Wolfgang D. Bauer,1
Jayne B. Robinson,2
John M. Farrow, III,3
Everett C. Pesci,3
Richard T. Sayre,5 and
Donald A. Phillips1
1Department of Plant Sciences, University of California, Davis 95616, U.S.A.; 2Biology Department, University of Dayton, Dayton, OH 45469, U.S.A.; 3Department of Microbiology and Immunology, Brody School of Medicine, East Carolina University, Greenville, NC 27858, U.S.A.; 4Department of Soil and Water Science, University of Florida-IFAS, Gainesville 32611-0290, U.S.A.; 5Department of Plant Cellular and Molecular Biology, Ohio State University, Columbus 43210, U.S.A.
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Accepted 13 May 2008.
Many bacteria use quorum sensing (QS) as an intercellular signaling mechanism to regulate gene expression in local populations. Plant and algal hosts, in turn, secrete compounds that mimic bacterial QS signals, allowing these hosts to manipulate QS-regulated gene expression in bacteria. Lumichrome, a derivative of the vitamin riboflavin, was purified and chemically identified from culture filtrates of the alga Chlamydomonas as a QS signal-mimic compound capable of stimulating the Pseudomonas aeruginosa LasR QS receptor. LasR normally recognizes the N-acyl homoserine lactone (AHL) signal, N-3-oxo-dodecanoyl homoserine lactone. Authentic lumichrome and riboflavin stimulated the LasR receptor in bioassays and lumichrome activated LasR in gel shift experiments. Amino acid substitutions in LasR residues required for AHL binding altered responses to both AHLs and lumichrome or riboflavin. These results and docking studies indicate that the AHL binding pocket of LasR recognizes both AHLs and the structurally dissimilar lumichrome or riboflavin. Bacteria, plants, and algae commonly secrete riboflavin or lumichrome, raising the possibility that these compounds could serve as either QS signals or as interkingdom signal mimics capable of manipulating QS in bacteria with a LasR-like receptor.
Additional keywords:agonist, lasI, red fluorescent protein, rsaL.
© 2008 The American Phytopathological Society