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AHL Signals Induce Rubrifacine Production in a bruI Mutant of Brenneria rubrifaciens

February 2012 , Volume 102 , Number  2
Pages  195 - 203

Ali E. McClean, Breck A. Duerkop, E. Peter Greenberg, and Daniel A. Kluepfel

First and fourth authors: Crops Pathology and Genetics Research Unit, United States Department of Agriculture–Agricultural Research Service (USDA-ARS), 259 Hutchison Hall, Department of Plant Pathology, One Shields Avenue, University of California, Davis 95616; and second and third authors: Department of Microbiology, University of Washington School of Medicine, Seattle 98195-7242.

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Accepted for publication 20 October 2011.

Several members of the bacterial genus Brenneria are pathogenic on different tree species. Cell-free extracts from the bacterial phytopathogens Brenneria rubrifaciens, B. salicis, and B. nigrifluens induced production of the red pigment rubrifacine in the B. rubrifaciens bruI insertional mutant Br-212. Analysis of the bruI locus identified an adjacent open reading frame, designated bruR, with homology to luxR. High-performance liquid chromatography and mass spectrometry analysis of ethyl acetate extracts from wild-type B. rubrifaciens and Escherichia coli expressing the bruI gene identified two acyl homoserine lactone (AHL) peaks, N-(3-oxohexanoyl)-homoserine lactone (3OC6HSL) and N-hexanoyl-homoserine lactone (C6HSL). Addition of synthetic 3OC6HSL and C6HSL at 10 μM to the bruI mutant, strain Br-212, induced rubrifacine production and the ability to elicit a hypersensitive reaction (HR) in tobacco leaves. Synthetic C6HSL was less effective at inducing pigment production than 3OC6HSL at 10 μM. The bruI mutant Br-212 did not produce detectable AHLs, indicating that C6HSL and 3OC6HSL are the major AHLs produced by this species. The AHLs N-heptanoyl-DL-homoserine lactone (C7HSL), N-octanoyl-DL-homoserine lactone (C8HSL), and N-(3-oxooctanoyl)-DL-homoserine lactone (3OC8HSL) also induced pigment production in Br-212 and restored its ability to elicit an HR in tobacco, suggesting that cross-talk with other bacterial species may be possible.

This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 2012.