumefaciens. It is found that Tn5 insertional mutation of the gene results in about 90% decrease in AHL biosynthesis, and the efficiency of Ti plasmid conjugal transfer of the mutant is decreased by about 1000 folds than that of the parent strain K588. The gene has been cloned and characterized. It has been demonstrated that the AHL signal, N-(3-oxooctanoyl)-homoserine lactone (OOHL), can freely diffuse in and out of the bacterial cells. However, expression of the cloned gene in E. coli and in A. tumefaciens significantly enhances the formation of TraR-OOHL complex. The molecular mechanism of promoting formation of TraR-AHL complex will be discussed.